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Home , Carduelinae, Crossbill, Filipendula ulmaria, Fringilla, Greenfinch, Hawfinch

1967 I. NEWTON : EVOLUTION AND ECOLOGY OF 33

THE ADAPTIVE RADIATION AND FEEDING ECOLOGY OF SOME BRITISH FINCHES

I. NEWTON

Received on 15 December 1965 CONTENTS Page Page Introduction - - - - - 33 The relationship between body-weight, Thestudy areas - - - - 35 leg proportions and feeding habits 71 Methods of assessing the food of finches 36 The feeding positions of finches - 71 Field observations - - - 36 Leg-structure, body-weight and Gut-analysis - - - - 36 feeding behaviour - - - 75 The habitats of finches - - - 38 The use of the feet in feeding - 76 Breeding habitats - - - 38 String-pulling behaviour - - 77 Feeding habitats - - - The foodoffinches - - - - 3839 Ecological isolation among finches - 77 - - - - - 39 Movements and distribution - - 77 Goldfinch - - - - - 44 Habitat-and food-selection - - 78 Siskin --_-- 47 Some special cases - - - 84 Lesser - - - 47 Some theoretical considerations - - 86 Linnet - - - - -49 Speciation and the development of -__-- 53 feeding behaviour - - - 87 Chaffinch - - - - - 54 Evolutionary trends in finches - 89 - - - - - 60 The food of nestling finches in relation Social behaviour and feeding habits - 90 to breeding habits - - - 61 Flocking - - - - - 90 The relationship between bill-structure The role of social experience in the and feeding habits - - - 63 ontogeny of feeding behaviour - 91 and seed-husking 63 Recent changes in the habitats and food Differences in bill-structure and of finches - - - - 92 feeding behaviour between species 65 - A difference in feeding habits Summary - - - - - 93 between male and female Gold- References - - - - - 95 finches ---- 70 Appendix1 - - - - - 97 Efficiencyinfeeding - - - 71 Appendix2 - - - - - 98

INTRODUCTION When several species of inhabit the same area, their continued existence there depends not only on the maintenance of a high degree of reproductive isolation between them, but also on the reduction of competition for food and other biological essentials (Lack 1954, Hinde 1959). Gause’s hypothesis, that related species with similar ecology cannot live together in the same area, has already been supported by many laboratory (refs. in Crombie 1947) and field studies (Lack 1944, 1954). Under natural conditions, closely related species normally differ in their choice of food, or of habitat, or both, and the differences are often greatest at those times of year when food is most likely to be limiting. The ecology of the Fringillidae, which live primarily on the kernels from various seeds, has already attracted the attention of several workers. In particular, Kear (1962) has briefly discussed the ecology of some species in Britain and studied their food-selection under experimental conditions; while Eber (1956) has described in detail the ecology of various species in . There has, however, been no detailed study of the food of finches in Britain and, apart from Kear’s investiga- tions, only the most general attempts to relate the feeding habits of different species to anatomical features (e.g. Hinde 1959, Promptov 1956). In this paper, the habitat and food selection of ten species of finches near Oxford from October 1961 to August 1964 are described, and differences in feeding habits between them are related to differences in bill-structure, leg-proportions and body-weight, and behaviour. C VOL. 109 34 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

The following species were involved :-

SUBFAMILY Fringillinae Fringilh F. coelebs Chaffinch F. montifrinfflla Brambling SUBFAMILY Genus Coccothruustes C. coccothruustes Genus Curduelis C. chloris Greenfinch C. curduelis Goldfinch C. Siskin C.flommeu Redpoll C. cunnubinu Linnet Genus P. pyrrhulu Bullfinch Genus Loxiu L. cumirostru Crossbill The Chaffinch, Hawfinch, Greenfinch, Goldfinch, Linnet and Bullfinch were present in Oxford throughout the year; the Brambling, Siskin and Redpoll were winter visitors; and the Crossbill was present for several months following the invasions of 1962 and 1963. Some other European finches, the jlavirostris, the Loxia pytyopsittacus and the Two-barred Crossbill Loxia leucoptera were not recorded in Oxford but are discussed where relevant. The feeding methods of these various finches were studied both in the wild and at close quarters on three to 12 captive specimens of each species that were caught from the wild. The food of all species is described here, but that of the Hawfinch and Bullfinch, which is discussed only briefly, has been described for the Hawfinch in detail by Mountfort (1957) and for the Bullfinch by Newton (in prep.). During the three years over a thousand finches were ringed in the study area in an attempt to trace their subsequent movements; these are here discussed only briefly. It should be stressed that any food and habitat preferences which now segregate the different species of finches from one another ecologically were evolved in an environment that was probably very different from, and much more stable than, that in which they now operate. It is becoming increasingly difficult to study land animals in their natural environment, and all the habitats in which I worked, including the woodland, were artificial. Furthermore, the modern environment is changing (under man’s influence) much more rapidly than most natural habitats would, and at a steadily accelerating rate. As a result, many animals, especially those of agricultural land, must now be in continual process of adjustment to an ever-changing situation. As far as finches are concerned, some of their commonest food- at the beginning of this century are no longer available in most areas, as a result of changed agricultural methods (see later). On the other hand, several artificial foods are being provided by householders on an increasing scale, and at certain times of year in Oxford, the Greenfinch is now almost wholly dependent on them. In view of the artificiality of the modern environment, any ecological isolating mechanisms in finches could well be less effective now than in the more stable environment in which they evolved. But despite this, several species of finches now live together over most of southern and, unless their numbers remain permanently below the level at which they run short of food-which is most unlikely-they should still be separated from one another ecologically. To the student of evolution, it may seem that a disproportionately large amount of this paper is devoted to a description of the food of different finches. But in an environ- ment where the need for conservation becomes increasingly urgent, a knowledge of the food of animals is of prime importance. Furthermore, since the diet of some species has changed considerably over the past 50 years, a detailed knowledge of their feeding habits is required now so that any future changes may be detected. Both these aspects are important in helping to predict the effects on finches of future changes in land-use, and in indicating the sort of changes they could tolerate. Nevertheless a familiarity 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 35 with the sections on the food of each species is by no means essential for an understanding of the rest of this paper. Usually Latin names are used for plants, except that the English name is also given at the first mention and is also used for crop-plants and for collective terms, such as thistles (Carduus, Cirsium, Onopordon, etc.), docks (Rumex), and grasses (Graminae). The term “cardueline” is used to cover the , Bullfinch and Hawfinch as well as finches in the genus Carduelis.

THE STUDY AREAS I worked in two areas, about two miles apart on the west side of Oxford. One consisted of woodland and farmland on the University’s Estate at Wytham, and the other of allotment gardens and a municipal rubbish dump just outside the city on Port Meadow. Wytham Estate is on a hill, the lowest slopes of which are of Oxford Clay, the inter- mediate areas calcareous grit, while a cap on the top is of Coral Rag. All around is mixed farming land with a few isolated copses. Of the thousand or so acres (=ca. 417 hectares) which constitute the woodland estate proper, about 700 are deciduous woodland; the rest is divided between a park, plantations of various ages, rough grassland and some small enclaves of farmland. Some 500 acres of woodland on the north, west and south slopes form a continuous block known as the Great Wood, to the southern third of which I restricted my activities. The geological and soil zonation of Wytham Hill causes the cover to decrease in density as the ground rises. The clay ground is covered mainly with rather open Quercus spp. forest with luxuriant Bracken Pteridium aquilinium and brambles Rubus fruticosus. The intermediate areas have , Ash Fraxinus excelsior and Sycamore Acer pseudo- platanus, with ground cover varying, according to the depth of soil, from pure Dog’s Mercury Mercurialis perennis to Bracken and Bramble. The Coral Rag cap has mainly oaks, Sycamore, Beech Fagus silvatica and Betula spp., with grass and Bramble in unshaded parts, and here and there small open commons. A mature conifer plantation (ca. 40 acres), consisting of Picea abies and , grows on the calcareous grit, and there are about ten acres of recently cleared ground on which various grasses, thistles, ragworts Senecio spp., burdocks Arctium spp. and teasels Dipsacus spp. grow profusely, and in the damper areas, Meadowsweet ulmaria and various willowherbs (especially hirsutum). About half a mile to the east of the Great Wood, and joined to it by a narrow strip of woodland, is Marley Wood of 66 acres. In contrast to the Great Wood, Marley is no longer managed; about a fifth of the area is devoid of tree or shrub cover and much of the open ground is marshy. About two-fifths of the canopy is dominated by hawthorn Crataegus spp. and Elder Sambucus nigra, but Hazel Corylus avellana and are also common. The ground cover consists mainly of Bracken, Bramble, Dog’s Mercury or Nettle Urtica dioica, except in the marshy areas where Phragmites is dominant. About 150 acres of farmland, lying just outside the woodland, also formed part of the Wytham study area. Most of the fields were of six to ten acres and were divided by hawthorn hedges. About three-quarters were rough pasture, and the rest arable. The allotment gardens of Port Meadow, also on Oxford Clay, cover about 40 acres. About half are no longer cultivated and are covered mainly with grasses, thistles, docks and nettles, with clumps of brambles on the more derelict parts. The rest are still tended but various weeds are common. The rubbish dump, also covering about 40 acres, supported most of the common food-plants of finches. Much of the area is overgrown with grasses, thistles and burdocks, but on the more recently tipped areas, Fat-hen Chenopodium album, Artemisia spp., Rumex spp. and in spring, Chickweed Stellaria media and Groundsel Senecio vulgaris, are the commonest plants. To summarize, the total area covered comprized about 250 acres of woodland, 150 of farmland, 40 of allotment gardens, and 40 acres of rubbish dump. The area contained 36 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

a much smaller proportion of farmland in relation to other habitats, than was typical of surrounding areas, or of southern England as a whole; and suburban gardens were not represented.

METHODS OF ASSESSING THE FOOD OF FINCHES FIELD OBSERVATIONS Repeated field observation was the chief method used in the present study, and results obtained in this way reflect the amount of time spent by each species in obtaining various foods. The study area was covered on foot three to six times each month by different routes, and the food and feeding stations of all the finches encountered were noted. An arbitrary rule was adopted: one , one food=one record. Unknown food-plants were identified from the flora by Clapham, Tutin & Warburg (1952). (Their nomen- clature is followed except that all brambles are here classed for convenience as Rubus fruticosus.) In summer, finches fed mainly in the early mornings and evenings, when they were usually assembled at places where food was most plentiful. In cold weather, however, they fed more or less continuously and data were collected throughout the day. The percentage of the total feeding time spent on various foods by each species was then worked out each month by combining the data from different surveys. The method is not suitable for the Chaffinch which feeds largely on the ground, and the results for this species are based almost entirely on gut-analyses. Cardueline finches, however, are easily studied by observation, since they feed largely on the seed-heads of plants and are therefore easily noticed; the presence of discarded seed husks on the ground below provides a useful check on the records. Their habit of flocking also helps, since it is much less easy to overlook a noisy flock than single . The results of observation might be subject to bias if the birds are not equally conspicuous in all their feeding places, but this is unlikely once the observer becomes familiar with them. Furthermore, the observational data outlined for each species prove to be reasonably consistent with the results of gut-analyses.

GUT-ANALYSIS After ingestion, food passes through the gullet to the proventriculus, where it is softened, and thence to the gizzard where it is broken up with the help of grit. When the gizzard and proventriculus are full, food is stored in the gullet which is expandable, but otherwise undifferentiated and therefore best not termed a crop. When the gullet is full, the accumulated food appears as one or two swellings on either side of the vertebral column. Its contents can be seen easily, and with practice identified, through the transparent skin of the neck if the feathers are blown apart (see Fisher & Dater (1961) for a photograph of a full gullet of a Redpoll). The gullet of the smallest species examined here, the , will hold about 0.8 C.C. of food, and that of the Greenfinch, one of the largest species, up to 2.5 C.C.

Gullet and gizzard analyses of shot specimens This method was used to confirm and supplement the observational data, and examination was confined to the gullet and gizzard because little or no digestion occurs there. Whereas seeds in the gizzard were sometimes fragmented and difficult to recognize, those in the gullet were almost unaltered. Analyses were carried out on the same day as the specimens were collected. The gullet and gizzard were removed and their contents washed into a dish. The various items were then sorted into separate piles and counted; but for large seeds which had been broken into several pieces before ingestion, the equivalent number of whole grains was estimated. Kernels from the gut were identified by comparison with whole seeds in a reference collection. Any not recognized were differentiated on size, shape, etc. and given a code 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 37 number. Most were subsequently identified, but in some groups, such as brassicas, specific identification of the seeds was often impossible because of their similarity to one another. It was hoped to identify some by growing them, but apart from certain grass seeds, they failed to germinate. Usually, it was not possible to identify inverte- brates further than to the family or even the order, since most had been crushed before ingestion, but any intact specimens were preserved and identified later.

Gullet analyses of live birds It was usually possible to identify seeds in the gullets of live finches through the skin of the neck, visually and by manipulating the gullet between thumb and finger. Much information was obtained by netting birds as they came to roost, for then their gullets were usually crammed with seeds. A full gullet was scored as ten, and each type of food present as tenths of the maximum possible. For final analysis, the figures obtained for different foods were totalled and converted to percentages. Results obtained in this way were checked by killing some birds and examining their gullet contents more closely. The chief tendency was to overlook seeds which occurred in very small numbers and so were lost among the mass of common ones. But since such seeds occurred in only a few of the birds examined and formed only a small part of the food, the error must have been small. Most of the gullets examined contained only one or two types of seeds. Corn grains sometimes disintegrate in the gullet to form a yellowish paste in which individual grains cannot be distinguished, but all the other types of seeds encountered retain their shape and colour until they are broken up in the gizzard. Large seeds always figured more prominently in results obtained in this way, than in those obtained by observation (see later). This is to be expected since the latter reflect the amount of time spent on different foods, and the former their respective volumes in the diet. Gullet analysis was most suitable for , Linnets and Chaffinches which, in winter, roosted communally in low bushes and so could easily be caught in mist nets; in summer most analyses were carried out on shot specimens. The remaining species always roosted too high to be caught, and observations on these were checked only by examinining the gullet and gizzard contents of a few shot under licence.

Gullet analyses of live nestlings The percentage composition (by volume) of the diet of nestling cardueline finches was assessed by examining the gullet contents of live nestlings, in the same way as in the adults. Unlike the adults, however, nestlings had food in their gullets at most times of day. Invertebrates in the gullet were easily distinguished from seeds by their darker colouration, but it was sometimes not possible to tell which types were present. But blackish flies, caterpillars, beetles and slugs were easily distinguished from one another by manipulating the gullet between thumb and finger. If results obtained by this method are compared with the observational data, not only do large seeds figure more prominently, as in the adults, but also various animals. This is partly because the adults feed most of the animals they collect to their young, and also because it is more difficult to record animals than seeds by the observational method. The chief asset of this method is that there is no need to kill the nestlings; the chief difficulty is to find enough nests, especially at the beginning of the breeding season when the contents of many were taken by predators. Gullet analyses could not be carried out on live young Chaffinches, since they do not normally retain food there, probably because they receive smaller meals than young cardueline finches (see later). 38 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS 109

THE HABITATS OF FINCHES Since almost all habitats in modern Britain have either been moulded by man’s influence or are less extensive than under natural conditions, the original habitat-relations of most species are now obscure. Of the finches studied here, the natural habitats are known only for the Crossbill, Redpoll, Siskin, Bullfinch and Brambling, since these live primarily in the northern forests of and , which have apparently been little modified by man. To judge from their present habitat preferences, the Greenfinch and Goldfinch were originally birds of sparselywooded landscapes or of forest-edge abutting on more open country, and the Linnet of open bushy areas; but since throughout their range they now live primarily in man-modified habitats, especially areas of intense cultivation, it is dangerous to try to deduce their ancestral habitats more precisely. During this century the Redpoll has colonized parts of southern England, breeding in young conifer plantations and feeding from various weeds of waste and agricultural land. No one who had studied the Redpoll in this environment alone could have deduced that it was originally a bird of northern birch forest. In modern England, most species now choose specific places for nesting, but feed in a variety of habitats. The Carduel& finches now move around so much, even in the breeding season, that their young sometimes receive in one meal seeds which must have been collected in at least three different habitats. This is almost certainly a result of man’s influence on the land, since, as mentioned above, the countryside of today is occupied by a mosaic of small habitats with sharper boundaries between them than the original blocks probably had.

BREEDING HABITATS In England the Chaffinch now breeds in all areas where there are sizeable trees, including deciduous and conifer woods, parks, gardens and hedgerows, and it overlaps with all other species in breeding habitat except with the Twite. Among the cardueline finches, different species prefer different types of nesting habitat : the Hawfinch, woods and orchards ; the Greenfinch, hedgerows, parks and gardens ; the Siskin and Crossbill, mature conifer woods; the Redpoll, birch or sallow Salk spp. scrub and young conifer plantations; the Linnet, short hedgerows and bushy areas; the Twite, moorland and barren rocky places; and the Bullfinch, woods, gardens, hedgerows and parks. Although this suggests considerable overlap between some species, there is, in fact, but little, since each prefers vegetation of characteristic height and spacing. For instance, in an Oxford park, Bullfinches nested in dense shrubberies, Greenfinches in tall hedges and bushes, Linnets in low bushes in more open areas, and Goldfinches high in isolated trees.

FEEDING HABITATS In Oxford the rubbish dump and allotment gardens, where weeds grew profusely, were the most important feeding places for finches. Although they formed only a fifteenth of the total study area, they often held over half its finches; five species fed there throughout the year, and others occasionally. Deciduous woodland was also important, especially in years with good crops of birch and Beech seeds. Conifer plantations, with no shrub or ground layer, were usually devoid of finches other than Crossbills, except in April when several species fed there on the insects present on developing larch buds. Most species fed on farmland throughout the year-though this is probably a much less important habitat now than before the days of chemical herbicides-and also in gardens. The latter, together with farmyards, were particularly important feeding places for Chaffinches and Greenfinches in winter, but both were avoided altogether by Linnets. In Oxford most finches fed, at least occasionally, in all habitats from well-wooded to open ones, but preferred one or the other. The Greenfinch, Linnet and Goldfinch 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 39 were most closely associated with farmland, while the Hawfinch, Crossbill and Siskin rarely fed away from trees. The Chaffinch and Bullfinch were the only species that bred and occurred throughout the year in both woods and cultivated land. Although Bullfinches are usually considered as birds of woods and hedgerows, in the study area they frequently fed far out in fields, and in the winter of 1961 /62, when food was scarce in woodland, large numbers fed on open downland near Oxford. The tendency to feed so far from cover is evidently a new habit in the Bullfinch in southern England and may have facilitated its recent increase there. (In , however, there are records from the last century of them feeding far in the open on Heather Calluna vulgaris seeds.) In Oxford, the Chaffinch, Brambling and Redpoll fed largely in woodland in those winters when suitable seeds were available there, but on waste and agricultural land in other years. Generally speaking, the farmland species moved into woods only to exploit some temporary abundance of food there, while the woodland species moved into more open country only when food was noticeably short in their preferred habitat. Table 1 shows the main feeding places of different finches through the year. Some species concentrated into different places at different times of year. Although the sequence of preferences usually varied between them, this resulted mainly from differences in the distribution of their respective food-plants. I agree with Kear (1962) that food- selection, and not habitat-selection, is now the chief factor segregating most species from one another. Habitat-selection may, however, have been more important in primeval England than it is now, since most habitats probably occurred in larger blocks and movement between them would have been correspondingly more difficult. Eber (1956) has tabulated the various habitats through the year of certain finches in Holstein, Germany. For the most part these are similar to those found in Oxford, except that in Holstein the Goldfinch apparently does not usually feed in parks nor the Greenfinch in woods; the reasons for these differences are not known.

THE FOOD OF FINCHES It has been explained above that different methods of assessing the diet were suitable for different species. This has resulted in differences in the types of data collected, their accuracy, and the way in which they could best be analysed. In the following sections, which describe in turn the diet of each species, foods are normally given in order of importance and only those forming more than 10% of the diet during the period in question are mentioned in the text; less important foods are given either in the tables or in Appendix 1. GREENFINCH Greenfinches are common in the Oxford district throughout the year, but many leave temporarily during periods of snow. I recorded the seeds of 60 plant-species in the diet, more than for any other cardueline . The bulk of the food, as ascertained by both methods of investigation, consisted of the seeds of Compositae, Cruciferae, Polygonaceae and Gramineae, while those of the Betulaceae, important to most other species, were of negligible importance. Seeds varying in weight from 0.1 mg. (Artemkia) to 230 mg. (Fagus silvatica) were eaten, and over the year as a whole, those of Charlock Sinapis arvensis and other brassicas, cultivated cereals, Persicaria Polygonurn persicaria and burdocks were most important. The Greenfinch was the only cardueline finch which in Oxford fed extensively on cereals (obtained mainly from stubble) and on peanuts (the seeds of the legume Arachis hypogaea)-the latter were deliberately provided by householders as food for birds and are presumably not available to Greenfinches over most of Britain. Seeds from fleshy fruits formed about 6% of the total food in Oxford. I‘ Greenstuff ”, such as the of Stellma media, was taken through the year; I did not record buds in the diet, but they have been reported by other workers (e.g. Fryer 1939). Invertebrate animals were also taken, mainly in the breeding season. TABLE1. The chief feeding habitats of diyerent Jinches through the year near Oxford.

JAN. TO MARCH APRIL MAY TO JULY AUG. TO SEPT. OCT. TO DEC. SNOW-PERIODS 2 Chaffinch Farmland Farmland Wood 1and Farmland (Woodland)*Farmland Farmsteads (Woodland)* Farmland Woodland Gardens !0 Brambling Farmland Farmland - - Farmland Farmsteads 2 (Woodland)* Allotments (Woodland)* Allotments Hawfinch Deciduous Deciduous Deciduous Deciduous Deciduous Deciduous woodland woodland woodland woodland woodland woodland Greenfinch Gardens Farmland Farmland Farmland Farmland Gardens Farmland Allotments Woodland Allotments Rubbish dump Go1 d fin ch Allotments Allotments Allotments Rough pasture Rough pasture Rubbish dump Rubbish dump Rubbish dump Allotments Rubbish dump Rough pasture Siskin Alders - - Alders Alders Redpoll Birches Larches Sallows - Birches Birches (Rubbish dump)? Sallows (Rubbish dump)? (Rubbish dump)? Linnet Farmland Allotments Farmland Farmland Farmland Rubbish dump Farmland Allotments Allotments Rubbish dump Farmland Bullfinch Woodland Woodland Woodland Woodland Woodland Woodland Rubbish dump Orchards Farmland Farmland Farmland Orcliards Crossbill Conifers Conifers Conifers Conifers Conifers Notes. * Only when beechmast was available there. t Only when birch seeds were unavailable, 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 41

VEGETABLE FOOD THROUGH THE YEAR Table 2 shows the diet of the Greenfinch in Oxford; it is based on observations in the study area throughout the year, and on gullet analyses of 771 live adults from October to April (when they were roosting communally in Wytham), and of 34 broods of nestlings examined regularly from May to August. (In addition, 30 adults were shot in the breeding season as a check on the observational data and a list of their gut-contents has been deposited in the Edward Grey Institute.) Throughout the year seasonal changes in diet kept step with changes in the relative abundance of different foods in the study area. It may be seen from Table 2 that from May to August the same foods were recorded by observation as were found in the gullets of nestlings and in fairly similar proportions. The chief differences are the greater prevalance of invertebrates and large seeds (such as those of Wych Ulmus glabra, Mercurialis perennis and cereals) in the nestling data, but this would be expected owing to differences in the types of analysis used, as mentioned in the section on methods. Dandelion Taraxacum oflieinale seeds formed the main food of both adults and nestlings in May, and Mercurialis perennis seeds in June, while Ulmus spp. (mainly U. glabra) and Senecio vulgaris seeds were important in both these months. In July and August the seeds of various brassicas and cereals formed about four-fifths of the food, as determined by both methods, the remainder in July being comprized largely of Senecio vulgaris seeds. In September, Sinapis arvensis seeds predominated, followed by those of the burdocks Arctium pubens and A. minus, and cereals. From October to April each year, there were at least three large roosts of Greenfinches in Wytham Woods, at which over 700 birds were caught and their gullet-contents examined. The same foods were recorded in this sample as by observation, but in con- trast to the summer data, in markedly different proportions (see Table 2). This was largely because, as ringing recoveries showed, many birds roosting in Wytham Woods fed in farmland and gardens outside the study area, where different food-plants pre- dominated. In the study area Arctium seeds formed the main food from October to March, followed by those of Sinapis arvensis and in the latter four months also those of cereals. Senecio vulgaris seeds were also important in the study area in October-when they were especially plentiful in the allotment gardens, and those of Rubus fruticoms (from woodland) and PoEygonum persicaria in December. The fresh seeds of Stellaria media and Senecio vulgaris were also taken in quantity in April. By gullet analysis, on the other hand, Arctium seeds formed less than a tenth of the diet from October to March, while seeds available on farmland, such as those of brassicas, Polygonum persicaria and cereals were correspondingly more important. These are sometimes dug up from just below the surface of loose soil by the birds flicking the soil aside with their bills. Throughout the winter, there was constant movement between different feeding places, and birds shot by day for gut-analysis often contained food from several habitats. Few Greenfinches fed in the study area from January to April each year, though large roosts were still maintained in Wytham Woods. Ringing recoveries showed that some birds left the Oxford district completely with the first snow in January, while others moved into gardens where peanuts, deliberately put out for birds, were the main attraction. From November to April in the milder winters of 1961/62 and 1963/64, these became increasingly prevalent in the gullets of those caught at roost and at the end of this period formed a quarter of their total food. During the great frost from January to March 1963, however, Greenfinches in the Oxford district were almost wholly depen- dent on peanuts, for they were found in the gullets of almost all the 223 birds examined then, and comprized by volume 97% of the diet. (These abnormal data have been excluded from Table 2.) The few Greenfinches in the study area at this time fed around farmsteads and in woods and hedgerows on the seeds of Rubus fruticosus and rose Rosa spp. (especially R. canina which was the commonest species). TABLE2. The percentage composition of the diet of the Greenfinch Carduelis chloris in Oxford, based on three years' data. Thefigures in normal type are based on the results of field observations and those in italics on the results of gut-analyses of nestlings from May to August and of adults from October to April. (None was analysed in September.) Seeds are listed as far as possible, in order of their appearance in the diet from April onwards. Continuous lines indicate the main seeding periods of the d@went food-plants, and dotted lines the pm'od for which seeds are normally still available on the plant afterwards. Otherwise seeds are N picked from theground. Figures in parentheses are based on less than a hundred observations. +=Less than 1%. 0, Observations; G, Cullets.

IAN.TOM*RCH APRIL MAY m JULY AUO. SUP. om. NOV. DEC. AVERAOE % OG OG 00 OG OG OG OG OG OG OG(suons.) No. of observations or gullets examined 340 237 54 58 224 83 a. 1700 364 a.1000 402 0.3200 155 a.3000 - 0.3500 84 a.2050 67 a. 1100 102 SEEDS Stellaria media (24) 4 73 42 42 12 3 Pwannua (2) 1 + Senecio vulgaris (18) 2 11 8 15 12 12 8 11 1 22 16 84 7 Taraxacum oflcinale ' (6) 1 38 31 10 5 + + + 4Y UIrnus spp. (espec. U. glabra) 23 29 19 25 10 Mercurialis perennis I13 23 27 1 Alliaria petiolata Symphytum oflcinale Cynoglossum officinale Cultivated brassicas Wild brassicas (espec. Sinapis arvensis) 8 18 10 Sonchus oleraceus Rumex acetosa Docks Rumex spp. Tragopogan pratensis 32 21 12 Cultivated cereals 6 8 21 33 24 34 16 5 10 4 I2 16 13 Ranunculus spp. Hypochoeris spp. (espec. H. radicata) Capsella bursa-pastoris Polygonurn convolvulus Polygonwn persicaria Arctiurn spp. Rubus fruticosus ThiStlC-3 Chenopdium spp. (espec. C. album Rosa Spp. (am.R. Canin0 Agrimonia eupatoria Polyxonwn aviculnre Cotoneaster Peanuts Others (incl. unidentified) QRFJ3NSTUFP 1NVEmmsRAm 6 I2 310 13 + gg.- I -t3 11 Others + + + + Total "/ vepetable matter 100 >99 100 I00 94 89 96 87 98 96 >99 IM) 100 100 >99 100 >99 100 >99 Total 2 d matter + 6 11 4 I3 24 + + + + 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 43

ANIMAL FOOD THROUGH THE YEAR Over the year as a whole, invertebrates formed about 1% of the diet as determined by both methods. They were recorded by gut-analysis in every month, but from September to March consisted entirely of various beetle larvae obtained along with the seeds from the seed-heads of thistles and burdocks. At this time, however, food formed but a negligible fraction of the total diet. Invertebrates, especially caterpillars and aphids, were taken mainly from May to August and most of them were fed to the young. Aphids were picked from the leaves of the various food-plants and caterpillars mainly from the leaves of oaks, and hawthorns. No species were identified specifically. The only animals found in the gizzards of adults in the breeding season were two aphids in a female shot on 16 July. Table 3 shows the percentage by volume of animals in the food of nestling Green- finches according to age and time of year. Early broods received relatively more animals than late ones, but in all broods the proportion of animals in the diet declined with increasing age. Thus young hatched in May and June received an average of 10% animal-material to the fifth day, but this had fallen to 1% by the ninth. Those hatched in July and August received an average of 3% for the first three days, only 1% by the sixth day and none thereafter. There was also considerable variation between the diets of broods in the nest at the same time. Some very late broods may have been reared entirely on vegetable matter, for no invertebrates were recorded during 20 visits (15 on the first three days) to a brood in late August. It is of particular interest that Eber (1956) did not record any invertebrates in the food of adult Greenfinches in Holstein, Germany, at any time of year, despite the extent of her data; but she did not apparently examine any nestlings.

TABLE3. The percentage (by volume) of invertebrates in the food of nestling Gremjinches Carduelis chloris according to age and time of year. No. of broods Total no. of examined examinations' Nestling day 12 3 4 5 6 7 8 91Oll+ Young hatched May and June 22 520 101111 910 8 5 3 1 + + Young hatched July and August 12 484 33322100000 Note. One inspection of one nestling=one examination. There were normally 4-6 nestlings per brood.

COMPARISON WITH PREVIOUS DATA Newstead (1908) and Florence (1912, 1914) have published lists of the gut contents of 120 Greenfinches collected in various parts of Britain. It can be calculated from their data that of 87 birds examined between October and April, cereals were found in 43, various brassica seeds in 12, Stellaria and Rumex seeds in five. Various other seeds, found in one or two birds only, included those of Sunflower Helianthus annuus which were not recorded in the present study, possibly because it is no longer a popular garden . Of 12 birds examined between May and September, cereals were found in six, Stellaria and Sinapis seeds and aphids in three, Rumex and Corn Spurrey Spergula amensis seeds in two, and weevils, beetle larvae and dipterous larvae in one. These results are consistent with my own insofar as they indicate the importance of cereal and brassica seeds to the Greenfinch, but it is strange that Polygonum persicaria and Arctium seeds were not recorded in so large a sample. Cereals may be less important now than when these birds were collected, since the increased efficiency in farming methods and the earlier ploughing of stubble mean that fewer are available and for a shorter time. Jourdain (in Witherby et al. 1938) mentions cereals, Charlock, Sainfoin Onobrychis 44 I. NEWTON : EVOLUTION AM) ECOLOGY OF FINCHES IBIS109 vici$olia, clover Trifolium and Turnip Brassica rapa seeds, and spiders, beetles and ants, as well as aphids and caterpillars as occurring in the diet of the Greenfinch. Eber (1956) recorded the seeds of 55 plant species in the food of the Greenfinch in an agricultural area in Holstein. For the most part, the same seeds were important there as in Oxford and in other parts of Britain, especially those of various brassicas and cereals. But the most frequently recorded seeds were those of Beet Beta vulgaris, while those of Snowberry Symphoricat-pos rivularis and of Artemisia vulgaris were also important; neither of the first two were available in my study area, but Artemisia was common so it is strange that it was not exploited by Greenfinches there. Apart from Eber’s data, there seems to be little detailed information on the food of the bird outside Britain. Turcek (1961), however, lists 20 coniferous and 36 deciduous trees whose seeds are taken by Greenfinches in Slovakian forests, but unfortunately does not indicate their relative importance in the diet; they included Crataegus spp., Guelder Rose Viburnum opulus, Lilac Syringa vulgaris and Fraxinus excelsior among those which were available in Oxford but apparently not taken.

GOLDFINCH Although Goldfinches are present in Oxford throughout the year, most leave in October to winter elsewhere (mainly southern and northern ), and some of those remaining move out with the first snow; smaller numbers return in April. In Oxford I recorded the seeds of 56 plant-species in the diet, including those of 34 Com- positae which formed 76% of the total food as determined by observation. Seeds of Dipsaceae, Betulaceae and Coniferae formed most of the remaining food, while those of Chenopodiaceae, Polygonaceae and Cruciferae, important to most other finches, were of negligible importance to the Goldfinch. Seeds varying in individual weight from 0.05 mg. (willowherbs) to 50 mg. (elm) were eaten. Over the year as a whole, the seeds of various thistles formed nearly a third of the total food, and those of Senecio spp., Arctium spp. and Dipsacus spp. made up most of the remainder; all these seeds are available for at least eight months each year, and several others, such as those of Taraxacum ojfkinab, were important over short periods. The seeds of Compositae were most important in summer, forming, from July to September, almost the entire food; but they became progressively scarcer, and the proportion in the diet declined, as the winter progressed and Dipsacus fullonum, Alnus glutinosa and Pinus spp. seeds were taken in greater quantity. I did not see Goldfinches taking seeds from fleshy fruits in Oxford, but Turcek (1961) lists Rowan Sorbus aucuparia seeds among the foods of the Goldfinch in . “ Greenstuff ”, such as the leaves of Stellaria media and various cultivated brassicas, was taken throughout the year; I did not, however, record buds which were found in the gizzards of some birds examined by Collinge (1924-27). Various invertebrates were also taken through the year in Oxford, but mainly from April to June.

VEGETABLE FOOD THROUGH THE YEAR The diet through the year, as determined by observation, is shown in Table 4; and a list of the gut-contents of 36 adults shot at various times of year has been deposited in the Edward Grey Institute. All the foods found by gut-analysis were also recorded by observation, but the reverse was not true, presumably because the sample was too small. Further, I was unable to examine any nestling Goldfinches because nests were difficult to find, and the in those located were all destroyed by predators. In April and June, the most frequently recorded food was the seeds of Senecio vulgaris, in May those of Taraxacurn offi.inale, and from July to November those of various thistles (especially Cirsium vutgare and C. arvense), which, at their peak seeding period, formed 86% of the food. These same seeds also figured most prominently in the guts of those 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 45

TABLE4. The percentage composition of the diet of the Gold$nch Carduelis carduelis in Oxford based on geld observations over three years. Seeds are listed, as far as possible, in order of their appearance in the diet from April onwards. Continuous lines indicate the main seeding periods of dtjferent food- plants, and dotted lines the period for which seeds are normally still available on the plant afterwards. + =Less than 1%.

No. of observations JAN. m. MARCH APRIL MAY JUNE my AUO. SEP. om. NOV. DEC. AV. yo SEEDS 110 108 117 514 618 802 743 c0.1160 ca.2050 931 283 212

Tussilago farfora + 1 1 Sfellaria medio .. 6CI -7 Poa onnua -?I L Senecio vulgaris 49 12 55 28 1 5 26 14 2 11 Taraxacum oflicinale 2 68 10 + 1 3 2 1 7 fflmusSDD. (es~ec. U.~- dabrai , - 6 10 + I Ragworts Senecio spp. 3 Sonchus oleraceus 2 Hypochoeris SPP. (espec. H. radicata) - . + 1+ 1 2+ $. Phleum SDD. 5+ +

Sonchus arvensis Inula helenium

-.. . -- ... .. - Caterpillars 3 4+ + Aphids 16 3f 14- 2 Others +++++ +++++ + Total % vegetable matter 299 >99 >99 83 93 95 98 299 >99 >99 >99 >99 Total % animal matter <1 <1 <1 17 7 5 2 <1 <1 <1 <1 tl

shot at this time. Seeds of Senecio squalidus and Ulmus glabra were also taken frequently in June, of Senecio vulgaris in July, Senecio jacobaea in September, Filipendula ulmaria in October, and Arctium pubens, A. minus and Senecio vulgaris in November. From December to March the diet, as determined by both methods of investigation, consisted almost entirely of the seeds of burdocks, thistles and Dipsacus fullonurn; but Alms glutinosa seeds were also important in February, and various seeds in March when the cones had opened. Certain foods are strongly preferred to others, so that seasonal changes in the diet of Goldfinches in Oxford could not be attributed wholly to changes in the relative abundance of the different food-plants in the study area. Thus, Senecio vulgaris was one of the commonest food-plants in the study area, but its seeds were taken in quantity only in those months in which the preferred Taraxacum officinale or thistle seeds were scarce. Similarly, Dipsam seeds ripened in August and Alnus seeds in October, but neither were taken in quantity until December-March, when most other foods had become scarce. It was my impression that the seeds of knapweeds Centaurea spp. were preferred above all other foods, even to those of thistles, since they were always eaten completely as soon as they become available. These plants, however, were scarce in the study area, so their seeds did not figure prominently in the diet there. 46 I. NEWTON : EVOLUTION AM) ECOLOGY OF FINCHES IBIS109

In the study area, Goldfinches fed almost anywhere where suitable foods were available, but were usually commonest on waste land, in the allotment gardens and on the rubbish dump where food was most plentiful. From April to June they were also frequently seen in woodland where Ulmus glabra seeds, aphids and caterpillars were the main attraction. In winter, Goldfinches often fed on the same day at places several miles apart, and when leaving one patch of food-plants often flew out of the range of binoculars, presumably on their way to another. They also had definite feeding routines and could often be found at the same place at the same time on successive days. For example, three birds which fed from teasels in my garden arrived and departed at the same time, to within a few minutes, for at least 14 consecutive days.

ANIMAL FOOD THROUGH THE YEAR Over the year as a whole, invertebrates formed 3% of the diet as determined by observation. Various small beetle larvae obtained incidentally with the seeds from the seed-heads of Compositae, were recorded in every month, but in summer, various caterpillars and aphids were deliberately sought on the foliage of oaks and sycamores. It is not known what proportion, if any, were fed to the nestlings, but according to Sokolowski (1962) they receive invertebrates as well as seeds until the tenth day. It is possible that broods in the nest in August and September receive relatively fewer animals than earlier broods, as in the Greenfinch (see above), and in support of this view, invertebrates were recorded by observation mostly from April to June. As mentioned above, most Goldfinches leave Oxford in October and return in April. In 1963, their return coincided with the first flush of fresh seeds (mainly of Stellaria media and Senecio vulgaris), but in 1962 and 1964, occurred about a week beforehand. Most of the seeds from the previous year had disappeared by this time and until fresh seeds became available, Goldfinches fed largely on the small invertebrates present on developing buds. The gut-content of birds shot while feeding in this way showed that they visited larches for the larvae of Adelges spp. and Coleophora laricella, sycamores for various aphids, and the blossom of various fruit trees for aphids and small beetles. COMPARISON WITH PREVIOUS DATA Most books stress the importance of thistles to the Goldfinch, but Jourdain (in Witherby et al. 1938) mentions that their diet may also contain Alnus, Betula and conifer seeds, and the larvae of Diptera, Hymenoptera, Coleoptera, Lepidoptera and aphids. Collinge (1924-27) examined the gut-contents of 54 birds, apparently collected mainly in summer, but apart from buds (which were found in seven birds), all the foods reported by him were also recorded in the present study; however, he noted that Plantago seeds, which were unimportant in Oxford, occurred in 31 (58%) birds. Sokolowski (1962) has briefly described the main foods of the Goldfinch through the year in , and for the most part these seem to be the same as in Oxford, with the seeds of Compositae predominating. But he also mentions the seeds of Capsella bursa- pastwis, two species of cocklebur Xanthium strumarium and X. riparium, cultivated Hemp Cannabis sativa, and several garden plants, together with the shoots of Picea and Pinus, which I did not record even though some of these foods were available in Oxford. Eber (1956) recorded the seeds of 12 plant-species from four families in the diet of the Goldfinch in Holstein, Germany. As in Oxford, those of thistles and other Compositae and Alnus predominated, but seeds of Artemik and Rumex which I did not record in Oxford, were also taken in Holstein. On the other hand, Sene& vulgaris seeds, which were one of the most important foods of Goldfinches in Oxford, were not recorded by Eber, even though it was evidently a common plant in her study area. These differences are discussed further in a later section. In Slovakia, Turcek (1961) recorded Gold- finches taking the seeds of ten types of conifers and nine of deciduous trees, including various species of Betula, Alnus and Platanus. 1967 1. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 47

SISKIN Siskins were seen sporadically in the study area, in parties of up to 20 individuals, from mid-October to the end of April. None was shot for gut-analysis, so this account is based entirely on observations. Combining the data for different years, I have 15 records for October of birds eating Betula seeds and 62 from November to March of birds eating Alnus glutinosa seeds; the latter were obtained from the trees while they were available there, then at the very end of the winter, from the ground below, especially in places where they had been washed ashore in heaps. Each April, up to 15 Siskins fed with and Goldfinches on the larvae of Adelges spp. and Coleophora laricella in the larches of Wytham Woods; and in 1962, five were also seen extracting the seeds from some freshly opened cones. Elsewhere in England, I have seen the bird eating the seeds of Artemisia vulgaris, various thistles and knapweeds, Chenopodium album, and various conifers in winter, while P. R. Evans (pers. comm.) has recorded Filipendula ulmaria and Epilobium hirsutum seeds in autumn.

COMPARISON WITH PREVIOUS DATA Eber (1956) has described the diet through the year in Holstein where 16 types of seeds were recorded; the main ones were Alnus glutinosa, Betula and Artemisia vulgaris, followed by Rumex spp., Ulmus procera and Taraxacum oflieinale. Insects, especially caterpillars and aphids, formed a large part of the diet of adults in summer, and pre- sumably also of nestlings. Over its entire range the Siskin is seen most frequently in conifers in summer, birches in autumn, and alders in winter (see standard texts from various regions). Svardson (1957) mentions that in Siskins nest earlier than usual (in April) in years of good spruce crops, and feed their first young on these seeds before they have fallen from the cones. Turcek (1961) lists 25 conifers and nine deci- duous trees, including some with fleshy fruits, whose seeds are eaten by Siskins in Slovakia, and mentions also that while Siskins are unable to deal with unopened conifer cones, they can extract the seeds from cones already opened by Crossbills. The buds and shoots of Picea, Pinus and Larix were also recorded by Turcek (1961).

LESSER REDPOLL In all study years, Lesser Redpolls (C.f. cabaret) were present in Oxford from late September to mid-May, and during this time, the seeds of 12 plant-species were recorded in their diet. I also recorded the seeds of 16 other plants between May and September in north Derbyshire, where the bird breeds in small numbers. Combining the data for both areas, the bulk of their food consisted of the seeds of Betulaceae, especially birches, but those of Compositae, Graminae, Onagraceae and Chenopodiaceae were important when birch seeds were not available. Redpolls ate seeds varying in individual weight from 0.05 mg. (willowherbs) to 5 mg. (thistles). I did not record seeds from fleshy fruits in the diet, but greenstuff” was taken from March to August, and consisted mainly of birch buds in March and April, and of Stellaria media leaves during the rest of this period. Ovules from the of various Salix spp. were also important from March to May, both in Derbyshire and in Oxford. Invertebrates were taken from March to August, but mostly in April when seeds were scarcest.

THE FOOD FROM SEPTEMBER TO MAY IN OXFORD Table 5 shows the diet of the Lesser Redpoll in Oxford over three consecutive winters, as determined by observation. In addition, 36 birds were shot for gut-analyses, but mostly in April and May when the food was difficult to assess by observation. In the winter of 1961-62, there were no Betula seeds available in Wytham Woods, and few Redpolls wintered there, for I saw no more than six at any one time. In this winter, 48 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 small numbers fed on waste land and on the rubbish dump, where the seeds of the willowherbs Chamaenerion angustifolium and Epilobium hirsutum predominated in the diet. They also took Filipendula ulmaria seeds regularly in September and October while stocks lasted, Chenopodium album seeds in November and December, and Alnus glutinosa, Artemisia spp., and Tansy Tanacetum vulgare seeds from November to March. These last four seeds were available earlier in the winter, but were not taken in any quantity until the Filipendula and most of the Epilobium seeds had been eaten. In the following two winters, Betula seeds were available in Wytham Woods, and several flocks of Redpolls (totalling 400 and 200 birds in each year) fed there; very few Redpolls were seen in any other habitats in these years, even though these were visited several times each month. Despite the abundance of Betula seeds, Filipendula ulmaria and various willowherb seeds were also important in these years during their main seeding period in September-October. From November to mid-March, however, the diet consisted almost entirely of Betula seeds, which were obtained in the trees when- ever they were available there, but towards the end of the winter, on the ground below. Chenopodium and Artemisia seeds were also available near Wytham Woods in these years, but I did not see any Redpolls feeding on them there.

TABLE5. The food of the Lesser Redpoll Carduelis flammea cabaret in Oxford over three successive winters. 1961-62 1962-63 1963-64 Birch crop nil good moderate Approximate maximum number of Redpolls in the study area 20 400 200 No. of observations of food 103 1352 1104 Betula 0 95 86 Alnus 19 1 4 Willowherbs (espec. E. hirwutum) 41 3 4 Percentage composition of diet Filipendula ulmaria 3 1 3 September to March Chenopodium album 8 0 0 Artemisia 20 0 + Tanacetum vulgare 7 0 + Urtica dioica 1 0 + Salix ovules 1 0 + Salix ovules or seeds 27 38 49 I Buds (Betula) 10 10 7 Percentage composition of diet Invertebrates from buds of April to mid-May Larch 52 42 29 Sycamore 3 4 2 Oak 3 2 4 Ash 5 4 8

Although Redpolls and Siskins often fed together, both in birches and in alders, in the study area Redpolls always preferred birches and Siskins alders. Further, the number of Redpolls in the area was more closely related to the birch than to the alder crop. For instance, in the winter of 1961-62, alder seeds were plentiful, but birch seeds were not available, and Redpolls were scarce, as mentioned above. In all years, Betula buds and the flowers and seeds of various Salix spp. were taken from March to May, but the main foods in April were the various invertebrates present on developing buds, especially those of Larix. In all years, there was a large influx of Redpolls into the Oxford district in April, presumably on passage, and gut-analyses of birds shot while feeding from buds showed that the larvae of Adekes spp. and Coleophora larkella were obtained from larches, aphids from sycamores and ashes, and caterpillars from oaks. 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 49

THE FOOD FROM MAY TO SEPTEMBER IN DERBYSHIRE I have 104 observations of foods taken by Lesser Redpolls from May to September in Derbyshire. In May most of the birds fed on Stellaria media, Taraxacum oflicinale or Salix spp. seeds, in June and July on Betula, Sorrel Rumex acetosa or various grass seeds, and in August and September on Filipendula ulmaria or various willowherb seeds. Polygonurn persicaria, Crepis spp., Hieracium spp., Artemisia spp., Chenopodium album, Capsella bursa-pastoris, Centauria spp., and various thistle seeds were also recorded in their diet. In summer adults also took caterpillars and aphids off birch leaves, and at least some of these were presumably fed to the nestlings as well, though no young were examined.

COMPARISON WITH PREVIOUS DATA There seems to be little original information on the food of the Lesser Redpoll in Britain, but most books mention birch and alder seeds, while Jourdain (in Witherby et al. 1938) records " bulrush " seeds and " minute insects, larvae and eggs " as well. A bird examined by Newstead (1916) on 15 June contained seven Tortricid caterpillars and a weevil, and another shot on 18 December contained Milfoil Achillea millefolium seeds, which were not recorded in the present study. Evans (1966) has recently stressed the importance of Filipendula ulmaria seeds to Redpolls in Northumberland in August, and of various willowherb seeds in September. The larger Mealy Redpoll (C.f. jlammea) of northern and evidently takes more large seeds than the Lesser Redpoll, presumably because it has a corres- pondingly larger bill. Thus, while Betula seeds form its main food, it also takes freely the larger seeds of various conifers in Scandinavia (see for example Svardson 1957), and those of at least nine conifers and 19 deciduous trees (including 16 with fleshy fruits) in Slovakian forests (Turcek 1961). According to Peiponen (1962), Betula seeds predominate in the diet of the Mealy Redpoll in southern Finland for most of the year, but Alnus seeds are also taken in winter, and, when plentiful, those of Picea. Small animals, such as caterpillars, flies, springtails, insect eggs, Hemiptera, gnats and aphids, formed about a fifth of the food recorded by Peiponen in June and August, and about four-fifths in July. The rest of the food during these three months consisted of the seeds of various grasses, Stellaria and Rumex, as well as Betula. The nestlings received relatively more animals than were eaten by the adults themselves. Redpolls nesting in the arctic, where insects are extremely abundant in summer, probably take many more than those nesting in Britain. They are, however, apparently able to rear their young on seeds alone, for when Picea seeds are plentiful in northern Sweden, Redpolls nest earlier than usual and before insects are available. For example, in the spring of 1955, when spruce seeds were abundant, Witt-Stromer & Ingritz (1956) found several Redpoll nests with eggs and young when the ground was covered with 18 in. of snow and the temperature was -20°C. Later broods are apparently raised mainly on insects, and only the one brood is attempted in years when the spruce has fewer seeds (Svardson 1957).

LINNET Linnets are present in the Oxford district throughout the year, but many leave in October to winter elsewhere (mainly southern France and northern Spain), and most of those remaining move out with the first snow; smaller numbers return in April. The seeds of 46 plant-species were recorded in the diet in Oxford-mostly those of common farmland weeds, which were taken mainly from the plants in summer and from the ground in winter. The bulk of the food, as determined by both methods of investigation, consisted of the seeds of Cruciferae, Polygonaceae, Chenopodiaceae and Compositae, D VOL. 109 50 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 while those of the Betulaceae, important to most other finches, were not recorded in Oxford. Seeds varying in weight from 0.05 mg. (willowherbs) to 50 mg. (elm) were eaten. Over the year as a whole seeds of Sinupis amensis and other brassicas formed over a third of the total food, and those of Polygonum persicaria, Chenopodium album and Stellaria media were also particularly important. Seeds from fleshy fruits were not taken, and nor were buds, but other " greenstuff " such as the leaves of Stellaria media, was recorded in every month by gut-analysis. Invertebrates were taken from April to September but formed less than 1% of the total food.

VEGETABLE FOOD THROUGH THE YEAR Table 6 shows the diet of the Linnet in Oxford; it is based on observations in the study area throughout the year, and on gullet analyses of live adults from September to April and of live nestlings from May to August. In all, 379 adults were caught and examined at a roost in Wytham Woods, and 62 broods of young were examined regularly in nests that were found in the allotment gardens and hedgerows of the study area. A iist of the gut contents of 60 adults shot at various times of year has been deposited in the Edward Grey Institute. In April the diet, as determined by both methods of investigation, consisted partly of brassica, Polygonum persicaria and other seeds left from the previous year, and partly of the fresh seeds of Stellaria media and Poa annua. From May to August the same foods were recorded by observation as were found in the gullets of nestlings, but as expected, large seeds (Ulmus) figured more prominently, and small seeds less prominently, in the nestling data. Stellaria and Taraxacum officinale seeds predominated in the food of both adults and nestlings during May, but by June those of Ulmus glabra, Alliaria petiolata and Rumex acetosa were important as well. Seeds of Simpis amensis and some other brassicas then became available and figured prominently in the diet during July and August, but those of Catsear Hypochoeris radicata, Rumex acetosa and various Ranunculus spp. were also important in July, while various thistle seeds predominated in the food during their peak seeding period in August. A four-acre patch of small beech trees which retained their dead leaves through the winter held the only regular Linnet roost in Wytham Woods at which over 300 birds were caught from September to April for gullet analysis. It may be seen from Table 6 that all the foods recorded in this way were also recorded by observation; by both methods the seeds of brassicas (mainly Sinapis arvensis), Polygonurn persicaria and Chenopodium spp. (especially C. album) predominated in the diet from September to December, but only the first two through to April, by which time Chenopodium seeds had become scarce. But to judge from the food, the roost was comprised almost entirely of birds that had fed on farmland, since seeds available and eaten by Linnets in other habitats of the study area were poorly represented or absent from those caught at roost. For instance, in September and October, Filipmdula ulmaria and Artemisia vulgaris seeds figured prominently in the observational data, but were almost negligible in the gullets of those caught at roost. As with most other finches, seasonal changes in the Linnets diet paralleled changes in the relative abundance of the various foods, and the diet became progressively more restricted in winter as the number of seeds available declined. Each year there were about a thousand Linnets at the Wytham roost in September, but numbers fell to 400-500 in October when many left the Oxford area. (Ringing recoveries have shown that many British-bred Linnets move to southern France at this time.) Numbers at the roost then remained fairly constant until the first day of snow when they fell abruptly to less than a hundred. This sharp decline was probably due mainly to birds leaving the area, for large numbers of Linnets were seen moving south at this time at various places in southern England (J. L. F. Parslow, pers. comm.). It TABLE6. The percentage composition of the diet of the Linnet Carduelis cannabina in Oxford, based on three years' data. The Y figures in normal type are based on the results of field observations amd those in italics on the results of gut-analyses of nestlings from May to August and of adults from September to April. Seeds are listed, as far as possible, in order of their appearance in the diet from April onwards. Continuous lines indicate the main seeding periods of the dzj%wnt food-plants, and dotted lines the period for which seeds are normally available on the plant afterwards. Otherwise seeds are picked from the ground. + =Less than 1%.

AVERAGE IAN. TO MARCH APRIL MAY WNJl JWLX AUG. SEPr. OCT. NOV.ANDDEC. % OG OG OG OG OG OG OG OG OG(BYOBS.) No. of observations or gullets examined c. 1000 58 580 42 c.820 567 c. 1150 1836 c.2300 1054 C. 1850 522 c. 1760 77 C. 1030 96 c. 1080 132 SEEDS Sfellaria media + 34 22 43 40 32 26 22 9 Poa annua + 14 6 12 8 + 2 Taraxacum officinale 1 2 40 42 18 19 31 + 2 1 5 .. Ulmus spp. (spec. (I. glabra) 4 9 12 20 ------_14 2 Alliaria peiiolafa -12 10 - - - - -23 - - - - - 1 Senecio vulgaris + I+ 11 3 2' + Rumex acefosa 10 8 20 17 ------.2+ 3 Ranunculus spp. 66 8 10 --_----. 33 2 Hypochoeris spp. (spec. H. radicafa) 3 4 18 21 21 2 1 2 Capsella bursa-pasf oris 33 63 + 1 GI~SS- 2 2+ ------_--__- -___ + Brassicas (spec. Sinapis arvensis) 59 56 21 36 26 28 28 39 22 46 34 50- 49 6f- 33 Sonchus oleraceus 42 31 3 -1 ------_ - 1 Polygonwn aviculare ++ 22 Z6------_---__ 22 31 2 Thistles -----_46------2 + 46 42 84--_---_-_-__---___ 5 Polygonurn persicaria 11 29 21 28 24 2 4 10 16 12 18--_~5__-~-- 11 Ragworts Sene& SPP. - - _ - 2 1 ---____-_ + Chenopodium SPP. (spec. C. album) 10 8 24 8 3 18 20 23 24 17 16 11 Arternisia vulgaris 2---+--- 2- -- l8 10 2 ------3 3 Filipendula ulmaria 11 2 IL-2______- 2 Mafricaria mairicarioides 1 1 ------1 - - - - 1 Sisymbrium spp. ,- 24 ------2 ----2 ----______8 3 Willowherbs (spec. E. hirsuium) + 1 - - --2 - -- - + Planfago spp. (spec. P. mqior) 21 ---- ___-______1 1 Others 4 2 +2 ++ 15 +2 +2 ++ + ORCENSTLJFF ++ ++ ++ ++ ++ ++ ++ ++ ++ + I NVZRTEBRATES Caterpillars ++ ++ Aphids + + + -t wl Others + ++ + + CL 52 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 is not known whither these movements took them (though there was some slight con- centration on coasts and estuaries that were free of snow), or what proportion of thtse late emigrants returned to Oxford. The only noticeable influx into the study area occurred in April, but this might have been due entirely to the return of birds that had spent the whole winter abroad. In all years there was a marked change in the diet of the Linnets that stayed while there was snow, seeds remaining on upright plant stems providing the only source of food. Combining the data for all years, the diet during snow-periods was as follows:- Per cent of diet as determined by:- Food* Observation Gullet analysis (102) (32 birds) Artemisia spp. 34 44 Grasses 30 24 Plantago spp. 18 20 Chenopodium album 14 8 Sisymbrium qficinale 4 - Other brassicas (especially S. aretensis) - 4 * The data (collected in only one week each year) were excluded from Table 6.

As may be seen, seeds of Artemisia, various grasses, and plantains (especially P. major) were particularly important at this time, and some of them were not recorded in the diet at any other time of year; Polygonum persicaria seeds, which by this time had all fallen to the ground, were not recorded at all, and brassica (other than Sisymbrium) seeds were found in only one of the 32 birds examined at the roost. Periods of snow were probably the most critical time for Linnets in Oxford, since the few seeds remaining on plant stems were soon eaten and there was no evidence that Linnets concentrated round farmsteads or at other artificial food-sources at such times. Further, numbers in the study area and at the roost continued to fall while the snow lasted, a decline which was probably due mainly to mortality and not to emigration, since all those seen feeding seemed too weak to fly far. After the thaw, there was always a return to the previous diet in which Sinapis, Polygonum and other seeds picked from the ground predominated. At the end of the snow periods of 1962 and 1964, between 30 and 50 Linnets regularly fed and roosted in the study area until the influx in April raised their numbers, but in 1963, when the snow lay in Oxford from early January to early March, Linnets had disappeared completely by mid- January and were not seen again until April.

ANIMAL FOOD THROUGH THE YEAR Animals were less important to the Linnet than to any other finch. Although I recorded them in the diet from May to September, in each of these months they formed less than 1% of the food of both adults and nestlings. Invertebrates were recorded in the food of only two out of 62 broods, even though I examined some over 100 times. In one of these two broods, the young received about 15% of caterpillars and aphids for the first nine days (after which the young disappeared), and in the other the young once received amongst their food some small beetle larvae, probably from the seed-head of a thistle since these seeds were present as well. It is possible that such larvae are taken much more often than these records suggest, since, being pale, they are easily overlooked among seeds in the gullet. Nevertheless they can form at most only a small fraction of the nestling’s diet. Although adult Linnets were seen occasionally to pick caterpillars and aphids from elm trees, these were visited mainly for their seeds. Only one out of 38 adults shot in the breeding season contained any animals-two small beetle larvae, probably from the seed-head of a Candelion since these seeds were present too. 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 53

COMPARISON WITH PREVIOUS DATA Collinge (1924-27) listed 11 types of seeds in the gut-contents of 39 adult Linnets. They included those of Sinapis arvensis (which predominated), but also in three birds those of wheat, and in six birds those of docks, which were not recorded in the present study. Caterpillars, moths and other insect remains were found in eight of these adults, while the food of 39 nestlings he examined consisted of lepidopterous larvae, a few dipterous larvae, spiders, aphids, and in two birds beetle remains. Apparently he did not record any vegetable matter, which is particularly surprising as it comprised the entire diet of most broods in Oxford. Eber (1956) did not record any invertebrates in the food of the Linnet in Holstein. Newstead (1916) observed Linnets eating the seeds of Sinapis urvmsis, Self-heal Prunella vulgaris and the hawkweed Hieracium pilosella and found those of Rumex and Taraxacum in a bird shot in July: in five birds examined by Florence (1912) seeds of Rumex acetosa and Sheep’s Sorrel Rumex acetosella (not recorded in the present study) predominated. Several authors (e.g. Jourdain’ in Witherby et al. 1938) record among the foods of the Linnet in England the seeds of various cultivated brassicas, such as turnip, cabbage and rape. These are taken both when freshly sown and, if the crop is grown for seed, again at harvest time. Seeds of Hop Humulus, Linum and Cannabis are also mentioned as foods of the Linnet in a number of books.

CROSSBILL Large irruptions of Common Crossbills reached Britain from in 1962 (Williamson 1963) and mostly from Scandinavia in 1963 (Davis 1964). In the former year, birds first appeared in Wytham Woods in July, numbers built up to about 200 in August, and then declined steadily until all had gone by the following April. In the second year, about 50 appeared in August, but again had left by April. In both years, they made little impact on the supply of food available to them in Wytham Woods, and the decline each winter was almost certainly due to emigration. Although birds were present during the normal nesting season, breeding was not recorded in Oxford in either year. Nests were, however, reported from several other parts of Britain where Crossbills do not normally breed (see Davis 1964). In both years, conifer seeds formed the entire diet as determined by observations in Wytham Woods, and no birds were shot for gut-analysis. About 98% of the records were of birds feeding from the cones of Larix decidua (the dominant conifer on Wytham), and the rest from those of Picea abies or Pinus sylvestris. Larch seeds also formed the main food over the rest of Britain in these years (Davis 1964). This is surprising, since, as he points out, there were comparable crops on spruce and pine in these years, and over Britain as a whole, these two conifers have been much more extensively planted than larches. Further, Lack (1944) has argued that the Common Crossbill is adapted to feed primarily on Picea cones, so its preference for Larix in Britain is even more surprising. On Wytham, and also in the rest of Britain, seeds from opening Pinus cones became more important in the diet in spring, presumably because while Common Crossbills can deal easily with ripe and unripe Picea and Larix cones, they have difficulty in extracting the seeds from hard Pinus cones before they have opened. Although conifer seeds formed the entire diet of the Crossbill in Oxford, many other foods, such as the seeds from various fleshy fruits (including apples) and thistles, are eaten on migration, though usually only when conifer seeds are not available. All these alternative foods, many of which are listed by Barraud (1956 : 293-296), are ones that can be dealt with using the same behaviour patterns that are used to open cones. Few gut-analyses have been carried out on Crossbills from Britain, but a bird killed in January contained conifer seeds and some pieces of sclerenchymatous tissue (Florence 1914), while three killed in December contained Pinus sylvestris and Crataegus seeds 54 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

(Newstead 1908). In Slovakian forests, Turcek (1961) lists the seeds of 42 conifers and 26 deciduous trees, including 16 with fleshy fruits, in the diet of Crossbills. He also recorded them taking the buds of several types of trees, both conifer and deciduous. Small invertebrates, such as aphids and caterpillars, are often recorded, and after each invasion of Crossbills into Britain, there have been reports of birds tearing at lichen and prizing off bark, possibly to obtain the invertebrates beneath. There is little information on the food of the nestlings. Bailey, Niedrach & Baily (1953), who watched some nests of L. c. benti in Colorado, noticed that while older young were fed entirely on pine seeds, newly hatched young were also given a dark viscous material, which might have consisted of small invertebrates. While insects are taken when available, it seems likely that most broods are reared entirely on vegetable matter, since they are in the nest in the early months of the year when invertebrates are scarcest. In support of this, Olsson (1960) recorded only pine seeds in the food of three broods of the related Parrot Crossbill in southern Sweden, while Tordoff & Dawson (1965) have confirmed that Crossbills in captivity can rear their young on seeds alone.

CHAFFINCH Chaffinches are resident in Oxford throughout the year, though their numbers are augmented in winter by immigrants mainly from Scandinavia but also from Germany. With the onset of snow many move into gardens and farmsteads, while others (probably mainly continental birds) leave the area completely, as ringing recoveries have demon- strated. In the breeding season they are found only in areas with tallish trees and hedge- rows, and for the rest of the year, mainly round the edges of woodland or in large flocks in open areas. Chaffinches feed almost entirely on the ground for much of the year, so it is not usually possible to see what they are eating, and since I was able to take only a limited number under licence, relatively few data were obtained on their diet. A further difficulty was that the gizzards of most of those examined in summer were either empty or contained only a small amount of food; often this was unidentifiable. This is partly attributable to the preponderance in their diet at this time of soft-bodied insects, such as aphids, which are usually crushed beyond recognition and digested quickly. For instance, I shot one bird after I had watched it taking aphids continuously for about five minutes; on examination its mouth and gullet were empty and only two aphids and a few remains were found in the gizzard, the rest had already passed through to the intestine and were partly digested. Despite these difficulties, the seeds of 32 plant-species were recorded by gut-analysis, and those of another eight by observation; seeds of Gramineae, Cruciferae, Polygonaceae and Chenopodiaceae predominated, while those of the Com- positae, important to most other finches, were of negligible importance to the Chaffinch. They took seeds varying in weight from 0.1 mg. (Artemisia)to 230 mg. (Fagus syleratku), but over the year as a whole those of cultivated cereals were by far the most important part of their diet in Oxford, and were recorded in every month. Fragments of moss, buds and Stellaria media leaves were found occasionally, but not seeds from fleshy fruits which have been reported by Turcek (1961) for the Chaffinch in Slovakia. Throughout the year Chaffinches in Oxford ate a greater proportion and variety of invertebrates than the other finches studied, including a greater proportion of ground-living forms, such as weevils. In contrast to the young of cardueline finches, young Chaffinches are reared entirely on invertebrates, mainly defoliating caterpillars.

THE FOOD FROM MAY TO JULY Out of the 25 birds I shot over this period, only six contained any food: all six contained caterpillars, while aphids and cereals were found in three, and weevils, Stellaria 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 55

media and Ulmus glabra in one. In addition, seven Chaffinches were caught in mist nets while on their way to feed their young and the following items were obtained from their :-

Caterpillars : Operophthera brumata (from five birds), Tortrix viridana (from three birds), Allophyes oxyacanthae (from one bird) Moth: one specimen, species unknown (from one bird) Beetles: Rhyncophera (from one bird), Chrysomelidae (from one bird) Spider: one specimen, species unknown (from one bird)

The occurrence of small Tortrix viridana caterpillars in the beaks of three of these birds is of special interest in view of the fact that titmice, which have young in the nest at the same time as Chaffinches, hardly ever take them before they have pupated (T. Royama, pers. comm.). The predominance of invertebrates in the diet of the Chaffinch at this season is supported by field observations, since 81% of records obtained then refer to birds seen taking what appeared to be caterpillars (66%) or aphids (15%). Although the young are reared entirely on animal-material (Collinge 1924-27, Marler 1956), the adults themselves also eat seeds at this time (see above); and these are sometimes obtained at communal feeding grounds, such as farmland, outside the territory. RIarler has suggested that one function of territory in the Chaffinch is to ensure an adequate supply of food for the young, but even so, as he also points out, caterpillars are sometimes sought in other places, providing they do not lie within the territory of another pair.

THE FOOD FROM MID-JULY TO MID-APRIL IN OXFORD Marler (1956) has suggested that the large flocks of Chaffinches, which sometimes assemble at considerable distance from the nearest woodland, consist mainly of immi- grant birds, which also roost communally, while most resident Chaffinches remain near their breeding areas and roost singly. In agreement with this view, large feeding and roosting flocks first appeared in the study area in early October, which corresponds with the time of the main influx of continental Chaffinches into Britain. Witherby et al. (1938) give the wing-lengths of British Chaffinches as 83-9Om. in the males and 78-85 mm. in the females, and in male Scandinavian birds as 87-92 mm. (no figures are given for the females). The wing-lengths of all those handled in the present study were measured by the same method as described in Witherby et al. and are given in Table 7 according to the place of capture. It may be seen that the large roosting and feeding flocks that were sampled contained a larger proportion of long-winged individuals than were present among those caught round the edges of woodland or shot as they roosted singly, thus supporting Marler's suggestion that the different races are partially segregated in winter. Further evidence is available from ringing since five " singles "

TABLE 7. The wing-lengths of ChafJilaches coelebs examined between October and Apd according to the place of capture. The figures show the percentage of birds with particular wing-lengths. (For further explanation see text.)

NO. OF BIRDS WING-LENGTH (MM.) OF:- EXAMINED 78-80 81-82 83-84 85-86 87-88 89-90 91-92 Birds roosting singly or Male 126 - - 6 35 47 8 4 feeding in or near the - - edge of woodland Female 52 22 32 28 14 4 Birds roosting communally Male 204 - - 2 10 34 36 18 or feeding in large flocks in open areas Female 154 8 18 28 34 12 - - 56 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 shot in woodland in winter, but none of those caught at large communal roosts, had been ringed there in a previous summer. This is not to suggest, however, that there is absolute segregation of the different races in winter, since birds of all these wing-lengths were represented in both categories. (It is not possible to determine the feeding habits of German Chaffinches in winter, since they are probably present in only small numbers and have the same wing-lengths as British birds.) In view of the difference in feeding places, the diets of Chaffinches roosting singly and communally have also been analysed separately but the appropriate data for different years have been combined. Analyses of “single” birds are based on a thorough examination of both gullet and gizzard contents, and analyses of birds roosting com- munally, on the gullet contents of live birds.

TABLE8. The gut-contents of Chaflinches Fringilla coelebs from mid-July to mid-April near Oxford. MID-JULY TO SEPTEMBER OCTOBER TO MID-APRIL Roosting singly Roosting communally No. of birds examined 25* 5 0’ No. of items found 270 655 SEEDS Cultivated cereals 56 36 Grasses 4 2 Polygonum persicaria 1 2 P. convolvulus 1 2 Large Rumex - 4 Small Rumex - + Brassicas (mainly S. amensis) 3 9 Stellaria media 9 4 Cerastium 2 2 Lamnium purpureum 1 1 Polygonum aviculare - 2 Fagus silvatica - 4 Castanea sativa - 3 Thistles 2 + Senecio + + Artemisia + 1 Chenopodium spp. (mainly C. album) 4 15 Poa annua + 1 Other seeds 1 5 INVERTEBRATES Diptera imago 2 1 larvae Weevils 3 3 Other beetles 3 1 Spiders 1 + Earthworm coccoons + 1 Snails + + Caterpillars 1 + Butterfly or moth 2 - Aphids 3 + Notes. * Based on gullet and gizzard analyses of shot specimens. t Based on gullet analyses of live birds.

Although the data are few, they indicate the wide range of seeds taken by “ resident ” Chaffinches in winter (see Table 8). From only 50 birds examined between October and mid-April, 32 types of seeds were recorded. Further, although Chaffinches were frequently seen in woodland throughout winter, the analyses indicate that most of the food was obtained on farmland. Cereals predominated in the food of resident birds from mid-July to mid-April; these were obtained mainly from beneath standing corn in summer, from stubble in autumn, from stubble and farmyards in winter, and from sowings in spring. Stellaria media seeds were also important in August and September, and invertebrates formed about 16% of the food then, though the sample for these 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 57 months is small. In addition to cereals, Chenopodium and brassica seeds were important in winter, and about 8% of the diet consisted of invertebrates, weevils (mainly Sitones, also Apions and others), various other beetles and beetle larvae, earthworm Lumbricus cocoons, earwigs ForJicula and other ground-living forms predominated. During the study period, beechmast Fagus silvatica formed only a small part of the food, and was taken mainly in October. In view of the large number of records in the literature of Chaffinches eating beechmast, it would presumably have figured much more prominently in these Oxford data had a really good beechmast year occurred during the study period. The only other foods taken in woodland were chestnuts Castanea sativa (that had fallen on to a road through Marley and been crushed by passing vehicles), and the seeds of Red Deadnettle Lamium purpureum and various conifers; the latter were taken mainly in March and April, and were either picked out of the ripening cones or caught in flight as they fell. In marked contrast to the “ residents ”, which ate a wide variety of foods, only four types of seeds were recorded in the gullets of “ immigrants ” caught at communal roosts: those of brassicas (probably mainly Sinapis arvensis), cereals, Chenopodium (probably mainly C. album) and Polygonum persicaria. This may be partly a result of the less precise analyses carried out on those caught at communal roosts, but on the other hand, the gizzards and gullets of 12 such birds that were later killed did not on closer inspection reveal any other types of seeds. It would have been easy, however, to overlook certain foods, such as earthworm cocoons, among a mass of seeds in the gullets of live birds. (Small dark beetles, on the other hand, were easily distinguished, and formed about 3% of the winter food of “ immigrant ” Chaffinches.) In view of the disparity in the methods of analysis and of the small samples involved, this difference in variety of foods taken by the different races must be regarded as highly tentative, until it can be substantiated by further analyses. If Marler’s suggestion is correct, however, just such a difference would be expected; the immigrant Chaffinches tending to congregate at places where food was particularly plentiful (such as weedy fields), while residents, which tend to stay near their breeding places, might well be obliged thereby to take a greater variety of food. Male British Chaffinches normally take up their territories in January or February and so could presumably not afford to feed far away in these months.

COMPARISON WITH PREVIOUS DATA In the early years of this century a great deal of information was collected on the food of the Chaffinch in order to establish its “ economic status ”. The main analyses were carried out by Florence (1912, 1914, 1915) who examined 218 birds, mainly from farm- land in northeast Scotland, and by Newstead (1908), Theobald & McGowan (1916), Leigh (1916), and Collinge (1924-27) who examined 27, 527, 357 and 160 Chaffinches respectively from various parts of the British Isles. (Collinge’s total included 32 nestlings.) Although large numbers of birds were involved (a total of 1289), the results obtained are subject to the same bias as my own, in that soft-bodied insects are more easily digested than hard-bodied insects and seeds. In addition, however, it seems that many of the birds they examined were shot while actually eating food of economic interest (e.g. “ harmful ” or “ beneficial ” seeds or insects), which therefore receive undue emphasis in the final analysis. Further, almost all the specimens seem to have been obtained from farmland, orchards or gardens, and hardly any from woodland. Thus, caterpillars, which were important to Chaffinches in Wytham Woods in summer, formed only a small fraction of the invertebrates found in these earlier analyses, and beechmast was not recorded at all (though Newstead recorded it by observation). From the results of Theobald & McGowan and Florence in Britain, and Eber (1956) in Germany, I have calculated the proportions (by number of items) of vegetable and 58 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 animal material in the diet of the Chaffinch at different times of year (see Table 9), since my own data are inadequate. There is considerable variation in the results obtained, but all indicate that a much higher proportion of invertebrates is eaten in summer than in winter, while the average proportion over the whole year in each of these three studies works out at 15%, 33% and 25% respectively, against 25% given by Collinge (1924-27). However, it is likely that all these figures are underestimates, Eber's because it is based on observational data only, and the others for the reasons mentioned above. Neverthe- less, it is clear that the Chaffinch eats a much higher proportion of animal matter than the cardueline finches I studied, in whose annual diets invertebrates never exceeded 3%.

TABLE9. The percentage of animal and vegetable matter in the diet of the Chaflinch Fringilla coelebs at different times of year, based on the gut-analyses of Florence (1912, 1914, 1915) and Theobald &f McGowan (1916), and on the observations of Eber (1956). For further details see text. Average Jan. to April May to July Aug. to Sept. Oct. to Dec. percentage Florence (1912, 14, 15) No. of birds examined 138 305 - 41 Total no. of items found 3428 395 - 1032 Percentage" vegetable matter 93 64 - 98 85 Percentage" animal matter 7 36 - 2 15 Theobald & McGowan (1916) No. of birds examined 314 143 17 51 Total no. items found 1073 290 99 303 Percentage" vegetable matter 87 33 65 71 67 Percentage" animal matter 13 67 35 29 33 Eber (1956) Total no. of observations 2081 331 3 54 2070 Percentage vegetable mattert 97 30 63 99 75 Percentage animal mattert 3 70 27 1 25 Notes. * By numbers of items. ?This differs from the estimate given by Eber herself (p. 18 of her paper) since it was worked out differently from here.

In publishing the results of her analyses, Florence listed the gut-contents of each bird examined, but did not analyse the resulting data any further. I have therefore summarized her results in Table 10 for comparison with my Oxford data. The absence from her October-December results, of certain foods which she recorded occasionally between January and April can be attributed partly to the smaller sample examined in the earlier period. Similarly, the almost complete absence of caterpillars and the great prevalence of aphids from May to July might also be the result of a small sample, but another explanation is also possible. Thus, Royama (1966) has found that adult Great Tits Parus major with nestlings eat most of the small food items they find themselves and bring mainly the larger ones to their young, presumably because it is more efficient this way. If similar behaviour occurs in Chaffinches, this could well account for the preva- lence of aphids, and the absence of caterpillars, in the guts of those adults examined by Florence. As in Oxford, cereals were recorded in every month of the year and were one of the most important foods. In terms of their bulk, cereals were much more important than these figures, (which are based on the number, and not on the volume, of different items in the diet) suggest. Charlock seeds were also important in winter, as were those of Spergula arvensis; this plant in common with some other weeds of cornfields has now become rare in Oxford, probably through the use of herbicides, and was not recorded in the diet of any finches there. On the other hand, Chenopodium seeds, which were important in Oxford, were not prevalent in the food of any of the finches examined by 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 59

Florence, which is surprising since the plant grows commonly in northeast Scotland. Other seeds recorded by Florence as important in the diet of the Chaffinch were those of Stellaria media, Rumex spp. and Knotgrass Polygonurn aviculare. Among the inverte- brates found by Florence, weevils (mainly Sitones), various other beetles and beetle larvae, diptera and earthworm cocoons predominated throughout the year. Com- paratively few data were obtained by Florence from May to July when caterpillars and aphids apparently became more important in the food of Oxford Chaffinches. The results of the remaining studies, by Newstead, Theobald & McGowan, Leigh and Collinge, all agree on the importance to the Chaffinch of cereals and various weed seeds, such as those of Sinapis arvensis, Stellaria media, Polygonum spp. and Chenopodium spp., as well as on the relatively large proportion of invertebrates in its diet. These authors also recorded a number of seeds not found in the Chaffinches I examined in Oxford, and Collinge found that fruit buds made up 4.5% of the diet and fruit pulp 3.5%. These comparatively high figures are difficult to explain unless many of his birds were shot in orchards, since fruit pulp was not recorded by any other workers, and buds only rarely.

TABLE 10. The diet of the Chaffinch Fringilla coelebs in northeast Scotland, based on the gut analyses carried out by Florence (1912, 1914, 1915). The Jigures show the per cent (by number of items) of different foods in the diet. Jan. May Oct. Jan. May Oct. to to to to to to April July Dec. April July Dec. Total no. of birds L. album + examined 138 30 41 Anthoxanthium + No. with vegetable Raphanus raphanistrum + matter 136 26 40 Potentilla erecta 1 No. with animal matter 58 20 15 Unidentified seeds 367 Total no. of items found 3428 395 1052 OTHER VEGETABLE MATTER SEEDS Greenstuff and moss +1 Cultivated cereals 22 23 14 Grass ovaries 1 Polygonum spp . (especially P. persicaria) 1 6 INVERTEBRATES Rumex acetosella 1 1 Dipteran Frvae + + Rumex acetosa 1 8 imagines +5 Other Rumex + Coleopteran larvae + 3+ Hanunculus spp. + imagines + 3 Brassicas (especially Hemiptera 1 18 S. arvensis) 32 1 Lepidoptera larvae ++ Spergula arvensis 19 1 38 Weevils 271 Stellaria media 8 16 17 Springtails 1 + A triplex + Wireworms + Cerastium 1 4 Pupa cases + + Viola 12 Spiders + + Myosotis + Earthworm cocoons 1 + Galeopsis + 1 Snails + + Lamnium purpureum 1 14 Unidentified insects +I1

There is considerable information available on the food of the bird abroad. Eber (1956) recorded the seeds of 44 plant species in the diet of the Chaffinch in Holstein, Germany, including those of Sorbus which were not recorded in any of the British studies. It seems, however, that much of the diet is similar in the two areas. Cereals formed about half her records, beechmast nearly a third, while various Cruciferae, Artemisia, Rumex, and Betula were also important. On the other hand Chenopodium seeds, which were important in Oxford, do not seem to have been recorded by Eber. Invertebrates mentioned include Collembola, Aphidoidea, Coccoidea, Coleoptera, Hymenoptera, Diptera, and Lepidoptera. Turcek (1961) records the seeds of 29 conifers and 56 deciduous trees in the food of the Chaffinch in Slovakian forests, together with the buds of eight genera of trees, coniferous and deciduous. 60 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

To summarize, as many as 32 different types of seeds were found in the gizzards of the 50 Chaffinches killed in Oxford in winter, and if these data are combined with the observational data obtained in the present study and with results of the earlier British studies, the figure becomes 78. Hence the Chaffinch takes a greater range of seeds (and also of invertebrates) than any other finch studied. This is partly attributable to the birds comparatively large bill which allows it to exploit food over a wide size range. This is not the whole reason, however, since the Greenfinch has an even larger bill but eats fewer types of seeds and invertebrates. Probably the main reasons for such a varied diet in the Chaffinch lies in its catholicity in choice of habitat, especially in winter, and its habit of feeding primarily on the ground, as well as in its adroitness at catching moving prey (see later). On the ground it can feed much more efficiently than the cardueline finches and can therefore find enough food in places where seeds are too sparse to support other species (also see later). Further, the seeds of almost all species of higher plants are available on the ground, often in great local concentrations. It is presumably through exploiting such a wide niche, that the Chaffinch is one of the commonest birds over its entire range.

BRAMBLING were present in the study area from mid-October to late April; but were seen mainly from late October to December when beechmast was available there, and again in April when flocks of passage birds appeared. None was shot for gut-analysis and no roots were found, so this account is based entirely on observations. The seeds of 20 plant-species were recorded in the diet of Bramblings in Oxford; beechmast was most important in autumn, and seeds of various cultivated cereals, Polygonaceae, Chenopodiaceae and Cruciferae in winter. I did not see Bramblings eating buds or seeds from fleshy fruits in Oxford, but Turcek (1961) mentions both among the foods of the Brambling in Slovakian forests. Further, while invertebrates, other than aphids, were not recorded in the diet in Oxford, they are probably taken throughout the winter as they are by Chaffinches. The young are reared entirely on invertebrates, mainly defoliating caterpillars.

THE FOOD FROM MID-OCTOBER TO APRIL Six records for mid-October were all of Bramblings taking Betula seeds, still on the trees, while 27 records between late-October and December were all of birds taking beechmast, mainly from the ground. At this time Bramblings were also seen occasionally on farmland with Chaffinches, but I was unable to see what they were eating there. From January to March, however, Bramblings fed entirely on farmland, chiefly where spilled grain and various weed seeds were plentiful. In the study years, the Beech crop had always disappeared by the end of December, but had it been larger, it seems likely that Bramblings would have continued to feed on these seeds throughout the winter. A flock wintered in the study area only in 1962, but in all years large numbers of Bramblings congregated (with other finches) on the downland south of Oxford where they took the following seeds : Chenopodium spp., cereals, Polygonum persicaria, P. aviculare, Black Bindweed P. convolvulus, Artemisia vulgaris, Atriplex spp., Rumex spp., and various brassicas including cultivated mustard. In addition to these seeds those of Stellaria media and Poa annua were taken in the study area in April and were sometimes picked directly from the plant. Bramblings were also seen eating aphids off Sycamore leaves at this time of year.

COMPARISON WITH PREVIOUS DATA There seem to have been no gut-analyses carried out on Bramblings killed in the British Isles, but several authors (e.g. Jourdain, in Witherby et al. 1938) stress the importance of beechmast to the bird; in addition to this and to various cereals and weed 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 61 seeds, Jourdain mentions the fruits of Sambucus nigra, which I did not record in Oxford, even though they were available there. Eber’s (1956) data from Holstein, Germany, are for the most part consistent with my own from Oxford; thus about half her records refer to Fagus silvatica, nearly a third to cereals and the rest mainly to seeds of Cruciferae. Seeds of minor dietary importance in Germany included those of Betula, Polygonum, and Artemisia, and also Oenothera, Alnus, and Sorbus none of which was recorded in Oxford. In Slovakian forests, the Brambling has been recorded to take the seeds of 13 conifer and 27 deciduous trees, including some with fleshy fruits, together with the buds of Populus and Prunus (Turcek 1961).

THE FOOD OF NESTLING FINCHES IN RELATION TO BREEDING HABITS The fringilline finches, the Chaffinch and Brambling, feed their young entirely on invertebrates, especially -eating caterpillars; these are brought to the nest, a few at a time, in the bill. The nestlings therefore receive small, but frequent, meals and do not normally need to store food in their gullets. Compared with suitable seeds, caterpillars are fairly evenly distributed in woodland in summer, and Marler (1956) has suggested that one function of territorial nesting in the Chaffinch is to ensure an adequate supply of food for the young within easy reach of the nest. The cardueline finches, on the other hand, feed their young entirely, or mainly, on seeds, and all species studied nest either in “ loose colonies ” or solitarily, but are not territorial. Group nesting is commonest in the Linnet, Redpoll and Twite, less frequent in the Greenfinch, Goldfinch, Siskin, Crossbill and Hawfinch, and rather rare in the Bullfinch. The nesting groups are largest in the Linnet, and sometimes up to several dozens of pairs may be involved, with some nests only a few yards apart. Over 20 pairs of have been recorded nesting in one group (Mountfort 1957 : 57) and up to six pairs of Greenfinches (pers. obs.), but in the remaining species, the nesting groups rarely consist of more than three pairs. The food for the nestlings of all these cardueline finches, in contrast to that of young Chaffinches and Bramblings, consists primarily of seeds; these are found mainly in local concentrations which are continually changing in distribution during the breeding season, so territorial nesting would be of no advantage. Thus, among the Fringillidae, those species which feed their young on invertebrates and are territorial in the breeding season, feed mainly within their territories, whereas those that feed their young primarily on seeds and often nest in groups, obtain their food communally at some distance from the nest. In addition to the gullet in which food is stored, adult Bullfinches also develop in the breeding season a pair of “ buccal pouches ” below the lower jaw in which the special food for the young is kept; these pouches hold over one C.C. of food and are similar to those already described for the finches Leucosticte (Miller 1941) and Pinicola (French 1954), but I was unable to ascertain whether the other cardueline studied here also had them. The possession by the cardueline finches of a storage organ, in which a large quantity of food can be retained, enables the adults to collect food at greater distance from the nest than would be possible if food items were brought in the bill, a few at a time (as in Fringilla). The young of all carduelines are fed by regurgitation and receive large, but infrequent, meals which they store in their gullets. The food given to the nestlings does not appear to be digested in any way beforehand and, contrary to the suggestion by Lack (1954), is not supplemented by any special nutritive secretion comparable to the crop-milk of pigeons. But the various food items are bound together with a little mucous which might provide some water and protein for the young. The nestlings also receive grit and free water from their parents along with the food. The Hawfinch differs from the other finches studied in using two methods of conveying food to its young: seeds are swallowed and regurgitated to the young, but invertebrates are carried, several at once, in the bill (Robertson 1951, Mountfort 1957). 62 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

There are other differences between the fringilline and cardueline finches that can be related to their different nesting dispersion. For instance, in the Chaffinch and Brambling sexual behaviour and song are restricted to the territory and there is no courtship feeding before nesting. In the carduelines, pair-formation, accompanied by courtship feeding, occurs while the birds are in flocks; and the song, which may be heard in almost every month of the year, apparently has little or no territorial significance. Further, whereas the female Chaffinch is fed on the nest by the male only rarely (Marler 1956), the female cardueline finch is almost wholly dependent on the male during incuba- tion and he is also (in contrast to the male Chaffinch) responsible for collecting all the food for the first few days after the young hatch. Since young Chaffinches are fed mainly on defoliating caterpillars which, in southern England, are plentiful for only a short period in early summer, the breeding season is short (usually lasting only two months), and second broods are rare (Newton 1964 a). In contrast, second or even third broods are common among cardueline finches, most of which have breeding seasons lasting up to five months in southern England. Protein is probably the most important factor in the diet of growing nestlings. Carbohydrates and fats may be considered of secondary importance to young carduelines, since they comprise the bulk of most seeds, while vitamins and trace elements are almost certainly present in sufficient quantity. It is not, of course, the actual protein content that is important, but rather the proportions of various essential amino acids, the one in shortest supply being the limiting factor in the diet. If the amino acid requirements of a nestling are determined by the composition of its own tissues, then it is likely that its needs would be met more nearly by animal than by vegetable protein; and for normal growth the young of most vegetarian birds are known to require a good proportion of animal protein in their food. It is of particular interest, therefore, that the Crossbill and Linnet usually rear their young entirely on vegetable matter, and that other carduelines may do so occasionally. Moreover, the vegetable diet of young Crossbills (and possibly sometimes of young Siskins and Redpolls) may consist of only one type of seed. Other seed-eating birds known to be able to raise their young on seeds alone, at least in captivity, include the Canary (a cardueline finch), the Zebra Finch Taeniopyga guttata, the domesticated Bengalese Finch and the Budgerigar Melopsittams undulatus (D. Goodwin, pers. comm.), though many estrildine finches and parrot-like birds may do so in the wild. That the Crossbill rears its young without animal food is attributable to its nesting primarily in late winter when invertebrates are scarcest, but it is odd that the Linnet, which nests in summer, should do this as well. The breeding season of both species are obviously independent of a supply of invertebrates, and since the Crossbill has been recorded as nesting in every month of the year if suitable food is plentiful, its breeding season is apparently also independent of photoperiod (see also Tordoff & Dawson 1965). Although other carduelines give some invertebrates to their young, there is evidence that their breeding seasons too are dependent primarily on an abundance of seeds. For instance, the quantity of invertebrates received by nestlings of all species varies with the time of year. In Oxford, I found that the early broods of Greenfinches reared at a time when insects are plentiful, received proportionately more of these than late broods, of which at least one was probably reared entirely on vegetable matter. Further, in years of good spruce crops, Redpolls and Siskins occasionally nest much earlier than usual and this is often in cold winter weather when insects are scarcest (Svardson 1957). All records of abnormally early breeding in finches refer to species that depend primarily or largely on conifer seeds, the crops of which vary enormously in size from year to year. There are no comparable records of early breeding in the Greenfinch, Linnet and Gold- finch, but these species now feed primarily on agricultural land and rear their young mainly on the seeds of herbaceous plants. That seeds, and not invertebrates, are critical in determining the start of their breeding seasons (and that of the Bullfinch) is 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 63 suggested by the fact that they all begin laying soon after fresh seeds first become available (usually in early May), and after most of the resident invertebrate-feeders (including the Chaffinch) have started to nest. Further, while in most years these finches stop laying in July, they will breed longer in years when seeds are particularly plentiful in late summer. In the case of the Linnet, Greenfinch and Goldfinch, this occurs in relatively warm dry summers when seed-production by herbaceous plants is increased, and in the case of the Bullfinch, it occurs when certain tree-seeds are particularly plentiful, which may be in comparatively wet as well as in dry years (Newton 1964 b). In all these species, however, some other factor-perhaps population density-is also important, since late breeding does not occur in all otherwise suitable years. Since all these species may have young in the nest until early October in southern England, which receive very few, if any, invertebrates in their food, invertebrates are presumably not important in determining the timing of their breeding seasons. In all the carduelines which feed aninal as well as vegetable matter to their young, the proportion of invertebrates given declines with increasing age of the young, and after about the tenth day the young often receive seeds only. By this time they weigh a half to two-thirds as much as the adults. A similar pattern is followed by the Passer domesticus (Summers-Smith 1964) and the African weaver bird Quelea quelea (Ward 1965). It is interesting to consider whether young finches reared entirely on vegetable matter grow more slowly than those reared on invertebrates or on a mixture of both. The young of cardueline finches are in the nest no longer, on average, than those of the Chaffinch and Brambling, though the latter are reared entirely on invertebrates. Among the carduelines the nestling period of most species lasts 11-15 days, but that of the Crossbill, up to 20 days, or even longer (Jourdain, in Witherby et al. 1938). This may be due, not to the lack of invertebrates in the food of young Crossbills, but to their being in the nest at a time when days are short and cold. The nestling period of the Linnet, which breeds in summer, is slightly shorter on average, and not longer, than that of other carduelines. There is therefore no evidence that the growth of these young carduelines is slowed through the lack of animal protein in their diet, but the growth of nestlings of the same species fed respectively on vegetable matter alone and on vegetable plus animal material has not been compared. Although the young of most cardueline finches usually receive a good proportion of invertebrates in their food, only a small number of these are eaten by the adults themselves in the breeding season. Similarly young Chaffinches are reared entirely on invertebrates, but the adults also eat seeds at this time. Evidently, in all these species, a different process is involved in the selection of food for the young than for the adult. The situation is even more complex in those species which give fewer invertebrates to their young as they get older. It seems that this is a direct response to the appearance of the young themselves, for when I interchanged two Bullfinch broods of three and ten days respec- tively, the adults of both pairs changed their diets appropriately. But as mentioned above, the availability of invertebrates, as well as the age of the young, affects the proportion received.

THE RELATIONSHIP BETWEEN BILL STRUCTURE AND FEEDING HABITS BILL-STRUCTURE AND SEED-HUSKING The most obvious adaptations which enable finches to break open hard seeds are their heavy bills, strong skulls and large jaw muscles. These specializations have already been described by a number of workers (e.g. Sokolowski 1947, Bock 1960) and will not be discussed further here. The purpose of this section is to describe seed- husking in finches, the process by which the shells of seeds are broken open and peeled 64 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 off to release the kernel. Bill-structure and seed-husking have recently been described in detail by Ziswiler (1965) for several groups of granivorous birds, including the Fringillidae. The account below is based on my own observations (made before Ziswiler’s work was published), but emphasis is placed on those aspects least discussed by Ziswiler to whose paper the reader is referred for diagrams and further details of bill-structure. In most Fringillidae the bill is approximately conical. On the palate are two grooves, one down each side, which accommodate the edges of the lower mandible when the is closed. Each groove is narrow and shallow near the tip of the palate but broad and deep at the base, and is bordered on the outside by the edge of the upper mandible and on the inside by a longitudinal ridge. During feeding a seed is wedged on the groove of one or other side and the edge of the lower mandible is pressed onto it from below; this splits the husk. Large seeds are held at the base of the bill, where the palatal grooves are broadest, and small ones nearer the tip. This arrangement make efficient use of the crushing forces exerted as the beak is closed, since these decline in strength from base to tip. Hard seeds must be wedged firmly in the groove to prevent their being displaced when the beak is closed. Seeds are restrained from displacement outwards by the edge of the mandible and inwards by the longitudinal ridge. Movement along the groove is controlled because the forces exerted on the seed by the closing jaws tend to push it forwards until it becomes wedged in the narrowing groove. After the husk has been split, the edge of the lower mandible is worked up between the husk and the outer edge of the kernel, and at the same time the seed is rotated by the tongue so that the husk peels off. Seeds which have seams or other lines of weakness in the husk are always positioned so that the edge of the lower mandible presses directly on to them. Large seeds are repeatedly turned in the bill, with the aid of the tongue, until weak points are found and the husk can be split. Correct positioning of seeds in the bill is learnt during the first few weeks of life-at least in the Chaffinch (Kear 1962), and the position finally favoured is that in which the minimum force is required to crack the husk. This not only saves energy, but also allows the bird to open seeds it otherwise could not. Possibly finches prefer soft (wet or unripe) seeds to the equivalent hard dry ones for the same reason-that they can be husked with less effort. They may, however, be preferred because they differ in flavour or content from hard dry ones. The strength of the jaws, the extent of the gape, and the width of the palatal grooves limit the size and hardness of seeds which a finch can take. For soft seeds, which do not have to be held so firmly before they can be opened, the extent of the gape controls the maximum size the bird can take. For hard seeds, however, which have to be wedged firmly to be split, the width of the groove often determines their maximum size, for if the seed is too large to be wedged in the groove, it shoots out of the bill as soon as force is applied. (But the absolute limit to the hardness of seeds is of course set chiefly by the strength of the jaw muscles.) Certain large hard seeds, such as those of Fraxinus and Helianthus, have husks which can be split easily even though they are too large to be wedged in the groove; in these seeds the fibres of the husk run mainly in the same direc- tion, so that it can be split lengthwise simply by forcing the edge of the lower mandible into the seed as it is held in the bill. The time taken to crack the husk of a seed varies with its hardness, but once split, the husk is usually peeled off in one or two seconds. The kernels of smaller seeds are swallowed whole, but those of large ones are first broken into several pieces. Seeds are usually picked individually, but sometimes many small ones are taken together from the seed-head of a plant, and either husked in turn or, if unripe, sometimes swallowed whole. Some large seeds are swallowed whole when they are soft and green, but are first husked once they have hardened. 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 65

Many finches eat buds, shoots, leaves and various small invertebrates in addition to seeds. Buds and small snails are " de-shelled " in the bill in the same way as seeds, while leaves, shoots and arthropods are crushed before being swallowed.

DIFFERENCES IN BILL-STRUCTURE AND FEEDING BEHAVIOUR BETWEEN SPECIES Differences in diet between finches are of course connected with differences in the size and shape of their bills and with the way the bill is used. The length and depth of the bill of each species, based on my measurements of museum specimens from southern England, are given in Table 11. In all species there is some individual variation in both these measurements. Sometimes one of these measurements has the same average value in more than one species, but no two species have the same average in both. In other words, no two species have bills of the same shape and size.

TABLE11. The length and depth (in mm.) of the beaks of various jinches. In each case the range of values obtained is given in parentheses to the nearest 0.5 mm.

Ratio- .-.. No. measured Length Depth Length/depth Hawfinch Male 46 20.5 (18.5-22'5) 17.7 (16.5-19.0) 1.2 Female 30 19.6 (18.5-21.0) 16.7 (15.5-17.0) 1.2 Greenfinch Linnet Lesser Redpoll 40 8.4 (7.0-8.5) ' 6.6 (6.0-7.0) 1.2 Goldfinch Male 79 12.4 (10.5-14.0) 7.5 (7.0-8.5) 1.7 Female 38 11.3 (9.5-12.0) 7.0 (6.5-7.5) 1.6 Siskin 71 10.4 (9.5-11.5) 7.5 (6.5-8.0) 1.5 Chaffinch 100 13.0 (12.5-13-5) 8.0 (7.5-8.5) 1.6 Brambling 34 13.0 (12*5-14*0) 9.0 (8.5-9'5) 1-4 Bullfinch 42 10.5 (10.0-11.0) 10.0 (9.5-10.5) 1.1 Note. Bill-dimensions are given separately for males and females of a species only when there was a difference between them in their measurements.

In addition to seed-husking, there are at least two behaviour patterns involving the bill which are common to all species. First, all finches will pick up seeds from the ground-at least occasionally, and second, when presented with a mixture of seeds in captivity all will flick aside those they do not like with rapid sideways movements of the closed bill. This latter behaviour was seen in the wild only in those species (Chaffinch, Brambling, Hawfinch, Linnet, Greenfinch) which feed largely on the ground, and was used when they were searching for food among leaves or loose soil. Besides these general behaviour patterns, all species have certain feeding habits which are peculiar to themselves or shared only with other members of their genus. The descriptions of feeding behaviour given below are based mainly on observations of captive birds, but, except where mentioned, all were confirmed in the wild.

(a) Fringilla The Chaffinch and Brambling feed mainly on the ground in winter, but also in trees, especially in summer, and occasionally on the wing. Invertebrates are more prominent in the diets of these than of any other British finches. Compared with other finches which feed largely on the ground, the beaks of the Chaffinch and Brambling are relatively long (see Table ll), an adaptation, perhaps, for catching moving insects. Both species obtain almost all their food by rapid pecks; this method of feeding is of advantage in catching insects or in securing seeds embedded in mud, but of little value in detaching seeds from plant-stems, where a long sustained pull is required. Captive birds seemed unable to modify their rapid pecking movements when presented with plant-stems with E VOL. 109 66 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS 109 seeds attached. For instance, they never learnt to pull out the pappus of Compositae seed-heads lying on the ground even though they could watch other species do so. Sometimes, however, they managed to detach loosely held seeds (e.g. birch) or seeds attached to rigid stems (e.g. elm); but hardly ever did they manage to secure seeds attached to flexible stems (e.g. grasses) since their pecks simply knocked the stem aside. Both species usually obtain caterpillars and aphids from the undersides of leaves while standing on some firm perch below. They appear clumsy when compared with tits, and rarely search foliage at the ends of branches. Caterpillars are usually stunned by striking them on a branch before they are eaten. Flying insects are caught during short sorties from trees, and usually are taken back to a perch and dismembered and eaten there. Falling conifer seeds are often caught by a bird on the wing; the seeds are but rarely picked from hanging cones. The feeding behaviour of the Chaffinch and Brambling is very similar, except that in captivity the Brambling seemed more adept at detaching seeds from plant-stems than the Chaffinch, and in the wild it obtains slightly more of its food in this way. (Neither species, however, is nearly so skilful as the cardueline finches at feeding from vegetation.) As mentioned earlier, the beak of the Brambling is slightly deeper (and therefore pre- sumably stronger) than that of the Chaffinch, which may explain why it takes beechmast more often (see later).

(b) Coccothraustes I have had little opportunity to watch the feeding behaviour of wild Hawfinches and the following is based mainly on observations of three captive birds, supplemented occasionally from the account by Mountfort (1957). The Hawfinch has a larger beak than any other British finch and specializes on very large hard seeds from dry or fleshy fruits of trees; these it obtains either directly from the plant or from the ground below. Small seeds, favoured by most other finches, are hardly ever eaten, but buds are prominent in its diet in spring and invertebrates in summer. The bill of the Hawfinch is also more specialized in internal structure than those of other Fringillidae: behind the longitudinal ridges on the palate is a pair of finely ridged knobs which meet in the midline and overlie a similar pair of knobs in the lower mandible. I have noticed that, as in other finches, small seeds are wedged in the palatal grooves to be husked; but according to Sims (1955), large seeds such as those of cherries and other Prunus are held between the four knobs. In this way the strain of cracking hard seeds is shared equally by the muscles of both sides, and the resulting shocks are distributed more evenly over the skull. The Hawfinch deals with almost all its foods by crushing them in the bill and Sims (1955) has claimed that it can exert with its jaws forces up to 159 lbs per square inch. The pods of peas and other legumes are crushed or popped ” open in the bill, while seeds from fleshy fruits (e.g. Crutuegus) are extracted by turning the whole fruit in the bill so as to peel off the flesh against the edge of the lower jaw, before they are cracked open. Although Hawfinches will eat fallen conifer seeds, there are no records from Britain of them extracting seeds from hanging cones (Mountfort 1957); presumably the bird could insert its stout bill only into large cones that were fully open. Mountfort also described how Hawfinches on the ground obtain grass seeds by reaching up and nibbling along the stem to the seed-head.

(c) Carduelis Species of Curduelis take seeds from a wide variety of plants as well as from the ground ; invertebrates and buds form only a small fraction of their food. The Greenfinch, Linnet and Redpoll have short broad bills similar in external shape to that of the Haw- finch; they feed more than do other finches from plants whose seeds are relatively exposed 1967 1. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 67

(e.g. grasses and docks), or enclosed within capsules and pods (e.g. Stellaria and various brassicas).* Also they frequently pick up fallen seeds from the ground. The Goldfinch and Siskins have longer narrower bills than these three species. The Goldfinch feeds largely on the seeds of Compositae and the Siskin on the cones of Alnus and various conifers, but both species take more of these seeds than do the other Carduelis finches. The species with short broad bills are the most adept at feeding from plants with relatively exposed seeds since each seed can be enclosed completely in the bill to be plucked. The Goldfinch and Siskin, however, hold each seed precariously at the tip of the bill, as between narrow tweezers, and unless very small, it may slip out several times before being secured. The difficulty Goldfinches and Siskins have in obtaining relatively exposed seeds presumably accounts for the small proportion of them in their diets. All the Carduelis finches open unripe seed-heads of Compositae by tearing down the involucre to expose the seeds, which are then picked out singly from above. But only the Goldfinch and Siskin, with their long sharp bills, can pierce the tough involucre of unripe thistle heads and reach the seeds within. Other species eat thistle seeds only when the pappus is loose enough to be pulled out from above, but even then the Goldfinch, Siskin, Linnet and Redpoll can get the seeds more quickly than the Greenfinch, since they use their feet to hold down the extracted pappus while the seeds are picked off with the bill. The Greenfinch does not normally use its feet in this way (see later) and consequently some of the pappus is blown away before the bird can pick off all the seeds. Once their bills have been inserted closed, both Goldfinch and Siskin often use a gaping movement to open the seed-heads of Compositae, or to prize apart the bracts of cones. Thus, not only can they open seed-heads of Compositae more easily than other finches, but also they can obtain conifer and alder seeds before the cones are fully open, and so for a longer period each year. Other finches, with the exception of the crossbills, can normally obtain conifer seeds only when the cones are fully ripe or when the seeds have fallen. Sokolowski (1947) has noted that the muscle for lowering the lower mandible, and the process on which this muscle inserts, are particularly well developed in the Goldfinch, and the same is true of the Siskin (pers. obs.) (but not of other Carduelis finches, which were never seen to use their bills in this way). A similar specialization has been described in the North American Meadowlark Sturnella magna, the Starling Sturnus wulgaris, and various other birds (Beecher 1951) which also " gape " to obtain food. Seeds enclosed within various capsules, such as those of brassicas, are usually obtained by Carduelis finches only after the capsules have burst open, but if partly split, they are often torn down further to release the seeds. The Greenfinch, however, often opens small pods and capsules, as well as small seed-heads of Compositae, and fleshy fruits, by crushing them; for it is probably the only Carduelis finch with jaws strong enough to do this. It also eats a larger proportion of seeds from fleshy fruits than do other members of its genus, and in these respects resembles the Hawfinch. Although the Greenfinch, Linnet and Redpoll resemble one another in bill-shape and in the nature of their preferred foods, they differ in bill-size and tend to concentrate on seeds of different sizes, though there is a good deal of overlap in the size-range of items taken (see Table 12). The Greenfinch has the largest bill and eats mainly large seeds, the Redpoll has the smallest bill and eats mainly small seeds, while the Linnet is inter- mediate both in bill-size and in the size of seed it prefers. (As mentioned above, the Hawfinch, which has an even larger bill than the Greenfinch, specializes on very large hard seeds, many of which cannot even be opened by the smaller finches.) Although in

* In Oxford certain food-plants were particularly common, and formed an unusually large part of the diet of some-of the finches living there. I have therefore based these generalizations on all the available data, not only my own. 68 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

Table 11 the Redpoll's beak appears to be of similar proportions to those of the Linnet and Greenfinch, it is in fact much narrower near the tip, an adaptation, perhaps, for picking out the seeds of birch, which forms its chief food. This bill-shape also makes it more adept than the Greenfinch and Linnet at extracting seeds from alder and conifer cones, but it is not as efficient in this respect as the Goldfinch and Siskin. For a given bill-shape, the depth of the bill is presumably the best indication of its crushing power; and it may be seen from Table 11 that in bill-depth the Goldfinch and Siskin are more similar to one another than are any other pair of finches. I have insufficient information on the food of the Siskin for full comparison with that of the Goldfinch, but in Oxford they both ate seeds of the same size range (from birch to pine). The beak of the Goldfinch, however, is longer and this enables it to reach seeds embedded deeply in the heads of thistles and other large Compositae more easily than the Siskin. In addition, the Goldfinch (especially the males-see later) is the only species that can reach teasel seeds, which lie at the bottom of long tubular involucels-though the Siskin will eat them in captivity if the seed-head is razored down. It seems therefore that while Carduelis finches with short broad bills select different diets from one another mainly because of differences in overall bill-size, the Goldfinch and Siskin are segregated from one another chiefly by the difference in bill-length, since both species feed largely by probing. There are, however, several other factors which help to isolate all five species ecologically (see later).

TABLE12. The size of seeds eaten by four jinches with diSferent sized bills. The jigures in bold type indicate the main size-range of seeds eaten by each species. The percentage composition of the diet by weight' of individual seeds Mean bill-depth up to 0.5 0.5-1.0 1.-10 10-100 over 100 (-4 (mg.) (mg.) (mg.) bg.1 (mg.) Lesser Redpoll 6.6 80 18 2 - - Linnet 7.6 15 31 52 2 - Greenfinch 11-5 8 9 27 54 2 Hawfinch 17.7 - + 1 30 68 Note. * Since the shape of seeds is enormously variable, I have used weight instead of dimensions as an index of size. The weights of many seed-species were taken from Salisbury (1961); the rest I weighed myself.

(d) Pyrrhula The Bullfinch eats a greater proportion of buds and of seeds from fleshy fruits than any other finch studied (Newton, in prep.). Buds were taken in late winter and spring when seeds were least readily available; and in years when seeds were particularly scarce, buds formed almost the entire food from January to April. Buds formed a negligible fraction of the food of all other finches except the Hawfinch which ate larger buds than the Bullfinch. Conifer seeds were not recorded in the food of Bullfinches in Oxford, though they have been recorded abroad (Jourdain, in Witherby et al. 1938), but are apparently obtained mainly from the ground (see later). The Bullfinch's beak is short and rounded. Unlike other finches it uses its bill to bite into buds, fleshy fruits and other food-objects, so needs to apply considerable force at the tips. Bowman (1961) has shown that a short beak can withstand a greater force at the tip than a long one, and that a convex culmen is more resistant to fracture than a straight one, so that its shape is clearly well suited to deal with buds and fleshy fruits. In addition, the edges of the beak are unusually sharp compared with those of other finches. The Bullfinch uses similar bill movements for almost all food-objects, whether seeds, buds, fleshy fruits, pods or capsules: the object is nipped off, positioned lengthwise in 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 69 the bill, and turned by the tongue against the edge of the lower mandible so that the outer layer-the husk of a seed, or the flesh or pericarp of a fruit-is peeled off. Small snails are first crushed and then " de-shelled " by the same process. The bird deals with large items, such as Salix flowers, by biting out small pieces, which are then manipulated in the same way as other objects. For extracting seeds of Compositae, the Bullfinch uses a different method from Carduelis finches. As mentioned above, the latter have pointed beaks which are inserted from above into a seed-head, and the seeds are picked out one by one. The Bullfinch, however, attacks the seed-head at the side and bites out small pieces which are then turned in the bill to extract the seeds. Thus the Bullfinch is limited to feeding on those plants, such as Sonchus and Senecio, which have small soft seed-heads, and does not normally feed on large ones such as thistles in the genera Circium, Carduus and Onopordon. Small seed-heads are sometimes nipped off the plant and carried to the ground before the seeds are extracted; and often Bullfinches will reach from the ground to pluck the seeds of low plants, but only rarely do they pick up fallen seeds-at least in Britain. Although this might be thought difficult for a species with a rounded bill, especially if the seeds are small and the substrate soft, I have seen Bullfinches several times picking up large seeds of Acer from a closely cropped lawn.

(e) Loxia Crossbills feed almost entirely on conifer seeds and, unlike all other finches, they can extract them from hard unripe cones. They attack large cones (such as those of certain ) in situ, often while hanging from them. Smaller cones are wrenched off at their base, carried in the bill to a horizontal perch, and then clamped between feet and perch while the seeds are extracted. If the cone is gripped by both feet, it is held alongside the perch, but if held in one foot, the apex of the cone points forwards and slightly to one side. Usually a bird with the lower mandible deflected to the right holds the cone in the right foot (or if both feet are used to grip the cone, its base lies on the left) and vice versa. The correct positioning of the cone is presumably learnt; but as a result the lower mandible is brought to bear on the inner bract and the upper of the outer one. The bill-tips are inserted from the sides between two bracts, and the lower mandible is moved sideways towards the body of the cone, so that the bract is raised by the tip of the upper mandible. When dealing with soft cones the bill is never closed completely, for the seed, once released, can be scooped out by the protrusible tongue. If, however, the seed is still tightly embedded the bracts are opened further by closing the bill and rotating it sideways, so that the crossed tips of the jaws are brought to bear on opposing scales, thus forcing them further apart as the movement continues. Robbins (1932), who has also recorded this latter process in an American Crossbill L. c. minor, compares the action to that of a " knife blade inserted horizontally between the two scales, and then turned until it is perpendicular to them ". If the seed is still held firmly, Robbins observed a further stage in the process. The bill, once inserted, was closed and rotated until perpendicular to the scales, and then raised so that the scales were forced and held apart by the upper mandible alone (the tip resting on the lower bract, while the culmen pressed against the upper one). The lower mandible was then free to open, and the seed was secured by the tongue. There are thus three stages in the process, at each of which the seed may be released: the first involving a sideways movement of the lower mandible; the second in which the bill is closed and rotated between the scales; and the third in which the upper mandible is used as a lever to prize apart the scales. In practice the first process is usually suffi- cient to release the seeds of soft cones, such as those of larch, the second movement is used on harder cones, while the third (which I did not observe in Common Crossbills) is apparently used only on very hard pine cones. When working large cones the bird 70 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 gives the impression of using to the full the musculature not only of the head and neck, but of the whole body, as it strains to open the bracts. When attacking large pine cones, a captive bird first broke off some of the bracts in the middle of the cone, making it easier to lift the ones above. Normally only a few seeds are removed from each cone before it is dropped. This is surprising in view of the time taken to first open a cone. The crossed tips of the jaws severely restrict the number of alternative foods that crossbills can exploit efficiently. Since the bill-tips do not meet, it is difficult to pick up small seeds from the ground, though they can hook up large seeds such as beechmast. The tongue, however, is well developed and is sometimes used, along with the upper mandible, to pick up seeds. Most of the alternative foods are dealt with using the same bill-movements as are used on cones-for instance, when prizing off the bark from trees (to obtain invertebrates beneath), or opening sunflower seeds or beechmast, or splitting apples to extract the pips. Large apples are attacked in situ, but small ones are first detached and held in the feet like cones. Various fleshy fruits, such as those of Sorbus, are usually split open with the base of the bill. My captive crossbills took aphids by gently clasping a leaf between the jaws, and then running the bill along to scrape the insects together; they were then secured with the aid of the tongue. In Europe, three species of crossbills are recognized which differ in overall body-size and in the size of the beak. The largest heavy-billed Parrot Crossbill feeds primarily from large hard Pinus cones, the Common Crossbill from the softer Piceu cones, and the small slender-billed Two-barred Crossbill from small soft Lurix cones (Lack 1944). This is true as a general tendency but each sometimes feeds from cones of other types, especially on migration when the favoured food may not be available. Niethammer (1937) has noticed that when the Common Crossbill feeds from pine cones, it deals with them less efficiently than does the Parrot Crossbill. The is a race of either the Parrot or Common Crossbill, and is intermediate in bill-size between them. In its natural haunts, it lives mainly from Pinus cones, but also takes those of Piceu and Lanx where these have been introduced by man.

A DIFFERENCE IN FEEDING HABITS BIBWEEN MALE AND FEMALE GOLDFINCHES During the study period, 56 Goldfinches were netted from December to February as they fed on the seed-heads of Dipsacus fullonurn and 54 of them were males. Further- more, from about a hundred Goldfinches caught at the same time on year of other foods, such as thistles and burdocks, the males still predominated through the sex-ratio was then 4 : 1; presumably a greater proportion of females than of males winter abroad. The beaks of male Goldfinches average 1 mm. (9%) longer than those of females (see Table ll), and enable them to reach teasel seeds more easily-a fact which was known to Darwin (1871). Two captive female Goldfinches sometimes fed on teasel heads, but before inserting their bills, they first had to turn down the surrounding spikes; this was so time-consuming that they obtained, on average, only one seed to every four obtained by the longer-billed males. (A difference in bill-length of 1 mm. seems very small to cause such a marked difference in efficiency, but, on the other hand, the differences in bill-depth between species are sometimes no greater than this (see Table 11) and yet are sufficient to cause even more striking differences in feeding habits.) Teazle is an important food-plant of the Goldfinch in winter and a difference in feeding habits between the sexes at this critical time might be of benefit to both, but only if the females, with their shorter bills, could feed more efficiently than males on some other food. We have, of course, no way of telling whether the difference in bill-length between the sexes is the result of past competition for food between them, or whether it has evolved under some totally different selection pressure. Certainly, the relationship of bill-length to wing-length is constant among Goldfinches, the bills of males being longer simply because they are bigger birds, on average, than females ; unusually large 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 71

females have bills as long as those of males of equivalent size and vice versa. Neverthe- less a small difference in body-size, such as between the sexes of the Goldfinch, though initially perhaps merely a secondary sexual character, could be accentuated by selection if associated with a difference in feeding habits. It is presumably from small differences such as this that more marked ones, as between the sexes of the extinct New Zealand Huia Heteralocha acutirostris, originate.

EFFICIENCY IN FEEDING The success of a bird-and particularly its chance of survival through periods of food-shortage-must depend largely on its ability to obtain the most nutritious diet for the least expenditure of time and effort. Since finches differ, among other ways, in weight and bill-dimensions, they must also differ in the amount of food they require each day and in the speed with which they can deal with different types of food. Kear (1962) measured the speed with which different finches could husk seeds of various shapes and sizes, and, as expected, found that in general, large-billed species husked large seeds faster than small-billed species. A more pertinent experiment would be to measure the daily food requirements of different finches and see which size of seed would yield these most quickly for each species. But even if the seed-size most efficiently exploited was found to differ for different finches, it would still be difficult to relate this to the natural situation, where efficiency in feeding depends, not only on the size of seeds, but also on their day-to-day availability. In general, the deeper the bill of a finch, the more numerous the species of seed in its diet : while small-billed finches are restricted to small seeds, large-billed species can take large seeds as well, and moreover tend to concentrate on these since they provide more food per unit time. Large-billed finches also have larger bodies and need more food per day, so unless they could find and husk small seeds faster than small-billed species (for which there is no evidence, see Kear), the larger species could not survive at low densities of small seeds which would still be sufficient to support smaller finches. The Greenfinch, which eats mainly large seeds, takes small ones only when they can be obtained, several at once, from the seed-heads of plants; and this occurs chiefly when the seeds are unripe, for they can then be swallowed without being husked. Similarly, the Bullfinch, Goldfinch, Siskin and Redpoll all take the small seeds of Betula when they can be obtained several at once from the seed-catkins, but only the smallest species, the Redpoll, takes them when they have fallen to the ground where they are sparsely distribu- ted and can be obtained only one at a time. Much of the overlap in the diets of finches may occur because the foods concerned are sufficiently plentiful at the time to be exploited adequately by several species, whatever their bill-structure.

THE RELATIONSHIP BETWEEN BODY-WEIGHT, LEG-PROPORTIONS AND FEEDING HABITS THE FEEDING POSITIONS OF FINCHES Competition between species living in the same habitat is reduced if they feed in different places, even if they take the same type of food. Finches differ in the proportion of food they obtain from vegetation, from the ground, or from the air (see Table 13). The extent to which they feed directly from vegetation is related to the different positions in which they are able to feed. For example, those species that can most easily adopt clinging and hanging positions feed mainly from trees and herbaceous plants, while those least adept at this obtain most of their food from the ground. Kear (1962) has described four positions that are adopted by finches while feeding in the wild. She noted that the Chaffinch, Greenfinch, Goldfinch and Linnet spent different proportions of time feeding in each position, and of these species, only the Goldfinch fed while hanging inverted. 72 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

To assess by observation the ease with which different finches can feed in various positions, it is important to watch them on a wide variety of foods, for while it is usually assumed that a bird’s feeding places are governed by the positions it can adopt, the bird may also use different positions when dealing with different foods. For instance, Goldfinches spend most of their time clinging or hanging when feeding in alders, but standing when feeding on thistles. In an attempt to get comparable data for ten different finches (including the four species discussed by Kear), I therefore examined the behaviour of captive birds when given the same types of food. Various food-plants were presented in turn, each type being hung from the roof of the aviary, attached to the sides, and stuck in the ground at various angles; while fallen seeds were also available on the ground. The birds therefore had a simultaneous choice of obtaining food from any of a variety of positions or by hovering. They were tested in groups of six (two to three individuals of each species), and their feeding positions noted every minute or so for about half an hour on each type of food-plant. I have found it convenient to distinguish six different positions. Figure 1 shows a bird (a) in a standing position; (b) in a normal perching position on a plant-stem bent horizontal under its weight; (c) leaning forwards so that its centre of gravity lies well in front of its feet; (d) perching on a bent plant-stem, so that the bird’s centre of gravity lies over one of its feet; (e) clinging to a vertical stem; (f) hanging upside down. It can be seen that both feet are on more or less the same level in positions (a), (b), (c) and (f), and on different levels in positions (d) and (e).. As already noted, in addition to feeding in some of these positions, the Chaffinch, Brambling and Bullfinch frequently chase and catch flying insects, and (especially the Bullfinch) also obtain plant-food by hovering. Table 13 gives the percentage frequency with which each of these positions was adop- ted by different finches under experimental conditions, together with the proportion of time they spend in the wild feeding from vegetation, from the ground, and from the air. Although in captivity the Chaffinches and Bramblings tested occasionally caught insects in flight, most of their feeding was in a standing or normal perching position; the Bramblings were slightly more willing to settle on horizontal plant stems than the Chaffinches. From both these positions they would reach upwards and forwards for food. In the wild, Chaffinches obtained most of their food from the ground, about a fifth from the horizontal twigs of trees, and about one per cent from the air. During the time they were in Oxford, Bramblings also fed mainly from the ground, and their behaviour at this time differed little from that of Chaffinches (see later). The Hawfinch, Greenfinch and Linnet stood less on the ground but more on hori- zontal twigs and stems than the two previous species, and they also fed frequently on bent stems; but only rarely and momentarily did they cling to vertical stems. In the wild, all three species obtained just over half their food from vegetation and the rest from the ground. The Goldfinch, Siskin, Redpoll and Crossbill were the most agile species and fed in all positions; they often hung inverted and were able to cling to vertical stems with ease, but fed far less often in a standing position than the other species. In the wild they obtained almost their entire food directly from trees and herbaceous plants. The Bullfinch is less agile than the last four species and was never seen to hang inverted, but nevertheless obtained almost all its food directly from vegetation. In any case it has difficulty in picking up small seeds from the ground.

~ ~~ * My positions (a) and (f) correspond to positions (a) and (d) described by Kear (1962). I have subdivided the position she termed “ perching B ” into three separate positions: (b), (c) and (d). She did not describe my position (e), and I did not notice any of my captive finches adopt Kear’s “ perching A”. However, I thought I saw wild Redpolls adopt this position, while feeding from the pendant twigs of birch, but could not get close enough to see their legs: they were certainly using their tails for support. I have added to, and subdivided Kear’s original categories because it brings out further differences between the various species. TABLE13. The percentage frequency with which various positions were adopted by dzj$erent Jinches in captivity in relation to the amount of time spent feeding from the ground, from vegetation and from the air respectively in the wild.

THE PERCENTAGE FREQUENCY WITH WHICH THE FOLLOWING POSITIONS WERE ADOPTED THE PERCENTAGE TIME SPENT IN CAPTIVITY BY FEEDING FINCHES FEEDING IN THE WILD FROM" (a) (b) (4 !d) (el (f) Standing Normal Leaning Clinging Clinging Hanging Feeding Ground Vegetation Air on ground perching forwards to bent to vertical inverted on the stems stems wing Chaffinch 94 5 - - - - 1 81 18 1 Brambling 89 10 - - - - 1 It ? ? Hawfinch 38 51 2 9 + - - 49 51 - Greenfinch 35 53 + 11 + - - 48 52 - Linnet 30 54 + 15 + - - 45 55 - Goldfinch + 18 6 41 26 8 - + > 99 - Siskin + 9 2 27 34 18 - + > 99 - Redpoll 3 11 1 31 42 12 - 5 95 - Crossbill + 12 2 12 46 28 - + > 99 - Bullfinch 2 22 3 70 2 - 1 + 98 1 Notes. * These figures were calculated by combining the data for the whole study period, but in practice, several species changed their main feeding places at different times of year (see earlier). t No data for the summer period are available. 74 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

I never saw Hawfinches feeding while hanging inverted, but according to Mountfort (1957 : 100) they can do so. Furthermore, Chaffinches would sometimes cling to the netting sides of their aviary, but not to food-plants, while Greenfinches also occasionally hung from suspended baits (see Kear) and from metal peanut-holders in gardens. It must, however, be much easier for a bird to cling momentarily to some firm support than for long periods to flexible plant-stems especially in a strong wind.

FIGURE1. Various feeding positions of finches. (a) Standing position on the ground; (b) normal perching position on a plant stem bent horizontal under the bird’s weight ; (c) leaning forwards, so that the birds’ centre (d) perching on a bent plant stem sothat the of gravity lies well in front of its feet; birds centre of gravity liesover the lower foot ; (e) clinging to a vertical stem; hanging inverted. Dram by D. E. Baird. 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 75

It may be seen that the finches fall into three groups, those which feed mostly on the ground, those which feed primarily from vegetation, and those which feed commonly from both. The Chaffinch and Brambling are the only species that walk or run, and so can cover the ground (and find seeds) much more quickly than the cardueline finches, which can only hop. Hopping is usually considered a better method than walking for progressing through trees, and so presumably makes the carduelines more suited to an arboreal life. In the wild, even when several species feed together in the same tree, they sometimes search different parts of the tree. Although this was not studied in detail, I noticed that when hunting for insects, Chaffinches and Bramblings usually remained on the thicker horizontal twigs near the main branches, while the more agile Siskins, Goldfinches and Redpolls concentrated on the thinner, more flexible terminal twigs. I also noticed that while Bullfinches often stripped the buds from horizontal and sloping twigs of fruit trees, they usually left those on vertical twigs, since they could not hang on. If, however, all the more accessible buds had been removed from a tree, they would then take those from vertical shoots by hovering, but this was a less efficient method since it took longer to get each bud.

LEG-STRUCTURE, BODY-WEIGHT AND FEEDING BEHAVIOUR The leg-structure of various birds, including several species of finches, has been examined by Promptov (1956) (whose results were also discussed by Kear (1962)), and in detail by Ruggeberg (1960). Both these authors pointed out that the species most adept at feeding from vegetation have shorter legs than ground-feeding birds of similar size. However, neither author gives appropriate leg-measurements for all the finches discussed here, and those given for some species differ from measurements I made myself; this can be attributed to geographical differences (see Appendix 2). Only the length of various leg-bones in finches in relation to body-weight and feeding habits will be considered here; details of the structure of the pelvis and toes, and of the musculature, may be found in Ruggeberg’s paper, though he was not concerned primarily with differences between species. My measurements of femur, tibio-tarsus (hereafter called tibia) and tarso-metatarsus (hereafter called tarsus) were obtained mostly from birds shot for gut-analysis, but also from skeletons available in the British Museum (all were from specimens collected in southern Engiand) ; the weights I obtained myself. Among the finches, body-weight seems to be more important than the ratio of leg- length to body-weight in affecting a bird’s ability to cling and hang. Thus, apart from the Crossbill, the heaviest finches are less adept at feeding from vegetation than the lightest, even though they have relatively much shorter legs (see Table 14). The Redpoll, Siskin and Goldfinch feed almost entirely from vegetation and have relatively longer

TABLE14. The leg-proportions and body-weights of various English jinches. Mean total Body Ratio of No. leg-length Mean percentage length of weight+ leg-length to Species measured (mm.) Femur Tibia Tarsus (gm.) body-weight Hawfinch 6 79.5 28 44 28 55.0 1-4 Greenfinch 24 62-5 27 45 28 29.0 2.2 Goldfinch 18 50-6 26 46 28 15.5 3.3 Siskin 8 47-5 26 46 28 12.0 3.9 Linnet 16 55.2 26 46 28 18.5 3.0 Redpoll 36 47.4 27 44 28 11.5 4-1 Bullfinch 42 60.6 28 44 28 23.5 2.6 Crossbill 4 66.7 29 45 26 40.0 1.7 Chaffinch 21 63.1 25 45 30 23-5 2.7 Brambling 3 67.5 25 46 29 25.0 2.7 Notes. +The weight of all species varies through the year. I have used only the November values, since I have more data for this than for any other month, and the weights at this time are not affected by migratory fat deposition. The weights are given to the nearest 0.5 p. 76 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 legs, but lighter bodies, than other finches. Although body-weight is the most important factor affecting the agility of finches, leg-length also affects this, as shown by comparing birds of the same weight. Thus, the Bullfinch, Chaffinch and Brambling have similar weights, but the Bullfinch has shorter legs, and adopts a greater range of feeding postures, than the Chaffinch and Brambling. In addition, it seems that the Crossbill owes its ability to hang inverted largely to its very short legs; although it weighs half as much again as the ground-feeding Brambling, its legs are slightly shorter. Long legs are of obvious advantage to a ground-feeding bird, since they allow it to cover the ground more quickly and also increase its field of view. Presumably, the relatively short legs or smaller bodies, which are characteristic of arboreal finches, both serve to reduce the stresses and strains on the legs in clinging and hanging positions. Promptov (1956) also pointed out that in arboreal the shortening of the legs affected mainly the tarsus, to a lesser extent the tibia, and least of all the femur. Apart from any differences in total leg-length among the finches, the Crossbill, which is the most specialized tree-feeder, has relatively shorter tarsi (and relatively longer femora) than other finches, while the Chaffinch and Brambling, which are the most specialized ground-feeders, have relatively longer tarsi than other species (see Table 14). But apart from these differences, which are all extremely slight", there are no consistent trends in leg-proportions within the finches that can be related to feeding habits.

TABLE15. The extent to which the co-ordination between foot and bill is developed in diferent finches @or explanation see text). Key: 0, Occasionally; F, frequently; brackets, observed only in captivity. TYPES OF BEHAVIOUR SHOWN Fngthe,dl to Placing one foot Using the bill to Using the bill to pull in , but on a food-object place detached pull in and place not placing on the ground food-objects a flexible plant- " pulled-in " to anchor it under the feet stem under feet object under the feet+ Chaffinch - - - Brambling Bullfinch Hawfinch Greenfinch Linnet 0 Redpoll F Goldfinch F Siskin F Crossbill (F)

Note. *; Behaviour used for instance, to pull out the pappus of thistles to get the seeds.

THE USE OF THE FEET IN FEEDING The finches vary considerably in the use they make of their feet while feeding (see Table 15). The Chaffinch, for instance, never uses its feet to hold food-objects (such as the seed-heads of plants), but the Goldfinch does so regularly and can thereby exploit food-sources which might otherwise be difficult to use. Kear (1962) grouped the finches according to the frequency with which they use their feet in feeding and pointed out that those species that most often feed by using both bill and feet to deal with food-items are those most adept at hanging from vegetation. Both types of behaviour require a strong grip. My observations confirm those of Kear, that the Chaffinch, Brambling, Hawfinch and Bullfinch do not use their feet in feeding. Some of the remaining species I examined

* It should be mentioned, however, that these slight differences are accentuated if the lengths of the various leg-bones are expressed as percentages of the length of the coracoid bone as by Promptov (1956) and in Table 18 of this paper (in Appendix 2). 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 77 use one of their feet merely to steady a food-object lying on the ground so that it can be worked more thoroughly by the bill, while others can also pick up detached food-objects in the bill, or pull-in flexible plant-stems, place them under their feet, and hold them there while the seeds are removed. Presumably a stronger grip is required to hold a resilient plant-stem than a detached seed-head. All the Carduetis finches can steady food-objects lying on the ground with their feet and also pull with their bills to secure objects to which food is attached, such as plant- stems or the pappus of thistles. Furthermore, in all the Curduelis finches except the Greenfinch, these two types of behaviour are used in conjunction. This was seen only occasionally in the Linnet, but often in the Goldfinch, Siskin and Redpoll, especially when they were feeding in birches or alders. The catkins of these trees often hang beneath the branches on thin flexible stalks, and to secure them, a bird would often reach to pull in a catkin with its beak, and at the same time extend its front toes to clamp the catkin against the branch on which it stood. In this way, it could work thoroughly over those catkins that would otherwise be difficult to get. Although Crossbills were never seen to reach out and pull in plant-stems in the wild, they did so readily in captivity. At first sight it is surprising that the Hawfinch and Bullfinch never use their feet in this way, since they obtain respectively about a half and almost the whole of their food from vegetation. On the other hand, both species use their bills to bite into food-objects rather than to pick at, or probe into them, so perhaps there would be little need to use the feet anyway. It should be stressed, however, that the Hawfinch has been little studied in this respect, and it is possible that it does in fact use its feet, at least occasionally.

STRINGPULLING BEHAVIOUR Under experimental conditions, many species of birds are able to pull up food suspended on the end of a long thread, the pulled-in loop being held under the foot while the bird reaches with its bill for the next pull. This behaviour has often been regarded as an elementary form of tool-using and has also been cited as evidence for the occurrence of insight learning in birds (see Thorpe 1956). Among the finches, the Goldfinch, Siskin and Redpoll accomplish this task more quickly and frequently than other finches. The Crossbill does not appear to have been tested before, but my captive birds repeatedly and without hesitation pulled up a Larch cone suspended on four inches of string. Thorpe reported success in two out of four canaries tested, though they needed considerable practice to perfect the technique, and gives one instance of success with a Greenfinch. Two out of four Linnets I tested were soon successful at pulling up a Dandelion head on four inches of string, but the other two, like those tested by Thorpe, showed " pulling-in " behaviour, but did not learn to place the string under their feet. The results of these experiments can be explained largely by the birds natural feeding behaviour, those species which most frequently use their feet to hold food in the wild being most successful at pulling up and holding the string. But even species such as the Green- finch, in which the co-ordination between foot and bill is poorly developed in the wild, are sometimes successful with practice. On the other hand, species, such as the Chaffich, which do not naturally use their feet to hold food, seem completely unable to accomplish this task.

ECOLOGICAL ISOLATION AMONG FINCHES MOVEMENTS AND DISTRIBUTION The migrations of finches are an important aspect of their ecology. It will be recalled that the Greenfinches, Chaffinches and Bullfinches that breed in southern England normally remain there in winter, but all make local movements then in response to changes in weather and food supplies. Some Linnets and Goldfinches also remain 78 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 and winter in England, but the majority move out to France or Spain. On the other hand, southern England is an important wintering area for Redpolls (and possibly Siskins) from northern Britain and for Siskins, Chaffinches and Bramblings from Scandinavia. The way in which different species are dispersed within a common wintering area is sometimes an important factor reducing competition between them, especially when viewed on a European basis. For instance, the Goldfinch and Siskin overlap both in feeding habits and, for the most part, in wintering range. Within this range, however, Goldfinches rarely remain in any numbers to winter in the northern half, where Siskins are commonest in winter, and only in years of extreme food-shortage do large numbers of Siskins winter in the southern half (Mediterranean region) where Goldfinches are commonest. Thus, although the winter ranges of the two species largely coincide in Europe, in most years the bulk of their two populations is concentrated at different latitudes. As a further example, the Chaffinch and Brambling are closely similar in feeding habits and are geo- graphically isolated in summer, yet they share the same wintering grounds. But, whereas migrant Chaffinches from normally return to the same general area in successive winters, the winter quarters of an individual Brambling in different years may be several hundreds of miles apart (E.-W.), the birds tending to concentrate especially where beechmast is plentiful. In this way competition between the two species is reduced. Redpolls are also known to assemble in winter in areas of abundant birch seeds, and Evans (1966) has shown that more Redpolls leave Britain in poor birch years than in good ones. While those that stay in Britain in poor birch years have to turn to alternative foods and possibly compete with other finches (perhaps with Siskins for Alder seeds), this involves only a small fraction of the Redpoll population. In assessing the ecology of closely-related species, it is thus important to examine, not only their food and habitat selection, but also their distribution in the area in which they occur together. Although their winter ranges may coincide, the bulkof each species may be concentrated in separate localities where climate or food has assembled them. It is in areas where their main foods are not available, and where the finches themselves may be least common, that competition for food is most likely to occur. In my study area differences in food between finches were much less marked in the autumn of 1961 when several types of tree-seeds, and the finches that normally depend on them, were scarce, than in the following autumn when both were plentiful. In some species, competition for food between the sexes is reduced because they winter mainly in different areas. I have already mentioned that many more male than female Goldfinches winter in the Oxford district (where they are also partly segregated by feeding habits); and the name coe2ebs (i.e. bachelor) which Linnaeus gave to the Chaffinch was inspired by the fact that only males of this species remain to winter in Sweden. Deelder (1949) has compiled evidence which shows that females of the Scandinavian and German Chaffinch populations migrate further than the males. Scandinavian males are more numerous than the females in Scandinavia itself, in Holland and in Britain, but in at this time there is a marked surplus of females (refs. in Deelder).

HABITAT AND FOOD SELECTION On Gause's hypothesis, closely related species living together in the same area would be expected to differ from one another in choice of habitat, food, or feeding place, at least at certain times of year. Lack (1954) has shown that food-shortage is the most likely factor controlling the numbers of most types of birds in nature; it follows that differ- ences in food-selection between species are of paramount importance if competition is to be avoided. It will be recalled that the Crossbill, Hawfinch, Redpoll and Siskin occur mainly in woodland", the Greenfinch, Goldfinch and Linnet mainly on farmland, while

Riparian alders are here classed as woodland. 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 79 the Chaffinch and Bullfinch breed, and occur throughout the year, in both these habitats. Despite these differences, all species are seen, at least occasionally, in all habitats from the most densely wooded to the most open ones, and food-selection is the chief factor segregating them from one another. While seeds predominate in the diets of all these finches-and form almost the entire food of the Linnet and Crossbill-invertebrates are more important to the Chaffinch and Brambling than to other species, and " greenstuff" (buds) to the Hawfinch and Bullfinch. It is of interest first to compare the degree of segregation in diet between the various woodland finches with that between those feeding primarily on farmland. The wood- land species are more different from one another in bill-structure than are the farmland species and this is reflected in their diets. The main foods, that is, those forming more than 10% of the diet in different months, are shown for each species in Table 16. It may be seen that throughout the year the woodland species almost always differ from one another in their preferred foods, but there are a few cases of apparent overlap. Among other things, the Hawfinch and Bullfinch both depend largely on Ulmus seeds in early summer; the Chaffinch and Hawfinch on various caterpillars in summer and on beechmast in some winters; the Siskin and Crossbill on Pinus seeds in spring; and the Siskin, Redpoll and Bullfinch on Betula seeds in autumn. In all these cases, however, the food concerned is very plentiful at the time, so it is reasonable to assume that there is little or no competition for it. Similarly, in Sweden the Siskin and Redpoll, as well as the Crossbill, all live primarily on Picea seeds only in those years when the crop is particularly good (see earlier in this paper). In other years the Crossbill depends on Picea seeds but the Siskin and Redpoll each depend on different foods. Thus, the wood- land finches are for the most part well segregated in diet and overlap in their main foods only at times when these are easily available. There is much more overlap in diet between the various finches living on farmland. Of the 30 commonest food-plants there, the seeds of all 30 are eaten frequently by the Greenfinch, at least 25 by the Linnet, 18 by the Goldfinch and 24 by the Chaffinch and Bullfinch. It may be seen that throughout the year (with the exception of snow-periods), all the main foods of the Greenfinch on farmland are also important to at least one other species there; almost all those of the Linnet and Chaffinch; and about half those of the Goldfinch and Bullfinch. Furthermore, although these finches differ from one another, among other ways, in bill-dimensions, body-weight and leg-proportions (as discussed earlier), these differences are not sufficient to segregate all five species in food choice, at least on farmland. Thus, not only do they have many foods in common there, but all except the Chaffinch feed mainly from the food-plants themselves in summer, and all except the Bullfinch from the ground in winter. The Bullfinch is segregated further from the other farmland species in winter because it then takes many seeds of Rumex spp., Urtica dioica and Rubus fruticosus (two of which are woodland plants that have invaded cultivation) and in spring, it alone takes buds. The Goldfinch is more isolated in food- choice than the other farmland species largely through its greater dependence on the Compositae. Since the Bullfinch and Chaffinch now occur throughout the year in both woods and farmland, it is interesting to assess how far they are segregated from other finches in the two habitats. All the foods eaten by the Bullfinch in farmland are also commonly eaten by one or more other finches there, but only 10% of its food-plants in woodland are shared with other finches (including those such as the Linnet, that feed there only rarely). In both woods and farmland young Chaffinches are fed entirely on invertebrates, but in farmland the adults themselves eat far fewer animals than in woodland. Instead they eat the seeds of cultivated cereals and various weeds, all of which figure prominently in the diets of other finches there. Whereas in woodland the Chaffinch is the only resident finch that eats small seeds from the ground (the Hawfinch takes larger ones), on farmland TABLE16. The main foods of various Jinches through the year near Oxfwd. Foods are listed, as far as possible, in order of importance in the diet, and where a plant name is used, seeds are to be infered except where otherwise stated.

I. THOSE SPECIES BREEDING AND OCCURRING THROUGHOUT THE YEAR IN WOODLAND. U

JAN. PPB. BiARcri APRIL MAY ILTNB AUG. SBP. Om. NOV. DEC. Hawfinch Carpinus Carpinus Carpinus Buds UImus c--y----.-l Cratageus Crataegus Fagus Fagus Carpinus betulus betulus betulus Prunus Buds UImus Runus Prunus silvatica silvatica betulus 4 Fagus Prunus Prunus spinosa Insects Insects Fagus Taxus Carpinus Fagus silvatica spinosa spinosa silvatica baccata betulus silvatica i2 Crataegus Rosa Rosa Crataegus Taxus TOXUS .. Buds Acer baccata baccata Crataegus Rosa Crataegw - 8 Siskia Alnus Insects Insects - - - e -Alnus glutirwsa glutinosa Pinus --Betula AInus glutinosa Pinus Alnus glutinosa

LesserRedpoU Betula Betulabuds Salix Betula Betula Betula Betula Betula Betub Salix Salix Insects Grasses Grasses Filipendda Filipendula Epilobium -5 Betula - Rumex ulmaria ulmaria (flowers (flowers &seeds) &seeds) Epilobium Insects 8 0 Bullfinch Buds Buds Mercurialis Betula Betula Betula Betula Rubus a Rubus Tree flowers -Mercurialis perennis Rubus Rumex Urtica Urtica Urtica Fraxinusexcelsior Ulmusperennis Alliariapetiolata Filipendulaulmaria Filipendulaulmaria RubusRumex RubusFraxinus Fraxinus excelsior 8 Buds Myosotis Rumex Rubus excelsior Betula Grasses Urtica Grasses Common Crossbill Picea Picea Picea Picea Picea Picea Picea Picea Picea Picea Picea Picea Larix Larix Larix Larix Larix Larix Larix Larix Larix Larix Larix Larix Pinus Pinus chaffinch’ I ,L , ’- - I J Fagur silvatica hV&.S. Fagua silvatka 11. THOSE SPECIES BREEDING AND OCCURRING THROUGHOUT THE YEAR IN FARMLAND

JAN. PEE, MARCH APRIL MAY "E JULY AUQ. SEP. Om. NOV. DEC. Greenfinch < ' Cereals Taraxacum Senecio Brassicas Brassicas Brassicas Arctium Arctium Arctium Polygonum Polygonum oflicinale vulgaris Cereals Cereals Arctium Brassicas Brassicas Polygonurn Arctium Stellaria Senecio Taraxacum Senecio Cereals Senecia Polygonum Brassicas Brassicas media vulgaris officinale vulgaris vulgaris Cereals Cereals Cereals Senecio Polygonum vulgaris Cereals Brassicas Goldfinch Arcfium Senecio Taraxacum Senecio Thistles Thistles Thistles Thistles Thistles Arctiurn Dipsacus -Dipsacus vulgaris officinale vulgaris Senecio Senecio Senecio Arctium Thistles Thistles Arctium Stellaria Senecio S. squalidus vulgaris vulgaris Senecio Dipsacus Thistles media vulgaris Taraxacum Arctium vulgaris officinale

Linnet Brassicas Stellaria Stellaria Brassicas Thistles L- --Brassicas Stellaria media media Rumex Brassicas Brassicas Brassicas Polygonum media Taraxacum Taraxacum acetosa Chenopodium Chenopodium Chenopodium Polvgonum officinale officinale Hypochoeris Polygonum Polygonum Poa annua Poa annua Rumex Ranunculus Artemisia acetosa Bullfinch Buds ------' Buds Stellaria Stellaria Rumex Brassicas Sonchus Chenopodium Rumex Buds Stellaria media media Brassicas Sonchus aleraceus Rumex Chenopodium Chenopodium media Taraxacum Taraxacum Ranunculus oleraceus Polygonum Rubus Rumex officinale officinale Sonchus Rumex Chenopodium Urtica Rubus Capsella oleraceus Chenopodium Rubus Urtica bursa- Rumex pastoris Senecio vulgaris

Chaffinch. I Cereals Inverts. Inverts. Cereals Cereals Cereals , 2 Cereals Polygonurn Stellaria Inverts. Brassicas Chenopodium Cereals Chenopodium Stellaria media Brassicas Chenopodium Brassicas media Brassicas Polygonum Po0 annua Polygonum

Note. Chaffinches fed mainly in woods in winter only in years of good Beech crops; otherwise they fed mainly on farmland. 82 I. NEWTON :EVOLUTION AND ECOLOGY OF FINCHES IBIS109 the Linnet and Greenfinch do this as well, especially in winter, and moreover, all overlap widely in the species of seeds eaten. Thus there is ample evidence that the farmland species are less well segregated from one another ecologically than are those that still live mainly in woodland; and that the Bullfinch and Chaffinch, which are now resident in both habitats, are better isolated from other finches in woodland than in farmland. It should be stressed, however, that only a small proportion of the population of each species remained on farmland during periods of snow: most birds moved out either into other places nearby (resident Chaffinches and Greenfinches) or left the area completely (Goldfinches, Linnets, most continental Chaffinches). The woodland species are more distinct taxonomically from one another (five species in five genera) than are those on farmland (five species in three genera). It might reasonably be argued that this itself would result in their taking more different diets from one another; but on the other hand, whenever the woodland species feed on farmland they take the same foods there as the residents. This might be partly attributable to super- abundance of foods, but this surely cannot hold for the whole year. On the other hand, a far greater proportion of the farmland than of the woodland plants produce relatively small seeds-and often in enormous quantities. They can therefore be exploited effi- ciently, not only by the small-billed finches which usually eat only one seed at a time but also by the large-billed species which can take several at once if they get them directly from the plant. It is also arguable that the greater segregation of the woodland species is related to the fact that they are living in an environment which resembles their ancestral one much more closely than does that of the species now living primarily on farmland. The woodland species have certainly had a much longer period of comparative stability of habitat for differences to evolve than have the farmland species. Not only is agricultural land a relatively recent habitat, but it is continually changing in character under man’s influence; this would make it more difficult for the various animals living there to adjust to one another ecologically than in natural habitats where such changes are probably slower. On farmland many of the food-plants (crops and weeds) themselves are also of comparatively recent origin, or at least have evolved under the selective influence of agricultural operations (Salisbury 1961). Furthermore, it is not known when farmland was first colonized by most of the finches now living there, but in the case of the Bullfinch it was probably mainly in this century, while colonization by the Redpoll is only just beginning. Whereas in woodland there are no small seed-eating passerines other than finches, on farmland there are also two ploceids (Passer domesticus and P. montanus) and three buntings (Emberixa calandra, E. citrinella and E. schoeniclus), though the last species is a very recent colonist (since about 1958 in Oxford). Little is known of the habits of these various birds on farmland except that, while they take more grass and cereal seeds than the finches, they nevertheless overlap widely in diet both with the finches and with one another. There is clearly much more extensive overlap in the ecology of the various seed-eating birds in this highly artificial environment than in semi-natural or natural woodland, and only further study will help to throw light on what is evidently an extremely complex situation. In view of the extensive overlap in the diets of many of the finches now living in southern England, it is of particular relevance to see whether they are isolated from one another at those times of year when food is most likely to be limiting. Most of the seeds eaten by finches are produced from May to October, and thereafter stocks are con- tinuously depleted until the following spring, when seed-production begins anew. One would expect, therefore, that seeds would be scarcest in early spring and at those times in winter when many are buried and unavailable under snow. 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 83

In my study area, most of the woodland finches were less affected by snow than those on farmland since food was still available on the trees. Nevertheless they were normally completely segregated from one another at such times. Crossbills fed exclusively on conifer seeds, Siskins on Alnus glutinosa, Hawfinches mainly on Blackthorn Prunus spinosa or Hornbeam Carpinus betulus seeds, and Bullfinches on Ash Fraxinus excelsiw seeds or on various buds. Redpolls fed entirely on Betula seeds if these were still available, and otherwise on those of various willowherbs. But in one year, some Redpolls and Goldfinches, as well as Siskins, fed on Alnus during two snow periods in January. By February, however, the seeds had become scarce in the catkins and only Siskins remained. Although most woodland finches were restricted to feeding in trees during snow periods, Hawfinches were also able to feed on fallen seeds under thick Blackthorn bushes that had held back the snow. Among the farmland finches, most Linnets and Goldfinches that had stayed in the area after October left the locality with the first snow; those Linnets that remained during snow periods fed on the few seeds left on upright plant-stems especially those of Artemisia, grasses and Plantago, while Goldfinches fed mainly on teasels, and sometimes in alder trees, since most of the seed-heads of their other winter food-plants (burdocks and thistles) had fallen to the ground by this time. Most Bramblings and continental Chaffinches and a few Greenfinches also moved out of the study area temporarily during snow-periods, but it is not known where their movements took them. Of those that stayed, a few Greenfinches moved into farmyards where they fed largely on grain put out for poultry, a few fed on Rosa and Rubus seeds still available in the hedgerows, but most moved into gardens and fed at bird-tables. Although this habit must be very recent, at least on this scale, its importance now should not be underestimated, since almost all the Greenfinches I caught at communal roosts during hard weather had eaten peanuts and other foods deliberately provided by householders. A small proportion of the Chaffinches from both woods and farmland visited gardens during hard weather, but most moved into farmyards where they fed on grain or weed-seeds (and also on various forms of " mash '' and other proprietary animal foods, which were not taken by other finches) ;they also ventured frequently inside buildings for food. (Stackyards presumably offer much less food now for seed-eating birds than in the days before combine harvesting; thus, earlier this century Greenfinches were recorded frequently on the side of stacks during hard weather pulling out stems bearing grain. Perhaps gardens have now replaced stackyards as snow-time refuges for Greenfinches.) To summarize, all the finches I studied, including the farmland species, were segregated in diet from one another during snow-periods, but in the case of Chaffinches and Greenfinches the isola- tion seems rather precarious, since it depends on an artificial source of food provided by man. It is of interest that none of the farmland finches moved in strength into woods during hard weather. As mentioned above, one might expect that a second difficult period for many finches would come in early spring when most of the seeds from the previous year had dis- appeared and fresh ones were not yet available. The only seeds which are most readily available in early spring are those of Pinus spp.; as the cones open these seeds are eaten not only by Crossbills, but also by Siskins, Goldfinches, and sometimes by Chaffinches. In one year the return of migrant Linnets and Goldfinches to Oxford in April coincided with the first flush of fresh seeds (Stellaria media and Senecio vulgaris), but in the other two years they arrived about a week too early. In these years, Goldfinches, together with Siskins and Redpolls, fed largely on the insects present in plenty on developing buds, especially those of larches. (It is of interest that the seed-eating African weaver bird Quelea quelea also feeds largely on insects at that period each year when seeds are scarcest (Ward 1965 a).) On the other hand, most Linnets (immigrants and residents), Chaffinches and some Greenfinches relied on weed-seeds turned up by fresh ploughing, or on spilled 84 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 grain, though most Greenfinches still fed largely in gardens at this time, on food provided by householders. Bullfinches fed almost exclusively on the small buds of Crataegus and various fruit trees in spring, while Hawfinches took the larger buds of Quercus and Fagus. In the study area, Bullfinches began eating buds earlier in years when seeds were scarce than in years when they were plentiful, and similar behaviour has been recorded for the Hawfinch (Mountfort 1957). In the early months of the year, however, Bullfinches are unable to maintain themselves on buds alone, and must obtain at least some seeds if they are to survive (Newton 1964 c). It would appear, therefore, that under modern conditions early spring is not such a difficult time for finches as one might expect; some turn to alternative foods, such as buds or the insects present on them, but others are again dependent on food directly or indirectly provided by man. In all these cases, there is a good deal of overlap in the food of the different species. All finches eat invertebrates, but in varying proportions. Although various cater- pillars and aphids were taken by all species, there were some differences in the other types of invertebrates sought. The Bullfinch was the only species that took small slugs and snails in any quantity (Newton, in prep.), the Hawfinch the only species that ate beetles as large as Melonunthus (Mountfort 1957), and the Crossbill the only species that extracted insects from various tree galls and from beneath bark. A more detailed study of the invertebrate food might well reveal further differences; in particular, it is likely that different sized caterpillars are preferred by different finches, according to differences in their bill-sizes.

SOME SPECIAL CASES Some species among the European finches are closer taxonomically to one another than they are to other finches. The three Crossbills form one such group, the Chaffinch and Brambling another, and the Redpoll, Linnet and Twite a third. The first two groups are now given generic status by all authorities, and the third by some. The ecology of the Crossbills was discussed earlier and will not be considered further here, but it is of interest to examine the other groups in more detail.

Chaflinch and Brambling As mentioned earlier, in the breeding season these two species are for the most part geographically isolated: the Brambling inhabits the northern part of the belt and the Chaffinch occurs further south. In Scandinavia the zone of overlap is narrow and advancing northwards, supposedly in response to climatic amelioration (Merikallio 1950). Where both species occur together, the territories of individual Chaffinch pairs sometimes overlap those of Bramblings, without, apparently, any interspecific hostility (Udvardy 1956). While the Brambling completely vacates its breeding range in autumn, some Chaffinches (males) remain in Scandinavia throughout winter. It was mentioned earlier that, unlike Chaffinches, individual Bramblings sometimes winter in widely different areas in different years; and some have been recovered in winter several hundred miles to the east or west of where they were found in a previous winter (see for instance Bannerman 1953). Bramblings also perform more frequent and extensive movements during a winter than Chaffinches, and sometimes congregate in enormous numbers in areas where beechmast and other foods are plentiful. For instance, in the hard winter of 1946/47, an estimated eleven million Bramblings fed on the abun- dant beechmast near Porrentruy, Switzerland, and assembled each night in one small valley to roost (Gueniat 1948). Within Britain, Bramblings, resident Chaffinches and immigrant Chaffinches are in most winters differently distributed : resident Chaffinches are fairly evenly distributed, immigrant Chaffinches are concentrated in the south, and 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 85

Bramblings in the east (especially northeast). In the southeast, including Oxford, all three occur together every winter, but immigrant Chaffinches and Bramblings almost always exploit some local abundance of food, and in this way mitigate competition both between one another and with resident Chaffinches. Although the Chaffinch and Brambling are nearly identical in structure and feeding behaviour, there are some slight differences in these respects. The Brambling’s beak is some 10% deeper, and presumably stronger, that that of the Chaffinch, and its edges are sharper. As mentioned earlier the Brambling occasionally feeds directly from plants in winter (unlike the Chaffinch), either by hovering, or by reaching for seeds while perching on the ground or precariously on some horizontal twig or stem. For example, in 1965 most of the beechmast remained on the trees in Oxford until late autumn, and while many Bramblings picked out the seeds from the cusps by hovering (albeit rather clumsily), or perching on nearby twigs, most of the Chaffinches fed on fallen seeds on the ground below. Bramblings have a stronger preference for beechmast than Chaffinches, for there are always more Bramblings to be seen in a good beech year than in a poor one, and at any one time a greater proportion of Bramblings than Chaffinches in an area may be found under these trees. When beechmast is not available in winter, Bramblings usually occur in large mixed flocks in fields where grain or weed seeds are plentiful. Unlike Chaffinches they visit gardens and farmsteads only in very hard weather. Seeds from fleshy fruits were not recorded in the food of either species in Oxford, but according to Voous (1960) the Brambling eats a larger proportion of these in autumn than the Chaffinch. In Oxford at this time, Bramblings were almost always seen in birches while Chaffinches (resident and immigrant) fed mainly on farmland. Chaffinches (residents?) are perhaps more susceptible to cold and snow than Bramblings, for when in the winter of 1961-62, both species fed beneath some Rumex plants in the study area, with the onset on snow the Chaffinches were fluffed and reluctant to fly, whereas the Bramblings were tight feathered and apparently healthy. To sum up, the Brambling varies its main wintering areas from year to year, more readily moves long distances in winter, almost always exploits some local abundance of food, more frequently eats beechmast, is more adept at feeding directly from plants, and is perhaps better able to tolerate cold and snow than the Chaffinch. Another difference between the species, which might have some ecological basis, is the fact that the Brambling migrates mainly by night and the Chaffinch mainly by day.

Redpoll, Linnet and Twite Some authorities (e.g. Vaurie 1959) group the Redpoll, Linnet and Twite together in a separate genus, Acunthis, because they are closely similar in structure, build, and bill-shape, and also in colour, in which they differ markedly from other European finches. Although all three species are widely distributed in Europe, only in parts of Britain and Scandinavia do all three occur together. Discussion of these species is hampered by the fact that less is known of their ecology and movements than of those of the Chaffinch and Brambling. Further, the Redpoll varies geographically (in colour, size and bill- shape) to an extent unprecedented among other northern passerines; in Europe alone it shows a wider range of habitat-choice and feeding habits than the Linnet and Twite together. Over much of its range it is a forest species, living mainly on Betulu but also on other tree-seeds which it obtains, for the most part, directly from the trees. In the arctic, however, it feeds on the tundra and in other open places, largely on the ground or from low plants, and breeds in areas with only the sparsest covering of vegetation. It is of particular interest, therefore, that where its range overlaps those of the Linnet or Twite, it is completely segregated from them by habitat, differs in feeding methods, and prefers smaller seeds. 86 I. NEWTON :EVOLUTION AND ECOLOGY OF FINCHES IBIS109

The Linnet and Twite are closer to one another ecologically than either are to the Redpoll. Both live in open country, and feed mainly on the ground in winter, when they often take the same foods from the same coasts and salt-marshes. In general, however, the Twite inhabits areas which are colder and (especially in the breeding season) usually higher and more sparsely vegetated than those in which the Linnet is found, and in this respect they may be regarded as ecological replacements. The most important wintering grounds for Twite in Britain are on the north and west coasts of Scotland, the Scottish Islands (residents), and the Wash (immigrants). Since Twite remain near the coast in winter, they are one of the few ground-feeding birds which are able to spend the entire winter in such high latitudes. Most Linnets move from the north of their breeding range, either before the winter begins or with the onset of snow. As a result, the Twite is usually the only finch to be found in winter on the more northern coasts, but further south, Linnets and various other finches also occur on coasts and salt-marshes. Although both Linnet and Twite will readily take the seeds of Sea Aster Aster tripolium, Marsh Samphire Salicornia europaea, Sea Rocket Cakile maritima, Cord grass Spartina maritima andThrift Armeria maritima, I have noticed that the Linnet feeds more frequently on fallen seeds on the ground than does the Twite, and the latter more frequently from the seed-heads of plants; these it often holds down with one foot while standing on the ground with the other. A further difference between the two species is that while the Linnet normally avoids human habitation, the Twite regularly feeds round stackyards and farmsteads in the northern Isles.

SOME THEORETICAL CONSIDERATIONS It is now widely accepted that geographical isolation is a necessary first step in speciation (Mayr 1942). Individual populations may then diverge by adaptation to local conditions, and any differences they acquire may be sufficient to permit them to coexist and behave as separate species if they later meet. Even if some interbreeding does then occur, reproductive isolation can still be achieved if individuals produce more viable offspring by mating with their own than with the other incipient species; and any slight differences in ecology between them can be accentuated by selection if this leads to reduced competition for food. Competition for food is often held partly responsible for the evolution, and also for the maintenance, of ecological differences between related species; but it need not, of course, be solely responsible for their production, since it can only operate once the species come together, by which time they might already differ in ecology. The fact that the various finches differ most in ecology at times when food is scarcest, suggests, how- ever, that competition was important in their evolution. Further, it is difficult to see why the Redpoll should differ more strongly from its two closest relatives (Linnet and Twite) in habitat and feeding behaviour in those areas where all three occur together than elsewhere, if not to avoid competition for food, or some other limiting factor. Even if two incipient species did have similar ecology on first meeting, one would as a rule be more efficient than the other on certain foods or in a certain habitat. The first require- ment for successful coexistence would then be that each developed a preference (through natural selection) for that habitat or food with which it was most successful. In accentuating differences in feeding behaviour between species, selection could theoretically act on any behavioural or structural characters that would affect food-choice. Probably the immediate result would not be complete segregation in diet, but differences in the efficiency with which different species could obtain particular foods when these were least readily available. The consequence would be that when food was scarce, each would prefer a different kind of food. In theory there is no reason why closely related incipient species should differ in feeding behaviour if food is available in excess of their joint demands, so selection would act most when food was scarcest. In practice, 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 87 however, different polyphagous animal species usually select at least slightly different diets from even a superabundance of foods, perhaps mainly because they differ in struc- ture and requirements and not necessarily to avoid competition. It is usually difficult to assess the relative importance of habitat selection as against food selection in the ecological segregation of related species, for the habitat preferences of different species might have been evolved under the influence of one or two selection pressures. For instance, in two sympatric species with very similar food requirements, distinct habitat preferences might have been evolved primarily to reduce competition between them for food, while in a third species a habitat preference might have been evolved primarily to enable it to find its food (and other requisites) more easily (in which case, habitat selection is now merely a stage in food selection). The essential difference between the circumstances which have led to these habitat preferences is that competition for food was important in the development of the first type, but not the second. Although we may often have no way of knowing the chief causes of the differences in habitat now shown by closely related species, we may surmise that competition for food was important in the development of habitat differences between those sympatric species, such as the Linnet and Twite, which have very similar food and feeding behaviour. Otherwise it seems that habitat selection does not play a major role in the ecological segregation of different finches in modern England, where differences in actual feeding habits are more important. In the following sections, the ontogeny of specific feeding behaviour, and some possible methods of its evolution and maintenance, are discussed for finches in more detail.

SPECIATION AND THE DEVELOPMENT OF FEEDING BEHAVIOUR As mentioned above, the way in which the feeding habits of different species arise during ontogeny and evolution are relevant to the problem of speciation. Hinde (1959) has pointed out that the young of birds which have a varied diet must either recognize each kind of food specifically, or respond to generalized stimuli common to many foods. For animals that take a wide range of food, the first view is unlikely because of the wide range of foods taken, and on the second, differences in food selection between closely related species are difficult to understand. Hinde has suggested, however, that the problem can be resolved by assuming that each bird responds initially to a wide range of potential foods which is later narrowed by the bird’s learning to concentrate on those it can take most efficiently. This learning would be conditioned by the particular struc- tures and behaviour patterns of a bird, and since these differ between species, could result in their learning to prefer different foods, even though they responded initially to a similar range of foods. The learning could also be facilitated by the young bird associating with other individuals of its own species, but this aspect is discussed later.

The ontogeny of seed-husking behaviour In an attempt to test Hinde’s views, Kear (1962) examined the ontogeny of seed- husking behaviour in some captive Chaffinches. Initially the young pecked at any small spots which contrasted with the background, and picked up and mandibulated a variety of objects, including seeds. They first learned to discriminate edible seeds from other objects, and then to prefer the largest seeds they could efficiently manage, so gaining the most food in a given time. She found further that three species of finches of different bill-sizes studied as juveniles initially selected small seeds from a mixture, but differed in the speed with which they included large seeds in their diet. I have repeated some of Kear’s observations (Newton, in prep.) using young Green- finches and Linnets, species which differ in size of bill. Four of each species were reared from eggs placed under the canaries. They all left the nest on the 14th day and 88 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 could just about feed themselves by the 30th, though they continued to accept some food from their foster parents for several days more. The initial feeding behaviour of these birds was essentially the same as described by Kear for the Chaffinch, and they too eventually preferred larger seeds to those they first managed to open. The young Green- finches, however, (with large bills) learned to husk large seeds sooner than the young Linnets (with smaller bills), and eventually settled on a diet containing a greater propor- tion of large seeds. It seems therefore that from a similar initial range of potential food-objects, individuals of each species learn to concentrate on different-sized seeds, according to the size of their bills. Hence, differences in diet between species are controlled by differences in bill-structure, rather than bill-structure being adapted to diet (see below).

The ontogeny of other feeding behuviour As with seed-husking, the ontogeny of behaviour patterns used in obtaining food involves not only perfecting their use, but also learning to apply them under appropriate circumstances. For instance, before learning to feed themselves, captive young Gold- finches picked at a variety of objects, such as leaves, twigs and paper, using behaviour patterns that were later restricted to the seed-heads of Compositae; and the young of some other species often attacked the nodes of plant-stems instead of the seed-heads. It is often difficult to determine whether behaviour patterns used in feeding are under direct genetical control-which would sometimes entail the encoding of a complex series of actions in the central nervous system-or whether they develop wholly or mainly as a result of learning conditioned by structure. Sometimes, however, there are indica- tions that a behaviour pattern is mainly learnt as the use of the feet in feeding by young Great Tits (Hinde 1959). Similarly, I have noticed that some of the finches that feed in this way often settle on plant-stems and pull the seed-heads towards themselves with the bill before hopping on to them. From this it is but a short step to using the feet in conjunction with the bill in feeding. Different finches differ in their ability to cling to vegetation, and those most adept at it obtain a large proportion of their food in this way. This difference could be due to direct genetically determined differences in tendency to hang, or to individually learned differences consequent on structural differences. The latter seems more probable especially since there is a correlation between leg-proportions, body-weight and ability to hang. It seems likely, therefore, that those behavioural differences between species which affect diet depend on structural differences that conduce to the development of particular behaviour patterns. Structural differences alone between species could result in different foods being taken either (as with bill-structure) by acting directly on food- choice, or indirectly through influencing the behaviour patterns that develop. For ecological isolation, two forms need only to diverge in structure, not necessarily in innate feeding behaviour. Nevertheless, some of the finer differences in feeding behaviour between finches, especially those between different genera, are almost certainly inherited irrespective of structural features. For example, all Curduelis finches can learn to pull out thistle fluff to get the seeds. This is a simple action for which presumably no structural specializa- tion is required, yet the Fringilla finches were never seen to do this, even though in my aviary they had the example of other finches and would pick off the seeds from fluff pulled out for them. Furthermore, it is known that many species of birds will repeatedly perform their hunting and feeding behaviour irrespective of any food reward, especially when young (see Hinde 1959). It is therefore possible to conceive of inherited differences between species in the extent to which they will persist in practising behaviour patterns without the reward of food. This would then make it more likely that some species would acquire certain behaviour patterns than others. 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 89

EVOLUTIONARY TRENDS IN FINCHES The finches, irrespective of habitat-preference or taxonomic position, form series, showing gradation in bill-size, body-weight, relative leg-length and other characters. The resulting differences in food-choice between them are mostly differences of degree : different finches prefer seeds of different sizes, though there is a good deal of overlap; and species differ also in their ability to obtain food from the ground or directly from regetation. There are very few absolute differences in feeding habits between them, except for instance that the Hawfinch, and to a lesser extent the Greenfinch, can open seeds that the smaller species cannot. The change from a small- to a large-billed species is more than a mere change in overall body-size, since the large species have disproportionately larger bills than the small species. It is as though selection, while producing larger-billed forms, has tended to minimize the concomitant increase in body-size-probably because a small body needs less food to maintain it than a large one, and makes it easier for its owner to cling to vegetation. Theoretically, the most efficient type of finch is one with a large bill (able to take large items of food) and a small body (needing little food to maintain it). It is tempting to suggest therefore that evolution in cardueline finches has progressed from small towards large-billed forms, such as the Hawfinch, since this has the smallest body in relation to bill-size. It is of interest that there are many estrildines that are smaller than the smallest cardueline finch, yet with proportions similar to those of the Hawfinch. Although a correlation between structure, behaviour and food is commonplace, it is often difficult to decide which evolved first. Sometimes, however, there are indications that a structural change was essential for the evolution of a new behaviour pattern or feeding habit. For instance, in finches an increase in bill-size would be necessary before a bird could feed efficiently on larger seeds; and a change in relative leg-length before a ground-feeding form could become arboreal, or vice versa. In the latter case the con- comitant strengthening of the grip would also permit the holding of food in the feet. Within each species, there is some variation in bill-dimensions, leg-proportions and weight. That individual differences in bill-size affect the diet is indicated by the fact that the sexes of the Goldfinch differ in the ease with which they can obtain teazle seeds. Further, one out of four captive Goldfinches that had an unusually large bill was the only one which managed to open sunflower seeds, though the others tried repeatedly; and the smallest of three captive Hawfinches was unable to break open sloe stones. Individuals also differ in the shill with which they can use particular behaviour patterns, and apparently in their ability to learn to do so (see Thorpe 1956). Kear (1962) has recorded variation in the skill with which Greenfinches hung on suspended baits, Thorpe (1956) among various finches in their ability to pull up food at the end of a string, and Josefik (1952) in the ability of individual Bullfinches to obtain Sorbus fruits by hovering. Individuals adept at a particular behaviour pattern tend to use it repeatedly, probably because its performance is consistently rewarded with food. While the differences between individuals of any one species are not normally as great as those between different species, intraspecific behavioural differences could result from slight structural differences. Structural variability, or any behavioural variability resulting from it, provides ample scope for selection. Individual differences in structure might be enough to permit exploitation of different foods. If this led to competition with related species, the deviants might be eliminated, but if on the other hand they could exploit untapped food-sources, they could be at an advantage over members of both their own and other species, and so the change may be perpetuated. This sort of selec- tion could lead, with genetic isolation, to the evolution of large- from small-billed forms, and arboreal from ground feeders, and vice versa. It is presumably competition with related species that limits the range of structure and behaviour shown by any one species, since it is usually the individuals with extremes 90 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 of structure and behaviour which overlap and compete most with related species. Lack (1947) has shown how the presence or absence of related forms affects the bill-dimensions, and hence the food, of certain geospizid finches in the Galapagos Islands.

SOCIAL BEHAVIOUR AND FEEDING HABITS FLOCKING The Chaffinch and Brambling normally feed in flocks only outside the breeding season (but cf. later), but for cardueline finches feeding is always a social affair. Although feeding birds are sometimes seen singly, they are usually in flocks of a few to several thousand individuals. There is a marked tendency for flocks of all species to become largest and best integrated in late winter, when food is most localized. Although flocks of over a hundred individuals are common in most species, they are rare, but not unknown, for the Hawfinch and Bullfinch, probably because suitable food is rarely abundant enough at any one place to attract large numbers of these birds. Flocks of finches form wherever some temporary abundance of food has assembled them and throughout the day birds are continually joining and leaving the flock. Ringing has shown that there are usually many more birds feeding at a particular place than may be seen there at any one time, while gut-analyses showed that individual birds often feed at more than one place each day, since they often revealed several types of food which could have been collected only in different habitats. Familiarity with many good feeding places is of advantage to a finch, since any one supply may suddenly be exhausted, be lost under a fall of snow, or, on agricultural land, be harvested or ploughed under. Finches show a remarkable ability to locate and concentrate in areas of abundant food, and a small flock that has found a good feeding place may rapidly swell in size as it is joined by others. For instance, in early July 1962, I noticed about five Greenfinches feeding on a patch of freshly seeding Sinapis; later in the day there were about 20 birds there, the following day over a hundred and on the fourth day several hundreds. I caught about 300 birds from this flock which consisted of feeding adults, independent juveniles and family parties. The youngest juveniles remained in the hedges nearby, where they were visited and fed by their parents. Since such large numbers accumulated in this field during the breeding season, some of the adults (which comprized about a third of the flock) might have flown several miles from their nests to collect food. The flock persisted for only ten days, then dispersed with equal rapidity as the seeds were eaten. That passing finches respond to the presence of those already there, and not only to the food-plants themselves, is indicated by the fact that they often accumulate on ploughed fields and other bare areas where there are no food-plants to be seen. This method of feeding is most easily used in open country where the birds can readily see one another. It is certainly in open country that finch flocks build up most rapidly and where the largest floch occur. In woodland, where flocks are not in sight of one another, the build-up is noticeably slower and the flocks smaller even though food may be locally plentiful. The term " local enhancement " has been used (see Hinde 1961) to describe the behavioural mechanism whereby the attention of some individuals is drawn to a food- source discovered by others; in this way the number sharing the supply rapidly increases until it is exhausted. To appreciate the advantages in this method of feeding, it is necessary to remember that for the most of the year the food of finches is distributed patchily. As the winter advances, the productive patches become scarcer and more difficult to locate, but this is facilitated by the method outlined above. Ward (1965 a) has described similar behaviour in the seed-eating Quelea quelea, and has pointed out that the method is beneficial only if the amount of food available is greater than can be immediately consumed by the birds that find it. As mentioned above, foods of finches 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 91

often disappear quickly irrespective of the attentions of the birds themselves (e.g. under snow); and as far as the individual is concerned, the advantages of defending a patch of food or of not sharing it with others, is, I believe, outweighed by the advantages of feeding socially since it may thereby learn of many other food-sources.

THE ROLE OF SOCIAL EXPERIENCE IN THE ONTOGENY OF FEEDING BEHAVIOUR In gregarious species social experience may be especially important in influencing food-preferences, and Kear (1962) has briefly discussed its role in the feeding of finches: the origin of a new food-habit can be attributed to the chance sampling of a potential food-source by one or more individuals, and its spread to local enhancement. Cases of the spread of new food-habits among birds include the opening of milk bottles by titmice (Hinde & Fisher 1951), the eating of Daphne mezereum seeds by Greenfinches, and the attacking of fruit blossom by Redpolls in New Zealand (Stenhouse 1962), a habit which has also been recorded recently in England (Newton, in prep.). Since few such cases have been described, it is worth recording two more I saw among finches. In November 1958, a few Linnets were seen eating birch seeds (which was previously unrecorded for the species) in a small wood in north Derbyshire; but the habit spread and by the following January there were several large flocks in this and in adjacent woods. There was no apparent scarcity of the Linnet’s usual winter foods in the area, or an unusually large birch crop. The habit has not been seen there since, though Goodwin (1964) observed similar behaviour among Linnets on Hampstead Heath in 1962, and Ash (also Goodwin, Zoc. cit.) on several occasions in Hampshire. A further instance on unusual feeding behaviour concerns some Siskins which fed on beechmast in the winter of 1956/57, also in north Derbyshire. They were unable to open the seeds in the normal way, but obtained the kernels by jabbing their bills into the husk and peeling it back-behaviour normally used to open to seed-heads of Com- positae. This first occurred in one small wood but soon spread to adjacent areas, and the number of Siskins feeding in this way increased through the winter. There seem to be no previous records of Linnets eating birch seeds, nor of Siskins taking beechmast. In Derbyshire the habit seems to have disappeared in both species with those particular seed-crops, but with the Linnets it arose independently in several different areas and in different years. Since local food-habits can easily arise among finches, it would not be surprising if two populations of a species living in widely separated areas had different diets even though a similar range of foods were available to both. Extensive data are available on the diet of various finches in East Holstein, Germany (Eber 1956). Eber’s study area contained the same habitats and in most respects a similar flora to mine near Oxford. In addition to the finches found in Oxford, the Serin canarius was also resident there and the Siskin was present in summer as well as in winter. Within each species, bill-size is the same in birds from Holstein as in birds from Oxford (as confirmed by measurements of specimens in the British Museum), yet there are some striking differences in their diets. Each finch species takes seeds of the same size range in Holstein as it takes in Oxford, but often different types of seeds are involved. Senecio vulgaris seeds formed the main food of the Goldfinch in Oxford for about six months each year, but were not recorded at all for this species in Holstein, even though they were important to the Linnet and Greenfinch there. Further, cereals predominated in the diet of the Linnet in Holstein, but were not recorded in Oxford, despite the quantity grown here. Further differences are given in Table 17. A possible explanation is that they result from differences in the food traditions of the birds in the two areas. This is the more probable since most of the differences occur in summer when a wide range of abundant foods is available to choose from. In winter, on the other hand, when only a limited range of foods is available, the diet of most species is similar in the two areas. Thus in winter in both areas, 92 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109

Goldfinches lived mainly on alder, thistle and burdock seeds; Linnets on small weed- seeds; and Chaffinches and Bramblings on beechmast and cereals. Only the Greenfinch and Bullfinch had markedly different winter diets in the two areas: the Greenfinch mainly beet and turnip seeds in Holstein, and the Bullfinch mainly Maple Acer campestris seeds; but none of these seeds was available in quantity near Oxford. Theoretically only two behavioural factors are necessary for the spread of various food-habits through a population, or for their transmission from one generation to the next: the ability of a bird to copy in some way the behaviour of another, and some degree of social organization or period of post-fledging parental care to bring individuals together. Young finches are dependent on their parents for two or three weeks after leaving the nest, so parental influence in introducing them to traditional foods could be a strong factor directing the development of feeding behaviour. Further, as shown above, they feed in flocks for most of the year, so there is ample opportunity for new food-habits to spread.

TABLE17. The relative importance to jinches in Holstein, Germany (from Eber 1956) and in Oxford, England (present study) of certain seeds common in both areas. Percentage of Finch species Seed species total records in Holstein Oxford Greenfinch Artemisia vulgaris 7 0 Goldfinch Senecio vulgaris 0 17 Artemisia vulgaris 11 0 Linnet Cultivated cereals 18 0 Chenopodium spp. 0 11

To sum up, it is suggested that while the feeding habits of an individual are ultimately formed by its structure and behaviour patterns (following Hinde 1959), in finches this is directed by local enhancement of traditional feeding habits. This could account for the fact that, when plenty of the same range of foods is available to both, two populations of the same species may have different diets. But this will not explain all the facts of diet selection, for an individual will always select a varied diet, even when one food is super- abundant and others scarce (Tinbergen 1960). Further, many finches select different diets for their young, though this may involve behaviour quite distinct from their nod feeding. Seasonal changes in diet can largely be explained by assuming that the bird selects those foods which are preferred and most easily available at the time.

RECENT CHANGES IN THE HABITATS AND FOOD OF FINCHES As mentioned earlier in this paper, several species of finches have recently begun to colonize other habitats: the Redpoll now occurs in several parts of southern England where birches are absent, nesting in young conifers and feeding on the seeds of agricul- tural weeds; the Bullfinch will now tolerate more open habitats in southern England than a few decades ago; and it is apparently only since the beginning of this century that the Greenfinch has colonized the inner suburbs and the centre of (Homes et al. 1954) and the gardens of central Europe (Sokolowski 1958). The two trends in land management which are currently making the greatest impact on finches are the replacement of varied deciduous woods by dense monocultures of conifers and the increased use of herbicides in agriculture. In deciduous woodland a dozen or more species of trees and shrubs produce seeds each autumn, and many remain on the trees and are available to finches during periods of snow. There is also a rich and 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 93 varied ground flora. On the other hand, though conifer plantations may provide nesting places for finches in the early years of their growth, they produce seeds only rarely and these are unavailable to most finches; moreover they permit only the sparsest, if any, of ground floras. Larches seem to produce seeds more often than most other conifers and also provide invertebrates for several finch species in spring when seeds are scarcest. The use of herbicides is becoming more widespread as hedgerows are destroyed and waste land cultivated and brought under chemical control. Thus, the quantity of food available to finches in Britain must have declined enormously over the past few decades. The diets of those finches living primarily on farmland have also changed considerably over the past 50 years, as a result of changes, due chiefly to herbicides, in the types of seeds available. Thus, Spmgula arwensis and other cornfield weeds, whose seeds were prominent in the diets of various finches in the early years of the century, have how almost disappeared from most areas, and so from the diets of the finches living there. The deliberate provision of new types of food by householders has provided alternative fare for two or three species, at least during hard weather when other foods are least available. Finches seem to adapt easily to new kinds of garden and crop plants, and other artificial sources of food, and even under more natural conditions their diets vary markedly from place to place, and sometimes from year to year. The species of food- plants seem to matter little, providing their seeds can be obtained using the characteristic behaviour patterns of the birds. They should, therefore, find little difficulty in adapting to further changes in the composition of the flora providing a wide range of foods is still available.

ACKNOWLEDGMENTS I would like to thank Dr. Janet Kear for help and advice before I started this work, various farmers and landowners for free access to their property, the Nature Conservancy for licenses to take finches, dead and alive, and D. E. Baird for drawing Fig. 1. In writing up my main debt is to Dr. P. R. Evans and Mr. R. E. Moreau for much constructive criticism of earlier drafts. Dr. D. Lack, Dr. C. M. Perrins and Dr. T. Royama read the whole of a later draft, and Dr. J. F. Monk parts of it, and to all of these I am also indebted for many useful suggestions. The work was carried out while I was holding a D.S.I.R. grant.

SUMMARY The habitats and foods of ten species of finches studied near Oxford, England, are described in detail, and differences in feeding habits between them are related to differences in bill- and leg- structure, body-weight and behaviour. The Hawfinch, Siskin, Redpoll and Crossbill live primarily in woodland, the Greenfinch, Linnet and Goldfinch primarily in farmland, while the Bullfinch and Chaffinch breed, and occur throughout the year, in both these habitats. Habitat differences between species were probably more marked in primeval England than now, and the problems of studying animals in man-modified environments are discussed in this context. Diet was studied by observation and by gut-analyses of live and dead finches. Before roosting, finches usually accumulate food in their gullet, which is expandable but otherwise undifferentiated (the term ‘‘ crop ” is thus inappropriate). The Lesser Redpoll, the smallest species studied, can store up to about 0.8 C.C. of food in its gullet, but the Greenfinch, one of the largest finches, up to 2.5 C.C. Among the Curduelis finches, the Greenfinch lives mainly on the large seeds of various trees, cereal crops and agricultural weeds; the Goldfinch on the seeds of Compositae; the Siskin on alder and conifer seeds; the Lesser Redpoll on birch and other small seeds; and the Linnet on the seeds of various weeds of farmland. The Hawfinch and Bullfinch eat a greater proportion of buds and seeds from fleshy fruits than do other finches; but the Hawfinch prefers larger ones than does the Bullfinch. The three European crossbills feed almost entirely on conifer seeds; specializing on different tree species. In summer, the Chaffinch and Brambling live largely on invertebrates but in winter on beechmast or small seeds taken from the ground. In winter, Chaffinches reaching Britain from northern Europe tend to feed in large flocks in open areas and to roost communally, while residents tend to remain near their breeding places and roost singly. The migrations and distribution of finches in Europe are described briefly. At any time of winter, closely related species with similar feeding habits are often concentrated in different parts of a common wintering range. Furthermore, in some species, such as the Goldfinch and Chaffinch, the sexes winter mainly in different areas. In Oxford, food was least readily available during hard (winter) weather and there was then complete segregation in diet between different species, but at other times their diets often overlapped 94 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES IBIS109 considerably. The overlap was much more pronounced in the species living in farmland (which is an artificial habitat) than in those living in natural or seminatural woodland; some tentative explanations for this are offered. The fringilline finches, the Chaffinch and Brambling, feed their young entirely on invertebrates, are territorial in the breeding season and collect food mostly within their territories. The cardueline finches, on the other hand, feed their young mainly, or entirely, on seeds, often nest in I‘ loose colonies ’I, and usually gather food communally at some distance from their nests. The fringilline finches carry food in their bills to the young, which therefore receive small, but frequent, meals; whereas the carduelines feed their young by regurgitation and at longer intervals. Among the carduelines, the Hawfinch is exceptional in that seeds are first swallowed and regurgitated to the nestlings, whereas insects are carried in the bill. The Bullfinch develops in the breeding season special buccal pouches in which food is carried to the young. In general, most finches select diets for their young which differ from their own diets in the breeding season. The Crossbill and Linnet often feed their young on seeds alone, and some other species may do so occasionally. The breeding of these carduelines is therefore independent of a supply of invertebrates, but always coincides with an abundance of seeds. They breed at seasons when other birds do not; the most extreme cases are the three crossbills, which, given an abundance of suitable seeds, will nest at any time of year. The process of seed-husking is described; the strength of the jaws, the extent of the gape and the width of the palatal grooves limit the size and hardness of seeds which a given species can take. No two species have bills of the same shape and size, and differences in diet between species are connected with differences in the structure of their bills and the way the bill is used. In general, the deeper the bill of a finch, the more numerous the types of seeds in its diet. The Greenfinch, Linnet and Redpoll have relatively short broad bills and feed more than do other Curduelis finches from plants whose seeds are relatively exposed (e.g. grasses) or enclosed within pods or capsules; they also pick up many fallen seeds from the ground, but each species concentrates on different sizes of seeds. The Goldfinch and Siskin have reIatively long, narrow bills and obtain much of their food by probing into cones and into the seed-heads of Com- positae; unlike other finches, they also use a gaping movement while feeding. The Goldfinch has a longer bill and eats more Compositae seeds than the Siskin, while tlie latter eats more tree seeds than the Goldfinch. Further, male Goldfinches have slightly longer beaks than females, and hence can obtain teasel seeds more efficiently; females feed only rarely from these plants. The Bullfinch and Hawfinch obtain much of their food by crushing fruits, seed-heads, etc. in their bills and peeling off the outer layer to get the seeds. The methods used by the crossbill species to open cones of varying degrees of hardness are described in detail. The Chaffinch and Brambling obtain almost all their food by rapid pecks; they show none of the behaviour patterns used by carduelines to open various types of seed-heads. Species also differ in the proportion of food obtained from the ground, from vegetation, or on the wing. These differences are related to the various positions in which each species is able to feed. Those species (Goldfinch, Siskin, Redpoll and Crossbills) which are most adept at clinging and hanging feed mainly from trees and herbaceous plants, while those that are least adept at this (Chaffinch and Brambling) obtain almost all their food from the ground or from firm horizontal twigs. The remaining species are intermediate in the proportion of time spent feeding from the ground or from vegetation; and only the Chaffinch, Brambling and Bullfinch obtain an appreciable amount of food on the wing. Differences between species in the frequency with which various positions are adopted during feeding can be related to differences in their average body weights, and (to a lesser extent) in their leg-structure; the most agile species are either light in weight or have relatively short strong legs. Body-weight, leg-proportions and bill-size (and hence feeding habits) may vary considerably between different populations of the same species. In Appendix 2, the leg-proportions of certain English finches are compared with those of their German and Russian counterparts. Some finch species use their feet in coordination with their bill to obtain food. The extent to which various species do this in the wild is discussed in relation to the ease with which they can be taught experimentally to pull up food suspended on the end of a long thread. The ecology, structure and behaviour of finches is discussed in relation to some current ideas on speciation and the ontogeny of feeding behaviour. The young of several species of finches respond initially to a similar range of potential food-items (both in size and appearance) and all attempt to deal with them in similar ways. However, each individual soon learns to concentrate on those foods it can obtain most efficiently with its own particular structures and behaviour patterns. It is thus the structural and behavioural differences between closely-related species which lead the individuals of each to prefer different foods. Further, some of the behaviour patterns themselves probably develop mainly as a result of learning conditioned by structure, so that some of the behavioural differences between species that affect food-choice are in turn dependent on structural differences. This implies that, from an evolutionary viewpoint, two forms need diverge only in structure (and not necessarily “ psychologically ”) for some ecological segregation to be achieved. There are, however, certain differences in feeding behaviour between the fringillines and carduelines that cannot be attributed merely to structural differences between the two groups, so presumably some “ psychological factor ” is also important in the development of these particular behaviour patterns. A close relationship between the structure, feeding behaviour and food of an animal is usually taken for granted, but it is often difficult to decide which of these came first in evolution. Among finches, however, there are sometimes indications that a structural change was necessary before a 1967 I. NEWTON : EVOLUTION AND ECOLOGY OF FINCHES 95 new behaviour pattern or feeding habit could evolve, though further modification of structure may then occur through adaptation to the new foods thereby made available. Some evolutionary trends among finches are described, and the role of competition in the evolu- tion and maintenance of ecological differences between species is discussed. The effect of social experience on feeding behaviour is also discussed, and some examples are given of the spread of novel food-habits among finches, and of presumed traditional differences in feeding behaviour between different populations of the same species. Finally, some recent changes in food, and habitat-selection by finches are discussed in relation to problems of conservation.

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