Studies of West Palearctic 192. Bullfinch*

Ian Newton n many respects, the handsome Bullfinch pyrrhula is quite distinct I from most other of the West Palearctic region. Its coloration is striking, more different between die sexes than with other finches, and both adult and juvenile lack any hint of streaking. The feathers themselves have a soft, silky texture, quite unlike those of other finches. The bill structure is also unique, both the rounded shape and the pattern of grooves on the palate, which function in feeding. For while, like other finches, the Bullfinch cats mainly , it includes a much greater proportion of fleshy fruits and tree buds in its diet than do the other species. Behaviourally, the Bullfinch has been described as 'quiet and unobtrusive'. It remains inconspicuous, even in the nesting season, and, as explained later, it has unusual courtship and breeding behaviour. Another peculiarity, which is well known to -ringers, is that it seldom struggles when handled, but usually lies limply with open bill. No other European behaves in this way. Despite the bright of the males, Bullfinches are never easy to see. They usually betray their presence by tiieir piping calls or by the flash of white rumps as a small party is flushed from a feeding site. The piping call is quite unlike the multisyllabic twittering calls of Carduelis finches, and is uttered mainly by isolated individuals, apparently wishing to re-establish contact, or by startled birds, suddenly flushed from a feeding site. It is also given in flight. Otherwise, Bullfinches in a group maintain contact with one another using a faint pipping note, which precedes or accompanies short moves within a tree or bush. In distribution, the Bullfinch extends from Ireland, across Eurasia, to Japan. In general, individuals are larger and brighter towards the nordi and towards the tops of mountain ranges. The British birds are given subspecific rank (P. p. nesd) because they are smaller than P. p. pyrrhula from northern and

*This paper, and others in this long-running British Birds series, will be published in a forthcoming HarperCollins book.

638 [Brit. Birds 86: 638-648, December 1993] Studies of Bullfinch 639 , and darker and duller than other continental forms (notably P. p. coccined). The most curious race is P. p. murina of the Azores Islands, in which the male has lost die bright coloration typical of other Bullfinches, and looks like the female (Bibby et al. 1992). Over most of their Eurasian range, Bullfinches breed at low density in dominated by coniferous trees, but in western Europe they also extend into broadlcaved woodland. In Britain, they are widespread, breeding in woodland undcrgrowtii, thickets, shrubberies and tall straggling hedgerows, and in the parks and gardens of towns. In various parts of Europe, densities of up to five pairs per knr have been recorded, rising to more than 20 pairs per km2 in patches of especially good nesting habitat, such as scrub or thicket spruce. They arc usually seen singly or in pairs, but, at favoured feeding sites, parties of up to a dozen or more are not infrequent, especially in autumn and winter. Such groups are only loosely bound, however, and throughout the day individuals continually arrive at and leave the feeding site, apparently behaving largely independently of one another. When disturbed, they retreat rapidly into the nearest cover. When numbers of Bullfinches arc feeding together, for example in a fruiting tree, aggression between them is frequent. In the typical threat display, one crouches with its tail twisted to one side, head feathers sleeked and open bill directed towards an opponent, uttering a hoarse braying sound, which carries only about 20 m (Hinde 1955). Where feeding positions arc scarce, diere are also frequent supplanting attacks, in which one bird flies direcdy at another, which flees, allowing the attacker to perch in its place. In extreme cases, the attacker may chase its victim for a few metres, but such chases are more often associated with pair formation than with feeding.

Feeding behaviour For most of the year, as mentioned above, Bullfinches feed on the fruits of certain trees and herbaceous plants, switching from one favoured species to another as each in turn comes into crop. During the growing season, many seeds are eaten in a soft, unripencd state. In English woodland, preferred seeds include those of dog's mercury Mercurialis perennis, wych elm Ulmus glabra, birch Betula, meadow-sweet Filipendula ulmaria, bramble Rubus, common netde Urtica dioica, and ash Fraxinus excelsior, while on cultivated land the seeds of many common weeds are eaten, starting in spring with chickweed Stellaria media and dandelion Taraxacum officinale, and followed in turn by various buttercups Ranunculus, sorrel Rumex acetosa, sow-diisdc Sonchus okraceus, redshank Polygonum persicaria, fat-hen Chenopodium album, common nettle and various docks Rumex (Newton 1967, 1972). Towards the end of the growing season, Bullfinches turn increasingly to the seeds that will sustain them through die autumn and winter, initially those of netde, birch and Sorbus aucuparia, and later those of bramble, dock and ash (and, in upland areas, headier Calluna vulgaris). Where it is available, ash forms a major winter food, but Bullfinches feed chiefly from certain individual trees, sometimes completely stripping them during the course of a winter, while avoiding the majority of still-laden trees in the vicinity. Such highly selective feeding occurs because ash seeds contain poisonous phenolic 640 Studies of Bullfinch compounds (Grcig-Smith & Wilson 1985), which, to the human palate, give the seeds a bitter taste. The seeds from preferred trees have lower phenolic content than those from other trees, and also tend to have higher fat contents. As supplies arc not replenished during the winter, the size of the initial (Tops, and the rate at which they are depicted, influence the date when they run out, and Bullfinches have to switch from seeds to buds. In southern England, in years of good ash crops, Bullfinches can continue to feed on seeds until February or March, before switching wholly to buds. In years with no ash crop, however, the seeds of other food-plants arc usually eaten by January, and the switch to buds occurs earlier. In these poor seed years, Bullfinches can suffer heavy mortality because buds are often still small then, and poor in nutrients. In January, on a diet of buds alone, the birds may rapidly lose weight, and only later in the year, when buds arc larger, can they subsist on buds alone (Newton 1964). The implication is that, in years of poor seed crops and late bud-swell, food supply can be an important factor limiting Bullfinch numbers (but sec later). Among the buds of wild trees that arc eaten in spring, favourites include blackthorn Prunus spinosa and hawthorn Crataegus monogyna, and, where available, also crab apple Mains sybestris. It is only the centres of the buds which are swallowed, the parts otherwise destined to become fruit. The outer parts are peeled off in the bill and discarded, littering the ground below. Within any one tree species, the birds tend to return repeatedly to those individual trees whose buds arc most advanced. In late spring, as buds open, Bullfinches turn to the flowers, shedding the outer parts and swallowing the ovules. Flowers of sallow Salix, oak Querents and crab apple arc especially favoured, and form the bulk of the diet until fresh seeds become plentiful again. For fruit-growers and gardeners, the Bullfinch creates problems, because it cats the buds from fruit and ornamental trees, reducing the blossom and hence the crop. Cultivated fruit trees have buds of the size most acceptable to Bullfinches, and arc derived from wild species whose buds arc preferred in natural conditions. Various ornamental trees, such as forsythia Forsyihia, arc also attacked in spring, partly because their early flowering requires early bud- swell, ahead of native trees. A single Bullfinch can remove the buds from fruit trees at 30 or more per minute, and in winter the feeding is remarkably systematic, as a bird works along each branch taking all but the terminal buds (Newton 1972). As Bullfinches enter orchards from the adjacent woods and hedgerows, they attack the nearest trees first, penetrating farther into the orchard as the days go by. For this reason, damage is often most marked on the edges of orchards, and declines towards the centre. In general, among cultivated fruits, the* buds of plum and pear arc most preferred, with gooseberries and currants next, followed by apples and cherries, but within any one of fruit certain varieties are preferred to others. Among pears, for example, 'Conference' is preferred to 'Cornice', so that, in a mixed orchard at blossom time, 'Conference' trees may be almost denuded of flower, while the adjoining 'Cornice' are in full bloom (Newton 1964). The preferences for certain varieties are again linked with earlier

A donation from HarperCollins has subsidised the publication of plate 232 in colour. Studies of Bullfinch 641 bud-swell, with higher nutrient content, notably protein and fructose, and in some varieties with lower concentrations of offensive chemicals (Summers & Jones 1976; Greig-Smith 1985a). In January, captive Bullfinches lose weight less rapidly when fed on 'Conference' pear buds than when fed on 'Cornice' pear or wild hawthorn buds (Newton 1964; Summers 1982). In England, the Bullfinch was considered an orchard pest as long ago as the sixteenth century, when one penny was offered in reward for 'everic Bulfynche or other Byrde that dcvoureth the blowthe of fruit'. In southeast England, however, Bullfinch numbers increased enormously in the 1950s, making this for a time the biggest problem that the fruit-growing industry had to contend with. Almost every fruit-grower had little option but to trap Bullfinches (using cage-traps with a live decoy) throughout the winter and spring, and many growers in well-wooded areas caught more than a thousand Bullfinches each year. Although this trapping helped to reduce the damage, the fact that the catches were maintained year after year showed that it had no sustained effect on Bullfinch numbers. Then, gradually, from the mid 1970s, Bullfinches became scarcer again, the catches on most farms declined, and the damage dropped to acceptable levels. Nowadays few, if any, fruit­ growers continue a regular trapping programme. As it happens, the rise and fall of the Bullfinch coincided with the fall and rise of its main predator, the Eurasian Sparrowhawk Accipikr nisus. This raptor declined in the 1950s, following the introduction of organochlorine pesticides, disappearing almost completely from the fruit-growing areas of southeast England. Its numbers recovered in the 1970s and 1980s, following reductions 232. Female Bullfinch Pyrrhula pyrrhula eating blackberries Rubus, Cambridgeshire, October 1991 (/. Wyllie). These fruits form a major food item, being eaten from the time they ripen in late summer until long after the flesh has withered in late winter "4* Studies of Bullfinch

233. Juvenile Bullfinch Pprhula fiyrrhula eating berries of honeysuckle Lonicera periclymenum {John Markham). Juveniles of both sexes have brown body plumage and lack the black cap and bib of adults in organochlorine use (Newton 1986). Moreover, in the West, where Sparrowhawk numbers recovered up to ten years earlier than in the east, Bullfinch damage also declined earlier. If these events were causally connected, there are two possible explanations. First, Sparrowhawks, by their predation, might have had a direct effect on Bullfinches, holding their numbers at a much lower level than occurred in the absence of Sparrowhawks. Alternatively, Sparrowhawks might have affected Bullfinches indirecdy, the absence of the predator encouraging the prey to venture farther from cover than usual, thereby bringing more food within reach, which in turn could have promoted the rise in numbers (Newton 1967). At the time of their peak numbers in the 1960s, Bullfinches fed regularly in more open situations than formerly, and I saw several flocks of more than 100 individuals in fields, more than 100 m from cover. It is hard to say whether access to the food-plants in open habitat led to the increase in numbers, or whether the increase in numbers forced the Bullfinches to feed in more open areas than formerly. So, if the Sparrowhawk was indeed involved in the changes in Bullfinch numbers, the precise mechanism is uncertain. It is ironical, however, that chemicals used to destroy arthropod pests in orchards may have indirectly created a more serious bird pest. The Bullfinch uses the same bill movements for dealing with almost all its foods, whether these are seeds, buds, berries, seed-pods or capsules (Newton 1972). The object is nipped off, held lengthwise and crushed in the bill, then turned by the tongue against the lower jaw, so that the outer layer—the husk of a seed or the flesh of a fruit—is peeled off. It is also the only European finch known to eat small snails, crushing and deshelling them in the bill by the Studies of Bullfinch 643 same procedure. The jaws are weak, however, and a peck from a Bullfinch is trivial compared with a bite from the similar-sized Greenfinch Carduelu chloris. With dandelions and similar plants, the Bullfinch attacks the seed head at the side, biting out small pieces which are turned in the bill to extract the seeds. It is thus limited to feeding on those Compositae, such as sow-thistles, which have small, soft seed heads, and docs not normally tackle the larger thistles. With its rounded bill, the Bullfinch cannot easily take small seeds from the ground, but it will take large ones, such as those of sycamore Acer pseudoplatanm. It also has difficulty in picking seeds out of cones, so does not normally feed dirccdy from . In its feeding, the Bullfinch is able to cling to twigs and plant stems, and can also hover to obtain fruits from the ends of branches or other difficult sites. Unlike some Carduelu finches, however, it does not hang upside-down to feed, nor does it hold food-items under its feet while they are worked with the bill. Parent Bullfinches raise their young from hatching on a mixture of soft seeds and smaE invertebrates, especially caterpillars, spiders and small snails. This diet is selected especially for the chicks. As the young grow, the proportion of material is gradually reduced until, by the time they leave die nest, they arc getting seeds alone. The adults carry food to their young in special throat pouches, which open one on each side of the tongue. When full, these pouches give the bird a swollen-throated appearance. Some other finches, notably the Pine Grosbeak Pinicola enucleator, the trumpeter finches Bucanetes and die rosy finches Leucostkte, have similar throat pouches, perhaps reflecting a close affinity between these genera. Other carduelinc finches carry food to their young in their gullets, and have no special structure for the purpose.

Breeding behaviour In its breeding behaviour, the Bullfinch again departs markedly from the usual cardueline pattern (Newton 1972). The bird is not obviously territorial, nor does it nest in loose colonies like die Carduelis finches. It has no flight-display or otiier conspicuous behaviour, and die song, which is usually delivered from widiin cover rather than from a vantage point, is so weak that it carries no more than a few metres. Indeed, in the breeding season, the pairs seem to keep diemselves to themselves, 'maintaining a low profile', and having little or no contact with other Bullfinches except when diey meet at feeding sites. On the otiier hand, tfiose types of behaviour connected witii the pair-bond are gready elaborated, compared with outer finches. All die displays are mutual, and may be initiated by either sex, witii the hen playing almost as active a role as die cock, and adopting similar postures. In die typical display, the belly feadiers are puffed out, and the tail twisted towards die partner, while the birds make bowing and nibbling movements with the bill. The cock feeds die hen by regurgitation, reaching up and placing die food in her bill, while she pivots from side to side. The statement that Bullfinches pair for life was frequent in early bird books, and was probably based on die fact that pairs are often seen in winter, as well as in the breeding season. In a study of Bullfinches in southern England, 234. Female Bullfinch Pyrrhuk pyrrhula brooding small chicks, Cambridgeshire, June 1992 (J, Wyllie). Until the young are half grown, the female stays at the nest while the male collects the food. When the young are larger, both parents collect the food and visit the nest together 235. Male Bullfinch Pyrrhula pyrrhula feeding on seeds of common nettle Urtka dioica, a favoured autumn food, Cambridgeshire, October 1991 (/. Wyllie). Bullfinches can cling to vertical stems with ease, but, unlike some other finches, they cannot hang upside-down to feed Studies of Bullfinch 645 Wilkinson (1982) recorded the sex composition of all the groups he encountered outside the breeding season. In groups of two individuals, a male- female combination was significantiy commoner than expected by chance, while groups of two males or two females were significantly less common. Moreover, in larger groups an equal sex ratio was again commoner than expected by chance. Aggression within feeding groups was found to increase with group size, but whenever a group contained more males than females fights were more frequent than expected on the basis of group-size alone. Males started more attacks than females, and directed them almost entirely at other males; when females initiated aggression, they attacked other females more often than males. These findings again suggested that activities associated with pair-bonding were frequent in winter. In his study of captive Bullfinches, Nicolai (1956) found that each young bird formed a close liaison with one of its siblings when only six or seven weeks old and still in juvenile plumage. The birds 'caressed each other', fed each other, and invited each other to mate, but none of their actions was proficient and no mating took place. At this stage, there was no colour difference between the sexes, and two cocks or two hens often paired together. Such pairs remained together, performing mutual displays throughout the winter, but broke up in the following spring when each bird formed a normal relationship with an unrelated bird of the opposite sex. Nicolai suggested that this represented the appearance, in incomplete form, of behaviour which would keep the pair together in later life. Proof from ringing that pairs stay together in the wild, either through the winter or from year to year, is, however, lacking. The social system of the Bullfinch would clearly repay further study. Like most other , Bullfinches normally breed for die first time when they are less than one year old. As the breeding season approaches, the pairs separate from the groups, avoiding all contact with other Bullfinches. Both sexes pick up nest material, but the female does the building, at all times accompanied closely by the male. This would now be interpreted as 'mate- guarding', by which the male protects his paternity. The nest is usually built well within a thick shrub 1-2 m above the ground, occasionally higher. It is well hidden, and is placed on a flat branch or tangle of twigs, seldom in a fork. It is a distinct two-layered structure, having a shallow base of thin dry twigs and a lining of rootlets, again quite different from the nests of Carduelis finches. The eggs number three to six, and are bluish-white with purple- brown spots. Incubation takes 12-14 days and the young stay in the nest for 15-17 days if undisturbed. The hen incubates the eggs and broods the chicks, being fed at the nest by the cock, who calls her off and regurgitates food into her bin. She returns to the nest and in turn regurgitates the food into the open bills of the chicks. Once the young are about half grown, and can be left unbrooded, both parents collect the food and feed the young, foraging and visiting the nest together. If necessary, the adults may regularly fly more than 1 km from the nest to reach good feeding areas. After leaving the nest, the young are fed by their parents for a further 15- 20 days. For about half this time, they remain near die nest, but then begin to accompany their parents to feeding sites. The young become fully independent at about 35 days old. Much of dieir food in die post-fledging

Donations from HarperCollins have subsidised the publication of plates 234 and 235 in colour. 646 Studies of Bullfinch

236. Pair of Bullfinches Pyrrhuk jryrrh.uk feeding young, Lancashire, summer 1974 (Dennis Green). Note the swollen throat pouch of the right-hand adult, in which food for the young is stored. The young themselves hold the food temporarily in the gullet, and it can be seen through the transpar­ ent neck skin, enabling different items to be identified period may be provided by the male, because die female often begins anodier nest then (Nicolai 1956; Bijlsma 1982). The breeding season varies widi latitude, but, as witii most seed-eaters, is relatively long. In soudiern Britain laying usually extends from late April (in early springs only) to late July, so that die latest young fledge in August. But, in some years of abundant food, laying extends into September, so daat the last young fledge in October. This would give time for up to three broods per pair in a short season, and up to four in a long one, but few (if any) pairs could raise this number, because of heavy predation on the eggs and chicks. In Wytham Wood, near Oxford, about 85% of the nests that were started in May were lost to predators, declining to 50% in June and 30% in July- August. In farmland, predation was less, declining from 56% to 33% and 16% (Newton 1972). The main predators were probably weasels Mustek. nivalis, Eurasian Jays Garmlus glandariiis and Magpies Pica pica, and the seasonal Studies of Bullfinch 647 decline in predation was associated with a gradual thickening of cover through plant growth which made the nests harder to find. The greater success of farmland nests was probably because bushes were thicker there (through hedge-clipping) and predators were scarcer. In addition to predation, some nests failed through desertion, especially during spells of wet weather. Similar seasonal trends in nest success were noted in the Netherlands (Bijlsma 1982). Because so many nests fail, it would be easy to overrate the role of predation in limiting breeding success. A repeat nest is usually started within a few days of the loss of a previous one, so that a pair might lose several clutches and still have enough of die season left in which to raise young. The wild Bullfinches studied by Nicolai (1956) in Germany usually reared two broods each year, but laid up to five clutches to get them. In captivity, if the eggs were taken away, the number sometimes rose to seven clutches a year. Despite die high predation in my own Oxford study, the ratio of young to adults as determined from mist-netted samples at the end of short breeding seasons (last young in August) was usually around 3:1, and after a long season (last young in October) it was 5:1.

Moult, mortality and movements After breeding, Bullfinches moult. The adults take 10-13 weeks to replace their entire plumage, and the juveniles take seven to nine weeks to replace their body feathers, retaining the flight and tail feathers for anomer year. In bodi age groups, the shorter periods are recorded from individuals that begin latest in die year (Newton 1966). Most adults start moulting while they are feeding their last brood and, because individuals vary greatly in the dates of their last nests, they also vary in the dates they moult. In five years near Oxford, the start of moult in the population I studied was spread over eight weeks from mid July, but, in a sixth year when some pairs prolonged their breeding, the start of moult was spread over 13 weeks from mid July. The average annual mortality of British Bullfinches has been calculated from ringing recoveries at 52 ± 3% (mean ± standard error) for males and 59 ± 3% for females (Dobson 1987). This difference between the sexes is statistically significant, and may account for the fact that, among large samples of Bullfinches seen or trapped, males are usually more numerous man females (Newton 1972; Grcig-Smith & Wilson 1984). In Britain, Bullfinches are classed as 'resident', because mey do not migrate but simply disperse in any direction from the natal area. In autumn, they can appear at many places, including offshore islands, where they do not breed. Of 1,552 ringed Bullfinches recovered in Britain during 1910-74, 80% had moved less than 5 km from where they were ringed, and only about 5% had moved more than 25 km (Summers 1979). Significandy more long movements were recorded after 1960 than before, associated mainly with years of high population and poor tree-seed crops. Movement was especially marked in the winter of 1961/62, a year of widespread tree-crop failure, and again in 1964/65 and 1967/68. More recent studies, with radio-tagged birds, have revealed that individuals may remain for weeks or months within a short distance of a good food source, before suddenly moving up to several kilometres to a new site (Greig-Smith & Wilson 1984; Greig-Smith 1985b). 648 Studies of Bullfinch Such movements are often associated with the exhaustion of a food supply, and a fall of snow will often bring Bullfinches into new areas, where mere was previously none, if food is locally available. Because there is no territoriality or other social restriction on movements, any given locality in wooded terrain may be within the range of hundreds of Bullfinches, which may account for the large numbers killed over several months in particular orchards, far more man could live there at any one time. Farther north in Europe, Bullfinches perform regular migrations, but again the movements are much more marked in years of widespread failure of relevant tree-seed crops. In northern Fennoscandia, Bullfinches that remain in years of tree-crop failure depend largely on handouts from human beings, for the birds are regular visitors to garden feeding trays, taking sunflower and other seeds. It is strange that this habit has never caught on in Britain.

References BIBBY, C. J., CHARLTON, T. D., & RAMOS.J. 1992. Studies of West Palearctic birds. 191. . Brit. Birds 85: 677-680. BIJLSMA, R. G. 1982. Breeding season, clutch size and breeding success in the Bullfinch Pyrrhuk pyrrhuk. Ardea 70: 25-30. DoBSON, A. 1987. A comparison of seasonal and annual mortality for both sexes of fifteen species of common British birds. Ornis Scand. 18: 122-128. GREIG-SMITH, P. W. 1985a. The importance of flavour in determining the feeding preferences of Bullfinches (Pprrhuk pyrrhuk) for die buds of two pear culoVars. J. Appl. Ecol. 22: 29-37. 1985b. Winter survival, home ranges and feeding of first-year and adult Bullfinches. In: SIBLY, R. M., & SMITH, R. H., Behavioural Ecokgy, pp. 387-392. Oxford. , WILSON, M. F., BLUNDEN, C. A., & WILSON, G. M. 1983. Bud-eating by Bullfinches Pyrrhuk pyrrhuk, in relation to the chemical constituents of two pear cuMvars. Ann. Appl. Biol. 103: 335-343. , & WILSON, G. M. 1984. Patterns of activity and habitat use by a population of Bullfinches (Pyrrhuk pyrrhuk L.) in relation to bud-feeding in orchards. J. Appl. Ecol. 21: 401-422. , & WILSON, M. F. 1985. Influences of seed size, nutrient composition and phenolic content on the preferences of Bullfinches feeding in ash trees. Oikos 44: 47-54. HlNDK, R. A. 1955. A comparative study of the courtship of certain finches (Fringillidae). Ibis 97: 706-745. NEWTON, I. 1964. Bud-eating by Bullfinches in relation to the natural food-supply. J. Appl. Ecol. 1: 265-279. 1966. The moult of the Bullfinch lyrrhuk pyrrhuk. Ibis 108: 41-67. 1967. The feeding ecology of the Bullfinch. (Pyrrhuk pyrrhuk L.) in southern England. J. Aram. Ecol. 36: 721-744. 1972. Finches. London. 1986. The Sparrowhawk. Calton. NlCOIAI, J. 1956. Zur Biologie und Ethologie des Gimpels (Pyrrhuk pyrrhuk L.). £ Tmpsychol 13: 93-132. SUMMERS, D. D. B. 1979. Bullfinch dispersal and migration in relation to fruit and damage. Brit. Birds 72: 249-263. 1981. Bullfinch (lyrrhuk pyrrhuk) damage in orchards in relation to woodland bud and seed feeding. In THRESH, J. M, Pests, Pathogens & Vegetation, pp. 385-391. London. 1982. The survival of Bullfinches on cultivated fruit buds. J. Appl. Ecol. 19: 813-819. , & JONES, F. J. S. 1976. The importance of protein in the selection of fruit buds by Bullfinches. Experimental Horticulture 28: 47-50. WnxiNSON, R. 1982. Group size and composition and the frequency of social interactions in Bullfinches lyrrhuk pyrrhuk. Ornis Scand. 13: 117-122.

Dr Ian Newton FRS, Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS