The incidence of albinism and melanism in British birds By Bryan L. Sage
INTRODUCTION IN 1956, I PUBLISHED appeals for records of albinism and melanism in various journals, including British Birds (49; 512) and Bird Study (3: 279). Similar requests for information -were broadcast on the radio on my behalf by Dr. Bruce Campbell and James Fisher. It was hoped to amass sufficient data to discover some of the causes of these phenomena and to ascertain their incidence among British birds. The first of these aims has already been dealt with (Sage 1962) and the present paper is concerned with the second. As a result of the appeals for information and a fairly extensive search of the literature, a total of 3,134 records of partial or complete albinism and 113 of melanism in British birds were brought together for analysis. The treatment here is primarily at the family level and more detailed discussion on certain species groups may be published elsewhere. For various reasons I have found it convenient to base all calcula tions on the Check-list of the Birds of Great Britain and Ireland (19 5 2) and I have ignored subsequent additions and deletions which do not, in any case, materially affect the results. There are, however, two points where I have departed from the Check-list treatment: I have regarded the Bean* and Pink-footed Geese as separate species, and the Carrion and Hooded Crows as conspecific. These departures should be borne in mind in any reference to the Check-list of 1952.
ALBINISM An analysis by families of the 3,134 instances of albinism is given in table 1. Of the 59 families on the British List in 1952, no less than 42, or 71.2%, have provided records. The condition has been noted in 163, or 38.3%, of the 426 species included in the Check-list, these representing 105 genera.
continued...
*Sclentific names of all species mentioned in the text ate given on page 416.
409 BRITISH BIRDS Table i. Analysis by families of 3,134 records of albinism in British birds The numbers of species shown in the first column of figures are those included in the Check-list of the Birds of Great Britain and Ireland (1952), ignoring later additions and deletions. The Mallard (Anas platyrhynchos) and the Pheasant (Pbasianm colcbicus) have been omitted from the remaining columns for reasons given in the text, however. In the last column percentages are given to the nearest whole number and those less than 1% are not shown Species with No. of records of No. of % of total species albinism records records Colymbidae (divers) 4 I 1 - Podicipidae (grebes) 5 2 6 - Procellariidae (petrels, shearwaters) 16 1 6 - Sulidae (gannets) 1 1 1 - Phalacrocoracidae (cormorants) 2 2 11 - Ardeidae (herons, bitterns) 10 2 10 - Anatidae (ducks, geese, swans) 45 16* 69 2% Falcoflidae (birds of prey) 22 9 38 1% Tetraonidae (grouse) 4 5 23 _ Phasianidae (partridges, pheasants) 4 2* 97 ,03 / o Rallidae (crakes, rails, coots) 8 4 7° 2% Haematopodidae (oystercatchers) I 1 38 1% Charadriidae (plovers) 12 5 96 3% Scolopacidae (waders) 41 14 137 4% Burhinidae (stone curlews) I 1 1 _ Stercorariidae (skuas) 4 1 1 - Laridae (gulls, terns) 27 11 34 1% Alcidae (auks) 7 3 T9 - Columbidae (pigeons, doves) 5 4 40 1% Cuculidae (cuckoos) 4 1 5 - Strigidae (owls) 10 3 6 - Caprimulgidae (nightjars) 4 1 10 - Apodidae (swifts) 3 1 15 - Picidae (woodpeckers) 4 4 4 - Alaudid&e (larks) 8 3 64 2% Hirundinidae (swallows, martins) 4 3 233 7% Corvidae (crows) 9 6 356 11% Paridae (tits) 8 5 H - Sittidae (nuthatches, wallcreepers) 2 1 1 - Certhiidae (treecreepers) I 1 1 - Troglodytidae (wrens) I 1 12 - Cinclidae (dippers) I 1 2 - Turdidae (thrushes, chats) 25 12 902 29% Sylviidae (warblers) $8 7 28 - Regulidae (goldcrests) 2 1 2 - Muscicapidae (flycatchers) 5 1 9 - Prunellidae (dunnocks) 2 1 65 2% Motacillidae (pipits, wagtails) 10 5 51 2% Laniidae (shrikes) 5 2 4 T0/ Sturnidae (starlings) 2 1 216 7*% /o Fringillidae (finches, buntings) 33 15 203 6% Passeridae (sparrows) 2 2 233 7% •Mallard and Pheasant excluded 410 THE INCIDENCE OF ALBINISM AND MELANISM The records were also classified under partial or complete albinism. Pure or complete albinism, in the strictest sense, involves a complete lack of pigment in the soft parts as well as the whole plumage. How ever, the vast majority of field observations do not describe the colour of the soft parts and so in this study it has been necessary to treat in the category of complete albinism all records of birds reported to have the plumage pure white or nearly so. Division on this basis showed 63.4% partial and 36.6% complete albinos. So far as I am aware, the only previous comparable analysis is that of Glegg (193I)> which was based entirely on Essex records. Table 2 is adapted from his results. If we use the same criteria as in the previous paragraph, his records can be separated as 69.7% partial and 30.3% complete. Table 2. Analysis by families of 201 records of albinism in British birds, adapted from Glegg (1931) No. of % of total records records
Colymbidae (divers) 1 0.5% Anatidae (ducks, geese, swans) 2 1.0% Phasianidae (partridges, pheasants) 18 9-o% Rallidae (crakes, rails, coots) 4 2.0% Charadriidae (plovers) 3 1-5% Scolopacidae (waders) 5 i-5% Laridae (gulls, terns) 4 2.0% Columbidae (pigeons, doves) 3 l*5 /o Apodidae (swifts) 1 0 *°/ Alaudidae (larks) 7 3-5% Hirundinidae (swallows, martins) 5 2-5% Corvidae (crows) 18 8-9% Troglodytidae (wrens) 5 2-5% Turdidae (thrushes, chats) 54 26.9% Sylviidae (warblers) 1 0.5% Prunellidae (dunnocks) 2 1.0% Motacillidae (pipits, wagtails) 5 2-5% Laniidae (shrikes) 1 0.5% Sturnidae (starlings) 24 "•9% Fringillidae (finches, buntings) 20 9-9% Psssseridae (sparrows) 20 9-9%
Table 1 shows that, although there are 42 families of British birds in which albinism has been recorded, a mere 19 families are responsible for 93% of the total observations. The great bulk of the records (67%) have occurred in the Turdidae, Corvidae, Hirundinidae, Passeri- dae, Sturnidae and Fringillidae, in that order. The percentages of records for the Anatidae and Phasianidae would have been far higher than they are, however, if those for the Mallard and Pheasant could
411 BRITISH BIRDS have been included, but semi-domesticated and inbred populations of these two species provide so many cases of albinism that to have used them in the calculations would have unbalanced the whole analysis. Study of Glegg's data shows that the families he found most affected were, in order of frequency, the Turdidae, Sturnidae, Fringillidae, Passeridae, Corvidae and Phasianidae (still excluding the Pheasant). In America, Lee and Keeler (1951) tabulated all the records of plumage variations of this type that they could find in English language publica tions available in the libraries of Chicago. The results involved 36 families and those with the greatest number of records were the Fringillidae, Corvidae, Icteridae (New World blackbirds and orioles), Anatidae, Phasianidae and Turdidae. Considering the wide differences in these studies, there is a remarkably close agreement in the families most affected by albinism. It is appreciated that this method of analysis, whereby the incidence of albinism is expressed as a percentage of the total number of records, does not take into account the relative abundance of each species, but I am unaware of any method which would allow for this. Neverthe less, it is perhaps significant that the species which account for the greatest percentages of the records are the Blackbird (19.7%), House Sparrow (7.3%), Starling (6.9%), Swallow (4.9%), Rook (4.0%) and Jackdaw (3.7%). According to Fisher (1946), but allowing for the recent calculation of Summers-Smith (1963) regarding the House Sparrow, the most numerous British birds are, in order of abundance, the Chaffinch, Blackbird, House Sparrow, Starling, Rook and Jackdaw. In addition, there are other factors which may well bias the results of a study of this nature. Species such as the Starling, Robin, Chaffinch, Blackbird and House Sparrow are all common in the vicinity of human habitation and therefore quite familiar to the lay public. It follows that albinistic examples of these species stand a greater chance of being seen, identified and reported. Different degrees of conspicuousness must also play a part: albinism is readily seen in such dark-coloured species as the Blackbird and Carrion Crow, but it is much more difficult to detect in gulls or other birds which already have much white in the plumage. At present it is impossible to do much more than guess at the reasons why albinism is fairly regular in some families and almost unknown in others. However, consideration of the species involved in the six families which make up the bulk of the records on which this paper is based provides some clues. In the Turdidae over two-thirds of the records relate to the Blackbird, followed by the Robin and Song Thrush. The Rook and the Jackdaw account for the majority of those involving the Corvidae, though the Carrion Crow makes up nearly 20% (incidentally, white barring on the wings appears to be fairly wide-
412 THE INCIDENCE OF ALBINISM AND MELANISM spread in this species). In the Fringillidae, the Chaffinch, Corn Bunting, Linnet and Greenfinch together total 55.7% of the records. The Swallow is responsible for 66,1% of the observations involving the Hirundinidae and this is the only migratory species showing a high incidence of albinism. The House Sparrow accounts for 98.7% of the records in the Passeridae and the Starling for all of those in the Sturnidae. The picture that begins to emerge is that nearly all migratory species (with the striking exception of the Swallow), as well as those which tend to breed as isolated pairs, show a very low incidence of albinism. The Sylviidae, for example, an almost entirely migratory family com posed of species that are not social nesters, account for less than 1% of the 3,134 records. The highest incidence of albinism appears to be found in species that are both social in their breeding habits and also fairly sedentary. In such conditions the chances of matings between individuals heterozygous for albinism must be relatively high. The data also support the theory that the majority of cases of albinism are genetically based and that other factors such as diet and trauma (see Sage 1962) are of minor significance. Such an analysis as this, involving an accumulation of individual records, does not give any indication of the frequency of albinism in natural populations of individual species. In some areas, for instance, albinistic Blackbirds may be sufficiently numerous to give the impres sion that they constitute a large proportion of the total population, but without actual counts of both normal and abnormal birds it is impos sible to know how correct this may be. So far as I am aware, however, very few studies covering this aspect of the subject have been made. Hicks (1934) examined 10,000 Starlings during ringing operations and found only 11, or about 0.1%, with signs of albinism. Michener and Michener (1936) checked 30,000 birds, excluding House Sparrows, in the course of ringing and found 17, or about 0.05%, with traces of albinism. Piechocki (1954) examined 20,931 House Sparrows that had been killed by poisoning; he found no pure white birds and those exhibiting traces of partial albinism amounted to less than 1%. More recently, Ilyenko (i960) stated that albinism is characteristic of bird populations in cities and heavily populated districts, and that it is found less frequently in rural areas. He based his conclusion on an examination of 3,605 House Sparrows and 267 'Field Sparrows'* *I have not read Ilyenko's paper in the original and the information given here was taken from the summary in Biological Abstracts, vol. 40 (1962), abstract 17106. There the term 'Field Sparrows* is used with the scientific name Spi^ella pusilla, but the latter must presumably have been inserted by the abstractor since this is a species •which is confined to the United States and Canada. It has not so far proved possible to clarify this matter, but it seems likely that by 'Field Sparrow' Ilyenko meant the Tree Sparrow {Passer montamis).
413 BRITISH BIRDS collected in Moscow and the rural area of Chashnikov. No complete albinos were found, but partial albinos accounted for 1.8% of the House Sparrows and 1.7% of the 'Field Sparrows' in Moscow, com pared with none of either species in the Chashnikov sample. The condition was found 2§ times as frequently in females as in males.
MELANISM Melanism is clearly of much less frequent occurrence than albinism, although the Buzzard, Montagu's Harrier, Partridge, Pheasant, Red Grouse, Snipe and Woodcock all have a melanistic phase in the normal range of plumage and the Mallard is also very prone to produce melanistic variants. Excluding these eight species, I have collected a total of 113 records of apparent melanism in 39 species. These involve seventeen families, as shown in table 3. The relative in- frequency of melanism is further demonstrated by the fact that 23 of the 39 species, or 59%, are able to show only one record. The bulk of the records (72%) have occurred in the Paridae, Passeridae, Laridae, Phasianidae (excluding both Partridge and Pheasant), Turdidae and Charadriidae, in that order.
Table 3. Analysis by families of 113 records of melanism in British birds The numbers of species shown in the first column of figures are those included in the Check-list of the Birds of Great Britain and Ireland (1952), ignoring later additions and deletions. Eight species which produce regular melanistic phases or variants (see above) have been omitted from the remaining columns, however, as have reports of melanism in captive birds. In the last column percentages are given to the nearest whole number and those less than 1% are not shown Species with No. of recotds of No. of % of total species melanism records records Anatidae (ducks, geese, swans) 43 3* 3 3% Falconidae (birds of prey) 22 4* 5 4% Phasianidae (partridges, pheasants) 4 1* 10 9% Rallidae (crakes, rails, coots) 8 1 1 - Charadriidae (plovers) 12 3 8 7% Scolopacidae (waders) 41 3* 3 3% Laridae (gulls, terns) 27 3 11 10% Picidae (woodpeckers) 4 I 1 - Alaudidae (larks) 8 2 4 4% Hirundinidae (swallows, martins) 4 1 3 3% Corvidae (crows) 9 2 2 2% Paridae (tits) 8 3 28 25% Turdidae (thrushes, chats) 25 6 8 7% Sylviidae (warblers) 38 1 1 - Motacillidae (pipits, wagtails) 10 2 4 4% Fringillidae (finches, buntings) 35 2 5 4% Passeridae (sparrows) 2 i 16 14% •Certain species excluded from these families (one from the Anatidae and two from each of the others) 414 THE INCIDENCE OF ALBINISM AND MELANISM The melanistic phases of the eight species mentioned above are genetic in origin, but it is difficult to say how far this applies to other cases. However, the outbreak of melanism among Great Tits in Surrey (see Sage 1962)—which is mainly responsible for the Paridae heading the list—was almost certainly hereditary: melanistic indivi duals were recorded from 1954 to 1959 and in one instance eight out of a brood of nine young showed this condition. The melanism in the Herring Gull recorded by Stokoe (1954) was also probably of genetic origin as the bird's beak exhibited the type of pigmentation typical of hereditary melanics. Nevertheless, some of the examples of melanism reported in the Laridae may well have been due to oiling of the plumage and it is often difficult to know whether abnormally dark feathering is due to pigmentation or a surface covering of dirt. In this connection, there are several instances, where supposed melanism in House Sparrows has been proved to be due to 'industrial' contamina tion of the plumage and it is therefore important that a cleaning process such as that described by Harrison (1963) should be carried out befote any cases involving species living in urban environments are ascribed to true melanism.
ACKNOWLEDGEMENTS I am greatly indebted to the many hundreds of observers who kindly sent me records. It is impossible to list them all here by name, but without their generous co-operation this study would not have been possible. SUMMARY A total of 3,134 records of albinism in British birds have been analysed, involving 163 species of 105 genera in 42 families. Over two-thirds of the records concern only six families, however—the Turdidae, Corvidae, Hirundinidae, Passeridae, Sturnidae and Fringillidae, in that order. The six most commonly affected species are the Blackbird, House Sparrow, Starling, Swallow, Rook and Jackdaw, and these together make up nearly half the total. The highest incidence of albinism appears to be found in sedentary species that tend to form isolated populations and in social breeders. With the striking exception of the Swallow, migratory species and those of solitary habits generally have a very low incidence of albinism. Melanism is a comparatively rare condition and, excluding eight species which have a normal melanistic phase, the enquiry has yielded only 113 records involving 39 species in 17 families. Some of these may be due to discoloration rather than true melanism. REFERENCES FISHER, J. (1946): WatchingBirds. London. Revised edition. GLEGG, W. E. (1931):' Heterochrosis in Essex birds and in their eggs'. Essex Nat., 23: 171-202. HARRISON, C. J. O. (1963): '"Industrial" discoloration of House Sparrows and other birds*. Brit, Birds, 56; 296-297 and plate 46. HICKS, L. E. (1934): 'Individual and sexual variations in the European Starling'. Bird Banding, 5: 103-118. 415 BRITISH BIRDS IMENKO, A. I. (i960): 'O yavlenii al'binizma sredi vorob' ev Moskvy'. In Okhraua priredy i oyeknenie. Moscow. LEE, F. C, and KEELER, C. E. (1951): 'Pigment variations and their correlates in birds*. ./!»£, 68: 80-85. MICHENER, H., and MICHENER, J. R. (1936): 'Abnormalities in birds'. Condor 38: 102-109. PIECHOCKI, R. (1954): 'Statistische Feststellungen an 20,000 Sperlingen'. /. Orn., 95:297-305. SAGE, B. L. (1962): 'Albinism and melanism in birds'. Brit. Birds, 55: 201-225. STOKOE, R. (1954): 'A black Herring Gull in Cumberland'. Brit. Birds, 47: 132-133. SUMMERS-SMITH, J. D. (1963): The House Sparrow. London. Appendix—Scientific names of species mentioned in the text Mallard (Anas platyrhynchoi) Rook (Corpus frugikgus) Bean Goose (Anser fabalis) Jackdaw (Corpus moneduld) Pink-footed Goose (Anser Robin (Erithacus rubecula) brachyrhynchus) Great Tit (Parus major) Montagu's Harrier (Circus pygargus) Song Thrush (Turdus philomelos) Buzzard (Buteo buteo) Blackbird (Turdus meruld) Red Grouse (Lagopus lagopus) Starling (Sturnus vulgaris) Partridge (Perdix perdix) Greenfinch (Chloris chloris) Pheasant (Phasianus colchicus) Linnet (Carduelis cannabina) Snipe (Gallinago gallinago) Chaffinch (Fringilla coelebs) Woodcock (Scolopax rusticold) Dunnock {Prunella modularis) Herring Gull (Larus argentatus) Com Bunting (Emberi^a calandrd) Swallow (Hirundo rustics) House Sparrow (Passer domesticus) Carrion Crow (Conns corone) Tree Sparrow (Passer montanus)
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