What Colour Is That Bird? the Causes and Recognition of Common Colour Aberrations in Birds
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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/273348895 What Colour is that bird? The causes and recognition of common colour aberrations in birds Article in British Birds · February 2013 CITATIONS READS 65 4,521 1 author: Hein van Grouw Natural History Museum, London 33 PUBLICATIONS 364 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: White feathers in black birds View project Censo Neotropical de Aves Acuáticas en Venezuela View project All content following this page was uploaded by Hein van Grouw on 10 March 2015. The user has requested enhancement of the downloaded file. What colour is that bird? The causes and recognition of common colour aberrations in birds Hein van Grouw Abstract The naming of colour aberrations in birds still causes widespread difficulty and confusion. This paper introduces a uniform system of nomenclature and provides a simple identification key for the most common plumage aberrations. Six main aberrant plumage types are grouped and named by their pigment reductions (gene actions). Identifying colour mutations in the field can be extremely difficult but this paper should make it possible to name many mutations correctly. As might be imagined, correct identification of these various effects is difficult, and the literature abounds with errors. (P. A. Buckley, 1987, Avian Genetics ) n earlier times, when little or nothing was species in which a dark (melanistic) morph is a known about plumage pigmentation and standard colour feature. Imutations, aberrantly coloured wild birds Genetic studies of domesticated animals, were often regarded as new species or sub - in particular mice and chickens, furnished us species and several were formally named. with a greater knowledge of pigmentation Perhaps the oldest example of a colour aber - and mutations. At an early stage, it became ration named as a distinct species is the obvious that different mammal species had a ‘Mountain Partridge’ Perdix montana similar series of heritable coat-colour vari - (Brisson, 1760) . In Brisson’s time this ants. Similar mutations were soon allocated ‘species’ was known only from the mountains the same name in all species. The similarity of the French region of Lorraine, which was based on the relevant gene action on the resulted in it being named P. montana (‘of pigmentation process and not necessarily on the mountains’). However, it was subse - the appearance of the final coat colour, as quently revealed to be simply a melanistic this can differ among species. Despite the form of the Grey Partridge P. perdix . Sabine’s comparable nature of the pigmentation Snipe Scolopax sabinii (Vigors, 1825) is process in birds and mammals, establishing another example – this dark-coloured snipe some uniformity in the nomenclature of is actually a melanistic form of the Common genes (loci) between mammals and birds has Snipe Gallinago gallinago . so far been neglected. Consequently, the Aberrant plumage colour is not uncommon naming of colour aberrations still causes in birds. Indeed, in some species it is suffi - problems in the ornithological world. ciently common that the aberrant forms repre - A variety of names are still used seemingly sent a fairly large proportion of the whole randomly to identify the mutations. Most population and are thus considered to be a commonly misapplied is the name ‘albino’ or colour morph within the species. In such cases ‘partial albino’ (Rollin 1964; Buckley 1982, the term ‘polymorphism’ is often used instead 1987; van Grouw 2006, 2010). The term of aberration. Melanism is the most common ‘albino’ is widely used for all sorts of different polymorphism represented in birds (Mundy colour aberrations, but in only a tiny propor - 2006). Pomarine Stercorarius pomarinus and tion of cases is it used correctly. Albinism is Arctic Skuas S. parasiticus are examples of actually far less common than was previously © British Birds 106 • January 2013 • 17 –29 17 van Grouw thought by most ornithologists; in fact, aber - In some groups of birds, the colour of rant white feathers are hardly ever caused by the adult plumage is caused by eumelanin albinism and are usually due either to a form only, for example in most oystercatchers of leucism or (more commonly) to a non- (Haematopodidae), gulls and terns (Laridae), heritable cause such as disease, food defi - auks (Alcidae), woodpeckers (Picidae), crows ciency or trauma. Probably the most (Corvidae), tits (Paridae) and the male common mutation in birds is ‘brown’ (van Blackbird Turdus merula . However, in most Grouw 2010), yet this mutation is given birds both types of melanin are present. many different names in the literature – There are no species in which only phaeo - albino, partial albino, cinnamon, leucistic, melanin occurs. In feathers that contain both isabella, fawn, pale morph, non-eumelanic forms of melanin, the eumelanin is found form, flavistic, erythristic or schizochroistic mainly in the central part of the feather while (to name just a few). the phaeomelanin occurs at the feather edges. This paper aims to introduce a uniform Melanin is produced by cells called system of naming colour aberrations. The six melanocytes, which are found mainly in the most common heritable colour aberrations skin and the feather follicles. The in birds are defined, grouped and named by melanocytes develop from melanoblasts, their pigment reductions (gene actions), and which are formed at an early embryonic stage discussed in simple terms. At the end of the in the ‘neural crest’ – derived from the paper, a basic identification key for the most embryonic spinal cord. As a result of genetic common aberrations should make it easier processes, the melanoblasts migrate from the for birders to name the mutation correctly. neural crest to the skin and feather follicles, where they develop into melanocytes and are Melanins and plumage coloration then able to produce melanin to add to the The most common pigments in both birds feather cells as the feathers grow. and mammals are melanins (Fox & Vevers The addition of melanin does not always 1960) and the pigmentation process in occur at a constant rate. In most species, the mammal hair is identical to that in bird feathers have certain patterns and/or colour feathers (Lubnow 1963). The many muta - differences caused by the type, amount and tions that cause a change in the melanin pig - distribution of melanin. During feather mentation, and thus an aberration in an growth, sudden changes from the production animal’s colour, are also directly comparable of eumelanin to phaeomelanin may occur, between mammals and birds. giving rise to these different patterns. The Carotenoids are the second most common development of melanin is the result of a pigments in birds (Fox & Vevers 1960) and chemical process called melanin synthesis, in vary in colour from pale yellow to scarlet red. which the amino acid tyrosine (released from Changes in carotenoid-based pigments nutrients in the food) and the enzyme tyro - caused by mutations are rare and are there - sinase (present in the melanocytes) are neces - fore not discussed further in this paper. sary to start the synthesis. Every disturbance Carotenoid pigmentation is usually not or aberration in the melanoblast migration affected by melanin mutations and therefore or melanin synthesis can influence the final yellow or red remains clearly present in the plumage pigmentation. The aberration can otherwise aberrant plumage (and similarly in be caused by a temporary, external factor or the eyes, bill and feet). may have a heritable cause (mutation). There are two forms of melanin: eumel - The mutation names used for birds in this anin and phaeomelanin (Lubnow 1963). paper are based mainly on the names used Depending on concentration and distribu - for Feral Pigeons Columba livia . Where this is tion within the feather, eumelanin is respon - inappropriate, genetic nomenclature of the sible for black, grey and/or dark brown House Mouse Mus musculus is used. colours, whereas phaeomelanin is responsible for warm reddish-brown to pale buff. Both The mutations melanins together can give a wide range of There are many genetic mutations that cause greyish-brown colours. colour aberrations in birds. In domestic 18 British Birds 106 • January 2013 • 17 –29 Colour aberrations in birds pigeons, for example, more than 50 dif - ferent colour mutations (genes) are known, which cause about ten distin - guishable colour aberrations (van Grouw & de Jong 2009). The six most common heritable colour aberrations in birds will be discussed here: albinism , leucism , brown , dilution , ino and melanism . Some of these aberrations can be caused by several mutations with a comparable effect (van Grouw 2006). Both albinism and brown are caused by a single genetic mutation, which is the same in every species. Albinism is a recessive mutation and the responsible gene is symbolised as ‘c’, while brown is symbolised as ‘b’. Brown is ‘sex-linked’ recessive, which means that a brown individual with normal-coloured parents is always female. An albino can be of either sex. There are strong indica - tions that ino is based on a single, sex- s n linked gene in all species, too. a m s For leucism, dilution and melanism, e i r several genetic mutations can be respon - D y sible for more or less the same aberra - d u tion. In domestic pigeons at least 16 R dilution mutations are known, more 14. Albino adult House Sparrow Passer domesticus , bred in the wild but kept in captivity. than ten for leucism, and six for melanism (van Grouw & de Jong 2009). less tissue. Thus, as mentioned above, there is However, these different mutations all cause in fact no such thing as a ‘partial albino’. comparable effects in the pigmentation and The forming of carotenoid pigments is therefore they can all be distinguished as being ‘dilution’, ‘leucism’ or ‘melanism’.