Colour in the Parrots

Part 1 - Describing Colouration

The budgerigar (melopsittacus undulatus) was introduced to Europe in 1840 and was the first parrot to be bred in large numbers in captivity; since when it has become the most familiar and closely observed of all the parrots. As such, it was the natural starting point for studying colour in the parrots and the many colour forms, or varieties, which have occurred have helped greatly in this respect. In fact the budgerigar with its relatively large areas of solid even colour, and its willingness to breed freely and mature quickly in modest accommodation, is such an ideal subject for study that it might almost have been created for this very purpose.

It is fortunate indeed that these qualities attracted the attention of professional scientists and gifted amateurs in the earlier part of the 20th century; for their involvement and continuing influence has bequeathed us a sound framework of knowledge and sensible terminology. Against this we have to set the often ill-informed ideas of some of those who breed for the show bench, and have a tendency to use success in this sphere to propagate their own blend of myth and mumbo-jumbo. As well, there are those who breed colour varieties of various species for profit, whether commercially or in the back yard, and often appear to deliberately conceal the origins of new colour forms and the knowledge gained from breeding programs so as to retain a competitive edge.

Another point which must be made is that since that early interest of scientists, mentioned above, their successors in avian biology and genetics have shown remarkably little inclination to further expand knowledge of colour formation and inheritance in birds. Indeed they have not even developed an adequate language to describe the changes of colour brought about by chance genetic mutation in wild populations. Neither have they taken the opportunity, provided by aviculture, to investigate those many and various mutant colour forms which are bred in controlled and predictable conditions by enthusiasts. The best effort in this direction has been discussed by Paul Buckley in Chapter 4 of Diseases of Cage and Aviary Birds and is examined in an article by Terry Martin in these pages.

When discussing the colouring of parrots, or any other birds, it is essential to use language which everyone can understand and apply in visualizing the subject. With some species, due to the complexities of their colouring and patterning, there is no alternative but to learn and to use the whole range of technical terms describing the various areas of the bird's plumage. However, the colour scheme of the budgerigar is so straightforward that for general purposes we can make do with just three descriptive terms. Considering the wild budgerigar (the wild-type), or its domestic equivalent the Light Green, these terms are:

1. Ground colour

Those areas which are coloured yellow are due to ground colour. There is a little more to it than this though; for virtually the whole of the plumage is pigmented yellow, as can be seen in the Lutino variety where all other colour production has been inhibited. In most other varieties the ground colour is at least partially overlaid with other colours, as we shall see when discussing the other two terms.

Yellow, then, is the natural ground colour of the budgerigar (and most other parrots).

However, in the Blue series of budgerigars a mutant gene prevents the production of any yellow and the ground colour becomes white. Additionally, between the green birds and the mutant blue birds there is a range of forms in which the yellow is only partially inhibited, to varying degrees, by a number of genes in various combinations. These are the parblue genes which produce the various Yellowface varieties.

So, in the budgerigar, there are birds with the natural yellow ground colour; blue series birds which produce no yellow pigment and therefore have a white ground colour; and a number of intermediate forms in which yellow is reduced in varying degrees. The yellow pigment is usually known by breeders as psittacin although, confusingly, the term lutin has gained some currency.

This situation is echoed in the other parrot species with the added complication that many of these also produce red and/or orange ground colour pigmentation besides, or even instead of, yellow.

2. Body colour

Much of the body of the wild-type budgerigar is coloured bright grass green. This is body colour, and the area concerned is known as the body colour area. Various colour genes may change the nature and shade of this green to produce varieties known as Dark Greens, Olives, Grey Greens, etc. Of even greater significance is the fact that when no yellow ground colour is produced varieties such as Cobalts, Mauves, Violets, and the Greys are revealed. We can appreciate here how the hue of body colour depends upon the underlying ground colour. Further, we can deduce that budgerigars do not produce any green pigment: the green colour being produced by the mixing of yellow and blue.

This is also true of all the other parrot species which have green in their plumage; though they vary a great deal and it may, or may not, be appropriate to talk of body colour. Many however do have plumage which is almost completely green, or in which green forms a significant proportion of the whole, and in these we can confidently use the term body colour and safely infer that they have yellow ground colour.

3. The Markings

The budgerigar carries a bold pattern of black markings comprising the zebra striations of the head and neck, carrying through the undulations of the back into the patterning of the wings and tail, and also including the six throat spots. These markings overlay and conceal both ground colour and body colour. The markings are caused by heavy deposits of melanin, which we shall consider in more detail later.

Again, there is considerable variation in other parrots. Some, such as the Rosellas, have patterning similar to the budgerigar which could likewise be described as markings; whilst others have a much more delicate and subtle filigree on many of the feathers. This has aptly been called the melanin overlay by Jim Hayward and is often really only noticeable in certain dilute varieties.

From the above we can see that budgerigar feather colouring, and that of many other parrots, can be thought of as being built up from three layers of which ground colour is the first. Overlying the ground colour layer, and interacting with it, is the body colour layer. Finally, the markings or melanin overlay form the third and final layer and where extensive conceal the other layers beneath.

A number of parrots, such as the Cockatoos and African Grey, have lost the ability to display some colours in their feathers. These naturally occurring forms echo the effects produced by mutant genes in the colour varieties we cultivate in many of the more commonly bred species. We shall appreciate these parallels as we go on to discuss the genetics of colour at a later stage.

This more or less covers the plumage of the parrots, although there may be particular features in different species or groups of species. The budgerigar, for instance, has that unique and somewhat puzzling feature; the cheek flash. This tight little group of feathers has a structure and colour quite different to any other possessed by the budgerigar.

Other pigmented areas

Besides the feathers there are, of course, other pigmented areas. Many parrots have exposed areas of skin as well as the eyes, the beak, the nails or claws of the feet and, frequently, that prominent area of tissue above the beak known as the cere. All are pigmented to some degree; usually, but not exclusively, by melanin. In the same way as the feathers, the colour of some may be affected by the sex of the bird or by the effects of different colour genes.

The cere

This is perhaps most noticeable in the budgerigar where the only significant visual difference between the sexes is the colour of the cere. In a mature male the cere is smooth, quite shiny, and of a bright cobalt hue; whereas that of the female is brown and has a matt appearance which in older specimens can become quite rough and knobbly.

The nature of the colour produced in the male budgerigar cere has received little attention and I have seen no technical discussions on this subject. It does seem likely though that its colour is produced in much the same way as that of the green tree frogs. In these a skin layer contains very small crystals of guanine (a form of sugar) which scatter light and reflect back the shorter wavelengths in the blue spectrum. Overlying this is a layer containing yellow pigment and the mixture of the two produces green. Colour morphs (mutants) of these frogs are occasionally seen in the wild whose blue colour may be assumed to be due to the loss of yellow pigment.

The male budgerigar cere never contains yellow pigment and is normally seen as a bright cobalt blue. Melanin is involved, probably as a base layer, since those varieties in which melanin is inhibited in tissue as well as plumage lose the blue colouration. The female cere contains melanin, in brown form, but the guanine layer is either inactivated or not present. Occasionally, older females do develop areas of matt blue on the cere which indicates that cere colour is probably a secondary sexual characteristic influenced by the differing hormonal environments of the sexes.

The eyes

Birds in general have a highly developed sense of vision, in many instances exceeding that of humans to a remarkable degree, though there is much variation in the emphasis placed upon particular features depending upon the lifestyle of different species. But there are limitations too. The eyes of parrots are set to the side of the head giving a very wide field of vision but with little overlap to produce a binocular or three dimensional effect. And the bird’s eye has little movement within its socket. Head movements may sometimes be used to compensate for this and aid in placement and judgement of the distance of objects.

One feature of parrot vision which is quite outside our experience is their sensitivity into the ultra violet region and, furthermore, the ability of areas of their plumage to reflect ultra violet light. Whether this reflectance is a structural effect or a property of some of the pigments involved or, as seems quite likely, a combination of the two, is not yet common knowledge. In any event it is very evident that parrots see each other in a way quite different to the way we see them. Goodness knows how they see us! (See external article Exploring the Fourth Dimension at Bristol University and feature article Bird colour vision from the bbsrc magazine.)

External features of the parrots’ eye which vary between species and sometimes between colour varieties are the pupil which lies at the centre, is usually black, and varies in size with light intensity; the iris, which controls the size of the pupil and is therefore itself variable in width as well as assuming a variety of colours; and, surrounding the eye proper, there is often an area of bare flesh known as the periophalmic ring which, again, may be distinctively coloured.

The colours and visible features of the eye are affected by some colour genes and on occasions may be the only way to distinguish which gene is active in phenotypes of otherwise identical appearance: i.e. the German and English Fallows in the budgerigar.

Legs and feet

In marked contrast to the wonderful disguise provided by their feathers the legs and feet of birds have a scaliness, and in the case of parrots a marked prehensile quality, which betrays their line of descent and kinship to the reptiles; their closest living relatives.

The legs and feet are generally greyish, sometimes with a bluish tinge, which betrays the presence of melanin; although a number have a yellow or orange colouration indicating that psittacin pigments may also have a part to play. In the main we notice a lightening of the colour, ultimately to a fleshy pink, in some varieties due to a reduction or virtual elimination of melanin. This is an indication that in these varieties melanin reduction in the feathers is accompanied by a similar reduction in body tissue.

Beak and claws

As with the feathers, keratin is the main constituent of the beak and claws although this time more substantially laid down and having a fibrous structure which make these formidable weapons or tools in the larger species. Unlike feathers, which undergo a periodic moult, the beak and claws have a process of continual but very slow growth to counteract the ravages of wear and tear. Please don't ask me how growth almost always matches wear and tear and is so precisely regulated that each unique shape is perfectly preserved.

Both melanin and psittacin pigments may play a prominent role in the beak which is often strongly coloured by one or the other and sexual dimorphism quite frequently determines what colour that should be. Colour genes too may have an effect on beak colour and when pigments are eliminated the natural transluscent colour of the keratin may be described as horn. Sometimes the pink of underlying tissue may be seen. This also occurs in the claws which show much less variation in colour which is mainly imparted by varying concentrations of melanin.

The next step

Now that we heve become familiar with the three main areas of colour, our next step is to examine the pigments and structures responsible for the wide range of colours shown by these areas. We shall see that whilst some parts of parrot plumage are coloured by only one colour element, others require as many as three such elements acting together. It is this fact which allows so much diversity in parrot colour between different species and the dramatic colour changes within species brought about by the growing number of mutant colour forms.

Copyright: Clive Hesford, December 1997 (and revisions up to November 2001)

Next — The Elements of Colour

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