Colour in Birds

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BIRD NUTRITION and COLOUR MAINTENANCE

Many of the pigments in feathers originate from plant carotenoids, flavones and pterins.  Most of these pigments are fat soluble molecules that impart green, yellow and red colours to plants. Honeyeaters do not eat green leaf plant material and rely largely on insects as a dietary source of pigments.  Insects contain at least six chemically different types of pigments.  Melanin, pterins, flavins, carotenoids, anthoxanthins and aphins.  It is not known if all these pigments are incorporated into feathers, however the inclusion of carotenoids is well documented (Rawles 1970).  Once these pigments have been absorbed they may remain unaltered or be modified before being deposited into the feather barb at keratinisation.

Some of the carotenoids identified in feathers are xanthophyll, zeaxanthin, canthaxanthin,  rhodoxanthin, capsanthin, astacin, a-carotene, b-carotene and astaxanthin.  Xanthophyll, zeaxanthin, rhodoxanthin and canthaxanthin are widespread in cereals, vegetables and green leaf plants.  Capsanthin occurs in peppers and chillies.  Astaxanthin, xanthophyll, a and b-carotene and astacin occur in invertebrates.

Captive granivorous and herbivorous birds usually have vegetables and green leaf plants as well as grain in their diet and are not prone to “colour fading” due to low carotenoid intake.  Apart from seed most aviculturists would feed their parrots or finches one or more of the following; silverbeet, seeding grasses, corn, apples and carrots.  A diet containing this range of plant material would probably not only supply adequate levels of the desired carotenoids but also significant amounts of a precursor, b-carotene.  Canary breeders have long recognised the value of feeding thistle and chilli to canaries, gold finches and siskins to promote the yellow, orange or red colour in their plumage.  Canary breeders also feed hard boiled egg preparations to their birds during the breeding season.  Egg yolk is an indirect source of xanthophyll and zeaxanthin.

Captive honeyeaters may be prone to “colour fading” due to low carotenoid intake.  Substitute food may need supplementing with up to 1% of egg yolk or 5% of a  slurry made from equal proportions of carrot, corn kernels and a green  leaf vegetable.  Canthaxanthin, xanthophyll and b-carotene can be fed as colour promoters in the substitute food.  A suggested  feed rate for canthaxanthin and xanthophyll is about 20mg per kg of  dry weight feed and for b-carotene 1mg per kg of dry weight feed.  Be aware that all carotenoids have some vitamin A activity that will become additive to the vitamin A already in the substitute food.

Rawles, M.E. 1970.  The Integumentary System. In Biology and Comparative Physiology of Birds.  Edited by A.J. Marshall.  Academic Press, New York & London.

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