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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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