Biology Reference
In-Depth Information
egrets, and ptarmigans, are not considered albinos, except in the extremely rare situation
in which one also lacks pigment on the beak, feet, and eyes. If your robin had pink eyes,
and a pale pinkish bill it was a complete albino. Unfortunately, because complete albinos
lack pigment in their eyes, they have no protection from ultraviolet light and tend to be-
come blind, dramatically shortening their lives.
Albinism is rare: one researcher estimated that only about one in 1,800 birds is an al-
bino. In humans, the incidence of albinism is about one in 17,000. Albinism usually res-
ults from a genetic mutation that interferes with the production of tyrosinase, the enzyme
necessary to produce melanin. Some birds are partially albino, with only certain feathers
lacking melanin.
Few if any studies of the distribution or frequency of albinism in birds have been con-
ducted.SomeresearchershavenotedthatAmericanRobinsandHouseSparrowshavethe
highestincidenceofalbinismofanybirds,butthismaywellbebecausethesetwospecies
are both conspicuous in backyards and other habitats where people spend a lot of time,
making albinos more likely to be noticed and reported.
Q I love the little red finches that nest in my begonia basket. For some reason, last
spring the male was orange, not red, but their babies seemed healthy. What caused
his unusual color?
A
It was probably caused by his diet. House Finch colors are produced by carotenoid
pigments that are incorporated into growing feathers if the birds are eating foods rich
in carotenoids, which are found in a variety of wild fruits. In laboratories, when House
Finches are fed a simple seed diet, the feathers that grow in after they molt are fairly dull
and yellowish. When beta-carotene is added to the diet, the feathers that grow in after
they molt are pale orange. And when a red carotenoid found in some fruits called
can-
thaxanthin
is added, their next feathers grow in bright red.
In some areas where House Finches have been introduced, such as Hawaii, their nat-
ural diet is poor in these pigments and the birds have dull plumage. In other areas, such
as Michigan, their feathers can be brilliant.
Brighter males are more attractive to females. The dietary carotenoids that give males
these bright colors also give females a good idea of which males are able to find the
highest quality food, indicating directly which will be the best providers for their young.
Q I read that Sandhill Cranes don't have feathers on their faces, but when I saw one
up close, those sure looked like red feathers! What gives?
A
What you read was true, although the face does indeed look like it's covered with red
feathers,becausetheskinoftheforeheadandcrownofbothsexesiscoveredwithbumpy
structures called
papilla
that look very much like tiny feathers. Blood vessels run very
