"Soft Part" Coloration in Breeding Birds
Originally published in Volume 47, Number 5 (May 2001)
"Soft part" coloration is an ephemeral condition, unlike feather coloration which, once formed, never changes over the life of the feather except by physical wear. Since color of legs, bill, orbital ring, and even iris color of eyes is influenced by hormonal levels, it is subject to the overall physical condition of a bird. In terms of reliable field characters, these are the "softest" of all and any identification that rests solely on soft part coloration is on shaky ground.
For the most dramatic examples of soft part coloration change, see the incredibly intense, but also incredibly brief flush of colors on the bare facial skin and legs of many herons just at the height of the breeding condition (coming up here in a few weeks). The normally yellow facial skin of Great Egret turns bright chartreuse green; the normally yellow skin of Snowy Egret becomes blood red as do the yellow toes.
Even eye color, which we tend to think of as permanent, changes in some species. Breeding Brown Pelicans eyes (iris) becomes powder blue. Many immature raptors have yellow irises when young. These gradually darken as the bird matures to the dark brown color of the adults. All these conditions are shortlived, just a matter of a few days in many cases. But it is common to find Royal Terns with bills every bit as red as those of Caspians at the peak of the breeding season. And Laughing Gulls go through the red bill and legs stage each year, but again it is a very ephemeral phenomenon.
All these I have mentioned are regularly occurring phenomena... Right now is a great time of year to pay special attention to "soft part" coloration, since many species will be exhibiting changes of intensity and hue as they go through the breeding cycle.
From a TEXBIRDS post by John Arvin
San Antonio Audubon Society, 5150 Broadway
#257, San Antonio, TX 78209-5710, (210)
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