Oct 08 2010
Bare skin eyerings are often sexual cues for the birds who have them. Among peregrine falcons the eyerings on adults are yellow, on juveniles they’re blue-gray. This color difference is a cue that the juveniles are not breeding threats. The juveniles’ brown (instead of gray) plumage and blue-gray cere and eyerings probably save them from being attacked when they pass through adult breeding territories.
Eyerings are a useful fieldmark, especially among species that are otherwise similar. Connecticut warblers look similar to mourning warblers but Connecticuts have white eyerings. Many thrushes are similar, but Swainson’s thrushes have buffy eyerings.
A striking example of eyerings is the bright orange skin around the eyes of killdeer in the spring. The skin becomes intensely orange when breeding is about to begin and seems to shout, “I’m ready.”
There’s no need to mark up this photo. The eyering is obvious. This killdeer is ready to breed.
(photo by Chuck Tague)