Some birds have red eyes, some yellow, while others have brown, blue or green. This is because of the difference in pigments in their iris. The colours do not serve any purpose as far as sight is concerned. But in some species, the colour helps identify the maturity status, breeding readiness and the sex of the bird.
In some species, the male and female have different eye colours. For instance, female Brewer’s blackbirds have brown eyes, while the male of the species has bright yellow eyes. Male saddle-billed storks have dark brown, almost black, eyes, and females have bright yellow eyes.
In many species, the eye colour changes as the bird matures. In such species, the colour change signals adulthood – possibly an evolutionary adaptation that helps them identify potential mates. Bald eagles, ring-billed gulls, and ducks such as goldeneyes and scaups have brown eyes as youngsters, and yellow as they mature.
In some birds, eye colour changes according to the breeding season, for example, the iris of the brown pelican changes from brown to blue during the breeding season. The changes in colour with age and season are likely to be driven by hormonal changes, say scientists.
Picture Credit : Google