VARIATION IN IRIS COLOR OF ADULT THAYER'S GULLS

Abstract

Iris color is sometimes useful in bird identification, especially for gulls. A frequently quoted example is the separation of adult Herring (Larus argentatus smithsonianus) and Thayer's [L. (glaucoides?) thayeri] Gulls.

Typically, adult Herring Gulls have “staring” unmarked pale yellow irides, while adult Thayer's Gulls have dark irides—a view supported by numerous publications (e.g., Gosselin and David 1975; Lehman 1980; Grant 1986; Zimmer 1990, 1991).