Among features to note on the Thayer's Gull are the distinct brown caste in iris (pale yellow in Herring), the purply-red eyelids (paler and yellowy in Herring), duller tones to base of bill (see next photo with Herring Gull). Also characteristic of adult Thayer's are the rosy tones to the legs (paler flesh tone in Herring), the larger white spots on primary tips, and largely white primary underwing.