Bonaparte's Gull in St. Louis County
2010-05-14

Common in St. Louis County in the Spring season

Rare variant of the Bonaparte's Gull (Chroicocephalus philadelphia) showing extensively dark upperwings contrasting with a normal shade of gray on the mantle. This first-cycle bird was amongst a feeding flock of several hundred Bonaparte's Gulls, hundreds of Ring-billed Gulls (Larus delawarensis), 186 Herring Gulls (L. argentatus), one first-cycle Thayer's Gull (L. thayeri), and 1,187 Common Terns (Sterna hirundo) at the Superior Entry, 14 May 2010. Aberrant Little Gulls (Hydrocoloeus minutus) with blackish upperwings have been reported on multiple occasions (e.g., British Birds 75:88, 79:119-120, 83:503-504). Birders are likely to be aware of this possibility since it's mentioned in standard references including Grant (Gulls-a guide to identification, 1986), Harris et al. (The Macmillan Field Guide to Bird Identification, 1989), Olsen and Larsson (Gulls of North America, Europe, and Asia, 2004), and Howell and Dunn (Gulls of the Americas, 2007). Olsen and Larsson (Fig. 747, p. 532) and Howell and Dunn (Fig. 6.13, p. 70) both include photos of dark variant Little Gulls. Less widely known are dark variant Bonaparte's Gulls. Though mentioned by Grant (1986), apparently the first published photographs did not appear until 1999 (White, M. 1999. An unusual plumage of Bonaparte's Gull. Birders Journal 8:38-39).

Peder H. Svingen