|Lesser Black-backed Gull. Brevard County, Florida. January.|
This month's quiz bird has a relatively fresh set of feathers, undoubtedly in its first plumage cycle. Structurally, it appears long-winged and this is a helpful clue that may be used with some experience.
The very plain, blackish, secondaries as well as the dark greater primary coverts and outer greater secondary coverts give the impression of a black-backed species. There's also a straight, all-black, bill with a contrasting white head. These field marks are consistent with 1st cycle Lesser Black-backed Gull - an age group that often goes overlooked by many on this continent.
Several quiz participants were stumped by the apparent inner primary "window" and felt this looked better for Herring Gull. Although we don't usually associate pale inner primaries with Lessers, it's not unusual for the species to show this. Note that a much more faint window is visible on the right wing and this is simply an effect caused by the primaries on the left wing being more spread, and hence the pale inner vanes are almost completely exposed, showing the palest portions of those feathers. The window dissipates quickly depending on the bird's behavior or the angle the observer is viewing from (see here for another example).
Another point that was raised as evidence for American Herring is the wide tail band. The tail band is wide, and even wider toward the outer rectrices. Admittedly, most Lessers have thinner tail bands. But note the solid, white, base color to the uppertail coverts. In Herring, the uppertail coverts tend to be more concolorous with the rest of the upperparts, and at the very least, more barring is visible (like so, scroll down for a spread tail).
This month's quiz bird was designed to show two features on LBBG that our popular bird field guides don't necessarily discuss. Paler inner primaries and wider tail bands don't necessarily rule out Lesser Black-backed Gull.