#ringbilledgull

RING BILLED GULL - Composition Wednesday

September 29, 2024

Misidentifications I see on the Metro Vancouver eBird somewhat frequently involve Short-billed and Ring-billed Gulls, especially juveniles and first cycles (juveniles that have begun the first pre-alternate/pre-breeding moult).

Adults are the easiest to separate.

Ring-billed Gull gets its name from the black band towards the end of the bill. At most, Short-billed Gull will have dark markings in a similar position, but never a complete ring. Sometimes the bill tip of some Short-bills is yellow, and the basal portion greenish yellow.

Adult Ring-billed Gull in breeding plumage. Note black band around outer bill, pale yellow eye.

Adult Short-billed Gull in non-breeding plumage, undergoing prebasic/post-breeding moult. Head is all white during breeding season, like Ring-billed Gull. Note dusky, speckled eye.

Also, Ring-billed is larger than Short-billed, has a lighter grey mantle (upper body) and pale yellow eyes instead of dusky/speckled.

In flight, Ring-billed has smaller wing mirrors on p10-p9 than Short-billed Gull (white patches near the top of the outer two wing feathers).

Ring-billed gull in prebasic/post-breeding moult. Note limited wing mirrors on outer primaries.

Short-billed gull in prebasic/post-breeding moult. Note extensive wing mirrors on outer primaries.

The juvenile plumages of both species are reliably identifiable as well.

Ring-billed is whiter overall, with contrastingly dark brown patterning on upper body, wings and behind the tail. Short-billed is grey-brown overall, bleaching whitish over winter.

Both species's bills start off dark, then become pink at the base. The dark tip of Ring-billed is more clearly demarcated.