Hi Tweeters

Mike Patrick queries:

>I saw about a half dozen Bonaparte's Gulls off South Whidbey Island state
>park yesterday. Or, at least I *think* I saw immatures. These birds had a
>black terminal band on the tails, no hood (but a dark spot behind the eyes),
>somewhat mottled wings, with at least one having a blackish band on the tips
>of the trailing wing feathers (apologies for lack of the correct terms here
>would "tips of the primaries and secondaries" be more accurate?).

This is a pretty fair description of Bonaparte's Gulls in 1st alternate
plumage, which can be somewhat variable in the degree of 'hooding' or lack
of it; BOGU doesn't acquire its definitive alternate plumage until at least
its second summer.

>Question: are these likely immatures from this year's breeding, are they
>immatures from last year? The range map in the National Geographic guide
>indicates they are in their wintering grounds; does this imply that immatures
>migrate this early, or is this an atypical observation?

Actually, the immatures/subadults of a lot of migratory seabird species stay
on the wintering grounds, or go part but not all the way, or wander around,
learning survival skills until they're sexually and behaviorally mature
enough to compete for territory/mates, and then they undertake the complete
migration to the breeding grounds to slug it out with other adults.

The absence of immature birds from the breeding grounds means, too, that
they won't be disrupting adult birds' nesting (they've already got their
hands full competing with other adults, and raising and protecting their own
kids) nor will they be scarfing up food needed by the adults and their young.

You won't be seeing juveniles from this year's breeding until late July (the
13-yr average BOGU juv. arrival in Vancouver BC is July 24); the ones you're
seeing now are just young louts hanging around the A & W 'cause it's summer
and there's nothing to do :-)

Michael Price
Vancouver BC Canada
michael_price at mindlink.bc.ca