Re: Conowingo Dam: 01/31/98 -Reply

Rick Blom (rblom@blazie.com)
Tue, 3 Feb 1998 08:23:16 -0500 

On Feb 2, Howard Elitzak wrote:

>This message is in reference to Gene Scarpulla's Conowingo Dam
>report.
>
>You indicated you observed "1 fourth winter" and "2 adult" LBBG's.  Did
>you perhaps intend to report a third winter bird?  If not, what is the
>difference between a fourth winter and adult LBBG?  I was under the
>impression that this was a four-year gull.

        Lesser is a four-year gull, as is Herring. There are, however,
individuals that seem to be in fourth-winter plumage, based on retained
subadult characters. These are birds that appear to be full adults in
almost every respect and are certainly not third-winter. Typically they
have some dark on the bill. Sometimes they also have duller yellow legs,
reduced head streaking (usually heavier in adults), smaller white mirrors
in the primaries, and sometimes a slightly darker eye. The key is the bill.
It has long been assumed that these birds are in their first full adult
plumage (which happens in fourth winter) but have retained a few
indications of third summer plumage, which will presumably be lost in the
spring. If they are like Herring Gulls, a few will retain some indication
of subadult plumage right into their fifth winter. They may also retain a
few subadult brown feathers in the body plumage, but that is very hard to
see on Lessers as opposed to Herrigns because the back is so dark.
        It is not certain that these birds are in fourth-winter plumage of
course. It is based on assumptions about molt and the tendency of some
birds to be a little slow when it comes to changing soft part colors. We
have been using "fourth-winter" to designate them for more than a decade
and perhaps it should be considered an indication of a particular plumage
pattern (which is not that rare) rather than a precise age category.

Rick

"Everywhere I go I'm asked if the university stifles writers. My opinion is
that they don't stifle enough of them. There's many a bestseller that could
have been prevented by a good teacher."  Flannery O'Connor

Rick Blom
rblom@blazie.com
Bel Air, Maryland