Path: utzoo!utgpu!attcan!uunet!seismo!sundc!pitstop!sun!oliveb!oliven!mjm
From: mjm@oliven.olivetti.com (Michael Mammoser)
Newsgroups: rec.birds
Subject: Re: Forster's and Common Terns
Keywords: Differentiation, abundance
Message-ID: <34349@oliveb.olivetti.com>
Date: 15 Dec 88 17:23:01 GMT
References: <114@arcturus.edsdrd.eds.com> <719@picuxa.UUCP>
Sender: news@oliveb.olivetti.com
Lines: 24

In article <719@picuxa.UUCP>, gpasq@picuxa.UUCP (Greg Pasquariello X1190) writes:
 > Usually the shade of the tops of the outer primaries works well.  The Forster's
 > has frosty white tops, while the common has dirty grey ones.  I am only able
 > to see the dark tail edges if the bird is very close, and then only if it is 
 > in the right light and position.  

	Beware of first-winter Forster's Terns which can also show darkness
on the tops of the outer primaries. However, first-winter Forster's should
lack the dark bar on the top of the leading edge of the wing between the
shoulder and wrist.

	Forster's Terns are quite common here in the Bay Area and Commons
are quite rare (sounds like a contradiction). I remember watching for some
time a perched tern, which I was hoping to ID as a Common. The bird was
breeding plumaged (black cap and orange bill) but had dark-looking primaries
on the folded wing. I was sure that breeding plumaged Forster's shouldn't
show these dark primaries and was ready to call it a Common; then it took
to the air and suddenly the dark primaries disappeared and the open wing
showed the typical pale upper surface of a Forster's Tern. It also started
calling, and sounded like a typical Forster's. It was quite a confusing
moment for me. I now wonder if I'll be ready for the elusive Common when it
does finally show up.

Mike