Subject: identifying migrants vs residents
Date: Apr 21 10:53:35 1996
From: Don Cecile - dcecile at cln.etc.bc.ca


Every year, I attempt to increase my understanding of the arrivals of migrant
birds. I update my records seasonally, always trying to get a better
`picture` of the seasonal arrivals and relative abundances of each species.
(quite a task) And every year, I run into situations where I question
whether the birds I am noticing are truly migrants or whether they are
actually residents. I have developed a few `tricks`that I use to help
discern in certain situations ( some of them are species specific and some
are rather unscientific ie. gut feeling)the latter often lacking
substantiation and confidence. However, I am a bit stumped on the following:

on Saturday, I was enjoying the shorebirds in Tofino (west coast Vancouver
Island) and it was obvious that many were migrants: ie Western Sandpiper,
Semipalmated Plover, Dowitchers since they were not only in breeding plumage,
but also, none of these species overwintered and certainly not in the numbers
present! The problem lies with trying to distinguish the arrival
of Sanderlings, Dunlin and Black-bellied Plovers. EAch of these three
species overwinter. My first thought was, if I can find individuals that are
in definite alternate plumage, they must be migrants, this became an issue
when there were no sanderlings in alternate plumage (assuming no migrants),
dunlin were nearly in full alternate plumage (migrants???)( in this case I
relied on my judgement that dunlins were always the last of the shorebirds to
appear in southern ontario (mid to late may) therefore perhaps these are the
resident birds, and no significant increase in their numbers was evident.

Then came the Black-bellied Plovers, this period of time should, it seems,
fall within the spring migration window of this species. However the problem
is, that there was every plumage available from basic immatures (and adults?)
to definite alternate plumaged adults. The situation becomes more complex
because there were not large numbers of them (there never are in the spring).
In fact, it appeared as though there were fewer here now than there were in
the mid-winter. Does this mean that some migrated before achieving complete
moult? (I know many shorebirds do this) If so, how does one determine when
the Black-bellied Plovers began to arrive? At this point, one way that might
work would be to find out indirectly by noting the arrivals of plovers in
locations farther north or nearby where plovers do not overwinter, or just
post a message on tweeters and see if someone else knows.

By the way, there was a remarkably early Hammond`s Flycatcher, however my
`gut feeling` informs me that this is indeed a migrant!!

--
Cheers,

Don Cecile
Port Alberni, B.C. Canada
dcecile at cln.etc.bc.ca.