Hi Tweets,

Deb Beutler writes:

(snip)
> Variation in arrival dates arise due to conditions along the
>migration route. The day length starts the process. Then the bird starts
>migrating. If food supplies along the route are below average, the bird
>might have to spend more time at stopovers. If food is abundant, the trip
>may go faster. However, I doubt the process sped up by several weeks.

Perhaps in the cases of the Barn Swallows Hirundo rustica and--less so--
Rufous Hummingbirds Selasphorus rufus, I'd agree; quite a few of the former
have wintered further N than usual, and a some of the latter arrived in
California about ten days ago with the first Allen's Hummingbirds S. sasin.
They may be undertaking their first migratory steps as normal timing might
dictate, but many degrees of latitude north of their usual start.

> An alternate explanation for apparent "early migrants" are winter
>stragglers that never left and were never discovered. It is possible that
>every winter a few birds just don't leave; winter weather usually takes care
>of them. However, during mild winters, particularly El Nino winters, they
>can survive and are "found" on those early dates.

Attention to the plumage pays off here (and why databases tracking bird
records should, in my opinion, have a field for such): initially, male
Yellow-rumped Warblers Dendroica coronata migrate ahead of the females, so
any Definitive Alternate-plumaged singing male in a bunch of still
Basic-plumaged silent warblers is overwhelmingly certain to be a migrant
among wintering birds.

> I predict that most birds will be right on time.

For record-keeping, then, it may be useful to mark not only the first
arrival but the first significant number--and that would be whatever was
appropriate to the species, say, a flock of 50 Western Sandpipers Calidris
mauri, or three Pacific Golden-plover Pluvialis fulva. It would be easy to
see if the migration were generally accelerated compared to other years:
just compare the date of peak northbound numbers this year with peaks dates
of other years.

I'll join Deb in suggesting that though we may be seeing record-early
arrivals this year, some might be wintering survivors indistinguishable from
bona fide migrants and some might be jumping off from a starting line
several hundred to thousands of miles further north than usual, the
*majority* of each species will come in pretty much on time for the reasons
she describes.

When's someone gonna invent a bar-code and scanner to clear stuff like this
up? '-)

Michael Price A brave world, Sir,
Vancouver BC Canada full of religion, knavery and change;
mprice at mindlink.net we shall shortly see better days.
Aphra Behn (1640-1689)