Hi Richard and everyone,



A string on this same topic happened some time back, but there are obviously new folks on the list, so I'll attempt a paraphrase of that string.? First of all, Anna's do not migrate in the true sense of the term.? They are resident within their range, probably dispersing only short distances for territories and breeding but basically they are non-migratory.? While it seems plausible (or probable) that winter feeding?is a critical factor in?supporting certain individual birds and thus possibly a larger population than would naturally be here, the biggest factor historically for their range expansion northward probably was the introduction of non-native winter-blooming plants for ornamental purposes?that had the side effect of providing winter?food sources for the hummers, who expanded north with the availability of this food source.? Additionally, hummers typically eat some protein in the form of insects when they're available, and our winters are mild enough that there are some bugs around pretty much all year.? Finally, hummers are able to use 'torpor' - essentially voluntary short-term 'hibernation' in which the birds can reduce their body temperatures quite a bit at night to conserve energy and then 'turn up' the metabolism when the daylight and warmer temps show up.? The conventional wisdom that 'global warming' is what caused the northward expansion is, in this case at least, not considered by the experts to be the primary factor.



If I've missed or mis-stated anything here, the experts on the list will hopefully jump in and correct the info.



John Tubbs

Snoqualmie, WA

johntubbs at comcast.net

www.tubbsphoto.com


----- Original Message -----
From: "Richard Isherwood" <rjisherwood at gmail.com>
To: tweeters at u.washington.edu
Sent: Thursday, December 10, 2009 1:04:09 PM GMT -08:00 US/Canada Pacific
Subject: [Tweeters] Anna's Hummingbirds

Whatever do they do in these temperatures if there are no feeders?

In fact, what are they doing here in winter at all? There must be next to no nectar around even in normal temperatures.

What else do they feed on ?

????????? Richard Isherwood
????????? Port Townsend WA
????????? Rjisherwood at gmail.com


_______________________________________________ Tweeters mailing list Tweeters at u.washington.edu http ://mailman2.u.washington.edu/mailman/listinfo/tweeters ://mailman2.u.washington.edu/mailman/listinfo/tweeters