tweeters-

I took adantage of the three day weekend and the good road conditions (I'm a
real chicken when it comes to winter travel) and tried for the King Eider, Great
Gray Owl and Brown Thrasher. Got the Eider and Owl on Sunday, the Great Gray
being my 15th (and last) owl species for the state, about time after 10 years.

The Brown Thrasher was observed for 4 minutes as it gulped sunflower seeds.
It used its bill in a side-sweeping motion to clear seeds and picked down into
the ground a few times to dislodge seeds and berries Joanne had thrown out.
It was seen from inside using binoculars (from about 18 feet). Its left foot
and the distal 1/2 of its tarsus was necrotic. It looked like gangrene (dry).
It was not using the foot at all. It would occationally touch the ground with
it but did not bear weight. Otherwise the bird appeared healthy, no unusual
falt bars, and the plumage looked OK.

We hypothesized that it was caused by exposure during the cold snap.
Joanne said that it got down to about 30 below one night. There are winter
records of Brown Thrasher for all the Canadian Provinces except Alberta, and
virtually every state has a winter record(s). However, these birds rarely stay
very long as far as I know. Does any one know of a Brown Thrasher staying for
more than a few days in very cold conditions?

Brown Thrashers are found in any number during the winter only in areas where
the temperatures rarely get below freezing in January (Root, T. 1988. Atlas of
Wintering NA Birds). Perhaps their weak feet are susceptible to frostbite.
Is this a case of (and mechanism for) temperature determining the winter
distributional boundry of a bird species? Are energetic constraints (rather
than competition, habitats, etc.) more important in determining distribution
patterns than we thought?

Dan Stephens (509) 662-7443
Dept. of Biology fax: (509) 664-2538
Wenatchee Valley College e-mail: dstephen at ctc.edu
1300 Fifth Street
Wenatchee, WA 98801