>I have a 'bluebird trail' here in the Methow Valley (NC Washington)-
>50 boxes. Over the several years I have had boxes up I commonly get
>about 25% Tree Swallows. They have always seemed rather delicate of
>constitution but somehow successfully reproduce. This year when I
>checked boxes on July 15 (after an absence of one month), of 8 boxes
>containing Tree Swallows, 6 contained dead birds- usually 3-5
>nearly-ready-to-fledge nestlings. They no doubt died in June. It
>was rather pitiful. Any ideas on what could have happened?
>Neighboring Western Bluebirds fledged successfully, and in many boxes
>raised a second brood. It was even cooler than average this spring,
>right into June- but these nestlings were 3/4 grown.
>
>Dana Visalli

I think a good direction to look when you find extensive mortality such as
that is at the weather. Baby birds all too commonly starve when weather
conditions are such that the parents can't find enough for them to eat.
Bluebirds take their insects from the ground, Tree Swallows from the air,
and several days of weather bad enough to keep insects from flying around
can easily do in a family of swallows. For example, I encountered pretty
bad weather on a trip to Okanogan Co. on 22-23 Jun, and I recall some bad
weather over there in July, too.

Dennis Paulson, Director phone 206-756-3798
Slater Museum of Natural History fax 206-756-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416