Subject: Re: swainsons hawks
Date: Sep 4 14:17:05 1996
From: Dennis Paulson - dpaulson at mirrors.ups.edu


>This is a rather delayed report of observations I made Friday Aug. 30. I
>was traveling east on I-90 about 5-10 miles east of Moses Lake. For a
>distance of about 12 miles I counted at least 50 Swainson's Hawks,
>including one kettle composed of at least 30 individuals. I didnt see any
>Swainson's hawks before or after this particular stretch of highway. On
>the way back home on Monday I counted 12 Swainson's in this area.
>Perhaps this is some sort of migratory path these hawks follow through our
>state? Has anyone else observed a similar phenomenon? It appeared that it
>was in this area that the terrain changes from the Columbia Plateau to the
>rolling hills of the palouse. Perhaps the hawks are able to take some sort
>of advantage of the change in terrain.
>
> Mike Blue

The only other explanation that comes to my mind is that there is an
unusually high density of grasshoppers in that area. Swainson's Hawks
often concentrate where there are lots of them, in North America as well as
South America.

I don't know if rolling hills qualify for aerodynamic reasons. Hawks
typically take advantage of north-south ridges, where obstruction drafts
from easterly or westerly winds give them lift as they sail along the ridge
on their migratory path.

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