Stuart MacKay wrote:

>I often see such interactions in mixed warbler flocks in Fall both here and
>back in the "Old Country". I wonder whether this is a display of "high
>spirits" (whatever that means) rather than aggression as there never seems to
>be any contact even when the bird being chased was displaced from a perch.
>Chases also "seem" to start with birds from random locations - rather than
>birds in close proximity where agression relating to competition for food
>might be assumed to be an initiating factor.

I agree. Although the 3 species I mentioned do take some of the same prey,
it may be far-fetched to attribute the interaction to aggression to reduce
resource competition. Especially during migration, when a bird's better
strategy might be to spend its time foraging rather than chasing. My quite
fanciful thought was that chases might stem from unfamiliarity--the
chickadees in my yard rarely see bright yellow birds, and the warbler
(which was immature) might also be checking out an unfamiliar bird
(Stuart's "high spirits").

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