Subject: starlings do flock (temporarily) in summer
Date: May 11 10:06:10 2001
From: Dennis Paulson - dpaulson at ups.edu


To continue the thread of those little flockers, I just walked across
campus to run some errands and stopped to watch starlings at several
places. On one lawn there was a group of about 15, moving forward in
unison, the rearmost ones flying to the front just as they do in their
large winter flocks. Birds were constantly moving toward other birds, and
it's possible that these birds might fly toward feeding groups just because
a feeding group indicates a good place to forage. But the groups move
across the lawnscape, and when I went by one lawn a second time the whole
group was in a different area than when I walked by the first time.

I'm left with the distinct impression that they do aggregate with one
another rather than merely coming back to a productive feeding area. Of
course, by no means are these "flocks" anything other than temporary, as
birds fly back to their nests with mouthfuls of food and other birds join
the group. But I'm convinced that in many instances, after a bird has fed
its young, even a block away, it returns to the group rather than finding a
new place to feed. From the watching I've done, I'd say that crane fly
larvae are spread across the lawns more or less uniformly in amazing
abundance - I could see starlings picking them up one after another, almost
constantly, apparently seeing many of them without having to gape for them.
So a starling could surely find plenty of larvae by landing almost anywhere
on the lawn, yet they make a beeline for a feeding group. This could of
course just be a persistence of the behavior that serves them well in
winter, associating to reduce the chance of predation. I'm not sure
whether they are using one another as "beaters," but it is possible, as on
numerous occasions I saw a starling run right to where another starling was
feeding.

There's no doubt, however, that House Sparrows use the starlings in this
way. These groups were all accompanied by sparrows, much more common on
this part of campus than in the courtyard of my building. The sparrows
were hanging out with the starlings exactly as Cattle Egrets hang out with
cattle, moving around to the front of a foraging starling and presumably
watching for insects flushed by the starling or ready to snag a larva
dropped by a starling. On one occasion I saw a starling jump on a sparrow,
seeming to trounce it, but the sparrow got up and resumed its commensal
foraging. This is neat, because friends of mine did a study in which they
found that starlings regularly steal worms from robins, so they're being
kleptoparasitized also.

Dennis Paulson, Director phone 253-879-3798
Slater Museum of Natural History fax 253-879-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416
http://www.ups.edu/biology/museum/museum.html