Burt Guttman wrote:

>Dennis, interesting observations. You and I have had discussions before
>about the adaptationist viewpoint and whether every feature an organism
>displays has a function. This social feeding is probably functional, isn't
>it. Several birds moving across the grass together probably scare up more
>small invertebrate food than a single bird does, and together they may
>exploit the resource more completely than a single bird would. Have other
>people observed social feeding behavior like this and speculated on its
>function? In response to my suggestion, someone is likely to raise the
>objection, "Well, if social feeding of this kind is so valuable, why don't
>all passerines do it?" The answer, of course, is that a species can't
>simply order potentially adaptive features from some Great Warehouse in the
>Sky; it must wait to get the proper genes, more or less by accident, and the
>genes and the behavior must fit with the rest of the genome and the rest of
>its behavioral repertoire.
>
>What do you think.

Yes, I would say very functional, exactly as you outline it. This is how
starlings forage in winter, with the addition of the wonderful rolling
motion that a flock makes as the rear birds continually fly to the front of
the flock. Talk about organization! We need training to do such things,
and they do it automatically. What to me is fascinating is that they do it
also in the summer, even though each pair has its own nesting territory, so
they have to continually join and leave flocks - presumably simple enough
to do. I'm sure, however, that some starlings feed solitarily, just
because there are no others in sight. The flocks I've seen on the city
lawns lately are much smaller than the winter flocks that seem to stay
together through the day.

Social feeding functions both for more efficient exploitation of resources
(when birds are in dense flocks, as starlings, or even work together, as
pelicans herding fish) and for predator detection. With all the
bird-eating hawks out there, it makes sense for birds to flock, to benefit
by more pairs of eyes and the potential confusion and intimidation that a
flying flock furnishes. However, birds in flocks can also interfere with
each others' feeding, and the foraging behavior of the majority of species
probably precludes doing anything like the starlings do. Can you imagine a
flock of warblers all gleaning down the same branch, or a flock of creepers
all moving up the same tree? "OK, you creep up that side of the trunk, and
I'll stay on this side." It does make me chuckle.

Dennis

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