Earlier today, Mike Smith asked:

>So some corvids have cooperative breeding, have crows ever been shown
>to do this? [and...] another nesting pair nearby who will
>cooperatively chase away predators (me and Scout), or nest-helpers
>such as last year's young. It seems more likely that the former is
>true, but does anybody know if the latter part is true (ever?)? Or
>was I just being mobbed by all of them?

There are two separate issues here in danger of being confused:
cooperative breeding and mobbing. First, do crows ever breed
cooperatively? Yes. June Chamberlain Auger studies American Crow
breeding behavior on Cape Cod, MA and has compared two populations in
close proximity - one which regularly shows cooperative breeding
(aunts and uncles and last year's siblings sometimes forego breeding
to assist breeding relatives), and one which does not. The
cooperative crows are city birds; they nest in downtown Hyannis, the
Cape's largest city. Nest sites are limited, and food is limiting,
but if I recall correctly, predation is low. The "uncooperative"
crows are country birds; they nest on Sandy Neck in Barnstable, MA.
Nest sites abound in pitch pines on this wide and several miles long,
and relatively remote during nesting season barrier beach. I do not
have any papers by Dr. Auger; my recollections are based on a lecture
I saw her give about three years ago.

Mobbing is a somewhat separate issue. As far as I know, all crow
populations mob. The mobbers are often not closely related. And
often, mobbing takes place under seeming nonsense circumstances;
i.e., mobbers will go after predators at times and in places where
they pose no threat whatsoever. A birding Botany professor friend of
mine recently told me that he had read that mobbing serves more as a
group-bonding device than as a nest protection method, but it
obviously does serve this function at times. On a few different
occasions, I have stumbled upon a Great Horned Owl in the woods only
to see crows call in literally dozens of friends from what often must
be at least two miles away to harass the owl. Lasting guilt helps me
to recall the memories in too great detail.

Then Mike asks, will a neighboring non-related pair chase
away related nest-helpers at a given nest? It would seem that
whenever you have an aggressive instinct that is as strong as mobbing
is, there will be loads of "nonsense" (i.e., no observable fitness
advantage) occasions when that instinct is acted upon. Thus, I don't
know, but I strongly suspect that that sort of thing happens from
time to time. [This is essentially the same theory I employed a few
weeks ago to attempt to explain on Birdchat why grackles might kill
birds and then fly off. Is there a name for it? Have there been any
studies to support this idea?]

I have a beautiful book at home "The American Crow and the Common
Raven" by Lawrence Kilham which I have yet to read because I've
simply been too busy. Kilham has done a lot of behavioral work
with various birds. But I'll skim through it tonight and
see if there's anything to add. I don't have a copy, but Heinrich's
Ravens In Winter would be another likely place to look.

All this reminds me of a fellow grad student here, Lauren Gilson, who
is studying nest-switching in fledgling ospreys in Idaho's Cascades.
The adventurous little guys often hop into nests of non-relatives and
are adopted successfully usually by the unsuspecting foster parents.
Whoever said that nature is always cold and heartless?

Peter Whitlock
Raptor Research Center
Boise State University