When last I wrote about this (in answer to an inquiry from Mike
Smith), I promised to check Lawrence Kilham's _The American Crow
[AMCR for remainder of this post] and the Common Raven_ (Texas A&M
University Press: College Station; 1989) for any relevant comments
about cooperative breeding and mobbing in crows. Since then, Dennis
Paulson wrote an excellent reply concerning mobbing. Also, in
reviewing my earlier message, I realized that I spent so much energy
distinguishing cooperative breeding from mobbing that I failed to
realize that the last half of Mike's inquiry really concerns
territorial defense which also should not be confused with either
coop. breeding or mobbing. Here I'll try to summarize some of what I
learned from Kilham's excellent book.
Part I (pages 13-105) is entitled Behavior of Cooperatively
Breeding Crows on a Cattle Ranch in Florida; several other sections
of the book also deal with cooperative breeding. Here are some
select comments: "There are forty-two _Corvus_ spp. in the world, but
only the AMCR and the related Northwestern Crow are known to be
cooperative breeders, the latter only minimally....helpers assisting
at all stages of nesting, from nest building to feeding the
incubating female and then the nestlings and fledglings... But the
term cooperative breeders is to some extent limiting, since crows can
live as members of groups the year round." (p. 171) He presents data
from June Chamberlain-Auger (whose Cape Cod study I mentioned in the
last post). Both the urban (Hyannis) crows and the rural (Sandy
Neck) crows breed cooperatively (I was misleading on this point
before), but the rural birds have smaller groups in general at each
nest (rural nest group size in # adults attending each nest app. 3+-
0.5, range=2-6; urban nest group size app. 4.5+-1.3; range=2-8). The
data is presented as being from a pers. comm.; apparently, she had
not yet published it at that time. Has anyone seen a paper by Dr.
Auger summarizing this work?
Also, "Emlen's (1942) study of AMCRs nesting in a colony in Calif.
suggests that the social organization of AMCRs may differ in
different parts of the U.S. and Canada." (p. 180). Caffrey (1987)
studied western AMCRs and found that "' Pairs may breed (1)
unassisted, (2) w/ one or more yearling helpers, (3) with an adult
helper, or (4) with helpers of both age classes. Not all non-
breeding individuals involved with the breeding pair help, and a
behavioral continuum exists from remaining in the natal area and
interacting w/ the breeding pair, but providing no help, to providing
substantial amounts of assistance.'"
Kilham distinguishes between mobbing and attacks. "Mobbing is
when a number of crows caw together in seeming excitement as they
pursue, surround, or face either conspecifics in territorial
encounters or predators that are a special threat. ...mobbing may
take place in mid-fall with equal intensity...Attacks...are generally
made by only one or two crows and with fewer and lower
vocalizations." (p. 103)
Of course, as Dennis points out, "nonsense" mobbing was the wrong
term to use in my last post. Most of the time, mobbing is directed
towards a bona fide predator. Even if the predator is only a threat
to eggs or nestlings and the mobbing takes place in the fall, it can
still serve such purposes as group bond maintenance or teaching the
young about predators. (Lorenz has a good bit about this in his
book _On Aggression_.) But there are times when the behavior seems
especially curious. For example, Kilham has a list of published
reports of various corvids (including AMCRs) attacking piles of
feathers on the ground. On the extreme end, "...Lorenz (1970) noted
that Jackdaws would react to a single feather [by mobbing it]."
(p.103)
While Kilham lumps territorial encounters in with mobbing, I
would prefer to keep the two separate for the sake of clarity. Mike
Smith's question about birds of one pair chasing away the helpers
from another nest (hope I'm remembering it right) sounds like a
territorial affair. Kilham again: "NW Crows ... have at most a
single helper and... defend areas of 0.49 ha and do much of their
foraging outside of [those areas]. (Verbeek and Butler 1981) This
contrasts w/ the 90ha defended by crows in Fla. that had up to 5 or 6
helpers and did nearly all of their foraging w/in their territories."
(p. 47)
My apologies for the length of this post, but it's easier for me
to write everything on my mind. If anyone is interested in
crossposting to Birdchat perhaps they could edit it a bit (or
simply remove this paragraph) for ease of reading. This has been a
fun distraction from proposal writing, but I'm afraid I should get
back to work.


Peter Whitlock P.S. BTW, Ongoing controversy in
Raptor Resarch Center the national Raptor Research
Boise State University Foundation: are corvids raptors?
I'm not sure if the European RRF
has even included owls yet let
alone corvids.