>---------- Forwarded message ----------
>Date: Fri, 26 May 1995 18:33:42 -0400
>From: Byron Butler (GD 1995) <bbutler at MINERVA.CIS.YALE.EDU>
>To: Multiple recipients of list BIRDCHAT <BIRDCHAT at LISTSERV.ARIZONA.EDU>
>Subject: Re: Why do Am. Crows chase hawks?
>
>From: Byron K. Butler, Guilford, CT
>
>The behavior described, crows chasing a Red-tailed Hawk, is known as
>mobbing. Mobbing occurs when smaller birds ganging up on a
>bigger bird to drive it away from an area. This can be because the
>larger bird is a threat in some way to the smaller birds, or because
>the smaller birds are extremely territorial. Smaller birds are able to
>go on the offensive against larger birds in this manner because, as a
>rule, smaller species are more manuverable.
>
>But what goes around comes around as they say. Birders can frequently
>witness crows mobbing Red-tails one minute, then see mockingbirds mobbing
>crows the next. The little Northern Mockingbird is extremely territorial
>and will attack anything in its territory including larger birds, cats,
>dogs, and even humans. Red-tailed Hawks will mob larger birds, too. One
>of my most memorable field experinces occurred about a decade ago in the
>Rocky Mountains of Montana. I watched a red-tail mob a Golden Eagle
>in open airspace by rising well above the eagle then diving down on it,
>the eagle simply flew a steady course. After several dives the hawk rose
>again, but on its next dive the eagle rolled over and dramatically shot
>out its talons as the hawk neared. Perhaps I'm being a bit
>anthropomorphic, but it appeared to me that the hawk was rather surprised
>by this manuver and put on the breaks stopping just short of the eagle's
>feet. The hawk then broke off the pursuit and left the area. The
>eagle casually rolled back over, completing a 360, and flew away just as
>easily as it had flown in - seemingly without a care.
>
>Contact and alarm calls can be used to recuit other species. Small
>passerines often do this in wooded areas to mob owls. Owls will take
>small birds as prey so here mobbing can be dangerous, vegetation
>structure allows escape routes for the smaller birds in the event the
>owl decides to pursue one of them. I have a 30 minute continuous tape of
>the Eastern Screech Owl call and have hidden it in the brush while I hid
>about 30 feet away. This tape has resulted in 20+ species of birds
>comming in to mob the owl at one time. The birds do not have to actually
>see and owl, they key right in on the location of the tape and mob in the
>general vicinity of the sound with what appears to me as the same
>behavior displayed when a real owl is present. Although I've never tried
>it, I understand that using an owl decoy or a stuffed owl in conjunction
>with the tape excites the mobbing species more resulting in even greater
>aggressive behavior. When we "spish" for birds we are simulating these
>alarm calls and are in effect recruiting a mobbing flock.

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