Re: Why mob a Purple Martin?

Hello, BirdChatters.
 
Rick Wright wrote:
 
> I've posted at http://birdaz.com/blog a couple of lackluster photos
> of Purple Martins mobbed by House Finches. This is a very common
> behavior here in the southwest, but I can't figure out why they would
> do it: what, besides the fairly remote potential for nest site competition,
> could move the finches to such enmity? Somebody out there must
> know the answer!
 
I don't know the answer.
 
In thinking about the question, though, I realized, once again, how we birders are so adept at "thinking inside the box," if you will. Well, at least *I* do a good job of that.
 
My first reaction was to think of an episode, several years ago, in which I was tricked into believing that a Purple Martin was a falcon. It was a bird on apparent diurnal migration, well out of range and way out of habitat, and it just looked like a little falcon powering toward the birding group I was in. Note, by the way, that "swallows (especially Purple Martin) are very similar in shape to Merlin and can easily be mistaken," according to The Sibley Guide (p. 128). My think-inside-the-box reaction to Rick's question was something along the lines of, "Well, Purple Martins can be falconlike...and mobbing is directed toward falcons and other raptors...so that must be the explanation."
 
The problem, I think, is the assumption that mobbing (Rick's "enmity") ought to be directed against big, mean birds like falcons, hawks, crows, and the like. Yes, we're trained to think that way (well, I've trained myself to think that way), and we somehow turn a blind eye on all the other instances of interspecific aggression out there. Such instances are ubiquitous, once you start to pay attention.
 
Yesterday, for example, I made an effort to pay attention and I noticed Bushtit-on-Black-headed Grosbeak violence, American Robin-on-House Finch violence, and Blue-gray Gnatcatcher-on-Bushtit violence--all during the course of 1 hour of observation. Meanwhile, an aerial aggregation of dozens of White-throated Swifts, 2 American Kestrels, 2 Red-tailed Hawks, and 1 Peregrine Falcon was perfectly well behaved.
 
Here's a recent account of how two Spotted Towhees totally whaled on a poor Northern Waterthrush:
 
http://groups.google.com/group/cobirds/browse_thread/thread/3660d822d246d80d/55ed21c7999d04c0?lnk=gst&q=tedfloyd#55ed21c7999d04c0
 
Because we've been conditioned to look for a particular sort of "mobbing behavior" (kingbirds chasing crows, blackbirds divebombing hawks, etc.), we're good at noticing it. Sure, that happens a lot. But I think bird-on-bird violence--for example, House Finches on Purple Martins--is a pervasive, "broadband" phenomenon.
 
Ted Floyd
tedfloyd57@...
Lafayette, Boulder County, Colorado
 
-------------------------------
 
Ted Floyd
Editor, Birding
 
-------------------------------
 
Please support the American Birding Association: Click on http://www.goodsearch.com/?charityid=884482 to search the internet.
 
Every search provides support to the ABA's programs in Education, Conservation, and Publications.
 
Please visit the website of the American Birding Association: http://www.aba.org 
_________________________________________________________________
Windows Live™ SkyDrive™: Get 25 GB of free online storage.
http://windowslive.com/online/skydrive?ocid=TXT_TAGLM_WL_SD_25GB_062009
BirdChat Guidelines: http://www.ksu.edu/audubon/chatguidelines.html
Archives: http://listserv.arizona.edu/archives/birdchat.html