The Mafia Hypothesis

tag:blogger.com,1999:blog-904085113272281323.post-70921250198545540202008-06-15T10:36:00.001-07:002008-06-15T11:22:15.064-07:00The Mafia Hypothesis<a href="http://bp2.blogger.com/_jNBj9pNnE4A/SFVTSapKuMI/AAAAAAAAA9c/TmVQVQhraUE/s1600-h/061408-272BL.jpg"><img id="BLOGGER_PHOTO_ID_5212163719605958850" style="DISPLAY: block; MARGIN: 0px auto 10px; CURSOR: hand; TEXT-ALIGN: center" alt="" src="http://bp2.blogger.com/_jNBj9pNnE4A/SFVTSapKuMI/AAAAAAAAA9c/TmVQVQhraUE/s400/061408-272BL.jpg" border="0" /></a> After leaving the mourning doves (previous post) and continuing on my way back to the Jeep, I heard the incessant cheeping a young bird makes when it wants to be fed. I quickly spotted the bird and noticed it was being fed by a white-crowned sparrow. The thing that didn't compute was that the young bird was significantly larger than the sparrow. After asking about it online I learned that the youngster is a Brown-headed Cowbird, a species known to deposit its eggs into the nests of other species. The BHC doesn't even bother to build a nest of its own, a habit it probably picked up in the days when it followed the bison herds around. A bird that needs to pick up and leave when the bison do has an advantage if it doesn't have to abandon its nest.As for why the victim of this scam doesn't simply eject the trespasser's egg, the so-called "<a href="http://en.wikipedia.org/wiki/Brood_parasite">Mafia Hypothesis</a>" (with studies backing it up) explains that a victim who doesn't comply ends up with a trashed nest and its own young killed by the adult cowbirds. Other studies show that over the course of the breeding season, the host birds usually still manage to raise their own young. (<a href="http://www.audubon.org/bird/research/">This Audubon page</a> has lots more info.)It's tempting to simply demonize the cowbird, and in fact over the last 25 years various government agencies have killed cowbirds in the belief that doing so will be good for other species (especially if that species is threatened or endangered). But cowbirds were doing their thing long before Europeans arrived. The greatest threat to songbird populations isn't predation by cowbirds (whose number also are declining), but almost certainly habitat destruction brought about by you-know-who. John W. Wallhttp://www.blogger.com/profile/03857907425270640823noreply@blogger.com