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Re: Cowbirds and such



There is one problem with the following bison herds explanation. There are
other species of parasitic cowbirds living outside of the range of bison.
In Argentina there is a species of cowbird which lays its eggs only in the
nest of another, non-parasitic species of cowbird. This is thought to be a
"primitive" species from which the habit of laying eggs in a variety of
species evolved. Many species lay eggs in the nests of other individuals of
their species. There are many other species of brood parasites, of which the
European Cuckoo is the best known example..hence the word "cuckolded"
There is little question that Brown-headed Cowbirds have become much more
abundant in the east, that they like short grass & the company of large
grazing animals. Harold Mayfield has speculated that the recent in expansion
in range & abundance of cowbirds is because of the increase in lawns, golf
courses & c, allowing for good habitat for cowbirds in close proximity to
the nests of woodland species that formerly had very limited, or no exposure
to cowbird depredation.

-- Helmut C. Mueller  Ph.D

 Professor Emeritus
 Dept. of Biology & Curriculum in Ecology
 University of North Carolina
 Coker Hall CB# 3280
 Chapel Hill, NC 27599-3280
 Phone: 919-942-4937

 Permanent email address: hmueller@email.unc.edu




> From: Alex Netherton <alexnetherton@charter.net>
> Date: Thu, 08 May 2003 23:41:57 -0400
> To: Carolina Birds <carolinabirds@duke.edu>
> Subject: Cowbirds and such
> 
> Hi folks. I have been amused by the "smoke" war (no flames yet) about
> Cowbirds; I daresay I might remove a cowbird egg from a Bluebird nest,
> maybe even a nestling. Some might remember the story of "The Last
> Bluebird", which died in our clothesline post over 40 years ago and I
> did not see it, and thought I would never in this life see one. A pair
> is again nesting in a box in our front yard. There has also been a
> female Cowbird hanging around. Maybe ought to go check on something,
> just to make sure... Hmmmmm.
> Cowbirds are thought to have evolved in the Great Plains, following the
> great Buffalo herds, their main source of food, or rather, source of
> scaring up their food. With this mobile food source, it makes sense that
> any female that might have had a tendency to "dump" her eggs in a
> nother's nest would have left far more of her genes, and the tendency to
> "dump" along with them.
> There are other nest parasites in the Eastern US, but I don't think any
> are "obligate", that is, having to do it. (Cowbirds have no ability to
> make a nest or care for young.)
> With the breaking up of the Eastern forest, the turning of much of the
> land int pasture, they spread into this "new" habitat, and into bird
> populations which had no resistance to them.
> Shame; they are right interesting, but I don't think I want one in my
> front yard...
> Trees are full of warblers here, but darn if I can ID any of them.
> 
> -- 
> Alex Netherton
> The Appalachian Naturalist
> Asheville, NC
> alex@alexnetherton.com
> http://alexnetherton.com
> 
> 
>