[CT Birds] Bird Thugs

Scott Kruitbosch kbosch at gmail.com
Thu Mar 22 16:41:52 EDT 2007

I would love to know how big that sample size was - "clearly it is
retaliation" is an assumption without proof, unless I'm missing something.
The researchers even stated they did not witness the cowbirds destroy the
nest/eggs. It could have been a coincidence with many other species of
birds, or even mammals/snakes, committing the acts. Or maybe the act of
removing the cowbird eggs from those nests by researchers caused something
else. Catbirds recognize the eggs, but they do not suffer this same fate,
correct? In my opinion, I think the simplest answer of the fact the parents
do not recognize the foreign egg(s) still sounds good - but I'd love to hear
other thoughts.

And speaking of Bird Thugs - the top thugs, European Starlings, have an even
bigger bully here - Monk Parakeets. One Starling was trying to eat my suet
today while a Parakeet was trying to climb onto the cage. It decided it
couldn't fit on the cage with the Starling, and it couldn't push it off very
well, so it bit down on the Starling's leg as it held onto the cage. He flew
off as fast as he could. It's been a week full of pests in addition to the

Scott Kruitbosch

On 3/22/07, Craig Repasz <crepasz at hotmail.com> wrote:
> Bird Thugs
> >From "Science News" March 10, 2007 vol. 171
> We all know that Brown Headed Cowbirds parasitize other birds by laying
> their own eggs into the nests. They then fly off leaving their eggs to be
> incubated by the parent couple. The fledgling cowbirds usually grow faster
> and out feed the other chicks. This leaves the parents bird with a big
> demanding mouth to feed often at the expense of their own brood. One may
> wonder why the parent birds do not toss the foreign egg out of the nest.
> Researchers of the Illinois Natural History Survey in Champaign have
> concluded that Brown Headed Cowbirds will retaliate against a nest if their
> efforts to parasitize have been undermined.
> Researchers have removed the cowbird eggs from warbler nests to find that
> more of the warbler eggs were later smashed or carried off (56% destruction)
> compared to warbler nests that left cowbird eggs in place (6% destruction.).
> Clearly it is retaliation.
> Oddly enough the researchers did not witness the cowbirds in their
> destructive acts.
> Nests that had cowbird eggs removed produced 40% as many warblers as nests
> that kept the cowbird eggs. There is a degree of starvation of warbler
> chicks in nests that host an interloper, however, nesting success is still
> higher then nests that were destroyed by retaliating cowbirds.
> Paper to be released in "Proceedings of the National Academy of Sciences."
> Personal note: The warblers are forced to take the lesser of two evils.
> The real problem may be forest de- fragmentation as a result of urban sprawl
> that creates both the grass-forest border habitat that is ideal for cowbirds
> and splinters the warbler's breeding habitat.
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Scott Kruitbosch
Stratford, CT
kbosch at gmail.com

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