Subject: [Tweeters] Research Article: Most birders love to hate Brown-headed
Date: Jun 22 19:19:16 2007
From: Bill Clemons - willclemons at yahoo.com


I got the following interesting article from the
University of Florida web site. I originally read it
in recent library obtained issues of:
* "Science News" (Mafia Cowbirds: Do they muscle
birds that don't play ball?; March 10, 2007)
* "New Scientist" (Raise my chick, or your eggs get
it; March 10, 2007),

Both magazines require a subscription to view on line,
so I traced the researchers to the University of
Florida.

Bill Clemons
SW of Portland in Mtn Park
Willclemons AT Yahoo dot com
*******************************************

University of Florida study first to document evidence
of ?mafia? behavior in cowbirds

Filed on Monday, March 5, 2007.

GAINESVILLE, Fla. ? ?The Sopranos? have some
competition ? brown-headed cowbirds.

Cowbirds have long been known to lay eggs in the nests
of other birds, which then raise the cowbirds? young
as their own.

Sneaky, perhaps, but not Scarface.

Now, however, a University of Florida study finds that
cowbirds actually ransack and destroy the nests of
warblers that don?t buy into the ruse and raise their
young.

Jeff Hoover, an avian ecologist at the Florida Museum
of Natural History, is the lead author on the first
study to document experimental evidence of this peeper
payback ? retaliation to encourage acceptance of
parasitic eggs.

Findings will be published online in the Proceedings
of the National Academy of Sciences March 5.

?It?s the female cowbirds who are running the mafia
racket at our study site,? said Hoover, who has a
joint appointment with the Illinois Natural History
Survey. ?Our study shows many of them returned and
ransacked the nest when we removed the parasitic egg.?

So-called ?brood parasitic birds? lay eggs in the
nests of host birds that raise the parasite?s
offspring, usually at the expense of some of their
own. The brown-headed cowbird parasitizes more than
100 host species, including many Neotropical migratory
birds such as warblers, tanagers and vireos.
Prothonotary warblers were used for this study because
they almost always accept cowbird eggs, Hoover said.

Hosts that use their beaks to grasp or puncture
parasitic eggs and remove them from the nest are
called ?ejecters.? ?Accepter? hosts raise parasitic
eggs.

?Retaliatory mafia behavior in cowbirds makes hosts?
acceptance of cowbird eggs a better proposition than
ejection,? Hoover said. ?The accepting warblers in our
study produced more of their own offspring, on
average, than those where we ejected cowbird eggs.?

Hosts may lose some, but not all, of their biological
offspring by accepting parasitism. The retaliatory
behavior of ransacking nests encourages warblers to
raise the cowbirds? offspring.

?We wanted to determine if the cowbirds were
responsible for nest predation after we removed
cowbird eggs from parasitized warbler nests,? Hoover
said. To test for this, Hoover collaborated with Scott
Robinson, Florida Museum Ordway eminent scholar and
natural history chair, to manipulate cowbird access to
warbler nests in the Cache River watershed of southern
Illinois. The researchers monitored 182
predator-proofed nests over four breeding seasons.

Hoover and Robinson found that warbler nests were
ransacked 56 percent of the time when researchers
experimentally removed the parasitic eggs and cowbirds
were allowed nest access, versus only 6 percent when
the cowbird eggs were accepted and cowbirds had nest
access. No nests were ransacked when researchers
removed cowbird eggs and cowbirds were denied nest
access. Together, these results implicate cowbirds and
provide evidence of mafia behavior.

?We also found evidence for ?farming? behavior,?
Hoover said. ?Cowbirds ?farm? a non-parasitized nest
by destroying its contents so that the host will build
another. The cowbird then syncs its egg laying with
the hosts? ?renest? attempt.?

Hoover found that warbler nests that were never
parasitized but that cowbirds had access to, were
ransacked 20 percent of the time. ?Cowbirds
parasitized 85 percent of the renests, which is strong
supporting evidence for both farming and mafia
behavior,? he said.

Hoover and Robinson?s results imply that cowbirds
actively monitor nests they parasitize ? which
supports the idea that cowbirds continue to visit
nests they have parasitized to see the results of
their handiwork.

Stephen Rothstein, a zoology professor at the
University of California in Santa Barbara, said other
studies have shown evidence contrary to mafia and
farming behaviors.

?Video surveillance would show the proportion of nest
predation attributable to cowbirds,? Rothstein said.
?The phenomenon may be perfectly true for these
warblers, but that doesn?t mean it holds true for
other species, especially those that aren?t nesting in
special circumstances. Nevertheless, this new study
may extend our knowledge of the extent to which
parasitic cowbirds may have evolved tactics to
facilitate their parasitism.?

Hoover said his future research includes video
surveillance of individually banded female cowbirds
and warbler nests.

Credits
Writer: DeLene Beeland
Media Contact: Paul Ramey, pramey at ufl.edu,
352-846-2000, ext. 218
Source:
Jeff Hoover, jhoover at flmnh.ufl.edu, 352-392-1721, ext.
511
Source:
Scott Robinson, srobinson at flmnh.ufl.edu, 352-392-1721,
ext. 509




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