Parasites benefit by sharing
Many brood parasites kill host nestlings, but some cowbirds do better with
hosts present
By Nick Atkinson

Although half the known brood parasites-birds that lay their eggs in other
bird's nests-set about murdering their nest mates just after hatching, some
parasitic species, such as Clamator cuckoos, Vidua finches, and Molothrus
cowbirds, seem to tolerate the presence of other nestlings. And new findings
published this week in Science show that brown-headed cowbird chicks
actually grow fastest when they share the nest.

"Our results contribute to a growing literature which suggests that
individuals can enjoy personal benefits from living in groups, even if they
are unrelated to the other group members," lead author Rebecca Kilner, at
the University of Cambridge, UK, told The Scientist.

Kilner, together with colleagues at the University of Auckland and the
University of California, Berkeley, first looked at the results of previous
research from a new angle, by asking how cowbird chicks fared in relation to
the number of host chicks present in the nest. They found that parasitic
cowbird chicks grew fastest when two host chicks also survived to fledging.
But how did sharing the nest-and food-lead to faster growth?

At their study site in Tompkins County, NY, the scientists manipulated the
broods of some 20 Eastern phoebe Sayornis phoebe pairs, parasitizing each
nest with a single brown-headed cowbird egg. All phoebe eggs were removed
from 10 of the nests, so that the cowbirds were reared alone. Eggs were also
removed from the other 10 nests, but two newly hatched phoebe chicks were
introduced in their place to provide the cowbirds with competition.

After just 8 days, cowbirds that shared a nest with phoebe chicks were on
average 14% heavier than those that did not. Video footage of the parents'
behavior showed why: adult phoebes returned to provision shared nests more
than twice as frequently, and the cowbird chick took more than half of the
food that they brought. As a result, cowbirds in shared nests actually
garnered more supplies than their solitary counterparts.

Read the rest at TheScientist
http://www.biomedcentral.com/news/20040806/02

Posted by
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