Common cuckoos and oriental
cuckoos in eastern Russia appear to be expanding their breeding range into
western Alaska, where songbirds are naive to the cuckoos' wily ways,
researchers report. A new study suggests the North American birds could suffer
significant losses if cuckoos become established in Alaska.
Like brown-headed cowbirds,
cuckoos are "brood parasites,"
laying their eggs in
the nests of other species, said University of Illinois animal biology
professor Mark Hauber, who led the new research with Vladimir Dinets of the
University of Tennessee, Knoxville. Cuckoos time their egg-laying so that their
chicks will hatch first. The chicks then kick the other eggs out of the nest,
"thereby eliminating the entire reproductive success of their hosts,"
Hauber said.
"Brood parasitism is a rare
strategy among birds. Only about 1 percent of birds engage in it," he
said. "Obligate brood parasites do it always. They never build a nest,
they never incubate the eggs, they never feed their chicks. Instead, they sneak
their eggs into somebody else's nest, forcing the foster parent to take care of
the young."
Birdwatchers and ornithologists
occasionally report seeing oriental cuckoos and common cuckoos in Alaska, and
Alaskan natural history museums already contain a handful of cuckoo specimens
collected locally, Hauber said. These birds are likely traveling from sites in
Beringia, in eastern Russia.
"We don't have evidence of
them breeding in Alaska, but it's likely already occurring," Hauber said.
"We wanted to know whether the potential Alaskan hosts are ready for this
cuckoo invasion."
In the new study, researchers
tested whether more than a dozen Alaskan bird species had
evolved defenses to counter the cuckoos' parasitic ways. Such defenses are
common among bird species that frequently encounter brood parasites elsewhere.
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