FOR RELEASE: April 3, 1997
Contact: Roger Segelken
Office: (607) 255-9736
Internet: [email protected]
Compuserve: Larry Bernard 72650,565
http://www.news.cornell.edu
ITHACA, N.Y. -- Much too common for some people's tastes and largely
neglected by ornithologists, the plain old American crow gets special
attention from one Cornell University researcher. Kevin J. McGowan and his
Cornell student helpers prepare their climbing gear each spring and ascend
to the tree-top nests where they tag young crows four weeks after they
hatch. As one result of his study, under way since 1989, hundreds of crows
around the Ithaca, N.Y., home of Cornell look like they're about to run a
marathon, with color- and letter-coded tags on their wings.
In a sense they are, although the birds' behavior when they return home is
of more interest to McGowan, the associate curator in the university's
Mammology and Ornithology Collections and a senior research associate in
the Section of Ecology and Systematics. He documents a none-too-common
inclination among birds of any kind: American crows (Corvus brachyrhynchos)
tend to hang around home for years to help their parents raise more crows.
"Most young birds leave their parents soon after leaving the nest --
probably because they're chased away -- and never see the parents again,"
McGowan explained. "But American crows never chase away their offspring.
Some crows stay with their parents for up to five years or longer. There's
a 6-year-old crow I marked during the first year of my study that's still
associated with its parents and younger siblings."
Such helping behavior is of particular interest to evolutionary biologists,
who try to understand why sexually mature animals sometimes forgo breeding
and instead help closely related kin. With each crow coded by year of
birth and parentage, McGowan can return to the ground with his binoculars
and watch the extended family dynamics.
"Crows almost never breed before they're 2 years old. Most don't leave
home to breed until age 4 or 5," he said. "While they wait for a breeding
opportunity, most crows help their parents raise young in several ways.
They help feed the incubating female, they feed the nestlings and
fledglings, they defend the nest and surrounding territory and they stand
guard over other family members while they forage."
With an average production of three fledgling crows per year, and the
likelihood that two will survive to the next breeding season, extended
families can grow quickly, McGowan said. "I've seen five adult crows at a
single nest at once, all with their heads in the nest feeding the young."
Extended families of 15 crows are not unusual. Of the 350 nests McGowan
has chronicled, 80 percent were attended by three or more adult crows.
Crows don't nest in eye-level birdhouses, so McGowan takes his eyes and
other tools of the trade where his subjects are -- usually in coniferous
trees as much as 120 feet off the ground. Crows tend to prefer evergreens,
he notes, because the foliage protects the early-spring nesters in the
weeks before deciduous trees leaf out, although crows sometimes nest in
deciduous trees anyway.
The scientist learned early on in his research project that a man climbing
trees or parked in a car with a spotting scope attracts unwanted attention,
even in a college town. Now he notifies police agencies before leaving the
ground, and he always asks permission of private property owners to tag
and observe their backyard crows.
His student assistants learn some elements of their unusual craft from
rock-climbing instructors in the university's Outdoor Education program.
McGowan, who also is an accredited climbing instructor, teaches the rest.
With a national reputation as one ornithologist who looks up to crows,
McGowan is often called on by news media to comment on apparent increases
in urban crow populations. His usual answer: There are probably no more
crows in North America than before; but they're learned to hang around town
to avoid hunters. McGowan grew up in Springfield, Ohio, the annual winter
roosting site for an estimated 150,000 crows.
And when the coded crows leave his adopted hometown of Ithaca, McGowan is
ready to track them. His observations help explain what some of the noisy
crow arguments are about. "If a female crow pairs with the male 'next
door,' that male crow can keep all the visiting crows away, including
visiting members of the female's family," McGowan reported. "But if a son
pairs with the girl next door, she can do little to chase away visiting
brothers-in-law. She may keep out her mate's sisters, but she can't drive
away the males."
The new home, when the crows finally leave, may be as near as 75 meters
from mom and dad, McGowan has learned. And he's had reports of his
Ithaca-tagged crows nesting in Geneva, N.Y., some 65 kilometers away.
That's about 40.365 miles. As the crow flies.
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