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A gathering of crows

January 14, 2009
By Richard Gast, Franklin County Cornell Cooperative Extension

"Birds of a feather." I can still remember my Aunt Blanche using the

term as an expression of displeasure and perhaps concern about the

company I was keeping. I was just 11 or 12 years old and,

along with several friends, was cultivating a growing interest in

blues and rock music. She was convinced that such an interest could

only lead to trouble.

It's a very old proverb, actually. It dates back to the 16th

century and, although it was used even then in alluding to people

with similar interests, motivation, loyalties or like minds, it is

also a straightforward reference to the fact that birds congregate

with others of their own species.

So, when I'm asked, as I have often been in recent weeks, about the numbers of crows that people have been observing in the village of Malone, I am inclined to answer

simply that "birds of a feather flock together," before explaining

that almost all birds gather to roost, and that some roost in much

larger groups than others.

Roosting is a period of inactivity for birds, a time of rest and/or

sleeping. During the breeding season, birds are likely to roost

individually or in small groups. But when winter arrives, well, birds

of a feather tend to spend their nights at larger, communal roosting

sites. This is almost certainly because they are particularly

vulnerable in winter, as food, and shelter from predators and the cold, become harder and harder to find.

We often take pleasure in seeing chickadees, finches or juncos

congregating at our winter feeders. These birds are here all year

round, but because they remain dispersed across the countryside

throughout the breeding season and are not dependent upon our feeders

for their survival, we are far less aware of their presence and of

their overall populations.

It is no different with crows. Their presence, especially in and

around populated areas, becomes more apparent as the communal

roosting season begins, usually in late fall. It isn't until the

winter really sets in, however, that they gather together to endure

the frigid nights in groups of anywhere from several hundred to

several thousand birds; assemblages so large that we can't help but take notice.

In fact, in urban areas, roosts of tens of thousands of crows are not

uncommon. For example, a roost that has varied from about 25 to 60

thousand crows has been documented for more than a decade in the town of Auburn in New York's Finger Lakes region. Incredibly

though, that's nothing. Roosts of hundreds of thousands of crows have been documented in several Midwestern cities, and one roost at a site in Fort Cobb, Okla., was estimated at two million crows.

No one is absolutely certain as to why crows gather like this, but

there are probably a number of reasons. First is the simple fact that

there is safety in numbers. Kevin J. McGowan, an ornithologist

and member of the Department of Natural Resources at Cornell

University who has been researching the social behaviors of crows in

the Ithaca area for decades, calls this the "wagon train analogy."

"Crows are most afraid of large owls, and sleeping with a

bunch of other crows could afford some protection for an individual

crow," McGowan said. "Before heading to roost, crows will congregate in some area away from the final roosting site, usually an hour or two before complete darkness. Here the crows spend a lot of time calling, chasing and fighting. Right at dark, the main body of the group will move toward the final roosting spot. Sometimes this final movement is relatively quiet, but usually it is still quite noisy."

McGowan added that he has "seen crows coming together from several separate congregation areas, heading to one final staging area where they all coalesce, then everyone heads to the final roost. The final roost can be a cohesive group in a single woodlot, or it can be rather diffusely spread out over quite a wide area of suitable trees."

He suggests that there may be several other reasons for crows

congregating as they do. One theory is that the birds are utilizing

locations that provide "protection from predators, protection from

the elements, the only trees suitable for roosting, etc." He compares

this to people at a crowded hotel where "everyone has the same

needs being met at the same place, but no one is really interacting

with anyone else."

Food may be a big factor as well. According to McGowan, it may be

that "roosts congregate around a large, non-defendable, reliable food

source so first thing and last thing in the day, food is available. It need not be the best food, but it is something to eat to get them going."

Another of McGowan's theories is that gathering allows individual

birds that are inexperienced or for some other reason have not been

very successful at locating forage, to "watch for other individuals

coming in to the roost that look fat and happy, that obviously found

some rich source of food. Then the hungry individual can follow

them out first thing in the morning to the good food source."

It's fairly easy to see how the village of Malone, which is surrounded by miles of extremely productive cropland, would give these birds, um, something to crow about. They are able to readily leave their collective roosting site during the day to forage in nearby fields, along roads and in yards, returning in the evening to spend the night in the relative warmth and safety of the "wagon train."

In spring, these large roosts will begin to break up as mated pairs

return to their home terrain. Unmated birds may continue to use the roost for several more weeks.

One last thing. Some of the folks I've talked with recently have

expressed fears that crows may transmit West Nile virus to people and pets. Perhaps this is because crows are especially susceptible to

West Nile virus infection and for years have been considered an

indicator species by health officials monitoring movement of the

disease. In fact, there is no evidence that West Nile virus can

spread directly from birds to humans. West Nile virus is spread by the bite of an infected mosquito.



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