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Urban phenology: it's party time for the crows
During a recent late-afternoon visit to the Mississippi Market co-op on West Seventh in St. Paul, I noticed that the stand of tall trees between the co-op's parking lot and the river appeared to be a crow gathering spot.
You've probably also noticed the beginnings of this annual crow flocking ritual. In late fall and through the winter, crows flock at dusk to large, raucous gatherings in tree tops, then move on to communal roosts for the night, which often grow to include thousands of crows, augmented by birds whose daytime feeding grounds may lie 12-13 miles away (a study in Ithaca, NY, traced them out 20 km from the communal roosting sites), and by seasonal migrants from farther north. According to experts at Cornell University, we don't really know why they do this, but some theories include safety in numbers (especially from great horned owls) and to share information about food sources.
Sorry we don't have a photo for you, but here's a link to Birdchick's site, where she posted some nice photos, thoughtful commentary, and even some video from last January at the somewhat famous crow roost around Loring Park.
If it seems that crows favor cities, you're right. On Cornell University's crow FAQ page , the following explanations are offered:
- In 1972, crows came under the protection of the Federal Migratory Bird Treaty Act of 1918; this means you can't just shoot them anytime and anywhere. This has made crows less afraid of humans.
- Hunting is prohibited within city limits.
- Cities are warmer than rural areas.
- Great horned owl populations are lower in the city. "Next to people with guns, Great Horned Owls pose the largest danger to an adult crow," say the folks at Cornell.
- Some of the largest trees, the ones that are best for large roosts, are located in cities. Surprised? It's because while our city fathers and mothers were planting trees, rural trees were being harvested for lumber or cleared for farming.
As spring approaches, this behavior ends as crows separate into small family groups to begin nesting.