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How can you tell a male crow from a female? How many different calls do crows make?
Why do crows hate owls? Do crows make good pets? Why do crows congregate in large numbers to sleep? One of the great animal phenomena of the world is the congregation of large numbers of birds into a single group to sleep together. Such communal sleeping groups are known as "roosts.
Most do this only outside of the breeding season. Some species, like starlings, also forage together in great numbers. Others, such as herons, disperse out from these gathering areas to forage singly.
For crows, roosts are primarily a fall and winter thing. Numbers peak in winter and then decrease near the beginning of the breeding season usually in March.
It appears that all crows will join winter roosts, even territorial breeding crows. Most breeding crows sleep on their territories during the breeding season, but join the roosts afterward. Just why birds congregate in such large groups is still largely a matter of conjecture. A number of hypotheses have been constructed to explain it: One is that the birds simply are congregating in the most favorable spot protection from predators, protection from the elements, the only trees suitable for roosting, etc.
This idea is kind of analogous to a crowded hotel: Another idea is that the birds get some protection from predators by being in a large group. This is the "wagontrain" analogy: Crows are most afraid of large owls, and sleeping with a bunch of other crows could afford some protection for an individual crow.
Another idea is the information center hypothesis, where information about profitable foraging areas is transmitted. The idea is that an individual that did poorly foraging for itself on one day can 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 either backtrack the happy ones' flight paths, or follow them out first thing in the morning to the good food source. Another food related idea is the patch-sitting hypothesis.
This theory is similar to the first one mentioned, in 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.
The birds can then disperse out and do whatever they need to do, having had some kind of breakfast first. Roosts, then, will form in suitable roosting habitat near these large food sources. For crows, such abundant sources might be landfills, commercial composting facilities, or certain types of agricultural fields.
Crows have been congregating in large roosts in the fall and winter for as long as there have been crows.Fulfillment by Amazon (FBA) is a service we offer sellers that lets them store their products in Amazon's fulfillment centers, and we directly pack, ship, and provide customer service for these products.
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