Each morning here in inner city baltimore hundreds of black crows (ravens?) gather in the trees and on the building across the street at sunrise. They stay about an hour and then disappear until about 1 hour before dark, when they return to watch the sunset. Why would they do this and why here? While the trees are high and the view is nice there are higher, nicer, and more nature oriented spots close by. There doesn’t appear to be any unusual food source. Is there something sinister going on here? Are they watching my every move for their dark master or what?
This topic was, I’m sure, intended for our General Questions forum. Hang on a sec while I bounce it over there for ya.
And welcome to the Straight Dope forums, jmayocpa.
I saw a documentary about this but I can’t remember much. They did explain this point though. The crows scatter during the day alone or in twos to get food and do whatever crows do, and then gather at dark again to do their social stuff. They show flocks so huge it was amazing and they showed the efforts of some towns to get rid of them, without much luck.
And if anyone wants to give a similar answer re starlings (especially those who congregate in Minnesota pastures in the spring) I’d be much obliged.
Why would they move for an hour? I don’t know, but roosts will move about during their buildup, usually within a few blocks of where they ultimately settle down for the night. They’re generally not foraging at this time, and it could be just some jostling for position to the point that the whole roost flies up and settles, but in a bit of a different location than before. Otherwise, we really don’t know why they do this. It’s pretty cool to see, though. 
But now you’ve opened the floodgates, jmayocpa as this is a favored topic of mine. Uh-oh…here she goes again.
Caccamise, D. F., L. M. Reed, J. Romanowski, and P. C. Stouffer. 1997 Roosting behavior and group territoriality in American Crows . Auk 114(4): 628-637.
Crows that roost during the winter are made up of two types: migrant and non-migrant. American Crows (Corvus brachyrhynchos) are “partial migrants,” that is, the more northerly populations leave territories in the fall and spend the winter in southern grounds. By northerly, I mean REALLY north and the ones that breed in Baltimore are still there during the winter. Baltimore crows (like the ones in New Jersey, and, according to Kevin McGowen and June Chamberlain, pers. comm., the ones in New York and Massachusetts, respectively) maintain a territory year-round. These territorial crows join up with the roosting crows, most often at traditional roost sites that have been used for years and years. They don’t necessarily join the roost each night - sometimes they stay on their territories. They might go once every few days, or every night or never. This appears to be an individual choice situation. Regardless of when they go, they all show the same behavior at dawn: they haul feathered butt back to their territories to display and defend it. This is their prized possession, so to speak. Without a territory, you can’t reproduce and can’t maintain and continue a family. (Crows do live in family units, with offspring many times staying for years to help raise their younger siblings - it does take a village to raise a crow.) Territories also offer protection (where else does one know most intimately the lay of the land and thus escape route, for example). But territories can become depauperate in food resources and this is one reason why we think that territorial crows may use communal roosting sites. (Migrant crows, of course, don’t go to territories, but most likely hang around abundant food sources.)
Roosts are often formed not too far away from reliable food sources, such as landfills, farms, or perhaps places where human foods are readily available. Ephemeral roost, those that form for a few weeks then disappear, may be based on an ephemeral superabundant food source. Food likely plays a major reason for the location of winter roosts.
And, as sailor points out, roosts provide crows with a lot of other crows to pal around with. Crows are highly social creatures and when you watch the roost, you can see (and hear) them interacting with each other. They’ll have coordinated flights up into the air, the entire roost moving a block or so before settling down for a period of time. There are announcement calls done when crows arrive at the roost. They sit close to each other (but perhaps not close enough to provide any thermal advantage).
Roosts may provide protection against their primary predator, the Great Horned Owl (Bubo virginianus) - cue scary music. But the protection is incomplete as Great Horns have been known to come through crow roosts, grab a sleeping adult crow, and chop its head off. :eek: However, the sheer number of crows in the roost may give any individual crow an advantage to roosting alone, in an unknown area (this unknown area NOT being a territory).
There was a theory called the “information-centered hypothesis” that suggested more naive birds would follow more older, more knowledgable birds to find food sources. But this is not the case, at least with territorial crows. Kids tend to stay at home, far more often than adults. This potential source of information is unused by them.
So, how does a typical territorial crow spend 24 hours in Baltimore? She might wake up in a tree on the family territory, with some sibs or a parent nearby. Family members coming in from distant communal roosts join up and the family may caw and even do patrolling flights around the territory, announcing their presence. They’ll forage around, dunking food in available water. The family may mob a predator or an errant migrant who wandered into the territory. Some may later in the morning go off to a communal foraging site, such as a compost pile, landfill, or large corporate lawn (if not covered by snow). She might engage in play with younger sibs. In the mid-afternoon, she might decide to make her way to the communal foraging site again. Perhaps a young sib will follow. There, they’ll socialize and forage. The younger sib is likely to go home, but she may make her way to the communal roost. If Mom, Dad or another older sib was with her, and decided to go to the roost as well, it is highly unlikely that they will stay together at the roost. But at dawn, both of them will hightail it back (at the fastest, yet most energetically cost-effective speed possible) to spend the day with the family.
Crows are unusual in this behavior of maintaining a territory, yet using communal roosts in the winter. The payoff comes in the spring, when they have an established territory in which to raise their family and from which they are not likely to be displaced. A crow without a territory is a dead end.
Since you’re in Baltimore, I’d guess you are seeing a mixed flock of Blackbirds, i.e., some combination of European Starlings, Red Winged blackbirds, Brown-headed cowbirds, Common Grackles, possibly others.
There are several explanations for the behavior, ranging from food aquisition to predator avoidance.
I don’t anymore, but as a child I would spend hours reading in our pasture. Sometimes I’d end up surrounded by starlings or blackbirds (never crows) who would - all of a sudden, and without any vocalization - rise up and fly off with a great whooshing sound. They’d settle in nearby trees for a time, then come back to their original trees. (Imagine a film of a great school of fish suddenly and as one hanging a left, with sound effects, and you get the idea.)
I’ve always wondered why they did that.
brachyrhynchos, I enjoyed your post. Crows are always on the edge of my mind.
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Why would you think that? It’s pretty hard to mistake a murder of crows, or to mistake a flock of anything else for a murder of crows.
Great post, brachyrhynchos.
I’d tell you, but then I’d have to murder you.
please gentlefolk
have a care:rolleyes: