Murder on the Mississippi

My bike ride to and from work takes me along the Mississippi River near the University of Minnesota. This winter, each night as I've been riding home at or near dark there have been thousands and thousands of crows congregating in the trees on either side of the bike path. A murder of crows, as they are called (not quite as complimentary as a creche or huddle or parcel of penguins, or an ostentation of peacocks, or a convocation of eagles; but on a par with a scold of jays. So it goes. I like crows. They're smart and adaptable. I guess they haven't become as popular as warblers, though).

I've been wondering why there are so many at night, and basically none in the morning. So I decided to try to see what the experts think is going on. It turns out there are lots of theories. The Hotel Theory: The crows are simply congregating in the most favorable spot (protected from predators and the elements), and they don't mind doing it with a bunch of other birds. Like in a crowded hotel: every crow has the same needs being met at the same place, but no one is really interacting with anyone else.

The Wagon Train: The crows get some protection from predators by being in a large group, safety in numbers. Crows are most afraid of large owls, and sleeping with a bunch of other crows could afford some protection for an individual crow.

The Information Center: Groups form to get information about profitable foraging areas. 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.

Apparently these roosts are moving to the cities for a couple of reasons. Cities are warmer. And there are fewer owls in the city. So those are the explanations for my winter friends.