Check out @neogonzo’s addictive photostream for photos of local hawks in action, including this incredible shot of a merlin snatching a songbird in mid-air. Merlins were once colloquially called “pigeon hawks,” not because they hunt pigeons but because they somewhat resemble them. They’re actually a kind of falcon. Other raptors, like red-tailed hawks, do go after pigeons. I was walking up my street last week and came across a carpet of feathers on the sidewalk. I looked up at the top of a telephone pole to see a hawk looking straight down at me with a freshly killed pigeon in its talons.

In addition to pigeons, red-tailed hawks eat rodents, other small birds, snakes, and sometimes even bats or whatever other small creatures they can find. In cities, squirrels have become a bountiful source of food for raptors. Both squirrels and hawks are adapting to city life, undergoing a process that ecologists call synurbization (or, increasingly, synurbanization). As they do, the relationship between them is changing.

Squirrels flourish and multiply wherever humans tend to make a lot of extra food available, such as in city parks. Gray squirrels are so common in many American cities that we hardly notice them, but to many visitors from abroad, they are exotic. In Boston, it’s not uncommon to spot a cluster of excited Europeans, cameras in hand, encircling a bewildered squirrel.

When there are a lot of squirrels living in an environment, they seem to become less wary, possibly because there are more squirrels nearby to warn of approaching danger. On the other hand, they become more aggressive towards other squirrels, since there are many squirrels competing for food.

While tourists find squirrels quite delightful, raptors find them quite edible. The presence of this seemingly bottomless food source is affecting raptor behavior in urban environments. Red-tailed hawks’ preferred hunting strategy is to find a perch somewhere with a good view and wait for prey to appear before swooping down to capture it. This works best where there are trees or other high places over mixed ground cover. Researchers have found that replacing environments like these with business parks and housing developments, which in the U.S. tend to be surrounded by lawns, displaces hawks and other raptors.

In some parts of the country, more and more red-tailed hawks are nesting in urban environments. As they get used to being around humans, the hawks sometimes start behaving in unusual ways, such as supplementing the perch-and-swoop strategy with other ways of capturing meals. They will chase squirrels into hollows in trees and try to fish them out with their beaks, or tear apart nests to try to shake the squirrels out. Since there are a lot of hawks around here, I’m going to keep an eye out for this.