I take crows for granted. They’re always around, easy to see, and not doing anything particularly remarkable.
Then, every winter, they gather in huge roosts in town, and I get curious about them all over again.
Talk about good timing! I recently received an email ad from the Cornell Lab of Ornithology, inviting me to check out a new online course: “Anything but Common: The Hidden Life of the American Crow.”
I signed up immediately.
Ornithologists routinely gain insights about an entire species, based on their close examination and tracking of individual birds. It’s much harder to study birds’ social interactions with each other.
Crows make excellent study subjects in this regard. They are widespread, sociable and easily watchable.
Most importantly, they can be outfitted with wing tags that are readable at a distance. Thus, it is possible to identify each individual crow in a study group as they interact with each other.
Kevin McGowan, PhD, of Cornell University has been researching crows for decades.
The Cornell campus in Ithaca, New York, is an excellent location for his long-term studies. There are many year-round resident crows. There are annual winter migrants from Canada.
And there is no shortage of grad students, willing to peer at crows for frigid hours on end.
Perhaps his biggest discovery shouldn’t come as a surprise. Crow society is built around strong family bonds.
Crows mate for life, and their offspring hang around for several years to help take care of successive broods.
Male crows don’t typically breed until they’re 4 or 5 years old. Females will typically mate sooner. But no 1-year-old crow has ever been observed mating.
Small wonder that you often see groups of crows foraging together. There are brothers, sisters, aunts and uncles in the mix.
Crows guard each other, often posting a sentry while the group forages. Crows groom each other and tend to sick relatives.
Crows defend family territories year-round, though they will sometimes allow “outsiders” into their family circles.
Many species mate for life, but most are not strictly faithful. DNA evidence reveals that about 17m percent of crow chicks were not fathered by the mate.
The majority of interlopers were breeding males from a neighboring family, but some of the fraternization came from within the family group.
Still, 17 percent is not a huge percentage when compared to the high promiscuity rate among other species, so crows are relatively faithful.
Crows have always gathered in big winter roosts, but it’s only recently that they began moving into cities.
Until the 1970s, crows in the United States could be shot at any time, usually by people who considered them pests. There is a limited season in Maine.
Naturally, crows tended to avoid people. After federal protections were extended to crows in the early 1980s, they started to become more comfortable around humans.
By the mid-1980s, crows were roosting in cities, where winter nights could be a little warmer and human food was available. Some got good at foraging mall parking lots and poking holes in garbage bags.
City lights also offered protection from predators. Nocturnal vision in crows is no better than it is in humans. It’s hard enough to see trouble coming at night, but imagine getting flushed from your roost and having to land on a tree branch in darkness.
Interestingly, it turns out that junk food isn’t any better for crows than it is for people.
Comparisons of rural versus urban crows show that birds who shun city living are bigger, stronger and raise healthier chicks. Unfortunately, rural crows also suffer more predation, so it’s a tradeoff.
Countless crows in our downtown winter flocks aren’t from here. Many come down from Maine’s northern forest and Canada.
It appears that crows benefit from their interactions in the group, but there’s no real cohesion. Birds come and go.
Researchers discovered that local crows join in these mass gatherings, but then return to their own family territories at night. Young crows attend the party, but they’re home by curfew.
It’s likely that the youngsters are testing themselves within these gatherings. Competing for territory is dangerous, and sometimes fatal.
Through all the chasing and frolicking in the treetops, youngsters may be able to judge if they are strong enough to go off on their own and compete for a mate.
Indeed, crows have breeding options. They can search for unclaimed territories, challenge for claimed territories, try to join a neighboring family, or even stay in their own family and await opportunity.
Crows are complicated. And fun to watch.
