By Nancy Olmstead
I stopped running because I was surrounded by hundreds of crows. It was dusk on the bike path along Lake Champlain. Great masses of crows were flying in from the east to roost on the cottonwood trees along the shore. They fed on sumac fruits along the train track; they mobbed the tree-tops and hop-flew from one twig to the next; they perched all over the bare branches of the trees. In the light of the setting sun, their black feathers shone glossy and strong. More kept arriving almost continuously from the east, flying in over the barge canal. As they flew in they gave these weird, multiple-part calls, not at all like the usual “caw-cAW-CAW!” What were they saying and why were they gathering here?
Crows get a bad rap: harbingers of death, marauding pranksters, cunning gang of villains. But they are ubiquitous, precocious, smart, social, and we get to see them. So many other birds skulk in the bushes, maddeningly out of sight. Crows are in your face, and never more so than when they are forming a winter roost. I’ve seen two of these big, dense roosts lately: the one on the Burlington bike path and one in downtown Portland, Maine, in a couple of scrawny trees sandwiched between a large parking garage and one of the city’s busiest streets. The city lights and traffic created a strange juxtaposition with the murmur of this great mass of wild creatures.
Ornithologists have several hypotheses for why crows roost together in fall and winter (during the breeding season, crows do not form large roosts). The idea that makes the most sense to me is that crows seek safety in numbers. Great horned owls are a crow’s night-time enemy; if an individual crow joins a large roost, it reduces its risk of becoming owl lunch. Fear of predation could also explain why roosting crows jostle for position – no one wants to be sitting exposed at the edge of the pack.
Another idea is that roosts form near big food sources, so it’s the location (as in, next to a landfill), rather than the company, that is the attraction. And yet another hypothesis is that crows can somehow sneakily glean information from one another, so that birds who didn’t find a lot of food today can check out everyone else, see who looks fat, and follow those birds to food in the morning. But that wouldn’t explain why the fat ones would come to roosts, unless sometimes they are the hungry ones and it all sorts out in the long run. And of course, these hypotheses aren’t mutually exclusive. It could be a way of avoiding predation and gleaning information.
It’s hard to study crows because they are crafty, wary, difficult to catch. Without a way to tell individuals apart (like colored leg bands), scientists can’t easily learn about crow behavior. But part of me is content with the mystery. There’s something special about not knowing. In a world where our facts and figures are only a touch-screen away, the noisy, hectic crow roost reminds me to stop running and appreciate the beautiful unknown.
Nancy Olmstead, a master’s candidate in the Field Naturalist Program, is wrapping up a natural community assessment of 24,000 acres of Maine’s Baxter State Park. When she’s not running with crows, she’s scheming about how to create her dream job back home in Maine.