The skies above Pittsburgh are getting darker, and it’s not because of stormy weather. Look up around dusk this fall and you may see flocks of black birds, preparing for their annual trip south through Pittsburgh.
While driving around the city, Good Question! listener Stephanie Burrows of Whitehall was surprised at the number of black birds perching in trees en masse.
“It was at least hundreds, if not maybe thousands,” Burrows said. “So I was wondering: Why do they do that, and what is bringing them there every night?”
Burrows said she’s seen the birds all around the city, but particularly in the East End, in Oakland, and near the Hill District. She described them as large black birds moving in tandem and crowding onto structures and branches.
National Aviary Ornithologist Bob Mulvihill said what Burrows is probably seeing is crows, and a mix of smaller species. Around this time of year, the birds are displaying a migratory behavior called staging.
“Most migratory birds are gluttonous right now,” Mulvihill said. “They’re just feeding and feeding and feeding to get fat. To, essentially, fill the gas tank so they can take their trip south.”
Within the mix of smaller dark-feathered birds, Mulvihill said, are likely European starlings, common grackles and redwing blackbirds. They can also be distinguished by their beaks and tail sizes. European starlings are a non-native species to the U.S., and create impressive sky formations, called murmurations. Mulvihill likened them to the synchronized movements of schools of fish.
“They mass and they create this shape-shifting flock behavior that is really just spectacular to see,” he said.
Grackles have long tails and are very noisy. Red winged blackbirds have a distinct red and yellow spot on their side. They gather in the hundreds of thousands and are omnivorous, eating insects, worms, and human food scraps.
“They’re very opportunistic,” Mulvihill said. “They don’t turn their beak up at anything.”
When they’re together, the migrating birds communicate with the local species and exchange information about food and the environment, like an avian Yelp.
“It’s kind of like the out-of-towners come in and say, ‘hey, where’s a good place to eat around here?’”
Crows are the larger birds Pittsburghers see this time of year. They prefer to roost in trees near low-level artificial light. Mulvihill said they likely choose spots that are warmer, which could explain why they flock to the densely-populated East End, where there’s human-generated heat. The smaller birds often rest near the water, beside reeds and cattails.
Sticking together provides protection. The birds’ biggest predator, the great horned owl, is less likely to attack a group. The Pittsburgh area sustains a fair number of these owls, which are nocturnal hunters and love to eat crows. To throw them off guard, Mulvihill said, crows often mob owls during the daytime.
“So if you ever hear crows going nuts in the daytime ... they’ve found an owl and they’re just making its life miserable,” he said.
Crows’ fear of owls is one reason why people put up likenesses of the wide-eyed bird, but Mulvihill said unless those figures are animatronic, they’re unlikely to deter crows. At the University of Pittsburgh, he advised maintenance crews to create a remix of owl sounds to distract crows from making a mess on buildings and sidewalks. But, he said, the audio would have to be random and sound natural because these crows are smart. If the mixed species of starlings, blackbirds and grackles are considered average students, then the crows are at the top of their class.
“They have a very high neuronal density. A lot of stuff is going on in their brains, a lot of connections,” Mulvihill said.
This is what makes them so adaptable. Just a few decades ago, he said, crows were rare in the Pittsburgh area. But now, city living suits them. Pittsburgh is less polluted than in the past, but the recent influx is also due to the bird’s versatility. Ornithologists refer to this as the urban crow phenomenon.
“They have seen an opportunity in the urban landscape and seized on it and done really well solving all the problems of how to live in the city,” Mulvihill said. “Now we think they’re everywhere.”