The birds, called grackles, were filmed at an ExxonMobil station in Houston by Christine Dobbyn, an anchor for ABC 13, who tweeted the footage on Feb. 2. She said she was getting gas and had seen lots of grackles at the station before, but never so many on the ground.
"Typically, they are up on the power lines," she said. "It was crazy that night. I ended up moving across the street to another gas station even though there were some there as well."
Dobbyn said she wasn't sure what the birds would do when she got out of the car, but eventually pumped the gas without any incident.
Dr. Kevin McGowan of the Cornell Lab of Ornithology told BuzzFeed News the birds should have been asleep in the trees, but were instead attracted to the bright lights of the gas station.
"Great-tailed grackles roost in large numbers regularly in parking lots across Texas," he said. "They should be asleep in trees, but these are attracted to the bright lights of the gas station. Perhaps they’re looking for food, but they might just be confused by the lights.
"Since this is post-sunset, the birds would typically be calmly roosting or sleeping, and naturally maintaining a certain spacing between individuals to avoid direct conflicts."
Yale Ornithology Professor Richard Prum added that the flock may have been disturbed from its original spot for the night and so moved to a well-lit spot.
"These birds are common grackles, which like to form large flocks in the winter. They gather in high concentrations at roosting (or sleeping) sites at night, usually in large trees. Sometimes those roosts can be in trees in urban areas or near areas that are well-lit. This provides good vantage to see predators like hawks and owls that might eat them.
"So what I think may have happened is that a night roost was disturbed so that the birds left the roost in the dark. They might flock away at this point looking for a safe space. That could lead to birds flying down to the well-lit gas station. They are obviously not feeding on anything, so there is no real reason to be there except that it is well-lit and not too disturbed. So better than all the alternatives at that moment."
As for the even spacing: "There is a social/spatial tension in any flock between trying to be away from the edges — where you are vulnerable to being picked off by predators — and being too close to other individuals who might harm you or get aggressive. The equilibrium or solution to these tensions is a uniform spacing like you see here. Nobody can peck anybody, but most birds are far from the fearful edges of the flock."
UCLA Ecology and Evolutionary Biology Professor Thomas Smith pointed out that we often see the even spacing behavior when birds are perched on a wire.
"They are maintaining individual space as a way of reducing intraspecific aggression; another reason might be to reduce contracting parasites/disease. This kind of individual space is seen in many species. Even primates like us — think of people on a train.
"I don’t know why they're on the ground; species such as these form communal roosts at night, but these are typically in trees — could they be confused by the bright lights of the gas station? They are not feeding… I don’t recall ever seeing this before."