It's not just the US where dead birds have been falling from the sky lately.
Just before midnight Tuesday, as many as 100 dead jackdaws were found on a street in Falköping, a small town in west Sweden. The event has mystified locals. Veterinarians are investigating the cause of the deaths and the emergency services have cordoned off the area, reported local media.
The mass bird death in Sweden follows similar events in Arkansas, where thousands of red-winged blackbirds tumbled from the sky on New Year's Eve, and in Louisiana, where a mixed flock of hundreds of birds died at the start of this week.
"It's a historic event," said Christer Olofsson from the Swedish rescue services.
Dennis Kraft, chairman of the Swedish Ornithological Society, says that the most likely explanation for the mass death is that the jackdaws, which sleep in flocks, were disturbed during the night by some noise, potentially firecrackers. They probably got confused and flew into objects and each other, he says.
The affected bird species in Arkansas and Louisiana – mostly blackbirds and starlings – also sleep in large groups.
Five of the dead jackdaws in Falköping have been given to the Swedish National Veterinary Institute for autopsies. Olov Andersson, head of communication at the institute, told the Swedish news agency TT that bacterial and virological tests would be performed. They will also be tested for bird flu.
Mr. Kraft stressed that while mass death among flocks of migrating birds is not uncommon, the recent events in Sweden and in the US are unusual.
"Migrating birds often come across bad weather, lose their sense of orientation, hit cable lines or run out of energy. What's strange about these cases is that the birds were not out flying, but were sleeping. Something must have happened to make them leave their resting place," he says.
The harsh winter in the west of Sweden, with freezing temperatures, heavy snowfall, and a lack of food for birds, could also have contributed to weakening the jackdaws' immune systems, making them more susceptible to stress, added Kraft.
According to the rescue services, fireworks were fired in the area Tuesday night, which could potentially have scared the birds. But a new theory emerged today after a professional truck driver claimed that he drove over a large flock of jackdaws in Falköping on Tuesday night.
Mr. Olofsson told the Swedish tabloid Aftonbladet that the driver contacted the county veterinary after reading news reports about the dead jackdaws. But according to the police, Aftonbladet reported, the birds did not have external injuries.
The Swedish National Veterinary Institute's test results are expected by the start of next week. So far, there is no known link between the Arkansas, Louisiana, and Falköping incidents.