A jackdaw. (Photo by foxypar4 via Flickr)

Between 50 and 100 jackdaws, dark-feathered birds in the crow family, died in the southern Swedish town of Falkoeping, police officials say.

Many of the fallen birds showed no outward signs of trauma. However, a few appeared to have been hit by cars.

Thousands of blackbirds had died in Arkansas on New Year's Eve. Preliminary reports suggest the Arkansas birds died from massive trauma that included blood clots and internal bleeding.

"The [Arkansas] birds obviously hit something very hard and had hemorrhages," said Karen Rowe, an ornithologist for the Arkansas Game and Fish Commission.

Officials said Wendesday the source of trauma for the blackbirds was likely New Year's Eve fireworks.

In Falkoeping, there were no reports of storms or fireworks at the time of the jackdaws' death. Veterinary officials said there could be a number of reasons, including poisoning or disease. A truck driver also came forward saying he was responsible. But the driver's account does not explain the majority of dead birds reported by police with no outward signs of trauma.

The jackdaws will need to be thoroughly examined before an official cause of death can be determined.