Almost 70 bats were found dead Monday morning along an east-side walking path - a mystery that has Arizona Game and Fish officials searching for answers.
One possibility: unseasonably warm Tucson temperatures.
"The whole situation is somewhat of a mystery in part because the bats are Mexican free-tailed and should have been long gone by now," said Mark Hart, a spokesman for the Arizona Game and Fish Department. "They should have migrated to Mexico two months ago. What they were doing there was unclear. Temperatures have been a little warmer. They may have overstayed their visit."
Early Monday morning, Grant Hawman was walking his border collie, Zellie, along the path that runs under a bridge on East Speedway where the road crosses the Pantano Wash when he discovered dozens of bat carcasses strewn across the walking path.
"I hike and bike a lot and go under a lot of bridges, and I've never seen anything like it," Hawman said.
Seven of the bats found on the ground were alive. All of the dead bats and three live ones were sent to the Arizona Department of Health Services laboratory in Phoenix for rabies testing. Four remaining live bats were sent to a U.S. Geological Survey laboratory, where they will be tested for white-nose syndrome, a fungal infection first documented in upstate New York in 2006. The syndrome has killed millions of bats in the East and has spread as far west as Oklahoma. The infection does not affect humans, Hart said.
Investigators could find no evidence of foul play in the death of the bats. Game and Fish officials used metal detectors to look for spent ammunition, but they found no sign that the bats had been shot. It's unlikely that the bats were sickened by chemical perhaps used in surfacing or de-icing the bridge, Hart said. And the chances are equally remote that almost 70 bats would simultaneously die of rabies.
The more likely hypothesis is that the bats died from the cold after failing to migrate south to Central America and Mexico for the winter.
Hart said bats are still roosting under the bridge, and he has a warning for recreationists who may find one of the mammals on the ground:
"Don't handle or come near a bat that appears to be either dead or injured," he said. "That would hold true of a lot of different species of wildlife, but especially bats, because they do carry rabies."
Contact reporter Kimberly Matas at firstname.lastname@example.org or at 573-4191.