Arizona Game and Fish officials are a few steps closer to unraveling the mystery behind the death of 69 bats under an east-side bridge even as more are found dead.

Another dozen bats were found dead Tuesday and Wednesday under a bridge on East Speedway where the road crosses the Pantano Wash.

Rabies has been eliminated as a cause of death after three bats found under the bridge Monday morning tested negative for the disease, said Mark Hart, a spokesman for the Arizona Game and Fish Department. Test results came back Wednesday morning.

It could be a week or more before the department receives the results of testing for white-nose syndrome, but officials say it is unlikely Tucson bats acquired the 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.

"White-nose syndrome would have to jump two states to get to Arizona," Hart said.

Now Game and Fish officials are investigating whether the bat die-off was caused by a liquid de-icing agent that was sprayed on the bridge Dec. 23.

"We cannot say, at this time, pending a necropsy, that was the cause, but we are looking at it," Hart said. In the event the de-icing agent did cause the bat deaths, representatives from Game and Fish and the Tucson Department of Transportation will work together to reduce the impact on bat colonies during the de-icing process.

"Public safety is of paramount importance during inclement weather and for safety reason those bridges have to be de-iced periodically," he said. "Some bat deaths may be the result, but hopefully we can find ways to minimize that."

Jim Glock, director of the city's Transportation Department, said the liquid de-icing agent containing magnesium chloride is a "relatively benign" salt solution applied to the approximately 70 bridges in Tucson. The city has been using the de-icing agent for 20 years and this is the "first instance when anyone expressed concern about health hazards," Glock said. "We have other bridges that host bats as well. We're skeptical that it is the cause."

If Game and Fish finds magnesium chloride caused the deaths, "we can find a way to work it out," Glock said.

Initially Game and Fish investigators were perplexed that bats were roosting under the bridge so late in the year. Department officials contacted a University of Arizona bat expert who told them Mexican free-tailed bats typically migrate south to Mexico in October.

"We have since unearthed our own data from the late '90s and early 2000s which clearly shows a fluctuating year-round bat population under that bridge. We don't know why. They are migratory by nature," Hart said.

Based on records from a decade ago, Game and Fish counted as many as 750 bats living under the Speedway bridge in December.

Contact reporter Kimberly Matas at or at 573-4191.