(CNN) -- The U.S. Fish and Wildlife Service has begun the first steps toward determining whether two species of cave-dwelling bats warrant federal protection under the Endangered Species Act.
The service announced Tuesday that a more thorough investigation into the status of eastern small-footed and northern long-eared species of bats will be conducted to determine whether the species can be added to the federal list of endangered and threatened wildlife.
Eastern small-footed bats are more common in the northern than in the southern United States while the northern long-eared bats occur across the eastern and north-central United States and throughout the Canadian provinces, officials said in a news statement.
The existence of the two species has been threatened by several factors, including continued destruction of their natural habitats and disturbance of hibernation areas, officials said in a statement on the service's website.
But the most deadly threat is a deadly fungal disease that has killed more than a million cave-dwelling bats since its discovery in 2006, officials said.
"White-nose syndrome causes high mortality in upwards of 90 to 100% of bats in some sites," said Ann Froschauer, communications leader for the disease investigation. "It's wiping out the cave-hibernating species of bats."
The disease is caused by a fungus called geomyces destructans, which was first discovered in caves in New York and has since spread to 16 states and four Canadian Provinces. The fungus has also been found in three other states, where the disease has not appeared yet.
The fungus is foreign to the United States and officials said humans could have accidentally brought it here from Europe.
Froschauer described the fungus as cold-loving and opportunistic, thriving on and killing bats during hibernation.
"When bats go into hibernation, their immune system slows down and their body temperatures drop to almost 50 degrees Fahrenheit and that's when the fungus attacks them," Froschauer said.
"Our bats can't fight it off becuase they've never been exposed to it before," Froschauer said. "There are 45 species of bats in America and over half of the bats are potentially susceptible to this disease."
Endangered species recognition could provide the bats with additional protection for their habits and extra levels of consideration for anything that might impact their habitat, Froschauer said.
Tuesday's announcement does not mean that the service has decided to protect the two species of bats under the Endangered Species Act. The service will continue to look into all of the biological information available on the two species and to collect information on other bats to determine if the disease is increasing their extinction risk.