White-nose syndrome may hit social bats the hardest
New research suggests that the impacts of a deadly fungal disease in bats may be worse for bats that like to hibernate together in tight clusters. The findings could help wildlife officials to identify vulnerable bat species and prioritize their recovery efforts. The research was published on July 2, 2012 in the journal Ecology Letters.
White-nose syndrome is a deadly fungal disease in bats. The fungus that causes white-nose syndrome, Geomyces destructans, is thought to be an invasive species that was recently introduced to eastern North America from Europe. The cold loving fungus invades the skin of bats and disrupts their ability to hibernate. The arousal of bats in wintertime by the fungus often causes the bats to die from starvation.
By early 2012, white-nose syndrome had spread to bat colonies in 19 different states in the U.S. and 4 Canadian provinces. So far, wildlife officials estimate that over 5.5 million bats have died in North America from white-nose syndrome.
In efforts to stave off extinction, scientists are trying to figure out what bat species may be the most vulnerable to white-nose syndrome so that they can prioritize recovery efforts.
In the new study published on July 2, 2012 in Ecology Letters, scientists took a close look at several years of data collected on six bat species both before and after white-nose syndrome arrived in bat colonies. The data were collected by state natural resources agencies in New York, Vermont, Connecticut and Massachusetts. In some cases, data were available from 1979 to 2010.
All six bat species surveyed showed declines in population growth rates after white-nose syndrome was detected in their habitat. However, four species appear to have been particularly hard hit. These four species included the little brown bat (Myotis lucifugus), the Indiana bat (Myotis sodalis), the northern long-eared bat (Myotis septentrionalis) and the tri-colored bat (Perimyotis subflavus).
While northern long-eared bats and Indiana bats are in dire trouble, the scientists were surprised to see some evidence that population growth rates for tri-colored bats and little brown bats were starting to increase and stabilize at about 4 to 5 years after white-nose syndrome was first detected in bat colonies.
In little brown bats, the first signs of post white-nose syndrome recovery may be related to changes in their social behavior. Little brown bats are highly gregarious and they like to cluster in tight aggregations during hibernation. Unfortunately, this type of social behavior can increase the spread of disease, according to the study.
In an interesting turn events, the scientists observed that the proportion of little brown bats roosting individually jumped from 1% prior to the detection of white-nose syndrome to 46% after white-nose syndrome arrived in the bat colonies. The scientists suspect that this change in social behavior may lead to reduced disease transmission among bats and could be contributing to their recovery.
Indiana bats, another highly gregarious species, were not found to have changed their social behavior by much (i.e., the proportion of Indiana bats roosting individually was 0.3% pre white-nose syndrome and only increased to 10% post white-nose syndrome), and populations of these bats did not show any significant signs of recovery.
Tri-colored bats, the other bat species showing some signs of recovery, are mostly solitary bats that prefer to hibernate alone. Hence, as their populations get smaller the impacts of white-nose syndrome are predicted to be less severe.
Still, it’s not entirely clear how big a role social behavior plays in the susceptibility of bats to white-nose syndrome. Northern-long eared bats are a solitary species and regardless of their social behavior, they are doing very poorly. The scientists believe that environmental factors such as temperature and humidity could also be playing a role in the spread of the disease.
Kate Langwig, graduate student at the University of California, Santa Cruz and lead author of the paper, commented on the findings in a press release. She said:
All six species were affected by white-nose syndrome, but we have evidence that populations of some species are beginning to stabilize. This study gives us an indication of which species face the highest likelihood of extinction, so we can focus management efforts and resources on protecting those species.
The research was carried out by a team of scientists from Boston University, the University of California, Santa Cruz, Oklahoma State University and the New York State Department of Environmental Conservation. The work was funded by the National Science Foundation, Bat Conservation International and the U.S Fish and Wildlife Service.
Bottom line: New research suggests that the impacts of a deadly fungal disease in bats may be worse for bats that like to hibernate together in tight clusters. The findings could help wildlife officials to identify vulnerable bat species and prioritize their recovery efforts. The research was published on July 2, 2012 in the journal Ecology Letters.