Dramatic Declines in Myotis Summer Activity

Bat biologists have known for some time that White-nose syndrome (WNS) is causing rapid declines in little brown bats in the Eastern United States. In 2006 biologist discovered a white fungus on the nose, wings, and ears of cave hibernating Myotis species (Figure 1). The fungus appears to cause the bats to arouse prematurely from hibernation, often in mid winter when lack of insect prey and cold temperatures result in high bat mortality.

Figure 1. A hibernating little brown bat with White-nose syndrome – a white fungus surrounding the nose and mouth (From Flickr/Jonathan Mays, Maine Department of Inland Fisheries and Wildlife)

First discovered in eastern New York State (near Albany), WNS has now spread northward into Canada and south to Tennessee and North Carolina (Figure 2). There are even several suspected cases west of the Mississippi River. In five short years,
Geomyces destructans, the fungus that causes WNS, resulted in the deaths of millions of cave-hibernating bats. Some estimates put the decline in hibernacula populations at over 90%.

Figure 2. The most recent map of localities with White-nose syndrome in bats. (Courtesy of Cal Butchkoski, PA Game Commission)

With cave hibernacula populations crashing, bat biologists are scrambling to survey summer maternity roosts across the Northeastern United States and Canada. They are worried that there will be few maternity colonies left. Two recent papers provide dramatic evidence that bat biologist’s worst fears are coming true.

Dzal and colleagues (2011) report in the journal
Biology Letters that summer activity of the little brown bat declined by 78% in the Hudson River valley (near the epicenter of the WNS outbreak) in the three summers following the outbreak. They recorded echolocation calls over a wide area and identified the species of bats present and the number of passes. They then compared the activity of Myotis lucifugus, a cave hibernating species, with hoary bats (Lasiurus cinereus), a species that does not hibernate in caves. Their results indicate that the summer activity of M. lucifugus declined by 78%, while L. cinereus activity increased slightly over the same three-year period (Figure 3).

Figure 3. Summer activity patterns of Myotis lucifugus (black bars) and Lasiurus cinereus (white bars) over a three-year period. (From Dzal et al., 2011)

In a similar study in western Massachusetts,
Brooks (2011) acoustically surveyed bats before and after the nearby 2006 outbreak of WNS. He found a 72% reduction in Myotis activity four years after the outbreak of WNS. Interestingly, there was a 47% increase in Eptesicus fuscus and L. cinereus activity over the same period; both of these species hibernate in buildings.

Declines in
Myotis populations are important because biologists estimate that small insectivorous bats provide valuable ecosystem services, including controlling insect pests. It may sound trivial that one little brown bat consumes 4 to 8 g of insects every night during the summer, but bear in mind that one million little brown bats consume between 660 and 1320 metric tons of insects each summer (Boyle et al., 2011). Boyle et al., (2011) estimate that bats save the agricultural industry approximately $22 billion dollars each year in reduced pesticide application and increased crop yields.

Note: In May 2011 the US Fish and Wildlife Service published a national plan for dealing with White-nose syndrome, titled “
A National Plan for Assisting States, Federal Agencies, and Tribes in Managing White-Nose Syndrome in Bats.”


Boyles JG, Cryan PM, McCracken GF, & Kunz TH (2011). Conservation. Economic importance of bats in agriculture. Science (New York, N.Y.), 332 (6025), 41-2 PMID: 21454775

Brooks, R. (2011). Declines in summer bat activity in central New England 4 years following the initial detection of white-nose syndrome Biodiversity and Conservation DOI: 10.1007/s10531-011-9996-0

Dzal, Y., McGuire, L., Veselka, N., & Fenton, M. (2010). Going, going, gone: the impact of white-nose syndrome on the summer activity of the little brown bat (Myotis lucifugus) Biology Letters, 7 (3), 392-394 DOI: 10.1098/rsbl.2010.0859