Author: NCWRC blogger/Friday, October 30, 2015/Categories: Blog, Conservation, Wildlife Watching
What’s scarier than bats at Halloween? A world without bats, that’s what.
While bats may get a bad rap, they are hugely important in the ecosystem, playing key roles in keeping us healthy and well fed.
But bats are in trouble. BIG trouble because of a deadly disease known as white-nose syndrome. It has killed millions of bats in the eastern United States, including bats in western North Carolina. Some bat hibernacula — caves and mines — in western North Carolina have seen dramatic population declines although these declines associated with the deadly disease appear to be leveling off in some areas.
White-nose syndrome, a fungal disease that has killed millions of bats in the eastern United States, continues to affect bat populations in western North Carolina, although the declines associated with the deadly disease appear to be leveling off in some areas.
Biologists with the N.C. Wildlife Resources Commission and the U.S. Fish and Wildlife Service completed winter surveys in bat hibernacula in four western counties in February of this year. While they found bats in all areas they surveyed, the numbers were small. In two mines in Avery and Haywood counties, they noted the same number of bats or only a small decline in bat numbers compared to last year’s surveys. These same areas had experienced steep declines in the number of bats in previous years. In the Avery County site, biologists found 15 bats, two less than what they found in 2014. In the Haywood County site this year, they found 30 bats, down from the 55 bats found during a survey last year.
Those numbers, while not great, are not declining as badly as they have been during the last three surveys biologists have conducted. The small decrease in bats in the Avery County mine might indicate a possible leveling off of mortality rate. Elsewhere, numbers continued to go down, with most surveys yielding the lowest counts of all survey years, according to Katherine Caldwell, a mammalogist with the Wildlife Commission.
“When we conducted the survey in that Haywood County mine in 2011, the number of bats was around 4,000,” Caldwell said. “Two years later, only 200 were counted, a decline of 95 percent. Last year that number was about 55, and this year it’s down to 30. While we’re still seeing declining numbers, the rate of decline has slowed and we’re still seeing bats without visible signs of WNS — and that’s a good thing.”
The surveys also revealed the spread of the disease as it made its way south, with a large decline in bat numbers noted in a Swain County cave. When last surveyed in 2013, the Swain County cave was a winter shelter for more than 1,000 bats and the first visible signs of WNS were present. Biologists counted only 58 bats this winter, with little brown bats and northern long-eared bats down 100 percent — from more than 200 to none this year.
Biologists also noted declines in McDowell County caves, which were last surveyed in 2012.
WNS is caused by a fungus that thrives in the cold conditions of caves and mines, killing up to 100 percent of bats in a colony. Biologists first detected WNS in North Carolina in February 2011, in a bat from Avery County. Since that time, the disease has stricken five bat species in 10 counties in western North Carolina. The tri-colored, Northern long-eared and little brown bat have shown declines ranging from 92 to 100 percent in sites that have been infected with WNS for three or four years, while the Eastern small-footed and big brown bat have experienced less drastic declines.
Neither the disease nor the fungus that causes it has been detected in any of the so-called tree roosting bats, which typically roost individually in or on trees in the warmer months and either migrate south for the winter, or remain in the area, hibernating individually outside of caves. The disease has not been detected on the two species of big-eared bats that occur in North Carolina, including the federally endangered Virginia big-eared bat.
White-nose syndrome is named for the whitish, fuzzy fungus that grows on the noses, wings and ears of bats during winter hibernation. Bats infected with WNS awaken more often during hibernation, which causes them to use essential fat reserves needed to get them through the winter.
Bats infected with WNS may spread fungal spores to other bats and roosts throughout the year. However, the fungus only grows in a narrow temperature range (41-56 degrees) in high-humidity conditions. Although these conditions are prevalent in caves and mines used for hibernation, bat houses are used during the summer months and have no more potential to spread fungal spores than do natural roosts, such as a hollow tree. More information about WNS can be found at www.whitenosesyndrome.org.
WNS is transmitted primarily from bat to bat but it can be spread to new sites by humans who inadvertently carry fungal spores from cave to cave on their shoes, clothing and caving gear. As a result, the Commission urges people to help bats by staying out of caves and mines. Linville Caverns, the only commercial cave in western North Carolina, is helping to reduce the spread of WNS by asking visitors to disinfect footwear after visiting the cave by briefly stepping onto a special decontamination mat outside the cave.
While WNS has a deadly effect on bats, it does not affect people — at least not directly. Indirectly, however, it can have a huge impact on humans by reducing the number of bats in North American ecosystems.
“Bats in these ecosystems are insectivorous and may consume their body weight in insects in a single night,” Caldwell said. “Many of insects eaten by bats are crop and forest pests.”
The U.S. Geological Service estimates that loss of bats in North America could lead to agricultural losses exceeding $3.7 billion annually.
Biologists have continued their long-term monitoring efforts of bats in western North Carolina. This summer, they used mist-nets to capture and count bats in summer roosts, and recorded bat calls through the N.C. Bat Acoustic Monitoring Program, a citizen-science effort to assess the effects of WNS and other threats to bat populations in the mountains over time.
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