A dark night for bats

Given the scale and diversity of most animal populations, it is a rare thing to talk about extinction on the same time scale we might use for the life span of an automobile. However, the little brown bat might have even less time than your Honda Civic.

According to a study published by Winifred Frick et al. in the journal Science, the little brown bat Myotis lucifugus may undergo regional extinction from eastern North America in 16 years. The culprit is a disease known as white-nose syndrome (WNS), which is named for the white powdery fungus that grows on the muzzles, wings and ears of afflicted bats.

While the lethal mechanism of the disease is unclear, it appears to be due to the fungus Geomyces destructans. The first record of this fungus appeared among North American bats in 2006. By the winter of 2009, the fungus had been detected in 14 states in the U.S., Quebec and Ontario.

The little brown bat is one of the most common bat species in North America and its extinction would have a major ecological impact. Furthermore, there are six other species currently known to be affected by WNS, and it is estimated that a million or more animals have been killed by the disease thus far.

While the impact on bat populations is devastating, the consequences of WNS may be even farther reaching. It is estimated that the million deceased bats would have consumed 700 tonnes of insects a year.

The ecologic impact of such rapid and drastic population change could be huge. While the severity of the disaster is apparent, what is not so clear is exactly how WNS affects the bats and what can be done about it.

WNS is believed to be the first disease characterized that will specifically target hibernating animals. Once a hibernaculum (where the bats hibernate) is infected by the disease, the mortality rate for the resident bats is over 90 per cent.

The mode of this astounding lethality is not fully known, but scientists believe it has to do with early arousal from hibernation. These tiny creatures rely on hibernation to make their energy reserves last throughout the winter until they can hunt again. The balance is so delicate that a single arousal can cost a month’s worth of fat. It appears that WNS causes the hibernating bats to awaken early and then leave the caves in a hopeless search for insects that haven’t emerged yet; eventually they starve.

While this seems to account for WNS mortality, what causes WNS is not exactly clear. Although G. destructans is believed to be the cause, this same fungus has been seen on bats in Europe without any large die-offs in the population. The fungus grows opportunistically on the hibernating bats whose slowed metabolism, lowered body temperature and possible immune suppression make it the perfect target. The little brown bat in particular prefers to hibernate in caves with the same temperature and humidity that G. destructans finds optimal. What causes this fungal growth to become the lethal WNS is not known and is the subject of research.

There are 45 species of bat residing in Canada and the U.S., of which about two dozen hibernate. If scientists are right, that WNS strikes through hibernation, then the disease is likely to continue to spread to more than the currently affected seven species. The impact of these extinctions is not merely ecological but economic. As an illustration, the Mexican freetail bats (which are unlikely to develop WNS), through their consumption of cotton bollworms and corn earworms, save farmers in south-central Texas roughly $740,000 annually due to decreased crop damage and savings on pesticides.

What can be done about WNS is the biggest mystery of all. The fungus is susceptible to antifungals, but these are often harmful to the bats. Even if some chemical, which would selectively kill the fungus and was ecologically safe, could be found, the application process would be almost impossible. The logistics of treating every hidden bat cave in a continent would be a nightmare. Caves have been closed to humans in some areas in an attempt to slow its spread, but for now it appears that praying for a miracle is all most of us can do. For the little brown bat, it is a dark night indeed.

1 Comment on "A dark night for bats"

  1. Joanie McGuffin | February 25, 2011 at 3:29 am |

    Hi , I listened with great dismay to this story on CBC a few weeks ago. I live in northern Ontario north of Sault Ste. Marie. There are some significant bat hibernation locations east and north of SSM (Desbarats near Echo Bay and along the Superior coastline near Theano Point. To compound the problem for the brown bat, I would like to highlight another challenge they face. At the current time, (under Ontario’s Green Energy and Green Economy Act) we are facing the potential of development of 800-1000 large scale industrial wind turbines throughout the Algoma region, up the Lake Superior coast. Without any scientific studies to comprehend the impact on the bats, (as well as one of North America’s most significant bird migration routes,) we are extremely worried. From worldwide reporting, it is estimated that 200,000 wind turbines cause 16 million bat deaths annually.

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