UP's batman shows bats' huge benefit to us agriculture

Posted on April 06, 2011

The study, led by Dr Justin Boyles from the University of Pretoria (UP), shows that pest-control services provided by insect-eating bats in the United States is likely to save the U.S. agricultural industry at least $3 billion a year. However, insectivorous bats are still among the most overlooked economically important, non-domesticated animals in North America. Teaming up with Dr Boyles were scientists from the U.S. Geological Survey (USGS), University of Tennessee and Boston University.

"People often ask why we should care about bats?” said Dr Paul Cryan, a USGS research scientist at the Fort Collins Science Centre and one of the study’s authors. “This analysis suggests that bats are saving us big bucks by gobbling up insects that eat or damage our crops. It is obviously beneficial that insectivorous bats are patrolling the skies at night above our fields and forests. These bats deserve help.”

According to Dr Boyles the goal of the study was a universal one: to convince people that bats are worth saving. He explained that 45 species of bats are found in the US, while Southern Africa – a much smaller area – is habitat to up to 60 species. “And the local bats play an equally important role in pest control,” Dr Boyles said.

The value of the pest-control services to agriculture provided by bats in the U.S. alone range from a low of $3.7 billion to a high of $53 billion a year, the authors estimated. They also warned that noticeable economic losses to North American agriculture could well occur in the next 4 to 5 years because of the double-whammy effect of bat losses due to the emerging disease white-nose syndrome and fatalities of certain migratory bats at wind-energy facilities. In the Northeast, however, where white-nose syndrome has killed more than one million bats in the past few years, the effects could be evident sooner.

“Bats eat tremendous quantities of flying pest insects, so the loss of bats is likely to have long-term effects on agricultural and ecological systems,” said Dr Boyles. “Consequently, not only is the conservation of bats important for the well-being of ecosystems, but it is also in the best interest of national and international economies. A single little brown bat, which has a body no bigger than an adult’s thumb, can eat 4 to 8 grams (the weight of about a grape or two) of insects each night, the authors wrote. Although this may not sound like much, it adds up – the loss of one million bats in the Northeast of the United States has probably resulted in between 660 and 1320 metric tons of insects no longer being eaten each year in the region.

“Additionally, because the agricultural value of bats in the Northeast is small compared with other parts of the country, such losses could be even more substantial in the extensive agricultural regions in the Midwest and the Great Plains where wind-energy development is booming and the fungus responsible for white-nose syndrome was recently detected,” said Prof Tom Kunz, a professor of ecology at Boston University, another co-author.

Although these estimates include the costs of pesticide applications that are not needed because of the pest-control services bats provide, Boyles and his colleagues said they did not account for the detrimental effects of pesticides on ecosystems nor the economic benefits of bats suppressing pest insects in forests, both of which may be considerable.

The loss of bats to white-nose syndrome has largely occurred during the past 4 years, after the disease first appeared in upstate New York. Since then, the fungus thought to cause white-nose syndrome has spread southward and westward and has now been found in 15 states and in eastern Canada. Bat declines in the Northeast, the most severely affected region in the U.S. thus far, have exceeded 70 percent. Populations of at least one species, the little brown bat, have declined so precipitously that scientists expect the species to disappear from the region within the next 20 years.

The losses of bats at wind-power facilities, however, pose a different kind of problem, according to the authors. Although several species of migratory tree-dwelling bats are particularly susceptible to wind turbines, continental-scale monitoring programs are not in place and reasons for the particular susceptibility of some bat species to turbines remain a mystery, Dr Cryan said.

By one estimate, published by Prof Kunz and colleagues in 2007, about 33 000 to 111 000 bats will die each year by 2020 just in the mountainous region of the Mid-Atlantic Highlands from direct collisions with wind turbines as well as from lung damage caused by pressure changes bats experience when flying near moving turbine blades. In addition, surprisingly large numbers of bats are dying at wind-energy facilities in other regions of North America.

“We hope that our analysis gets people thinking more about the value of bats and why their conservation is important,” said Prof Gary McCracken from the University of Tennessee. “The bottom line is that the natural pest-control services provided by bats save farmers a lot of money.”

Dr Boyles – an American scientist who joined UP’s Department of Zoology and Entomology about two years ago – predicts that economic effects might be felt even in Africa. “Financial losses in the US agricultural sector may play a part in, for example, food exports. White-nose syndrome does not currently pose a threat in Africa, but plans to erect more wind-turbines on the continent may have an impact on bats, and therefore, both economics and ecosystems in Africa.”

The authors conclude that solutions to reduce the impacts of white-nose syndrome and fatalities from wind turbines in the US may be possible in the coming years, but that such work is most likely to be driven by public support that will require a wider awareness of the benefits of insectivorous bats. The article, Economic importance of bats in agriculture, appears in the April 1 edition of Science. Authors are J.G. Boyles, P. Cryan, G. McCracken and T. Kunz.

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