Insectivorous bats save American agriculture billions of dollars a years through natural pest-control, but a new wildlife disease and getting killed by wind turbines is threatening populations of these hardworking and useful creatures, according to a new analysis published online in the journal Science this week.

Bats are voracious predators of insects that fly at night, including many that attack crops and trees.

In their analysis, Thomas Kunz, Warren Distinguished Professor in the Department of Biology at Boston University in the US, and colleagues, suggest that loss of bat populations in North America could result in agricultural losses worth at least 3.7 billion dollars a year.

They conclude that urgent efforts are needed to educate policy makers and the general public about the ecological and economic importance of insectivorous bats and to devise practical ways to conserve their populations.

The main threat to their populations is from white-nose syndrome (WNS), a condition believed to be caused by a fungus that appears on the noses and wings of certain types of bat, and also from the increased development of wind-power facilities, they write.

In a short video about bats on the University’s website, Kunz describes how they work hard and play a useful role in keeping down pests. They rarely carry any real danger, he adds, explaining that contrary to popular belief, only half of one percent of bats, of which there are over 1,000 species, carry rabies.

“Bats help suppress insect populations, particularly in agricultural regions where crop pests do an enormous amount of damage,” says Kunz, who has spent the past decade devising ways to count bats in various regions.

“One example of their favorite food is the corn earworm moth, which is probably the most damaging insect pest in the world,” he adds.

He and his co-authors write that despite their important and useful role, insectivorous bats are among the most overlooked economically important, non-domesticated animals in North America.

Co-author Paul Cryan, a US Geological Survey research scientist at the Fort Collins Science Center in Colorado, told the press:

“People often ask why we should care about bats.”

“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.”

In their analysis, the authors show that the value the bats offer as natural pest controllers is anywhere between a low of 3.7 billion to a high of 53 billion dollars a year in the US alone.

They also warn that significant losses may well occur to North American agriculture in the next 4 or 5 years because of the emerging white-nose syndrome and increasing fatalities at wind-energy farms.

The effects may appear sooner in the Northeast they write, because white-nose syndrome has already killed more than one million bats there in the last few years.

One type of bat, called the little brown bat, Myotis lucifugus, a species of mouse-eared bat, is no larger than a adult human thumb, but can eat 4 to 8 grams (the equivalent of one or two grapes) of insects every night. Multiply this by one million, and you have a pest control system that results in 660 to 1,320 metric tons of insects removed each year by bats. This is what has already been lost in the Northeast, suggest the authors.

Lead author Justin Boyles, from the Department of Zoology and Entomology at the University of Pretoria in South Africa, said:

“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.”

“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.”

Kunz explained that bats play a much larger role in pest control in other regions of the US such as the Midwest and the Great Plains, and here the effect of their loss will be much greater than in the Northeast, where their agricultural value is relatively small in comparison. The Midwest and the Great Plains are also the regions where wind-energy development is booming and the fungus that causes white-nose syndrome was recently detected, said Kunz.

While their analysis includes the cost of pesticides that are not needed while bats do the pest control, it does not take into account the harm that might be caused to ecosystems if bats had to be replaced with pesticides, nor does it take into account the benefits of bats suppressing insects in forests, both of which would be considerable, said Boyles.

White-nose syndrome starting killing off bats about 4 years ago, when it first appeard in New York. Since then, the fungus that is thought to cause it has spread south and west, and has now been found in 15 US states and also in eastern Canada. The bat population has taken a huge hit, with numbers in the Northeast of the US reduced by 70 percent and more.

The decline is so serious that scientists believe the little brown bat may disappear from the region altogether in the next 20 years.

Cryan said we don’t have enough continent-wide monitoring of bats killed by wind turbines, so how many die that way is a bit of a mystery, although we do know that several species of migratory tree-dwelling bats are particularly susceptible to wind turbines.

In 2007, Kunz and colleagues published one estimate that suggested by 2020 the US could be losing between 33,000 and 111,000 bats through wind-turbine fatalities just in the mountainous region of the mid-Atlantic Highlands alone. The cause of death is either from direct collision or because the bats’ lungs get damaged from the change in pressure when they fly near the turbine blades.

Kunz and colleagues say there are reports of large numbers dying at wind farms in other parts of North America.

Co-author Gary McCracken, a professor in the Department of Ecology and Evolutionary Biology at the University of Tennessee said:

“The bottom line is that the natural pest-control services provided by bats save farmers a lot of money.”

“We hope that our analysis gets people thinking more about the value of bats and why their conservation is important,” he urged.

The authors conclude that while it may be possible over the coming years to reduce the numbers of bats killed by white-nose syndrome and wind-farms, efforts are more likely to succeed if they have public support, and to get that, we need much more awareness of the good work that these hard working and useful creatures perform.

“Economic Importance of Bats in Agriculture.”
J.G. Boyles, P. Cryan, G. McCracken and T. Kunz
Science 1 April 2011: 41- 42.
Science 1 April 2011: 41-42.DOI:10.1126/science.1201366

Additional source: Boston University College of Arts & Sciences (30 Mar 2011).

Written by: Catharine Paddock, PhD