Bat Trouble and the U.S. Food Supply
In the News
May 29, 2011
Bats are an incredibly diverse order of mammals that occur all across the globe except in extremely cold areas that have ice throughout the year. There are over 1,100 bat species on Earth, and they are very ecologically diverse. As nocturnal animals, they have evolved to take advantage of a huge array of different food types that are not accessible to other animals. Most of the bat diversity in temperate zones, including the U.S., is built upon the seasonal availability of insects.
Paul Cryan, a research biologist with the USGS and one of the study’s co-authors, says that insect-eating bats in the U.S. are major predators of night flying insects and that many of those insects also damage or feed on our crops. In the U.S. and Canada there are 42 different species of bats eating these crop-damaging insects. Cryan says that it stands to reason that they likely decrease the need for additional pesticide applications in many areas.
“Bats are voracious insect predators and are constantly pursuing and eating flying insects, such as moths and beetles, which reproduce quickly and prey on our crops. We may not often see them, but they are usually there, providing silent pest-control services,” says Cryan.
Unfortunately, bats are currently facing two very dangerous enemies. WNS, or White Nose Syndrome, is an emerging infectious disease affecting populations of hibernating cave-dwelling bats throughout eastern North America. Likely caused by a fungus, WNS triggers a premature and often fatal depletion of energy reserves, forcing bats to wake early from hibernation – before their insect food supply has become readily available. To date, over one million bats are thought to have died from WNS.
Meanwhile, another serious issue – wind turbines – is threatening migratory tree-dwelling species of bats. Scientists have estimated that by 2020, 33,000 to 111,000 bats could be killed annually by wind turbines in the Mid-Atlantic Highlands alone. While wind turbines provide a great source of green energy, they are not kind to certain species of migratory, tree-roosting bats. Scientists have speculated that these tree bats might approach and investigate turbines during migration while looking for opportunities to feed on insects, rendezvous with travel groups or mates, or perhaps while searching for a place to take a break and rest their wings.
“My personal opinion is that it should not be a question of bats or wind energy, but rather how we make wind energy development compatible with bats,” says Cryan.
The main challenge of estimating the economic importance of bats in agricultural systems at a continental scale, says Cryan, is getting out there and somehow finding out exactly what they are eating, how much they are eating, and how their dietary habits vary across landscapes. This all happens high above the ground in the dark, which doesn’t make for easy study. When you add more than 40 bat species and scores of different types of crops and crop pests to the mix, things get complicated very quickly.
“Until recently we had the luxury of not having to care about how much bats might be helping agriculture, because their populations in North America were doing well,” says Cryan. “Things have quickly changed. The fatality rates we are witnessing in the wake of WNS and of certain species at wind turbines are unlike anything we have seen before. These are new problems that we must try and work quickly to solve. Bats are relatively long-lived animals that reproduce very slowly, and their populations do not rebound quickly after rapid declines.”
Cryan says that an easy first step to helping bats is getting to know them better, since many people harbor misconceptions. Easy actions, he says, can go a long way, like an Internet search, checking out a library book about bats, or just sitting on the porch at night during the summer and watching the darkening skies for the arrival of the flying night shift. People who get to know bats, says Cryan, are generally the people who understand the need and find ways of helping bats. Conservation efforts, of course, are crucial too.
Scientists are currently working toward better ways of conserving bat populations. New research indicates that limiting turbine blade rotation during certain wind conditions and brief periods of the year has a major influence on reducing bat fatalities, and a lot of work is going into finding ways of minimizing the effects of WNS on hibernating bats. Although the odds of quick and easy solutions are long, the hope is to have more options in the coming years.
“No matter how we look at the situation, we all rely on natural and human-modified ecosystems for nearly all of our food. Although we may not see them, bats are often present in those ecosystems, and they play important roles in keeping the status quo. Bats provide ubiquitous and free pest control service that we usually take for granted,” adds Cryan.