Beyond Billions: Threatened Bats are Worth Billions to Agriculture
Insect-eating bats provide pest-control services that save the U.S. agriculture industry over $3 billion per year, according to a study released today in the journal Science. However, scientists with the U.S. Geological Survey, University of Pretoria in South Africa, University of Tennessee, and Boston University who contributed to the study warn that these valuable animals are at risk: Bat populations are declining due to fatalities associated with White-Nose Syndrome and wind turbines, which could lead to significant economic losses on U.S. farms. Paul Cryan, USGS scientist and an author of the report, discusses these findings.
Marisa Lubeck: Welcome and thanks for listening to this episode of USGS CoreCast. I’m Marisa Lubeck.
Insect-eating bats provide pest-control services that save the U.S. agriculture industry over $3 billion per year, according to a study released today. However, scientists with the U.S. Geological Survey, University of Pretoria in South Africa, University of Tennessee, and Boston University who contributed to the study warn that these valuable animals are at risk. Bat populations are declining due to fatalities associated with White-Nose Syndrome and wind turbines, which could lead to significant economic losses on U.S. farms.
I’m here with USGS scientist, Paul Cryan, an author of the report, to discuss these findings. Welcome, Paul.
Paul Cryan: Thank you for having me.
Marisa Lubeck: Paul, you've estimated that the value of pest control services provided by bats in the US range from a low of $3.7 billion to a high of $53 billion. This is a huge range. What variables or pest control services make up these numbers and why is the range so large?
Paul Cryan: Our analysis is a simple first approach to this question of how much cost savings do bats provide to agriculture in the United States. To do that we needed some information on the pest control services that bats provide, some monetary estimates.
So, the values we used to estimate the pest control services are based on some studies that have been done by my colleagues, Tom Kunz, Gary McCracken, and they're co-authors on this paper. They've spent about a decade or more working down in Texas with a species called the Brazilian Free-Tailed bat. They spent a lot of time to really get good numbers of how much those bats saved cotton farmers on a per acre basis under a number of different scenarios. This is the only system in the United System or anywhere in the world that we know about where these kinds of data have been gathered on bats in agriculture.
So those per-acre savings that we extrapolated from our analysis are based on three different scenarios. That's why we see such a wide range of values. One of them is $172 per acre that the bat saved farmers. That's in situations where the pest species they're quantifying, the cotton bollworm, is a major agriculture pest.
That high dollar scenario area per acre is in years when the conditions favor growth of this crop pest, when the farmers lose more crops to it and they have to apply more pesticides. Those things are expensive.
The low scenario that we extrapolated is in years when conditions don’t favor the pest species, the farmer loses less crops to the pest and there’s less pesticide application.
That's why we came up with this final value of $3 to $53 billion.
This is a very simple analysis that we think is an important conversation to start scientifically and we're hoping that other scientists follow up, check our work, add to this conversation and that we can learn a lot more about what we think is an under-appreciated value of bats to agriculture.
Marisa Lubeck: How many bats are lost to White-nose Syndrome and wind turbines per year and how long will it take for population declines to begin having a noticeable effect on the agriculture economy?
For example, since its emergence in New York State, at what rate is White-nose Syndrome spreading across the country?
Paul Cryan: White-nose Syndrome was first observed in Upstate New York during the winter of 2007 and 2008. Since then, it spread rapidly and we just heard about another state affected, Ohio. The fungus that now is known to cause these diseases moved to as far west as Oklahoma and at this point, after four winters, five winters, we're looking at 16 states and three Canadian provinces being affected.
The mortality caused by White-nose is unlike anything we've ever seen before in bats and in the northeastern United States where bat populations have been monitored for a long time. White-nose is a disease of hibernating bats and so we're seeing these hibernating colonies decline precipitously.
The number of bats dying at wind turbines in the United States, we don't have a good feel for that yet, although fatality rates we've seen at certain wind facilities are higher than any fatality rates we've seen in this particular species in the past. There's something strange happening with bats and wind turbines. We don't know why this particular species are so susceptible and why they're showing up in these surprising numbers.
The harder question that you asked is how do we know how long it will take to see these population declines having a noticeable effect, and that's where we run into a lot of uncertainty. You know, in our paper we suggest it could be as soon as four or five years in the heavy agricultural regions of the central continent. Perhaps in the next few years in the northeast where White-nose syndrome had a substantial influence on bat population
Marisa Lubeck: What USGS-specific research contributed to the findings in this study?
Paul Cryan: I was involved in this analysis because my expertise is with bat fatalities at wind turbines. I'm also involved in the response to White-nose syndrome in trying to tease apart the pathology of the disease, understand behaviors of bats with the disease and hopefully work towards solutions of minimizing the effects of some of these.
Marisa Lubeck: What haven't you and your research partners accounted for in these economic estimates?
Paul Cryan: That's a good question. We only accounted for the actual savings to farmers from the reduced use of pesticides because the bats are there eating this pest insect, and the crop isn't damaged because the bats are there.
What we did not include is anything regarding forest agro-ecosystems. We know that bats suppress insects in forest systems as well.
We didn't account in any of these systems for the evolved resistance of insect pests to pesticides that are used against them or these genetically modified crops they can evolve around.
We didn't account for the downstream affects of pesticides on the environment. And we only extrapolated our values based on one insectivorous bat species feeding on one-type of agriculture pest in one region. The combined effects of multiple species feeding on many different agricultural pests particularly in agricultural landscapes with lots of different kinds of insects pests. There's a lot of things we couldn’t account for, so we feel that our estimates are likely conservative on that account.
Marisa Lubeck: One of your partner research universities is the University of Pretoria in South Africa. Do these numbers vary across this country and do you think they’re comparable in other countries?
Paul Cryan: In our analysis, the numbers suggest that the economic importance of bats are greater in the Midwest and Great Plains states where we have tremendous agricultural output and we know that there are a lot of bats occurring in those regions. Those are also the areas where White-nose syndrome is moving and also there’s a lot of wind energy development happening.
So the bottom line is that the economic value of bats varies across the country and we don't have good numbers for anywhere else, although there's over 1,100 species of bat that occur across the globe. Insectivorous bats are present in most temperate zones of the world and in the tropics. These are flying insect predators. They're at the top of these food chains that involve insects. So, pretty much wherever you are on Earth, I would say it's safe to reason that there's bats influencing the food web that those insects are in.
Marisa Lubeck: What will it take to decrease these losses? Is it possible to stop or at least slow the spread of White-nose syndrome and is there such a thing as bat-friendly wind energy?
Paul Cryan: That's what's on everyone's mind. What we really wanted to focus on is that these are a tremendously valuable asset we have in our world. They're out there eating bugs. It's a natural safe and free-pest control service and it's tremendously valuable to us, economically.
The losses that we're seeing due to White-nose Syndrome and wind turbines are unprecedented but there's still hope. We don't have a quick and easy solution to White-nose Syndrome but we're starting to understand the disease. We're looking for ways to at least minimize its impact and try to break the disease cycles if that's possible.
The same with wind energy, there's a lot of work going on. We work with the industry. We work with all kinds of other scientists to try and to find out why these bats are running into wind turbines. Is it an attraction? Is it some other factor that we can do something about at this point? So hopefully, our analysis will let people know that these are very valuable creatures and they deserve our help.
Marisa Lubeck: Paul, what sort of value, ecological or otherwise, do bats have beyond their economic worth?'
Paul Cryan: That's a very good question and bats play key roles in all of earth's ecosystems. In tropical areas and arid deserts of the Southwest, they pollinate flowers. The large desert cacti that we have down in the Sonoran desert that characterize that landscape in people's minds, bats play a very important role in the pollination of those plants.
The agave, as you go farther into the tropics, bats disperse seeds.
So there's an ecological importance no matter where on earth you are except for the Polar ice caps.
The less tangible to most people value of bats is that these are unique creatures that have millions of years of evolution behind them. These are mammals just like us yet they can fly and find their way around in complete darkness using sound, and how cool is that?
Marisa Lubeck: Certainly. Thanks for speaking with us today, Paul.
Paul Cryan: Yes. Thanks. Bye-bye.
Marisa Lubeck: This CoreCast is a product of the US Geological Survey, Department of the Interior.
I'm Marisa Lubeck. Thanks for listening.