Insect-eating bats are worth at least $3 billion — perhaps as much as $54 billion — per year to U.S. agriculture alone, say biologists who evaluated their ecological contributions.
With bats threatened by careless wind-turbine development in major flyways and, more pressingly, by the new and dreadful White Nose Syndrome, protecting them isn’t just ethical. It makes bottom-line sense.
If bat mortality “continues unabated, we can expect noticeable economic losses to North American agriculture in the next four to five years,” wrote the researchers, whose study was published online March 31 by Science. “A wait-and-see approach to the issue of widespread declines of bat populations is not an option.”
The estimates are an informed, back-of-the-envelope calculation based on earlier research by study co-author Tom Kunz, a Boston University bat specialist who in 2006 published the most detailed look ever at the relationship of bats to insects and agriculture.
In the eight-county Winter Garden region of south central Texas, Kunz’s group calculated that Mexican free-tailed bats annually saved about $740,000 in pesticide costs, or roughly $74 per acre. (The savings held steady for cotton genetically engineered to produce its own pesticides.)
The new study extrapolates those values, adjusted for local levels of agricultural productivity, to the United States at large. It’s necessarily a rough extrapolation: Some regions have more bats than Texas, or fewer. And they might eat fewer insects, or more. But even as precise values vary, the underlying truth is invariable: Bats eat bugs, lots of them.
Their taxonomic order Chiroptera contains more species than any order except rodents, and eating insects is what they’ve evolved to do. What’s more, there are many “downstream” costs to increased pesticide use — health problems in people, accelerated development of resistance in bugs — omitted from the study.
“Our estimate is very conservative,” said Kunz. “The devil is in the details, and the devil is that this is an extrapolation of one study over the entire U.S.. But that’s the only data we have, and we need to define this information.”
Estimated annual value of insectivorous bats in agriculture by county. Multiply values by $1,000, e.g., 2100 to 3400 equals $2.1 million to $3.4 million (Science).
Kunz’s emphasis reflects two critical threats to bats’ future. One is the installation near bat caves and flight routes of wind turbines, which suck bats into their blades. By 2020, wind turbines will kill about 60,000 bats each year in the mid-Atlantic states alone.
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