As Bats Die Off, So Do Human Babies
In places where bat populations have collapsed in the US, infant mortality has gone up. A new study by economist Eyal Frank, appearing in the journal Science, explains the connection.
Three species of bats in North America have been decimated by white-nose syndrome, a fungal disease that attacks the animals when they hibernate. Because the disease appears suddenly and spreads fast, Frank saw an opportunity: he could compare counties where bat populations plummeted with similar counties that had not yet been infected.
When bats die off in agricultural areas, insect populations skyrocket, so farmers douse their crops with more pesticide, on average an extra kilogram of insecticide per square kilometer of land, Frank found. After five years, they were spraying two kilograms more than before — a 31 percent increase. At the same time, infant mortality caused by disease or birth defects in these counties rose eight percent, while similar counties with healthy bat populations saw no such change.
Frank observed some 1,334 infant deaths linked to bat die-offs (and subsequently to insecticides) throughout 245 counties affected by white-nose syndrome, from 2006 to 2017. “This result highlights that real-world use levels of insecticides have a detrimental impact on health, even when used within regulatory limits,” Frank writes.
All this is very concerning for obvious reasons, and it gets worse. Some 40 US states and nine Canadian provinces have been hit by white-nose syndrome, which tends to infect three species of bats. However, more than half of the bat species in North America are at risk from other threats, such as habitat loss, climate change, or colliding with windmill turbines.
Earlier studies (also conducted by environmental economists) have estimated the agricultural value of bats to be in the billions of dollars per year. Another study found that even real estate – namely, land rental rates – have dropped in counties hit by white-nose syndrome. Now we know of another “negative externality,” in economist-speak: the lives of babies.
Photo credit: Jason Headley / USFWS
