In the warm summer months, bats are commonly seen darting across the night sky, swooping across urban backyards preying on midges and other insect pests. Bats also benefit farmers by feeding on insect pests that damage crops, so they serve as natural pesticides without the harmful environmental affects associated with their chemical counterparts.
As this is where the threat lies. As intensified agricultural practices spread throughout the world, the natural habitats on which they depend are being converted into croplands – typically intensively grown mono-cultures – causing bat population numbers to decline dramatically. Bat populations in North America are also threatened by white-nose syndrome – an infectious disease that is wiping out bat colonies.
According to Jean-Philippe Lessard, a biology professor at Concordia University, Montreal, Canada: “Many bat populations in Quebec have lost 80 to 100 percent in recent years.”
Concerned about the dramatic decline in local bat populations, Lessard, together with a research team from Concordia and the University of Tennessee, undertook a study to assess the importance of various habitat types for insectivorous bats that lived within or around agricultural areas.
Results of the study, which were recently published in Biological Conservation, reveal that by implementing measures to protect natural habitats in ecosystems that have been extensively modified by human activities could assist ailing bat populations.
According to lead author, Noa Davidai, who undertook the study while pursuing graduate research at the University of Tennessee: “Our key result indicates that within an intensive agricultural landscape, the proportion of natural habitat is very important for the bats. More natural habitat means increased bat activity, and possibly healthier populations.”
The research team analysed 9,552 hours of bat call recordings recorded over 243 nights, from 15 different monitoring sites all situated within an intensively farmed region in Texas. They used bat detectors to monitor bat activity, and insect pheromone traps to determine the abundance of prey – specifically the corn earworm moth, considered a favourite bat treat and highly destructive agricultural pest that can be extremely damaging to crops.
While intensively farmed areas do attract moths for bats to prey on, the supply is seasonal and fluctuates extensively throughout the growing season. Moths and other insects are attracted to fruit and flowers of crops, and when plants are not flowering or fruit is not ripening, they will no longer attract insects, an thus no longer provide bats with a source of prey. When crops cease to attract insects, bats in turn need to move on to other feeding grounds, and this is when natural habitats become essential for the survival of bat populations in agricultural areas.
The studies findings do not only have ecological implications, but economic implications too. It is estimated that bats provide a pest-control service worth more than US $741,000 (£540,000) per annum in Texas alone. This not only reduces the cost of purchasing and applying pesticides, but also reduces the environmental impact of pesticides, and because there are less pesticides circulating in the environment, reduces pesticide resistance in insects, and ultimately delays the need to bring out new/more potent pesticides to combat agricultural pests.
Lessard, a co-author of the paper, points out that these results resonate for bat populations across the USA. While the 80-100 % population declines seen in Quebec can be largely attributed to white-nose syndrome, “the destruction of their habitats is another major problem.”
He adds that this is something we can all help prevent. “One thing we can do is to make sure to preserve the habitats bats need to survive. This means preserving natural patches of habitat in areas where much of the natural forest has been cut for agricultural purposes.”
He also encourages residents in Canada to participate in online citizen science initiatives, such as batwatch.ca, to help protect bats.
“We’re asking the citizens across Quebec and Ontario to help us locate bat colonies they might encounter in nature or around their homes,” says Lessard. “This information is crucial, as it allows us to evaluate the status of bat populations and develop a plan of action for conservation.”
I’ll be keeping a close eye on the findings because these findings have global resonance, including for bats closer to home.
Davidai N, Westbrook J, Lessard JP, Hallam T, McCracken G. (2015) The importance of natural habitats to Brazilian free-tailed bats in intensive agricultural landscapes in the Winter Garden Region of Texas, United States. Biological Conservation. 190:107-114