A black bear walks across the ground in Lyme, N.H. (Cheryl Senter/AP)

The rising popularity of unmanned aerial vehicles (UAVs) has caused them to show up everywhere from private back yards to national parks, and the drones have proven useful for all kinds of applications, including recreation, military defense and even scientific research. As a result, although drones and wildlife might not seem like they should ever mix, more and more frequently they do.

One increasing use for UAVs is allowing scientists, conservationists and even ecotourists to get up close and personal with nature. They have been used to ward off rhino and elephant poachers in Africa and collect data on wild humpback whales. Amateur drone operators have used UAVs to collect videos and photographs of wildlife, such as dolphins, in their natural habitats.

But as much as UAVs are becoming more common among wildlife researchers and enthusiasts, there has been little research on how the animals actually react to the aircraft. Measuring animals’ reactions to drones buzzing around overhead is important for figuring out how much stress the aircraft may be putting on the local fauna, say researchers from the University of Minnesota. And they have just released a study that lead author Mark Ditmer, a postdoctoral researcher in the University of Minnesota’s Department of Fisheries, Wildlife and Conservation Biology, says he hopes will encourage more research on the subject.

The study, released Thursday in the journal Current Biology, suggests that black bears can be stressed out by the presence of UAVs, even if they don’t outwardly show it.

Ditmer and his colleagues outfitted four bears in northwestern Minnesota — two mothers with cubs, one hibernating female, and one young male — with GPS collars and cardiac “biologgers,” or devices that collect heart rate data. Then, they flew a UAV over each bear anywhere from one to nine times (for a total of 18 flights) while observing the bears’ movements and heart rates.

They found that each of the bears’ heart rates spiked every time the drone flew overhead, suggesting that they were stressed by the UAV’s presence. But surprisingly, even though their hearts were racing, the bears tended to stand still rather than run away. This reaction underscores the importance of conducting physiological tests on wildlife, such as heart rate monitoring, rather than just watching to see what they do when a drone is around, Ditmer says.

“Just because we can’t directly observe an effect doesn’t mean it’s not there,” Ditmer says. If the researchers had simply watched the bears’ movements during the UAV flights, he adds, “we would have incorrectly come to the conclusion that UAV flights weren’t having much of an effect on individuals.”

Ditmer also suspects that bears in other locations might have even more pronounced stress responses to UAVs: The bears in his study lived in areas heavily populated by humans and were probably used to a little noise from nearby roads and farms.

“These bears are in probably one of the most human-dominated parts of Minnesota, in terms of where bears are located anyway, so we thought they would be the most habituated to outside stressors,” Ditmer says. It’s another reason more research is needed: Animals in different locations or under different circumstances, even if they are members of the same species, may not react to stress factors in the same way. And similar physiological studies could be warranted for other animals that are commonly the subject of drone research or interventions.

Over a long period, the physiological stress response could be bad for the health of wildlife if they fail to get habituated to the presence of drones, Ditmer says. Even more worrying, animals that also exhibit behavioral responses to drones — by running away, for example — could become more “vulnerable to sources of mortality,” the authors write, such as fleeing into traffic or into another individual’s territory.

The end goal would be to figure out whether repeated drone use is likely to be harmful to animals. With the bears, for instance, Ditmer says there is a chance that the animals could become accustomed to drones over time and be less bothered by them. Other research could also examine whether different heights, speeds or even sound frequencies are less likely to bother the animals.

To be clear, Ditmer says, his team’s study is not meant to advocate against the use of UAVs, which have high potential for both conservation and research applications. “We’re just highlighting a potential issue that needs to come into closer consideration when we decide where and where to use them,” he says.

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