A study published Thursday claims that unmanned aerial vehicles used for research may be stressing out wildlife, including black bears. The study’s authors measured bear heart rates as drones buzzed overhead. While the animals did not flee, the scientists said their heart rate spiked—and the findings were even stronger for mother bears with cubs. “For them to mostly stay in one spot, and have this racing heart rate, was a little bit of a surprise for us,” lead author Mark Ditmer said, adding that the response was stronger than they expected. He warned that chronic stress may make the animals more susceptible to disease.