Study finds bears react, then habituate, to drones


  • Small drones increasingly serve as tools to monitor wildlife, detect habitat change, or search for poachers, but their use may be stressing out the animals being studied or other species.
  • A research team tested whether black bears would habituate to the repeated presence of drones flying overhead and, if so, whether they would remain habituated to additional flights conducted after a break.
  • The bears showed an increased tolerance to drone flights in the short term, which they maintained after a nearly four-month pause.
  • With the expanding use of drones in wildlife and habitat studies, the researchers expect their findings to help inform best practices that could reduce animal disturbance in the long run.

Noisy aliens flying above us might stress us out or cause alarm. As drones fly UFO-like over forests, wetlands, deserts, and oceans, serving as tools to monitor wildlife, detect habitat change, or search for poachers, they may be stressing out the animals being studied or other species.

Now, though, a team of researchers has found that bears can get used, over time, to a drone’s presence in their airspace — a result that could influence how drones are used for conservation and research.

A black bear enjoying a quiet moment, without drones or people. Image by Jitze Couperus via Flickr, CC 2.0.

Researchers have used drone images to count gharial crocodiles on beaches, sharks and turtles under the ocean’s surface, koalas in trees and cryptic nightjars in logging concessions. They’ve also used them to observe tree phenology, detect forest loss, measure seals and even assess sea level rise.

Drones can fly and hover at low altitudes, which facilitates observation but may disturb some animals more than either on-the-ground research or other aerial survey methods, even if they don’t show it outwardly.

A viral video taken by a drone from 2018 of a mother brown bear and her cub navigating a snowy cliff in the Russian Far East exemplified to Mark Ditmer and other wildlife ecologists the potential for drones to harass wildlife. The footage shows the mother reacting fearfully when the video zooms in, possibly from the drone physically approaching the bears, and the cub falling a long way down; the pair runs away from the drone after the cub finally reaches the top.

A multi-institutional team led by Ditmer, a postdoctoral researcher at Boise State University, tested whether American black bears (Ursus americanus) would habituate to the repeated presence of drones flying overhead and remain habituated to additional flights conducted after a break.

With the rapidly expanding use of drones in wildlife and habitat studies, the researchers hope their findings will help inform best practices that could reduce animal disturbance in the long run.

Part of the team had learned from previous studies on wild bears wearing heart rate monitors that their heart rates soared in response to a drone flying by, even though their behavior did not substantially change.

Pinpointing stress response

In their new study, the researchers implanted heart monitors subcutaneously in five bears in captivity to measure their heart rates as a sign of stress that could be monitored at the precise times drones flew overhead.

View from a drone. The researchers used measurements of the bears’s heart rate to assess their stress levels. The bears gradually stopped reacting to the drone overhead. Image by Mark Ditmer.

“The cardiac biologgers we use are incredibly safe and are developed for human use,” Ditmer told Mongabay. “We have monitored bears that have them over many years without any detriment to their health.” The biologger the team used is the size of a few matchsticks.

In their paper, the researchers acknowledged the balance between disturbing animals by fitting them with biologgers and the expected scientific and conservation benefits from the information gained.

The biologgers measured the bears’ heart rates before, during, and after a series of five-minute drone flights, repeated two times each week for four weeks. They flew and hovered the drone at 15 meters (49 feet) altitude, which was lower than a typical wildlife study would because the captive bears were already accustomed to some human noise and activity.

The devices measured average heart rate every two minutes to detect the short-term effects as the drone approached, hovered, and flew around the bears’ enclosure. The frequent updates allowed the researchers to observe both the increase in the bears’ heart rate upon discovering the drone and calculate how it attenuated throughout time.

Reaction and habituation

The captive bears were fairly familiar with human noises, such as voices, cars, and lawnmowers. Nevertheless, Ditmer said, the biologgers detected a substantial increase in the heart rate of the captive bears to the initial drone flights, albeit not as large as in the wild bears.

One of the study bears inside the enclosure. Studying the reactions of captive animals allowed the researchers to more closely monitor the bears and eliminate other factors that might also potentially stress out bears. Image by Mark Ditmer.

Video from the early drone flights “clearly shows some of the bears standing on their hind legs and running around watching the drone warily,” Ditmer said. “The sight and sound of the drone must be quite a different experience for bears,” he added, “regardless of previous human interactions.”

The researchers found that, after these initial physiological reactions, the bears habituated to the drones over a three- to four-week period and remained habituated, even after several months with no flights.

“It was also important to learn that even after the bears no longer showed a stress response to the drones, and we waited 118 days to fly overhead again,” Ditmer said, “that once we resumed flights the stress response did not return.”

Ditmer said he thought the sound of the drone was the biggest factor in eliciting a stress response from bears. In their paper, the researchers found greater stress response under windy conditions and suggested that wind may mask the sound of a drone approaching, potentially startling the bear more when the aircraft suddenly appears overhead. In addition, the team’s earlier study on wild bears took place mainly in thick forest and shrub vegetation, which would have made it difficult for the bears to see the drone approaching or hovering overhead.

Even small drones are noisy, a feature that lead researcher Mark Ditmer says he considers to most strongly contribute to the animals’ stress levels. Image by Mark Ditmer.

Ditmer said the data on drone use with wildlife suggest that using fixed-wing drones, which are quieter than copter drones, or making engineering changes that reduce the noise of copter drones could help alleviate stress from drone noise. In their paper, researchers also recommended collecting data at a given drone sensor’s maximum useful distance.

Alternatives for measuring physiological response

When asked about alternatives ways to assess stress on target animals, Ditmer said he hoped that future physiological devices would be able to record data and send it to the researcher remotely through an animal’s satellite-based GPS tracking tag, though he had not heard of any study using such technology.

“Stress hormones could be assessed noninvasively by collecting scat or hair samples from target species in areas with frequent drone flights and comparing the resulting stress levels with individuals living in areas without drone flights,” Ditmer said.

“However,” he said, “it would be hard to definitively link the stress measurements from the biological samples to the actual drone flights because there would be many other confounding sources of stress.”

Moreover, the hormones measure stress over a period longer than a drone flight.

“Collecting data on acute stress responses is very difficult because it is a temporary response to a stressor,” Ditmer said, “and that is where physiological biologgers are really great for providing us with a deeper understanding of the ways in which external stimuli, such as drones or crossing roads, may impact wildlife in ways that were previously impossible.”

A black bear relaxes in an enclosure in North Carolina, U.S. Image by Ken Thomas via Wikimedia Commons.

And drones continue to provide a uniquely quick and cost-effective way to survey, monitor, and understand wildlife, so the research team expects their use to expand.

Researchers already use drones to help track animals wearing standard VHF radio tags, Ditmer said, adding that he anticipated seeing an increased use of drones to track individual animals using thermal cameras.

Conducting drone-based surveys, such as of penguin nesting colonies or seal haul-outs, typically calls for researchers to fly multiple missions to look for variation in their counts or to look for changes through time, Ditmer said.

“We are just scratching the surface for how drones can revolutionize wildlife research and conservation,” he added.

The new study suggested that if drones needed to be flown near wildlife “for legitimate purposes, such as poaching patrols or collecting demographic data to better conserve or manage a species, that bears and potentially other mammals show they can habituate to drones over time,” Ditmer said. “The dramatic initial stress responses we saw in our studies will likely not repeat and impact individuals over the long term if regular flights are required for monitoring.”


Ditmer, M. A., Werden, L. K., Tanner, J. C., Vincent, J. B., Callahan, P., Iaizzo, P. A., … & Garshelis, D. L. (2019). Bears habituate to the repeated exposure of a novel stimulus, unmanned aircraft systems. Conservation Physiology, 7(1), coy067.

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This story first appeared on Mongabay

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