Responses of free-living horses and bison to a drone assessed in US national park

Wild horses in the Theodore Roosevelt National Park. It is one of the few national parks where visitors can observe free-roaming horses.
Wild horses in the Theodore Roosevelt National Park. It is one of the few national parks where visitors can observe free-roaming horses. Image by Jessica Rockeman

Flying a drone at 120 meters above ground level over free-living horses and bison in an American national park sparked behavioral changes, but no escape response.

Javier Lenzi and his fellow researchers noted the rapid increase in drone use in protected areas in North America. Over the past decade, they have contributed to the management of protected areas and species conservation by providing an alternative to traditional aviation and ground surveys.

Drones have been used to survey and monitor habitat and animal populations, and assess habitat suitability for a variety of species. The technology has provided additional tools for the tracking of radio-tagged animals, detection of organisms using thermal technology, and anti-poaching efforts.

It has also been used to enforce regulations, conduct environmental management, and improve disaster response protocols. Despite their many uses, their potential impacts on land-based megafauna have been largely unstudied, the researchers noted in the journal Drones.

The University of South Dakota study team set out to evaluate the behavioral responses of wild horses and bison to a drone in Theodore Roosevelt National Park in North Dakota.

Using a Trimble UX5 fixed-wing drone, the researchers performed two flights at 120 meters above ground level above herds of each species, recording video footage of their behaviors before, during, and after the flight. The footage was analyzed in periods of 10 second intervals, looking for changes in behaviour.

“Both species displayed behavioral responses to the presence of the fixed-wing drone,” they reported.

“Horses increased feeding, traveling, and vigilance behaviors, and decreased resting and grooming. Bison increased feeding and traveling and decreased resting and grooming.”

Neither species displayed escape behaviors, they said.

“Flying at 120 metres above ground level, the drone might have been perceived as low risk, which could possibly explain the absence of escape behaviors in both species,” they wrote.

“Our results showed that individuals did not display escape behavior, and even increased feeding activities in response to drone flights at 120 meters above ground level.”

They noted that evidence from other studies using drones as a source of disturbance shows that escape behavior is typically the normal way that land mammals respond to drones, but altitude is likely a key factor.

Their results, they said, provide new insights for guidelines about drone use in conservation areas.

Efforts to develop broad standards to regulate the use of drones in natural areas and elsewhere should persist, they said, but they also recommended the development of localized guidelines for protected areas, centered on place-based knowledge about the behavioral responses of local animal communities.

Future studies, they said, should consider standardized experimental designs that allow for comparisons at the group and individual levels. Data gathering should also expand to incorporate other factors such as time of day, seasonal and annual cycles, and food availability, among others.

Additionally, to have a better understanding of how time budgets are modified by drones, they suggested incorporating behaviors from ethograms instead of analyzing a limited number of behaviors, such as alertness and escape.

“Because the absence of escape and alert behaviors do not necessarily indicate the absence of impact, it could be beneficial to incorporate animal tagging technology to account for the physiological responses of horses and bison to drones.”

The study team comprised Lenzi, Christopher Felege, Robert Newman and Susan Ellis-Felege, with the University of North Dakota; and Blake McCann, with the National Park Service at Theodore Roosevelt National Park.

Lenzi, J.; Felege, C.J.; Newman, R.; McCann, B.; Ellis-Felege, S.N. Feral Horses and Bison at Theodore Roosevelt National Park (North Dakota, United States) Exhibit Shifts in Behaviors during Drone Flights. Drones 2022, 6, 136.

The study, published under a Creative Commons License, can be read here.

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