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To a hawk, an airport can look like the perfect place to settle down. The layout provides ample open space, perches, and nice habitat for a variety of prey species. However, congregations of birds, especially big birds, pose a safety issue for aircraft.

A new study focusing on Cooper's Hawks (Accipiter cooperii), in the Journal of Raptor Research, found that removing a hawk from an airfield and taking it somewhere else, called translocation, can serve as a method for reducing this risk.

Researchers also showed that the age and sex of individual hawks as well as the distance moved were all factors that impacted hawk return rates to the airport of origin.

Management teams have a higher chance of reducing the incidence of raptor-aircraft collisions, without needing to resort to lethal methods, if they incorporate species-specific research like this into their programs. Regarding the safety of the flying public and raptor conservation both, this matters.

Cooper's Hawks are medium-sized, aerodynamic raptors that specialize in hunting other birds. They have successfully adapted to populated areas, including the Los Angeles Basin of southern California where this study took place. As lead author Brian Washburn puts it, Cooper's Hawks "thrive in non-traditional environments," making them something of a suburban all-star in the world of wildlife.

From 2017 through 2022, Washburn and his colleagues from the U.S. Department of Agriculture Wildlife Services captured over 600 Cooper's Hawks at six different airports in the Los Angeles Basin and fitted them with individually coded leg bands.

They also noted the age and sex of each bird. After capture, the hawks were translocated away from their home airport at four different trial distances—24, 48, 72, and 96 kilometers. The goal was to investigate which factors most impact whether a hawk would return to the airport from which they came.

In tandem with this field research, the team asked the Federal Aviation Administration (FAA) to provide a report on the number of documented Cooper's Hawk aircraft strikes that occurred between 1990 and 2023 in the United States, to garner a sense of whether this species is in fact problematic at airports.

Over that time period, the FAA reported 217 Cooper's Hawk strikes, with a notable 3,200% increase in occurrence, including a substantial uptick after the year 2014.

In the big picture, this species is not a huge issue for airports compared to some other North American raptors. However, knowing which factors impact translocation success for Cooper's Hawks bolsters overall knowledge of how best to approach raptor-strike mitigation programs, especially as it relates to species that hunt other birds.

Of the captured hawks in this study, only 10% exhibited homing behavior, meaning they returned to their initial airport and were sighted by an observer. Although the authors deem this a conservative estimate, these results suggest that translocation, when done right, can indeed reduce the resident population of Cooper's Hawks at airports in the Los Angeles Basin.

Specifically, the team found that hawks in their second year of life demonstrated the highest return rate; females returned more often than males, and the further away a hawk was moved, the less likely they were to return.

In the United States, wildlife strikes with commercial aircraft result in over $1.5 billion dollars in damages per year, with raptors being one of the most frequently struck wildlife guilds.

Airport administrators are naturally interested in adopting efficient collision-reduction programs while also keeping costs of implementation low. Therefore, to facilitate the highest chance that a hawk will stay away once translocated, the authors recommend that authorities move them at least 48 kilometers from the airport and focus on translocating only hatch-year and adult birds, because young hawks have not yet established a territory.

Washburn says this study adds to the growing toolkit of human-raptor conflict mitigation techniques and "increases safety for the flying public using humane means while also minimizing the number of Cooper's Hawks removed from the wild population."

He hopes to conduct future work on what happens to the hawks after successful translocations, ideally using GPS transmitters to fine-tune understanding of movement patterns, survival, and habitat use.

The paper also recommends that management teams reduce the attractiveness of airports for Cooper's Hawks' favorite prey species, like House Sparrows (Passer domesticus) and Rock Pigeons (Columba livia).

Raptors are top predators and therefore their continued existence is an important thread in the fabric of a healthy environment. Raptor-strike management programs that reduce risk to public safety but also support the continued success of the species at hand offer a potential model for airports worldwide.