Drones Are as Good as People at Counting Birds

A new study compares traditional, ground-based bird surveys against unmanned aerial vehicles rigged with audio recorders.

Ornithology researchers from Gettysburg College put technology to the test, when they studied the effectiveness of drones as a means to assess songbird populations, and the machines were up to the task.

In a paper published in the journal The Auk: Ornithological Advances, the scientists reported on their recording of bird calls using pocket-sized digital recorders attached with fishing line to quadcopters.

Songbird surveys conducted by the team on game lands in Pennsylvania compared the counts acquired using the drones against traditional counts performed by surveyors on the ground.

The drones hovered and "listened" with the recorders, catching as many birds sounds as the recorder's "detection radius" would allow.

The ground surveys were performed using standard "point count" methods, in which observers count as many birds as they can see and hear at a given location over a set period of time.

Both methods were assessed at 51 locations.

According to the scientists, save for a few things the drones under-counted – mourning doves, with their low-pitched songs, were hard to pick up on audio; and there were too many gray catbirds to distinguish reliably – the two methods compared favorably.

Given the results, the researchers said bird surveys using drones could allow counts to be made in dangerous or inaccessible locations that would otherwise stymie ground-based surveyors. More broadly speaking, they said, drones with recorders attached are certainly good fits for counting songbirds.

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Any lingering questions revolve around the drones themselves. Do they affect bird behavior? The Gettysburg team did not observe a problem, but they urged further study on the matter.

Meanwhile, noisy things that dangle audio recorders can present a challenge to hearing what you're trying to record. "Excessive [drone] noise," the scientists wrote, "is a major hurdle to using [them] for bioacoustic monitoring, but we are optimistic that technological innovations to reduce motor and rotor noise will significantly reduce this issue."

Study lead Andrew Wilson said he came up with the idea for testing drones in bird surveys during a ground-based bird count of cerulean warblers. Gaps in the count, he noted, had been created by inaccessible locations.

"All of our survey work was done from roadsides or hiking trails for logistical reasons and to maximize survey efficiency," Wilson said in a statement, "but I was always aware that our sample locations were very biased and that we were missing key areas such as steep forested slopes."

Down the line, drones could significantly speed the entire counting process, offering up-to-the-minute readings of which birds are where.

"I have a vision that within a few years, quieter [unmanned aerial vehicles] will be surveying large areas of terrain within just a few hours, and that the technology will have advanced to the point where all bird vocalizations are automatically identified and plotted in real-time," Wilson told PLOS Blogs.

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