Bioacoustic recording devices – technology that records the sounds of living creatures –can help fill in some of the gaps for ecologists surveying bird populations, particularly when it comes to species that like to stay hidden. Better yet might be bioacoustic recording devices that dangle from drones, according to a new study designed to test the feasibility of this creative approach to conservation.

The hope is that by rigging up these flying recorders, researchers can use them to survey birds in accessible or dangerous terrain. Ecologists from Pennsylvania's Gettysburg College put this theory to the test by tying a lightweight audio recorder to a DJI Phantom 2 with fishing wire and carrying out trials in the Pennsylvania State Game Lands.

This involved counting birds at 51 different locations using standard methods, and then using the recorders dangling eight meters (26 ft) below the drones to do the same. The team found that in most cases, the counts gathered from the recorders were very similar to those tallied by experienced ornithologists. But there were some exceptions.

The researchers found that one species, the mourning dove, had its low-frequency song drowned out by the sound of the drone. Another, the abundant gray catbirds, belted out their songs in such high numbers that the researchers had trouble telling the individual birds apart when listening to the recordings.

There is also the issue of whether or not the presence of the drones impacted birdsong behavior. According to the researchers, there is no evidence that they do with the drones flying 60 m (196 ft) overhead, but further work is needed to know for certain.

In time, the researchers hope that advances in drone technology will make the aircraft much quieter, something that could remove this problem all together. In spite of this and the other current limitations, they conclude that the approach holds great promise not to replace traditional bird surveyors, but supplement their work and help fill in blind spots in their research.

"Surveying birds by ear is an impressive skill that encourages ornithologists to spend time out in the field getting to know their study species and their habitats," said study co-author Andrew Wilson. "We need to be wary about relying too heavily on technology, because that reliance could erode natural history skills and reduce an emotional connection with birds and the environment."

The research has been published in the journal The Auk Ornithological Advances, while you can see the fieldwork in action in the video below.