New paper alert - disturbance and seabird behavior

In collaboration with the Kloepper Lab, we recently published a paper on behavioral responses of common terns to disturbances. The work even made the cover of the journal!

Acoustic monitoring is a developing technique in the field of wildlife study and conservation. Passive recording devices can be a powerful way to gather large amounts of data on a species while maintaining a low cost.

Our species of choice for this technique is the Common Tern. With more than 3,000 nests on the islands of White and Seavey in the Isles of Shoals, their dense colony makes them ideal for passive acoustics. While in their colony, they communicate during feeding, courtship, colony defense, and many other behaviors. These calls dominate the acoustic landscape, and heavily overlap even during times of low activity, making individual identification difficult. Instead, we can look at metrics of amplitude to serve as an indication of overall colony activity at a given moment.

One behavior that we believed could be strongly detected acoustically is antipredator response. Many species make alarm calls in response to threats within their colonies and even modify these calls based on factors like severity or proximity of the threat. While anecdotal evidence indicated Common Terns behave the same way, this had yet to be quantified. Understanding the alarm response of a species can be extremely beneficial for the monitoring and conservation of that species. Recognizing when they are under duress, or when a disturbance is present within a colony can be critical for effective conservation efforts.

To acoustically assess the antipredator response of Common Terns, we set up an array of AudioMoth microphones across the Seavey Island tern colony. For around a month during peak colony activity, seabird technicians working in the colony were asked to record the times and locations they spent within the colony. From this, we calculated the distance between the disturbance and the microphones, and compared that with the recorded amplitude at each microphone. What we found was a consistent trend, disturbance within 20 meters resulting in a strong response, within 10 meters being even stronger, and outside of 20 meters having no significant response. This indicates a specific type of antipredator response called a graded alarm call, where the terns are adjusting their response based on, in this case, the distance of the perceived threat.

This demonstration of a graded antipredator response by the Common Tern is just the beginning of their acoustic journey. This study is part of a much larger ongoing project, focused on developing the technique of passive acoustic monitoring for dense colony species. Factors such as nighttime behavior, population censusing, and chick hatching are all potential uses of acoustic monitoring, which may hopefully develop into a powerful technique for conservation.