Real-time thermal imagery from an unmanned aerial vehicle can locate ground nests of a grassland songbird at rates similar to traditional methods

Abstract

Monitoring songbird reproductive output is a well-established method for assessing population persistence, but reproductive studies on grassland songbirds often suffer from low sample sizes, high labor costs, and high levels of disturbance due to the difficulty of finding nests. However, technological advances in unmanned aerial vehicles (UAVs or drones) might improve our ability to locate these hidden nests with minimal intrusion. We compared the effectiveness and efficiency of locating grassland songbird nests with a thermal camera mounted on a UAV versus traditional nest searching techniques. We used a paired experimental design to determine whether UAV-assisted searches could replicate the results from traditional search methods. Two independent teams surveyed field sparrow (Spizella pusilla) territories with active ground nests for up to 2 h on consecutive days. Each team recorded the outcome and time it took to locate the nest. Both methods were highly successful at locating ground nests. UAV-assisted searches located nests 28% faster than traditional methods, but the results from a survival-style analysis indicated that the methods were not significantly different. Although UAVs may temporarily increase stress and alter the behavior of animals, UAV-assisted searches are generally less invasive than traditional methods because piloting the aircraft from the territory edge drastically reduces the need to traverse and trample vegetation within the territory. Thus, UAV-assisted nest searches represent a promising technique for locating grassland bird nests. Continued advances in UAV and thermal technology are likely to increase the efficiency of UAV-assisted nest searches and may eventually remove the need for humans to enter target territories when monitoring nest success.