VIEWING HABITAT THROUGH ANOTHER LENS: BIRD NEST-SITE SELECTION AND PRODUCTIVITY ACROSS A BEACH THERMAL LANDSCAPE

In 2018, we studied the effects of the thermal landscape on the least tern (Sternula antillarum), in a breeding colony on Lea-Hutaff Island, NC. Little is known about the fine-scale temperature variations of the coastal landscape, which limits our ability to assess its effect on animal productivity. Our three hypotheses are: (1) the thermal landscape, as measured by thermal imaging, will be highly variable and will reflect ambient environmental conditions. (2) The thermal landscape, as measured from thermal images, influences nest-site selection by least terns. Specifically, we predict that birds avoid nesting in the hottest locations. (3) The thermal landscape, as measured from thermal images, limits nest success for least terns. We predict lower nest success for nests in the hottest locations.

To describe the thermal landscape, we recorded surface temperatures via a fixed-wing mapping unoccupied aerial vehicle (UAV). We established a detailed UAV flight protocol that minimizes disturbance in areas where species of conservation concern are located. These techniques included to launch the UAV ~250 m away from the colony, maintain an altitude of 122 m, fly on sunny days around midday, and paint the bottom of the UAV to blend in with the sky. The UAV carried a thermoMAP thermal camera with a temperature resolution of 0.1°C and a S.O.D.A camera to provide multispectral images and digital surface models. We used ice bags as ground control points to help measure the accuracy of the thermal imaging camera. We recorded ambient environmental conditions at ground-level throughout the season. The weather data will help determine which variables influence sand surface temperature and explore the cause of nest success. We recorded bird nest locations and elevations with a Trimble real-time kinematic GPS. We monitored 157 nests visually to assess successful hatching of chicks. Our preliminary results indicate that there is a wide range and variation of temperatures across the landscape, supporting hypothesis 1. Also, there seems to be a positive relationship between subtle sand elevations and sand temperatures. Tern nest locations varied in surface temperature. We have tentative evidence that birds appear not to nest in the hottest locations, supporting hypothesis 2.