Movements of post-breeding royal terns (Thalasseus maximus) in Virginia, U.S.A

Seabirds use a variety of strategies to maximize survival during migration. We studied the post-incubation movements of royal terns (Thalasseus maximus) from the largest seabird colony in Virginia, U.S.A. to understand their behaviors after nesting. We affixed GPS/GSM transmitters to nine incubating adult royal terns near the end of incubation (late June 2022) until migration (early December 2022). We used a hidden Markov model to describe royal tern behavior from late incubation through part of the migration season. Royal terns were classified as either resting or exploratory (e.g., flying, foraging) based on their speed and turning angles. Royal terns spent most of their time in the exploratory state (0.711, 95% CI [0.710-0.711]). Royal terns tended to move north following the breeding season before migrating to the south in October and November. We speculate that the post-breeding movement north was to track Atlantic menhaden (Brevoortia tyrranus), a primary food source. As threats to royal terns on the Atlantic coast such as declining prey fish stocks and offshore energy development increase, knowledge of their behaviors and movements will be essential to their conservation.