Black Terns (Chlidonias niger) beyond the breeding grounds: Occurrence, relative density, and habitat associations in the northern Gulf of Mexico

North American Black Terns (Chlidonias niger) breed primarily in the Prairie Pothole region of southern Canada and the northern United States, winter in Central and South American waters, and often migrate through the northern Gulf of Mexico (nGoM). This species has exhibited long-term population declines and is exposed to a myriad of anthropogenic threats in the nGoM, including oil spills, with an estimated 800–1,000 injured during the Deepwater Horizon oil spill, yet historical studies of Black Terns' use of the nGoM are sparse, with inconsistent spatial and temporal coverage. Using vessel-based observations collected from 2017 to 2019, we characterize Black Tern spatial and temporal occurrence in marine waters of the nGoM. We develop 2 separate habitat models: one describing spatial and temporal aspects of Black Terns occurrence and the other describing the relative density when present. In 10 months of survey effort, January–October, we observed Black Terns in 7 (Mar–May and Jul–Oct), predominantly on the continental shelf at