Satellite tracking reveals the home range and movement ecology across the annual cycle of a 32 g songbird

Understanding movement ecology across life-history stages is critical for conserving declining migratory species. The Bobolink (Dolichonyx oryzivorus), a grassland songbird, exhibits complex spatial behaviors shaped by annual cycle stage, landscape context, and environmental conditions. We investigated the movement ecology of adult male Bobolinks across three stages of the annual cycle using satellite tracking. We deployed Sunbird Argos satellite tags on 26 adult male Bobolinks from two breeding sites in the northeastern United States: one large, continuous grassland and one small, isolated site. Using continuous-time movement models, we estimated home range size and composition, analyzed movement patterns during nesting, post-fledging, and fall migration periods, and compared these parameters between sites. We documented nocturnal pre-migratory flights and used multiple linear regression to assess environmental and geographic factors associated with stopover movement. During nesting, males at the large site maintained larger home ranges with greater grassland cover than males at the isolated small site. By the post-fledging period, home range sizes no longer differed between sites, although home ranges at the large site still contained a higher proportion of grassland. We recorded temporary movements outside of established home ranges (forays) of up to 17 km during the nesting period, potentially linked to extra-pair mating, and provided evidence of nocturnal pre-migratory flights in most individuals. During migration, stopover home-range size was only moderately associated with temporal and environmental variables and was not influenced by landscape context. This study represents one of the first applications of fine-scale satellite tags on small migratory passerines across multiple annual cycle stages. It extends evidence of breeding-season forays and nocturnal pre-migratory flights to a grassland specialist, highlighting the behavioral flexibility of Bobolinks across seasons. Bobolinks adapted their space use and movement strategies to meet varying ecological demands. Our study emphasized the need to maintain connected grassland networks to support breeding populations and protect key Caribbean stopover sites to sustain Bobolinks along their long-distance migration route.