Differential migratory movements of geographically distinct wintering populations of a soaring bird

Abstract Background: Migratory soaring birds exhibit spatiotemporal variation in their circannual movements. We hypothesized that the circadian and seasonal movements of soaring migrants may depend primarily on exogenous factors such as thermals and wind conditions. Nevertheless, it remains uncertain how different winter environments affect the circannual movement patterns of migratory soaring birds. Here, we investigated annual movement strategies of American white pelicans Pelecanus erythrorhynchos (hereafter, AWPE) from two geographically distinct wintering grounds in the Southern and Northern Gulf of Mexico (GOM). Methods: We calculated average and maximum hourly movement distances and seasonal home ranges of GPS-tracking AWPEs. We then evaluated the effects of circadian hours, seasons, two wintering regions in the Southern and Northern GOM, human footprint index, and relative AWPE abundance from Christmas Bird Count data on AWPE hourly movement distances and seasonal home ranges using linear mixed models and generalized linear mixed models. Results: American white pelicans moved at the highest speed near 1200 hours at breeding grounds and during spring and autumn migrations. Both wintering populations in the Northern and Southern GOM exhibited similar hourly movement distances and seasonal home ranges at the shared breeding grounds and during spring and autumn migrations. However, AWPEs wintering in the Southern GOM showed shorter hourly movement distances and smaller seasonal home ranges than those in the Northern GOM. Hourly movement distances and home ranges of AWPEs increased with increasing human footprint index.Conclusions: Winter hourly movements and home ranges of AWPEs differed between the Northern and Southern GOM; however, the difference in AWPE winter movements did not carry over to the shared breeding grounds during summers. Therefore, exogenous factors may be the primary drivers to shape the flying patterns of migratory soaring birds.