Geographic and sexual variations in the movement patterns of American white pelicans

Background/Question/Methods – Mechanisms of animal movement are vital to understanding how animals are distributed over space and time. Spacing behavior and movements of migratory birds may change in response to seasonal and regional variations in environmental conditions. Sexual dimorphisms of bird movements may also tell how males and females act differently under sexual selection or in parental investment. Our main objective was to determine differences in seasonal home range size and circadian hourly movement distances of American white pelicans (Pelecanus erythrorhynchos) among seasons, population groups, and sexes. We attached GPS transmitters to 24 birds captured in North Dakota and 24 birds in Alabama, Mississippi, and Louisiana from 2002 to 2012. We analyzed hourly GPS location data by seasons (nesting and wintering), population groups (wintering in the Northern and Southern Gulf of Mexico), and sexes. We estimated seasonal home ranges using plug-in kernel density estimators. We then used linear mixed models to test for differences in home range size among seasons, population groups, and sexes with bird identity as a random effect. We also calculated and compared circadian hourly movement distances by seasons, population groups, and sexes using hourly consecutive GPS location data.

Results/Conclusions – Summer home range size did not differ between American white pelicans wintering in the Northern and Southern Gulf of Mexico. However, during wintering seasons, birds in the Northern Gulf of Mexico had larger home ranges than those in the Southern Gulf of Mexico. Additionally, females did not differ in home range size between nesting and wintering seasons, whereas males had significantly larger home ranges in nesting than wintering seasons. The results of circadian hourly distance analyses were consistent with those of home range analyses. Birds wintering in the Northern Gulf of Mexico had larger movement distances. Males moved more during nesting than wintering seasons. The differences in the winter movement of the pelican may result from differences in food availabilities between the Northern and Southern Gulf of Mexico. Higher food availability may lead to less movement and smaller home ranges of the pelicans in the tropic than subtropic regions, supporting NcNab’s energetic constraint hypothesis. Seasonal differences in the spacing behavior of male pelicans may be due to increased energetic demands for reproduction in nesting seasons. Our results provide better understanding the effects of spatiotemporal variation in resources on migratory bird behaviors of the pelicans.