Abstract
Spring migration phenology of birds has advanced under warming climate. Migration timing of short-distance migrants is believed to be responsive to environmental changes primarily under exogenous control. However, understanding the ecological causes of the advancement in avian spring migration phenology is still a challenge due to the lack of long-term precise location data. We used 11 years of Global Positioning System relocation data to determine four different migration dates of the annual migration cycle of the American white pelican (Pelecanus erythrorhynchos), a short-distance migrant. We also tested the hypothesis that increases in winter temperature and precipitation on the wintering grounds would advance pelican spring migration. Pelican spring departures and arrivals advanced steadily from 2002 to 2011. Spring departure timing exhibited high repeatability at the upper end of migration timing repeatability reported in literature. However, individual spring departure and arrival dates were not related to winter daily temperature, total winter precipitation, and detrended vegetation green-up dates indexed by the normalized difference vegetation index. Despite high repeatability, the observed between-year variation of spring departure dates was still sufficient for the advancement of spring departure timing.
Highlights
Phenotypic plasticity of life history traits may allow birds to track novel environments rapidly[3,8]
Significant advances in the spring departures of both populations and adults suggest that age and migration experience may not be the only cause of the observed advancement of pelican spring migration
Avian migration timing has the lowest repeatability (r) in a set of 12 behavioral traits analyzed by Bell et al.[31]
Summary
Phenotypic plasticity of life history traits may allow birds to track novel environments rapidly[3,8]. We hypothesized that advanced primary productivity phenology on the non-breeding grounds would lead to early spring departures of avian migrants including fish-eating birds, which we termed the ecological productivity phenology hypothesis[18]. The pelicans in the eastern sub-range are short-distance migrants: breeding mainly in the Northern Great Plains and wintering in the lower Mississippi River Valley and along the Gulf of Mexico[25,26]. We used 11 years of Global Positioning System (GPS) relocation data of 36 pelicans to determine whether the advancement of pelican spring migration phenology resulted from phenotypic plasticity. We tested the prediction of the ecological productivity phenology hypothesis that pelicans would fine-tune spring departure timing based on the phenological phases of primary productivity at the non-breeding grounds. Understanding the repeatability and responses of the migration timing of large-sized birds has important implications for the conservation and management of large-sized birds under predicted global warming
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