Sensitive to human disturbance and contaminants, American white pelicans (Pelecanus erythrorhynchos) and brown pelicans (Pelecanus occidentalis) are large migratory waterbirds that have been the focus of intensive conservation efforts since the 1970s. Both species are found throughout the United States, Mexico, and Central America, though white pelicans occur primarily in inland areas whereas brown pelicans are restricted to the coast. Across their large ranges, pelicans encounter asymmetric environmental and anthropogenic conditions, likely producing the spatial and temporal variation in these species’ population trajectories witnessed over the past century. However, migratory connectivity and survival of both pelican species are poorly understood, limiting our understanding of how threats, including acutely toxic pesticides and rapid anthropogenic changes to breeding, foraging, and wintering habitats, have incongruously impacted pelican populations. Using band and wing tag resight and recovery datasets from the USGS Bird Banding Laboratory (BBL), we fit multi-state capture-recapture models to estimate connectivity and spatial and temporal variation in pelican survivorship over the past eighty years. We jointly estimated nuisance parameters (i.e., band recovery and resight probabilities) using data from both pelican species in combination with resight effort data from other non-game species, improving estimates of species-specific parameters of interest.
Results/Conclusions
Results from this analysis indicate that both species show strong migratory connectivity within regions, with little mixing between populations. Movement between eastern and western populations was particularly low for brown pelicans, likely due to their strictly coastal distribution. Movement between the United States and Mexico/Central America, a wintering area for both species, was also low. Survival probabilities for both species increased through time, mirroring both aquaculture growth and increases in wetland protections across the continent. Survival varied between regions, but both white and brown pelicans exhibited similar trends across the landscape, suggesting threats to both species varied similarly across time and space. These results provide important context for understanding past changes in North American pelican demography and abundance and for managing populations of migratory species in the face of future threats across their annual cycle.