Ecological Drivers of Brown Pelican Movement Patterns and Reproductive Success in the Gulf of Mexico

The effects of environmental change on vast, inaccessible marine ecosystems are often difficult to measure and detect. As accessible and highly visible apex predators in marine environments, seabirds are often selected as indicators for studying the effects of disturbance at lower trophic levels, although data are restricted both temporally and spatially. For example, studies of seabirds have historically been limited to the breeding season, with limited data being available throughout the remainder of the annual cycle. Additionally, understanding of habitat associations and behavior of seabirds in the marine environment comes primarily from pelagic seabirds, whose habitat year-round is generally in remote marine areas removed from anthropogenic development, while similar data from nearshore seabirds are less common. Such data gaps limit our understanding or life-history traits among seabirds, one of the most imperiled avian groups globally, and subsequently our ability to inform conservation and marine spatial planning. My goal was to examine ecological relationships of diet, breeding biology, and movement patterns of a nearshore tropical seabird, the Eastern brown pelican, in the Gulf of Mexico, one of the most anthropogenically developed marine ecosystems worldwide. While my results supported previous findings that nutritional conditions are a key driver of seabird reproductive success and recruitment, they differ in suggesting that prey availability and delivery rates are more important to reproductive rates than energetic value of prey species. Since direct measurement of reproductive rates is time-consuming and difficult to collect, I also tested an integrated measure of nutritional stress during development, feather corticosterone, as a predictor of nestling survival and fledging rates. Corticosterone predicted 94% of inter-colony variation in fledging success and was also correlated with post-fledging survival, making it a powerful tool for measuring demographic patterns in this species. To measure adult movement patterns, I deployed bird-borne biologgers to collect highly accurate spatial data from pelicans throughout the annual cycle. I found that individual breeders quickly returned to normal behavior after capture and tagging. GPS tracking also indicated that pelicans were highly mobile, ranging over large areas during the breeding season and migrating up to 2,500 kilometers during non-breeding. Movement patterns were influenced by local conspecific competition during both breeding and migration, such that birds from larger colonies moved longer distances year-round compared to those from smaller colonies. I also found a high degree of spatial, temporal, and individual variation in exposure to surface pollutants across the population. I recorded a high degree of individual variation in movement, which interacted with pollutant exposure to create a complex and varying distribution of risk throughout the northern Gulf metapopulation of brown pelicans. Understanding the factors driving this variation will inform future monitoring, conservation, and mitigation efforts for this species