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You Are "Where" You Eat: Spatial Foraging Patterns Reflected in a Seabird's Ornament

Released: 2017
Michael, N., R. Torres, A. Welch, L. A. López-Márquez, A. Martínez-Flores, J. Felis, J. Adams, and A. Wiley. 2017 You are “where” you eat: Spatial foraging patterns reflected in a seabird’s ornament. General Session for the 2017 American Ornithological Society (135th Stated Meeting) and Society of Canadian Ornithologists. (35thStated Meeting) held July 31, 2017 – August 05, 2017 at Michigan State University [Spoken Presentation]

As populations of seabirds decline globally, it is critical to understand their foraging locations in order to facilitate preservation of their food resources. A thorough understanding of seabird foraging habitats may also inform our view of their breeding strategies, for example if sexual ornaments are shaped by where individuals feed. Foraging locations often differ in relative prey availability, and because carotenoids are derived solely from diet, geography may be an important determinant of carotenoid-based ornament condition. A declining population of Brown Booby (Sula leucogaster) in the Marietas Islands presents a valuable opportunity to explore these relationships; this seabird possesses a condition-dependent, carotenoid-based gular skin ornament and has access to geographically distinct foraging regions. Stable isotope analysis of 13C in Brown Booby feathers showed that a presumably more attractive green-skinned ornament in males is correlated with lower 13C values, an indicator of more offshore foraging (R2=0.57, p=0.0019). Tracking of birds with GPS tags (i-gotU 120, Mobile Action) confirmed that greener males foraged in more offshore locations, often beyond the continental shelf. Compared to coastal foragers, these individuals flew greater distances, and may have exploited carotenoid-rich prey items such as the Pacific sardine, a pelagic species heavily targeted by local fisheries. Importantly, our data showed that the relationship between foraging location and ornamentation persists through multiple breeding seasons and El Niño Southern Oscillation phases. In light of changing marine environments, the link between foraging habitats and ornaments may be critical to understanding the full extent of anthropogenic influence on seabird populations.

This product is associated with the following project:
Tracking the Movements and Migrations of California Current Seabirds

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