Seabird's pulsed abundance modulates breeding season ecology and mercury exposure of a highly associated bird of prey

BALZA, ULISES; LOIS, NICOLÁS; PÜTZ, KLEMENS; POLITO, MICHAEL J.; BRASSO, REBECKA; RAYA REY, ANDREA

Virtual

Congreso; III World Seabird Conference; 2021

World Seabird Union

The massive concentration of seabirds in small terrestrial habitats for breeding can encompass a pulsed, predictable, and high-quality feeding resource for terrestrial predators. The Striated caracara (Phalcoboenus australis) is a globally Near Threatened raptor specialized in the exploitation of seabird colonies during breeding season. In a 4 Km2 bay in Isla de los Estados, Argentina, near 300,000 seabirds breed between September and late March. In order to understand the level of dietary dependence on local marine resources, we examined breeding behavior and intra-specific variation in the trophic niche of caracaras during breeding season using stable isotope and pellet analysis. All nests of caracaras were associated mainly with the rockhopper penguin (Eudyptes chrysocome) colony on the island. Isotopic niche varied with, age, breeding status, and, year, but in all cases over 75% of their diet came from seabird colonies. Pellet analysis showed a similar pattern, with down feathers, feathers and eggs of penguins present in over 80% of the samples. Mercury (Hg) analysis in feathers suggest high levels of contamination, with adult feathers averaging over 26 mg/kg. Rockhopper penguins have been reported to present high levels of Hg in the area, thus this high dependence of caracaras on penguin prey represents a higher vulnerability for this caracara population. Overall, seabirds, and especially rockhopper penguins, appears to modulate trophic ecology and mercury exposure of its main terrestrial predator.