Species and Sex-Biased Predation on Hatchling Green Turtles by Frigatebirds on Europa Island, Western Indian Ocean

Europa Island is a major breeding place for green turtles (Chelonia mydas; 0.7 to 2.4 million juvenile turtles hatch there annually), Great Frigatebirds (Fregata minor; 700 to 1100 breeding pairs), and Lesser Frigatebirds (Fregata ariel; 1000 to 1200 pairs). By visual observation, we quantified the proportions of males, females, and juveniles of both frigatebird species prospecting over the hatching sites and preying on hatchling turtles. Of 1828 juveniles observed hatching at daytime (35 separate turtle emergences), 1632 were immediately eaten by male Great Frigatebirds. Only 10 hatchlings were preyed upon by female Great Frigatebirds; the remaining 186 were captured by juvenile Great Frigatebirds. Such feeding behavior was not observed in Lesser Frigatebirds. We suggest that the sexual and species differences in hatchling turtle predation are due to size differences between the two species and between male and female Great Frigatebirds.