Wood Storks (Mycteria americana) Prey on Eggs and Hatchlings of Olive Ridley Sea Turtles (Lepidochelys olivacea) at Ostional, Costa Rica

The foraging behavior of Wood Storks (Mycteria americana) has been studied extensively because of their dramatic population decline and endangered status. The foraging by Wood Storks at an arribada beach with olive ridley sea turtles (Lepidochelys olivacea; turtle) at Ostional, Costa Rica, was examined to determine their depredation behavior on turtle eggs and hatchlings. Wood Storks, in association with Black Vultures (Coragyps atratus), foraged on turtle nests exposed by stream, tidal, and wind erosion, and on nests dug up by dogs (Canis familiaris). Wood Storks also foraged on emerging turtle hatchlings and those crawling to the sea. Wood Storks concentrated near stream beds where nearly half of the predation events (eggs/hatchlings being eaten) occurred. Usually, one to three Wood Storks fed at a turtle nest; an average of 87% of the Wood Storks that were within 5 m of a turtle nest obtained eggs or hatchlings. The number of Wood Storks present and feeding, and the percent feeding, depended upon feeding location, time of day, and whether they were feeding on exposed nests or on emerging hatchlings. An average of two Wood Storks per 30 sec obtained food at nests with exposed eggs, compared with four at nests with emerging turtle hatchlings. Most Wood Storks fed at nests exposed at stream banks (60%) or by tides (23%). Wood Storks had little effect on success of olive ridley sea turtles at Ostional because of the very large number of nesting female turtles, the small population of Wood Storks, and that most turtle hatchlings emerge at night when Wood Storks did not forage. Wood Storks were scared off by people during the peak daylight hatching period, and most Wood Storks and Black Vultures foraged at turtle nests exposed by wind, rain, tides, and dogs. The only viable olive ridley sea turtle offspring Wood Storks fed on were emerging hatchlings and those that crawled to the sea during the daylight. Received 31 January 2013, accepted 14 March 2013.