Differences in Susceptibility to Predation during Nesting Between Pied and Black Stilts (Himantopus spp.)

Abstract

The nesting success of the Pied Stilt (Himantopus himantopus leucocephalus) and the endangered Black Stilt (H. novaezealandiae) was studied for three consecutive breeding seasons (1977-1979) in New Zealand. Black Stilts had a breeding success of less than 1%, compared with over 8% for Pied Stilts. Predation by feral mammals was the main cause of nest failure for both species, but the impact was greater on Black Stilts. Direct and indirect evidence (including trapping predators) suggests that these introduced ground predators kill many chicks. Several factors made Black Stilts vulnerable, particularly their nesting along stream banks that were often frequented by predators; Pied Stilts nested in swamps where predators were few. Black Stilt chicks took up to 2 weeks longer to fledge and their foraging patterns made them more vulnerable than Pied Stilt chicks. Other factors that possibly increased predation risk of Black Stilts include nesting at times of high predator activity, solitary nesting, high site fidelity, ineffective distraction displays, and lack of a disruptive camouflage pattern in adults. Introduced ground predators probably have contributed greatly to the decline of Black Stilts. Pied Stilts have not been affected similarly, because their evolutionary past has included long exposure to ground predators.