How do African Black Oystercatchers Haematopus moquini recruit into high-density populations?

Abstract

Theoretical and empirical studies of oystercatchers both suggest that levels of adult site fidelity, natal philopatry and age-at-first-breeding are interrelated consequences of life-history decisions made by potential breeders. All are fundamental to explaining population dynamics and have important conservation implications. The African Black Oystercatcher Haematopus moquini is classified as Near Threatened and virtually nothing is known of the biology of sexually mature birds that have yet to become established as breeders (i.e. ‘floaters’). Using an extensive ringing/ recapture/resighting data set from islands off the west coast of South Africa where densities of territorial oystercatchers are very high, this study aimed to explore (1) the degree to which African Black Oystercatchers exhibit natal philopatry, (2) the age at which they enter the breeding population, and (3) the factors that might determine age-at-first-breeding. Both natal site philopatry and adult breeding site fidelity for island-reared birds were high with almost 100% returning to their natal sites. There is a clear, age-based recruitment pattern of oystercatchers into the island breeding populations, but time spent at a site, rather than age per se, may determine a bird's success in establishing a territory.