Breeding ecology of the black turnstone: Hedging bets in a variable subarctic environment

The Black Turnstone (Arenaria melanocephala) is a monogamous sandpiper that breeds on coastal meadows of subarctic Alaska and winters along the Pacific Coast. This dissertation summarizes results of a five-year study on turnstone breeding ecology and social behavior. The first chapter examines seasonal and interannual variability in breeding chronology and success relative to variability in environmental conditions and predation pressure. Timing of breeding was more constrained for females than males: females arrived later and departed earlier than males and onset of egg-laying was limited by time needed for ova maturation. Reduced chick mass during years with a later spring suggested a physiological cost for females for delaying breeding. Extreme interannual variability in factors affecting reproductive success, including spring conditions, rainstorms at hatch, flooding by storm surges, and predation, swamped the more predictable seasonal variation in these factors. Conservative expenditure of breeding effort in a season may contribute to high adult survival rates and increase opportunities to experience more peak years of reproduction.; The second chapter examines the relationship between mate fidelity and breeding site tenacity and tests several hypotheses regarding divorce. Interannual return rates were among the highest yet recorded for any sandpiper. Mate fidelity was significantly linked to territory fidelity but influenced by the relative timing of arrival of pair members. Reunited pairs had higher fledging success than new pairs but the incidence of divorce was unrelated to success the previous year. Sightings of marked individuals suggested that pair members do not winter together, and breeding site tenacity provides a mechanism through which pair members can reunite. The “bet-hedging” hypothesis is proposed to explain the occurrence of divorce, in which an individual pairs with a new mate to avoid the cost of waiting for a previous mate to return. Such costs can include remaining unmated, if the former mate has died, or experiencing lower reproductive success because of delayed breeding.; The final chapter provides a detailed synthesis of the life history of the Black Turnstone, including information on distribution, migration, habitat, food habits, vocalizations, behavior, breeding, demography, conservation, molt, sexual size dimorphism, and priorities for future research.