Meeting Abstract
The ability for individuals to optimally time life-history events can be a key driver for fitness in birds. Pair formation is an important event within the phenology of seasonal breeding because it influences the timing of reproduction. Presumably, the timing of pair-formation reflects the relative costs and benefits of being paired; if paired individuals have better access to limited resources, then it seems logical that selection would favour individuals to pair as soon as possible. If pairing does not influence female condition it might be most adaptive to restrict pairing to later in the spring, closely preceding breeding. Little is presently known about the timing and flexibility of pair formation in arctic-breeding diving ducks. Common eiders nesting in the Arctic at East Bay Island, NU (EBI), are a model species with which to investigate the timing of pairing because both individuals of a pair are simultaneously captured during the pre-breeding period. We apply a recently developed method for determining the overwinter origins of common eiders, based on a stable isotope cluster analysis, to examine the phenology of pair formation. Eiders pairing in winter have a strong correlation in claw isotopic values, and individuals with a weak correlation in claw isotopic values but highly correlated values in blood have likely paired in spring. Our findings suggest that common eiders breeding at EBI exhibit a flexible pairing strategy, with some eiders pairing in the winter, and others in the spring. Pairing strategies impacted the breeding decisions of female eiders and varied between years over distinct winter conditions.
