Timing of migration and prebasic molt in tidal marsh sparrows with different breeding strategies: Comparisons among sexes and species

Abstract

Breeding strategies can shape the timing of other events and processes, including arrival on the breeding grounds, prebasic molt, and departure for fall migration. We studied these relationships in sympatric Saltmarsh Sparrows (Ammodramus caudacutus) and Seaside Sparrows (A. maritimus), 2 closely related species with notably different breeding strategies. On average, females of both species arrived on the breeding grounds later, initiated molt later, and departed from the breeding grounds later than did conspecific males. Furthermore, we found that female Saltmarsh Sparrows-which mate with multiple males and care for nests, eggs, and chicks alone-were last to arrive on the breeding grounds and last to initiate molt, had the shortest molt duration, and were last to depart for the nonbreeding grounds. Both species exhibited protandry, but Seaside Sparrows averaged earlier arrival on the breeding grounds than Saltmarsh Sparrows. Molt and departure timing also differed between the species, with Seaside Sparrows initiating molt and departing before same-sex Saltmarsh Sparrows. These observations support the hypotheses that breeding strategies can influence arrival timing and that reproductive investment can have carryover effects on molt and departure.