Nonbreeding distributions and potential carryover effects in a sentinel north pacific seabird, the Cassin's auklet

Abstract

Factors influencing animal fitness during the nonbreeding period are critically important but remain largely unknown for many species. Here, I employed tracking and physiological sampling to gain insight into nonbreeding distributions, migratory behavior, and potential carryover effects in a North Pacific seabird. From 2014-17, nonbreeding Cassin’s auklets from British Columbian colonies occupied nearshore waters from Alaska to Baja California, utilizing regions north of the colony in summer/fall, south of the colony in fall/winter, and returning to the colony region >1 month prior to laying in early spring. Four general migratory tactics were expressed – North, South, North-South, and Local migration – with individuals exhibiting substantial variability in finer-scale phenology and choice of residency areas. Diverse nonbreeding experiences were expected to drive variability in the strength of carryover effects; however, indicators of pre-breeding physiologic state and diet did not predict reproductive investment (egg size) in an additional year, potentially due to oceanographic context.