Shorter Migration Distance and Breeding Latitude Correlate With Earlier Egg-Laying Across the Northeastern Pacific Ocean Range of the Rhinoceros Auklet ().

Models of migratory behavior predict trade-offs between fitness costs and benefits with respect to migration distance. Shorter migration distances may confer a fitness benefit by facilitating earlier breeding, however this is rarely investigated. We tested this hypothesis using a large-scale geolocation (GLS) dataset from 109 rhinoceros auklets (), a differentially migrating seabird, that was tagged at 12 breeding colonies along the Pacific Coast of North America, spanning southern California to the eastern Aleutian Islands, Alaska. Using GLS-based position estimates, we determined the geographic centroid of the pelagic areas occupied by birds in winter (1 January-28 February) and then calculated the distance between their wintering centroids and colony of origin. We then used GLS light-intensity and salt-water immersion (wet/dry) data to determine each individual's date of egg-laying the following spring. Rhinoceros auklets were very widely distributed across the northeastern Pacific Ocean in winter. Among all individuals, the distance between winter centroids and breeding colonies ranged from < 100 to > 2500 km, being greater among individuals originating from colonies at higher latitudes. As predicted, migration distance and colony latitude were positively related to lay date: after accounting for colony-level differences in phenology, individuals that migrated shorter distances tended to lay their eggs earlier, a pattern that emerged across all populations. Our study links the migration distance of rhinoceros auklets to a fitness-related outcome, underscoring the selective pressure that migration exerts on subsequent breeding activity.