Strong wintering site fidelity contrasts with exploratory breeding site sampling in a socially monogamous shorebird

The migration behavior of an organism is supposedly shaped by selection to best utilize favorable environmental conditions and unevenly distributed resources to maximize survival and reproductive success. Repeated migration tracks of individual birds allow us to estimate individual consistency in the spatio-temporal patterns of migration, and thereby better understand the potential constraints or drivers of migratory strategies.

We caught 48 long-billed dowitchers (Limnodromus scolopaceus) on their nest in Alaska in 2019 and equipped them with a 2 g Solar Argos PTT-100 satellite transmitter. We obtained repeat migration data from 19 individuals (11 males, 8 females) for up to four years. First, we quantified the within-individual repeatability in migratory route and migratory timing during both southward and northward migration. Second, we defined the home ranges for breeding, staging and non-breeding sites for each individual, and assessed their spatio-temporal overlap across consecutive years.

Dowitchers were significantly more faithful to their wintering areas compared to any other stage of their annual cycle. Within their breeding range, individuals showed exploratory behavior and dispersed on average 159 [Formula: see text] 208 km (N = 42 bird-years) between breeding sites in consecutive years. The timing of migratory movements showed the highest individual repeatability when birds were at or near the wintering area.

Our study demonstrates that the within-individual repeatability in spatio-temporal patterns of migration and site use in dowitchers varies across different stages of the annual cycle. The birds' high fidelity to their wintering area contrasts sharply with a lack of fidelity to their breeding area. We suggest that the long-distance breeding dispersal - atypical for socially monogamous Scolopacids - is an adaptive response to unpredictable year-to-year variation in the physical and/or social environment during the breeding season.