Social connections across migration: Do Golden-crowned sparrows (Zonotrichia atricapilla) that socialize in winter also breed together?

Here, we study migratory golden-crowned sparrows with distinct, stable winter communities. The sparrows have winter site and group fidelity across years, and birds almost always rejoin the same social community each year. Sparrows in the same tightly-knit community migrated to highly disparate locations during summer, showing that social connections in winter do not continue in summer. We provide initial evidence that the birds have entirely separate social structures across seasons with long-term social memories allowing them to reform stable groups each winter. Our research uncovers a new pattern in this model system that could apply to other migratory animals.

Methods
GPS data was collected through GPS tags placed on Golden-crowned Sparrows at their wintering site at the University of California Santa Cruz (UCSC) Arboretum in California, USA. All GPS tags were programmed to take points along the birds' summer migration to the breeding grounds to see where the birds went during the breeding season. The GPS tags were archival, so data retrieval depended on physically collecting the tags when birds returned to the UCSC Arboretum field site the following winter season. We used social network analysis from visual band observations during the winter to see how these connections related to the birds' locations during the breeding season.