Various benefits (e.g. tracking of resources and of climate niche) and costs (e.g. distance travelled) are hypothesized to drive seasonal animal migrations. Until now, these potential factors have been investigated together at the species level, but migratory movements are made at the individual level, leading to intraspecific variability. Here, we use ringing/recovery data from 1308 individuals belonging to thirteen North American bird species to analyse patterns in intraspecific variability of migratory destinations in order to investigate which factors underpin bird migration and how individuals trade-off among multiple factors. Our results suggest that migratory destinations have been shaped by access to resources (most important during the breeding season) and climatic niche tracking (during winter, mostly). However, the benefits of resource surpluses and climate niche tracking appear to be traded off against the cost of migratory distance, which seems to strongly constrain where individuals migrate.

Data and codes used in this analysis are presented here.

This data was obtained from a dataset of bird ringing/recovery (USGS Bird Banding Lab), selecting individuals as described in the manuscript (only alive birds, at least one location in the winter and one location in the summer, etc.). From location data, environmental conditions were extracted, and distance between the breeding and the wintering locations was calculated for each individual.