Habitat conditions during winter explain movement among subpopulations of a declining migratory bird.

Abstract

BACKGROUND: Understanding animal movement patterns among subpopulations is crucial for identifying spatiotemporal patterns in animal abundance. Quantifying such movement rates enables a better understanding of population dynamics and how animals decide to move between habitats throughout their range. However, detailed assessments of animal movements among subpopulations are often difficult to obtain with typical capture-mark-recapture methods, limiting our ability to incorporate movement information into conservation planning. METHODS: We used six years of high-resolution Global Positioning System (GPS) tracking data in a Bayesian multistate model to quantify habitat drivers of monthly intra- (i.e., from one month to the next within a winter) and inter-winter (i.e., from the last month of one winter to the first month of the following winter) movements among eight different subpopulations of a declining migratory bird, the Greenland white-fronted goose (Anser albifrons flavirostris). RESULTS: We found that while Greenland white-fronted geese were highly philopatric to geographically distinct wintering subpopulations, individuals made intra- and inter-winter movements based on locally available foraging habitat. These decisions changed within and among winters; geese were more likely to make intra-winter movements to areas with fewer croplands and boglands, potentially in response to local food depletion, and more likely to make inter-winter movements to areas with more boglands and “greener” grasslands. CONCLUSIONS: We demonstrated a framework for using high-frequency GPS tracking data to discover movement patterns and test hypotheses about environmental drivers of movements, which could be linked with population dynamics and applied to other species of concern for an improved understanding of metapopulations across space and time. Implementing habitat management strategies that optimize foraging conditions throughout winter, including rewetting degraded peatlands to provide bogland food plants, provision of cereal stubbles in early winter and high-quality grasslands throughout winter may help improve conservation outcomes for Greenland white-fronted geese.