Preserving avian flyway connectivity has long been challenged by our capacity to meaningfully quantify continental habitat dynamics and bird movements at the temporal and spatial scales underlying long-distance migrations. Waterbirds migrating hundreds or thousands of kilometers depend on networks of wetland stopover sites to rest and refuel. Entire populations may rely on discrete wetland habitats, particularly in arid landscapes where the loss of limited stopover options can have disproportionately high impacts on migratory cost. Flyway connectivity was examined in water-limited ecosystems of western North America using 108 GPS-tagged greater sandhill cranes. Bird movements were used to reconstruct wetland stopover networks across three geographically unique sub-populations spanning 12 United States–Mexican states and Canadian provinces. Networks were monitored with remote sensing to identify long-term (1988–2019) trends in wetland and agricultural resources supporting migration and evaluated using network theory and centrality metrics as a measure of stopover site importance to flyway connectivity. Sandhill crane space use was analyzed in stopover locations to identify important ownership and landscape factors structuring bird distributions. Migratory efficiency was the primary mechanism underpinning network function. A small number of key stopover sites important to minimizing movement cost between summering and wintering locations were essential to preserving flyway connectivity. Localized efficiencies were apparent in stopover landscapes given prioritization of space use by birds where the proximity of agricultural food resources and flooded wetlands minimized daily movements. Model depictions showing wetland declines of 16% to 18% likely reflect a new normal in landscape drying that could decouple agriculture–waterbird relationships as water scarcity intensifies. To help mitigate this, the model suggests that migratory birds will benefit from conservation strategies to balance water allocations preserving agricultural and wetlands on private lands that accounted for 67–96% of habitat use. Study outcomes provide new perspectives of agroecological relationships supporting continental waterbird migration to support conservation prioritization of landscapes vital to maintaining flyway connectivity.
https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.3543
Sandhill crane spring (a) and fall (b) migration networks for Central Valley (green), Lower Colorado River Valley (red), and Rocky Mountain (blue) population segments. Node size scaled as measure of importance to maintaining connectivity of sandhill crane flyway stopover networks using normalized betweenness measures, which compare the total number of shortest paths at each node to the highest value in its network. Betweenness measures of 70–100% viewed as essential to sustaining network function.