Constructing and evaluating a continent-wide migratory songbird network across the annual cycle

Information about how migratory animals are spatially connected between periods of the annual cycle is essential for understanding the effects of environmental change and developing optimal conservation strategies. I constructed a migratory network for a songbird, the tree swallow (Tachycineta bicolor), using year-round movements derived from 133 light-level geolocators attached to individuals originating from 12 breeding sites across North America. I identified 10 autumn stopover nodes (regions) in North America, 13 non-breeding nodes around the Gulf of Mexico, Mexico, and the Caribbean, and 136 unique migratory pathways connecting these nodes. Using network-based metrics, I ranked the stopover and non-breeding nodes based on their contribution to network connectivity and identified three distinct ‘communities’ of nodes that corresponded to western, central, and eastern flyways. This study highlights how network-based metrics can be valuable for identifying overall network structure and prioritizing specific regions within the network, information that is crucial for effectively conserving migratory species.