Billions of migrating birds travel thousands of miles seasonally in search of two basic resources: food and nesting sites. To successfully reach distant locations, birds tend to follow preferred pathways, called flyways.
Many birds, particularly migrating waterbirds, utilize flyways that link a series of wetland stopover sites. Wetland stopover sites need to be sufficiently connected to allow birds to replenish energy reserves for long distance travel. Human activities such as land-use and climate change have resulted in loss of wetland habitat or deteriorated the function of important wetlands stopovers. By current estimates, waterbird populations have many of which are migrating species.
Deboelpaep, E., Partoens, L., Koedam, N. and Vanschoenwinkel, B. 2022. Highway(s) overhead: Strong differences in wetland connectivity and protected status challenge waterbird migration along the four Palearctic‐Afrotropical flyways. Diversity and Distributions 28(5): 1067-1080.
Wetlands along flyway routes have been protected for the connectivity they provide migrating birds. However, a large percentage of wetlands still go unprotected. The extent at which unprotected wetlands impact overall connectivity is not well known.
In a recent study, researchers estimated wetland suitability and network connectivity of four Palearctic-Afrotropical flyways. The Palearctic-Afrotropical flyways were divided into the East-Atlantic Flyway (EAF) and the Black Sea-Mediterranean flyway (BMF). The EAF links arctic breeding grounds spanning western Canada to central Russia to overwintering ground in western Europe and the west coast of Africa all the way to South Africa. The BMF links breeding grounds in western Russia to overwintering grounds in eastern Europe and most of Africa.
They compared the suitability of wetland network structure for birds with differing migratory strategies (long-distance jumpers or short-distance hoppers) by utilizing high resolution wetland map data and graph-theoretic metrics. Network structure and connectivity was estimated for two model species of hoppers (Euraisan Spoonbills and Ruddy Turnstones) and two model species of jumpers (Red Knots and Black-tailed Godwits).
They also examined the impact that increased habitat loss and degradation has on the connectivity of wetlands along flyway routes under current protection . By incorporating the directional nature of migration, known migration strategies, and protection status of wetlands, the vulnerability of flyways to habitat loss was estimated by comparing scenarios where wetland patches would be removed from the network.
The analysis revealed that fewer than 5% of wetlands support more than 70% of migration connectivity despite migration strategy. This suggests that a limited number of large wetlands have the greatest effect on connectivity.
Reducing connectivity by removing wetlands that lack formal protection was more evident in flyways that originally had the highest connectivity, and was shown to have more of an effect on jumpers compared to hoppers. This is evident that habitat loss of unprotected wetlands could compromise the connectivity of flyways.
Conservation planning and management, in the context of flyway connectivity, should take into account the quality of habitat patches and their location in relation to other habitat patches. Integrating migration ecology into conservation prioritization of habitat protects will help accommodate different migration strategies now and into the future.
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