Differences in network structure and connectivity of four (protected) Palearctic-Afrotropical flyways

Aim – Waterbirds that travel seasonally between Europe and Africa use
wetlands along four major Palearctic-Afrotropical flyways. However, it is
unknown to what extent the overall connectivity of these flyways may be
threatened by ongoing habitat loss and degradation. Here, we contrasted
the wetland connectivity along these four flyways, applying
graph-theoretic connectivity metrics on an intercontinental scale. We also
explored for which flyway connectivity is most at risk. We then identified
the most important wetlands by their contribution to connectivity in each
flyway. Location – Western Palearctic, Afrotropics Methods – Based on
high-resolution wetland maps, we calculated directional probabilistic
connectivity metrics. Estimates of overall connectivity of each flyway
were obtained, as well as the relative importance of wetlands, for birds
with different migration strategies: short-distance hoppers and
long-distance jumpers. Results – The East-Atlantic flyway and Eastern
Mediterranean flyway had higher overall functional connectivity than the
two central routes, reflecting the larger barrier represented by the
Mediterranean Sea and Sahara Desert. Fewer than 5% of all wetlands
supported more than 70% of the total connectivity of the network in each
flyway, regardless of the considered migration strategy. These wetlands
were either large, strategically positioned, or both. Removing
non-protected wetlands from the analysis showed that the connectivity of
some flyways could be jeopardised and that the East-Atlantic and Eastern
Mediterranean flyway may be most vulnerable to additional habitat loss.
Main conclusions – Our results illustrate (1) the major contribution of
unprotected wetlands to flyway connectivity, (2) the importance of
integrating migration ecology into site-based connectivity analyses, and
(3) the utility of graph-based connectivity metrics to inform conservation
prioritisation under present and future scenarios.