The identification of key wetlands for bird migration and the prediction of alternative routes when particular wetlands are deteriorated or destroyed is a relevant question of international importance for conservation biology. The complex network approach, mapping the connections between a large number of components, can be successfully applied to address how robust the migratory networks are in the face of perturbations. By integrating data from two information sources, the EURING Data Bank hosted by the British Trust for Ornithology that holds ring recovery data gathered by bird ringing schemes throughout Europe and the European Important Bird Areas Programme of BirdLife International that identifies key sites for birds all over the continent, we have traced the spatial routes of migratory birds across Europe. We have focused on aquatic birds because of their dependence on well-defined wetlands during their trip. These wetlands represent the nodes of the network. Species recovery data have been used to create the links between the nodes. In this way we traced the routes followed by these species during their migration and we were able to characterize the structure of the spatial network in which the species are embedded.

Results/Conclusions

This is the first representation and comparison of the structure of bird migratory networks across different bird species at a global scale. We have found a common modular organization in most species, but an independent ranking of wetlands from the point of view of their role as connectors of different modules. By module we refer to a set of wetlands highly connected among themselves by the migratory movements of the birds, but with a few connections to wetlands belonging to other modules. Quantifying the observed variability will inform us on what properties are general across groups of species and what properties are species-specific. This will help us best focus resources devoted to conservation efforts.