White stork movements reveal the ecological connectivity between landfills and different habitats

The datasets analysed during the current study are available in Movebank Data Repository.

[Background] Connections between habitats are key to a full understanding of anthropic impacts on ecosystems. Freshwater habitats are especially biodiverse, yet depend on exchange with terrestrial habitats. White storks (Ciconia ciconia) are widespread opportunists that often forage in landfills and then visit wetlands, among other habitats. It is well known that white storks ingest contaminants at landfills (such as plastics and antibiotic resistant bacteria), which can be then deposited in other habitats through their faeces and regurgitated pellets.

[Methods] We characterized the role of white storks in habitat connectivity by analyzing GPS data from populations breeding in Germany and wintering from Spain to Morocco. We overlaid GPS tracks on a land-use surface to construct a spatially-explicit network in which nodes were sites, and links were direct flights. We then calculated centrality metrics, identified spatial modules, and quantified overall connections between habitat types. For regional networks in southern Spain and northern Morocco, we built Exponential Random Graph Models (ERGMs) to explain network topologies as a response to node habitat.

[Results] For Spain and Morocco combined, we built a directed spatial network with 114 nodes and 370 valued links. Landfills were the habitat type most connected to others, as measured by direct flights. The relevance of landfills was confirmed in both ERGMs, with significant positive effects of this habitat as a source of flights. In the ERGM for southern Spain, we found significant positive effects of rice fields and salines (solar saltworks) as sinks for flights. By contrast, in the ERGM for northern Morocco, we found a significant positive effect of marshes as a sink for flights.

[Conclusions] These results illustrate how white storks connect landfills with terrestrial and aquatic habitats, some of which are managed for food production. We identified specific interconnected habitat patches across Spain and Morocco that could be used for further studies on biovectoring of pollutants, pathogens and other propagules.

The leading author was supported by a Juan de la Cierva postdoctoral fellowship (financed by MCINU/AEI, Spanish Government). The study was also supported by projects PAIRWISE PCI2021-121938 (financed by MCIN/AEI), WATERZOO PID2020-112774 GB-I00 (financed by MCIN/AEI) and GUANOPLASTIC PY20_00756 (financed by Junta de Andalucía/EU FEDER). This work was also supported by the Max Planck Society and by the German Research Foundation (DFG, Emmy Noether Fellowship to AF: 463925853). AF acknowledges support by the Hans und Helga Maus-Stiftung, and the James Heineman research award of the Minerva Stiftung.

Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

Peer reviewed