ACKNOWLEDGEMENTS
EPB was supported by funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 8444403. CB was supported by a DFG fellowship BA 5422/1-1. JJB was supported by NWO grant 823.01.006 awarded to Franjo Weissing and by NWO grant 823.01.009 awarded to SV, which also covered fieldwork and analyses costs. We thank Martijn Salomons, the late Cor Dijkstra and many students that contributed to the fieldwork. Fieldwork was approved by the University of Groningen animal ethics committee under license numbers (4071, 5871, 6832-A & 6832-B) before conducting research.