Predation-mediated edge effects reduce survival of wader nests at a wet grassland-forest edge

Edge effects occur when the matrix has adverse impacts on the patches of remnant habitat. A widely explored example of this is the hypothesis of a higher predation pressure on bird nests closer to the habitat edge. In parallel with the recent loss of open habitats through afforestation as a climate change mitigation measure, an interest in the impact of forest on species dependent on open habitats has re-emerged. We follow wader nest survival to study the issue of an edge effect in a system of wet grasslands fragmented by forests in a region where it has not been tested before, focussing mainly on northern lapwing (Vanellus vanellus), common ringed plover (Charadrius hiaticula), common redshank (Tringa totanus) and southern dunlin (Calidris alpina schinzii). To record nest survival, we monitored 753 nests of 10 wader species on coastal grasslands in Estonia for 3 consecutive years. A subset (n = 85) of these nests was equipped with camera traps to record nest predation events and predator association with forest edge. The distance to nearest trees and forest and a forest cover within a 1-km buffer around each nest was measured. We recorded extremely low daily nest survival rates (0.903-0.922 for different species), with most nests lost to predation. We showed that nest survival is lower closer to the forest edge and negatively affected by the proportion of forest within a 1-km buffer around each nest. Based on camera trap recordings, we suggest that the edge effect is caused by elevated nest predation rates by the most common predator, the red fox (Vulpes vulpes), closer to the forest edge. Future afforestation plans of open habitats need to acknowledge that the resulting fragmentation has a negative impact on nest survival of ground-breeding birds. On the other hand, our results imply that restoration efforts aimed at removal of most damaging forest plantations could benefit breeding waders.