Short-term effects of predator removal and habitat restoration on ground-nesting birds in drained forests

Artificial drainage of wetlands can increase nest predation risk through landscape changes that support higher predator numbers or expose the nests. We experimentally studied how nest predation responds to reversing such pressures by forested wetland restoration and predator removal. We studied two pairs of experimental and control landscapes in north-eastern (NE) and southwestern (SW) Estonia, where mammalian mesopredators were specifically hunted. Within the SW landscape pair, we simultaneously had a replicated before-after-control-impact experiment of restoring sparse pine wetlands for the capercaillie (Tetrao urogallus) by ditch blocking and partial cutting. Three years after the habitat manipulations, we found drastically increased predation rates of artificial ground nests across those restoration blocks (including uncut stands there), with no compensating effect of the predator removal. However, outside the experimental blocks of the SW predator removal landscape, higher reproductive success of the hazel grouse (Tetrastes bonasia) and capercaillie was recorded after the removal; there was also evidence of improved landscape-scale survival of artificial nests in both the SW and NE removal landscapes. These results indicate that wetland restoration can suppress grouse reproduction at least in the short term, but predator control can mitigate these effects on a broader scale. Restoring habitat quality in forested wetlands is a complex task that requires long-term studies of alternatives and precautionary approaches.