Non-native predator control increases the nesting success of birds: American mink preying on wader nests

The ongoing decline of breeding wader populations in Europe has been mostly explained by habitat changes and the increasing impact of native predators, but the influence of non-native invasive predators has been neglected. A seven year study of the nesting success of the northern lapwing, common redshank and black-tailed godwit was carried out in Biebrza National Park in north-eastern Poland, alongside the American mink control programme, which was undertaken with low and high intensities of mink control. Indices of mink density, based on the percentage of floating rafts with mink tracks and the number of mink trapped per 100 trap-nights, declined with the increasing number of mink removed in consecutive years. In our model, the mink control and water level covariates explained most of the variation in daily nest survival rates. A decline in mink density led to increases in daily survival rates of nests and to the overall nesting success of all three wader species. Lower water levels led to a decrease in the overall daily survival rate (DSR) but this covariate affected DSR differently throughout the breeding season. These results demonstrate that predation by an introduced species, alongside low water levels during the nesting period, can limit the nesting success of multiple wader species, and that American mink should be considered as a key predator affecting ground-nesting wetland bird populations. Conservation plans for many wader species declining in numbers should include local reductions in mink populations in order to increase nesting success. Thus, intensive continuous mink control is recommended for important nesting refuges, utilising adaptive management to ensure control efforts remain sufficiently high.