The impact of predator control on lapwing Vanellus vanellus breeding success on wet grassland nature reserves.
Abstract
Whilst the widespread declines in breeding grassland waders in many parts of Europe have been associated with changes in agriculture, there is concern that predation may compromise recovery of wader populations, even in situations where habitat is suitable, such as nature reserves managed for breeding waders. An 8-year cross-over experiment was used to examine the effect of red fox Vulpes vulpes and carrion crow Corvus corone control on breeding performance and population trends of lapwing Vanellus vanellus on 11 lowland wet grasslands. Predator densities in the absence of control measures were highly variable among sites, and consequently the numbers of predators removed were similarly variable. Overall, predator control measures resulted in a 40% decline in adult fox numbers and a 56% reduction in territorial crows. There was no overall effect of predator control on the failure rate of 3139 lapwing nests. However, the effect of predator control varied significantly among sites, reflecting the variation in predator densities. Predator control measures were more likely to result in increased nest survival at sites where predator densities were high. Nest-temperature loggers deployed at seven sites indicated that 88% of nest predations occurred during darkness, suggesting nocturnal mammalian predators. At seven sites predator control had no overall effect on chick survival, monitored by radio-tracking 459 chicks, but there were differences in the effect of predator control among sites. Densities of predators were low during years without predator control measures at the majority of these sites. At six further sites breeding success, assessed from the proportion of adults accompanied by young late in the season, was twice as high in years when predators were controlled. There was no overall effect of predator control on lapwing population trends across the experimental sites. Synthesis and applications. This study highlights the need for information on predator densities and the impact of predators on nest and chick survival, before embarking on predator control measures at a particular site. A decision tree for determining the circumstances in which fox and/or crow control may be both necessary and effective is recommended.