Tracking day and night provides insights into the relative importance of different wader chick predators

Poor reproductive success driven by nest and chick predation severely limits the population recovery of waders breeding on lowland wet grassland. Managing predation requires knowledge of the predators and because these can be grouped into nocturnal or diurnal hunters, detecting the timing of predation can help assess their relative impacts. Wader nest studies investigating the timing of egg predation have identified nocturnal mammals, primarily Red Foxes Vulpes vulpes, as the most important nest predators, but quantifying predator importance for highly mobile wader chicks is more difficult. Manual radiotelemetry can detect whether chicks are alive but cannot detect the time of predation, and predator identity can be determined only in the few cases where remains are recovered. As an alternative we used automatic radio tracking stations (ARTS) to constantly record the signals and predation timing of 179 radiotagged Lapwing Vanellus vanellus chicks, combining this with manual telemetry, inference about predator identity from predated remains and site-level Fox, mustelid and avian predator activity monitoring. This approach succeeded in detecting the time of predation for 60% of the 155 chicks that were predated. Diurnal chick predation accounted for a larger number of predation events, but nocturnal predation was more intensive in terms of predation likelihood per hour. Mammalian predation during both day and night had a larger impact on chick survival than did avian predation. Raptors were primarily responsible for predation by birds and Foxes for predation by mammals, with Foxes also having a larger influence on daily chick predation rates than other predators. Chick predation increased seasonally, implying that earlier-hatching breeding attempts are more likely to be successful. Higher Fox, raptor and mustelid activity resulted in higher proportions of chicks being predated by those predators, so quantifying the activity of those three predator groups on a site could be a quicker alternative to studying chicks when investigating which predator species to target with site-specific predation management.