Fences increase the hatching probability of Northern Lapwing Vanellus vanellus and Black-tailed Godwit Limosa limosa in the Dithmarscher Speicherköge

Abstract

The decline of grassland birds is increasingly attributed to clutch and chick losses caused by ground predators. As a result, anti-predator fences are increasingly being used to protect breeding sites. To test their eff ectiveness, we used nest-survival models to compare the daily survival and hatching probabilities of clutches of Northern Lapwing Vanellus vanellus and Black-tailed Godwit Limosa limosa inside fences with that of clutches outside fences in three areas in the Dithmarscher Speicherköge, Schleswig-Holstein, in 2022. The model that best explained the data for the Northern Lapwing assumed an age-dependent increase in daily clutch survival probabilities. However, inside fences it was signifi cantly higher than that of clutches outside fences. The model that does not account for nest age is a good approximation of the mean across all age classes. According to this model, the daily survival probability of a lapwing clutch inside a fence was 0.992 ± 0.003 se and outside a fence it was 0.954 ± 0.010 se. The corresponding probabilities of a clutch to hatch was 78.5% ± 0.8% variance inside and 24.3% ± 7.6% variance outside a fence. For Black-tailed Godwit, the model that best explained the data assumed only a diff erence in daily survival probabilities inside or outside fences. Accordingly, the daily survival probability inside a fence was 1 ± 0 se (no losses) and outside a fence 0.876 ± 0.025 se. This corresponds to probabilities of a godwit clutch to hatch of 100% ± 0% inside and only 3% ± 32.7% variance outside a fence. Fences are thus an appropriate means of increasing the hatching probability of ground nesting birds. However, in both areas, fences protect only a very small proportion of grassland bird population, resulting in a high potential to expand the use of this successful method in grassland bird management.