What effects do walkers and dogs have on the distribution and productivity of breeding European Nightjar Caprimulgus europaeus?

Abstract

Several successive studies of European Nightjars Caprimulgus europaeus (hereafter, Nightjar) on the Dorset heaths demonstrated negative effects of the proximity of urban development and associated disturbance from access on foot by people and dogs. Surrogate measures of human density and settlement, including the amount of developed land around each heathland patch and the number of houses, were significantly and negatively related to the density of Nightjars (using data from the 1992 national survey) on heathland patches, regardless of patch size. These findings prompted targeted field studies, the subject of this paper, which investigated the mechanisms and effects of recreational disturbance on breeding Nightjars. Fieldwork in 2002 focused on a suite of heathland sites representing a range of access from sites closed to the public to heaths heavily used for recreation, notably by dog walkers. Studies in 2003 concentrated on the heavily used heaths. Nests which failed were significantly closer to paths, tended to be closer to the main points of access to heaths, in areas with higher footpath density, notably of high levels of use, and in more sparsely vegetated locations. The proximate cause of nest failure was most frequently egg predation. Nest cameras, deployed in 2003 in an attempt to identify the predators of eggs or chicks, recorded just one instance of predation, that of an egg by a Carrion Crow Corvus corone, and two instances of the incubating bird being flushed by a dog, once from an egg and once from a chick, neither event preventing fledging. Flushing rate of Nightjars from the nest was associated with the height of vegetation around the nest and the extent of nest cover. The studies indicate that access disturbance interacts with environmental conditions for breeding birds. Birds flush more readily from eggs, which are highly visible when exposed, especially in areas with sparse nest cover, leaving them vulnerable to predation. Although Nightjar flushing rates were observed to be low in 2003, just one event leading to predation is enough to end that nesting attempt. Management measures are recommended to minimize the effects of walkers and their dogs on Nightjars.