Impact of a Semi-experimental increase in recreation intensity on the densities of birds in groves and hedges on a lake shore in The Netherlands

Abstract

The possibility of disturbance of birds by outdoor recreation is often mentioned, but has rarely been studied. This article presents the results of a disturbance field experiment which took place during three breeding seasons and was conducted along a 4·5 km long lake shore with hedges and groves. Parts of this area have probably undergone an increase in visitor numbers since 1979 as a result of the construction and opening of a car park nearby. The recreation intensity in other parts further away from the car park has probably not increased. Visitors and the breeding birds were counted during the breeding seasons in 1977 and 1978 (before the car park was opened) and in the breeding season in 1980 (after the car park had been opened). All but one ( Phylloscopus trochilus) of the 12 (most abundant) species showed a negative difference between experimental units and control units, indicating a disturbance effect. However, no significance was reached with regard to the following bird species analysed: Columba palumbus, Troglodytes troglodytes, Prunella modularis, Turdus philomelos, Turdus merula, Hippolais icterina, Sylvia atricapilla, Sylvia borin, Sylvia communis, Sylvia curruca, Phylloscopus trochilis, Phylloscopus collybita. The number of 11 negative differences out of 12, on the contrary, is highly significant using a sign test ( p = 0·003). Interpreting the results as a recreation effect is also supported by the fact that species show negative correlations between recreation intensity and density in 1980 ( p = 0·033; sign test). These correlations were significant for Hippolais icterina and Sylvia borin. Such correlations were not found for 1977 or 1978.