Is the Density of Redshank Tringa totanus Nesting on Saltmarshes in Great Britain Declining Due to Changes in Grazing Management?

1. Saltmarsh habitats support c. 50% of the population of redshank Tringa totanus breeding in Britain. Between 1985 and 1996, breeding densities declined significantly by 23%. This paper tests the hypothesis that this decline resulted from changes in the extent of important saltmarsh habitats for nesting redshank, and/or a change in the intensity of grazing. 2. We surveyed breeding redshank densities, the extent of saltmarsh habitats, and the intensity of grazing on a sample of 77 saltmarsh sites around the coast of Britain in 1985 and 1996. From these data, we constructed statistical models that described breeding densities in relation to a range of habitat and grazing variables for each of the surveys, and examined changes in breeding density between the surveys, in relation to changes in the important habitat and grazing variables included in these models. 3. During both surveys, breeding densities were lowest on heavily grazed plots, and there was some evidence, from the larger number of survey sites for which data were available in 1985, that breeding densities tended to be highest on lightly grazed saltmarsh. Multiple regression modelling, incorporating a range of habitat variables and grazing intensity, also showed this effect, although in 1996 interpretation of the relationship between breeding density and grazing intensity was complicated because both grazing intensity and a habitat variable accounted for a similar component of the variance in breeding density. These models also showed that certain habitat variables were significant correlates of breeding density, particularly the extent of seacouch grass, which was positively correlated with breeding density in both survey years. During 1985, breeding densities were also correlated with the extent of a number of other saltmarsh habitats, which did not significantly correlate with breeding densities in 1996. In addition to the measured habitat and grazing variables, densities also showed significant regional variation in Britain during both surveys. 4. Of the habitat and grazing variables included in the multiple regression models of breeding density, only the intensity of grazing changed between 1985 and 1996, showing a significant increase. Breeding densities declined most markedly on sites that had experienced an increase in the intensity of grazing from ungrazed/lightly grazed to moderate/heavily grazed. This suggests that an increase in the intensity of grazing was the most likely explanation