The effect of grazing intensity on redshank Tringa totanus breeding density in coastal saltmarshes around Britain
Published source details
Norris K., Brindley E., Cook T., Babbs S., Brown C.F. & Yaxley R. (1998) Is the density of redshank Tringa totanus nesting on saltmarshes in Great Britain declining due to changes in grazing management? Journal of Applied Ecology, 35, 621-634
Published source details Norris K., Brindley E., Cook T., Babbs S., Brown C.F. & Yaxley R. (1998) Is the density of redshank Tringa totanus nesting on saltmarshes in Great Britain declining due to changes in grazing management? Journal of Applied Ecology, 35, 621-634
In Britain, coastal saltmarshes support around 50% of the breeding redshank Tringa totanus population. In only 11 years, between 1985 and 1996, redshank breeding densities were estimated to have declined by 23%. This study investigated whether this decline resulted from changes in the extent of important saltmarsh habitats for nesting redshank, and/or a change in the intensity of livestock grazing.
Redshank surveys and modelling: 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 were surveyed in 1985 and 1996. Using these data, statistical models describing breeding densities in relation to a range of habitat and grazing variables were constructed. Changes in redshank breeding density between the surveys, in relation to changes in the important habitat and grazing variables were examined.
During both survey years, breeding redshank densities were lowest on heavily grazed sites, with some evidence, that densities tended to be highest on lightly grazed saltmarsh.
Modelling, incorporating a range of habitat variables and grazing intensity, also showed this effect, although in 1996 both grazing intensity and a habitat variable accounted for a similar component of the variance in breeding density. These models showed that certain habitat variables were significant correlates of breeding density, particularly the extent of sea-couch grass Agropyron junceiforme, 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. Densities also showed significant regional variation during both surveys.
Of the habitat and grazing variables included, only grazing intensity (a significant increase) changed between 1985 and 1996. Breeding densities declined most 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 grazing intensity was the most likely explanation for the observed decline in breeding densities.
Assuming that the grazing intensity data were representative of grazing management on saltmarshes throughout Britain, it was estimated that 1,665 ha of saltmarsh experienced an increase from ungrazed/light grazing to moderate/heavy grazing over the 11 years. It was also estimated that 6,388 ha (14.6%) of saltmarsh in Britain was heavily grazed in 1996.
Conclusions: Analysis of the redshank survey data, grazing regime and other important habitat variables, suggest that heavy livestock grazing is currently a significant threat to breeding redshank using saltmarshes in Britain.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.blackwell-synergy.com/doi/abs/10.1046/j.1365-2664.1998.355339.x