The density of redshank Tringa totanus breeding on the salt-marshes of the Wash in relation to habitat and its grazing management

Published source details Norris K., Cook T., O’Dowd B. & Durdin C. (1997) The density of redshank Tringa totanus breeding on the salt-marshes of the Wash in relation to habitat and its grazing management. Journal of Applied Ecology, 34, 999-1013.
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Summary

Coastal salt-marshes in Great Britain support nationally and internationally important breeding redshank Tringa totanus populations. These marshes are however under threat due to coastal erosion and changes in salt-marsh use for livestock grazing. There was a need for more information on the importance of different salt-marsh habitats and their grazing management to assist in development of management plans in order to create and manage salt-marsh habitats suitable for breeding redshank. The primary aim of this study was to describe the relationship between the density of breeding redshank, the extent of different salt-marsh habitats and their grazing management.

Study area: The study was undertaken in saltmarshes around The Wash Estuary (mostly in Lincolnshire) eastern England. Grazing on the saltmarshes is mostly by cattle (April to October), with a few sheep and horses. In some areas, grazing has been abandoned.

Redshank breeding surveys: Redshank breeding surveys were undertaken on a sample of 50 salt-marsh plots at 19 sites located around The Wash estuary. Each site was surveyed three times between 6 April and 30 May 1994, with at least 10 days interval between surveys.

Habitat and grazing data: Data on salt-marsh habitats, vegetation structure and grazing intensity were also collected. Salt marsh habitats were classified according to vegetation communities and the area (ha) of each calculated. Grazing intensity was estimated by a 4-point scoring system (0 = no grazing, 1 = light grazing, 2 = moderate grazing, 3 = heavy grazing).

Redshank breeding densities were positively correlated with the extent of the sea couch Elymus pycnanthus (Agropyron pungens) grass community, but this varied in relation to livestock grazing intensity. On heavily grazed plots, redshank breeding density increased significantly more rapidly as the extent of the sea-couch grass community increased, compared with ungrazed plots. The rate of increase on moderately grazed plots was intermediate. Breeding densities were negatively correlated with the extent of the glasswort Salicornia and annual sea-blite Suaeda maritima community, but the form of this relationship appeared unaffected by grazing intensity. Redshank densities also varied significantly between sites, in addition to any variation attributable to habitat or grazing regime.

Analyses suggested that the relationship between the extent of the sea-couch grass community and redshank density, under different grazing intensities, could be explained by vegetation structure. Heavily grazed plots, dominated by the sea couch grass community, supported the most structurally diverse vegetation and held highest redshank breeding densities. In contrast, ungrazed plots of similar sea couch habitat contained tall, uniform vegetation and supported significantly lower breeding densities.

Conclusions: Livestock grazing of salt-marsh sites dominated by sea couch grass on The Wash appears beneficial to breeding redshank. Current grazing regimes should be maintained at such sites and grazing re-introduced to those that were formerly grazed. The density of cattle on grazed sites in The Wash is equivalent to around 1 cow/ha of grazed salt-marsh, suggesting that this intensity of grazing would perhaps be appropriate. However, caution is required if lower salt-marsh dominated habitats are grazed, as any increase in breeding density resulting from grazing might be offset by an increased nest loss due to trampling. In such cases, it is recommended that cattle should, if possible, be put on to the marsh towards the end of the redshank nesting season (i.e. late May/early June) to minimize trampling risk.

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