Poole Harbour UK 1 – Shorebirds

February 2006

Poole Harbour, southern UK, is designated a Site of Special Scientific Interest (SSSI) for its habitats and the species they support, a Ramsar Waterfowl Habitat site and an SPA European Marine Site. During the winter, it supports internationally important numbers of black-tailed godwit Limosa limosa and nationally important numbers of dunlin Calidris alpina, redshank Tringa totanus and curlew Numenius arquata (Pickess and Underhill-Day, 2002; Rehfisch et al., 2003). The Harbour has an unusual double high water system, which is particularly pronounced on spring tides (Humphreys, 2005). It also has a limited tidal range, with spring tide heights of around 1.5 m. These two factors mean that the exposure time of intertidal flats is often very short compared with other estuaries and, on many tides and under certain weather conditions, some areas do not expose at all. As a result, many shorebirds supplement their estuarine diets by feeding extensively in nearby fields, water meadows and recreational grassland (Goss-Custard and Durell, 1984b; Pickess and Underhill-Day, 2002).

Issues

Does the disturbance caused by various human activities in certain parts of the harbour limit the number of overwintering waders that the Poole Harbour SPA can support.

Modelling

An individuals-based model, MORPH, was used to assess the quality of Poole Harbour, UK, for five overwintering shorebirds: dunlin Calidris alpina, redshank Tringa totanus, blacktailed godwit Limosa limosa, oystercatcher Haematopus ostralegus and curlew Numenius arquata. Site quality, and the effect of environmental change, was measured as predicted overwinter survival. Dunlin had the highest prey biomass densities and were the least likely to be affected by reductions in their food supply, lower temperatures or loss of terrestrial habitats.

Results

Black-tailed godwits and curlew had the lowest prey biomass densities and were the most likely to be affected by reductions in their food supply, lower temperatures and loss of terrestrial habitats. All five shorebird species were seriously affected by simulated sea-level rise. Conservation issues identified for the Poole Harbour SPA were the relatively low densities of larger size classes of polychaete worms, the importance of maintaining and managing surrounding terrestrial habitats and the effect of sea-level rise on the length of time for which intertidal food supplies are available.

Funding and Collaboration

Natural England, University of Greenwich.

Related Paper:

Durell, S. E. A. le V. dit, Stillman, R. A., Caldow, R. W. G., McGrorty, S., West, A. D. & Humphreys, J. (2006) Modelling the effect of environmental change on shorebirds: a case study on Poole Harbour, UK. Biological Conservation, 131, 459-473.