Poole Harbour UK 2 – Shorebirds

March 2015

Regime shifts in benthic invertebrates within coastal ecosystems threaten the survival of wading birds (Charadrii). Predicting how invertebrate regime shifts will affect wading birds allows conservation management and mitigation measures to be implemented, including protection of terrestrial feeding areas. An individual-based model was used to investigate the impact of regime shifts on wading birds through their prey (marine worms and bivalves) in the estuarine system Poole Harbour, (UK).

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

We used a pre-existing model of Poole Harbour (Durell et al., 2006) designed in MORPH (Stillman, 2008) which predicts the numbers of birds supported at the end of the non-breeding season due to the closed nature of the model compared with the real world where birds can move to different regions when faced with starvation. This model was validated against field observations from the British Trust for Ornithology’s Wetland Bird Surveys (Durell et al., 2006).

The model incorporated invertebrate survey data collected in 2002 (Caldow et al., 2005; Thomas et al., 2004) from a grid of 80 sample sites across the intertidal mudflats. In addition, forager parameters were added for the five species that are characteristic of the Harbour’s wading birds; the parameters for both the invertebrates and birds were drawn from both the literature and field studies and are referenced in Durell et al. (2006). Table 1 shows the parameter values used in the model.

Results

Our predictions reveal a weakness in using birds as indicators of site health and invertebrate regime shifts. Differences in bird populations would not necessarily be detected by standard survey methods until extreme changes in invertebrate communities had occurred, potentially beyond the point at which these changes could be reversed. Therefore, population size of wading birds should not be used in isolation when assessing the conservation status of coastal sites.

Funding and Collaboration

Natural England, University of Greenwich.

Related Paper:

Bowgen, K.A., Stillman, R.A. & Herbert, R.J.H. (2015) Predicting the effect of invertebrate regime shifts on wading birds: insights from Poole Harbour, UK. Biological Conservation, 186, 60-68.