Cardiff UK – Redshank

December 2006

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Issues

The change in winter mortality of a charadriid shorebird following removal of intertidal feeding habitat, the main effect of which was to increase bird density.

Modelling

The model predicted that mortality would increase by 3.65%, which compares well with the observed increase of 3.17%. The implication that mortality was density-dependent was confirmed by predicting mortality over a range of bird densities. Further simulations showed that the density dependence was due to an increase in both interference and depletion competition as bird density increased.

Results

The model predicted a mean increase in mortality in the 500 birds feeding post-barrage at Rhymney of 3.65% across the four calibration scenarios, for which the predictions were similar (Table 1). This compares favorably with the observed increase of 3.17%, even though C. volutator was not included in the model food supply. The calibration scenario used henceforth is the one believed most likely to represent the actual conditions at Rhymney; i.e., a 20% overwinter reduction in the AFDM of N. diversicolor and the prey densities recorded by Reading (1988).

Funding and Collaboration

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Related Paper:

Goss-Custard, J. D., Burton, N. H. K., Clark, N. A., Ferns, P. N., McGrorty, S., Reading, C. J., Rehfisch, M. M., Stillman, R. A., Townend, I., West, A. D. & Worral, D. H. (2006) Test of a behaviour-based individual-based model: increased winter mortality in a shorebird following habitat loss. Ecological Applications, 16, 2215-2222.