The impact of overwintering birds on the production ecology of estuarine benthic invertebrates

Abstract

The aim of this thesis was to study the impact of several species of overwintering birds on the production ecology of their prey populations. The study was carried out at Skinflats, a large intertidal mudflat on the Firth of Forth, between December 1975 and March 1978. Aspects of the breeding cycle, growth, mortality and production of Hydrobia ulvae are given in Section 3.3. Hydrobia was found to live for two years, breed once or twice depending on the size attained in the -1 first year and produce 3.9 g AFDW yr from a mean annual biomass of 3.32 g. The results of population studies of Macoma balthica, Cardium edule Nereis diversicolor, Manayunkia aestuarina, Pygospio elegans, Tubificoides benedeni and Corophium volutator are shown in Section 3.A. T. benedeni was the most productive species. The diets and feeding habits of shorebirds on the estuarine Firth of Forth in winter are described in Section 3.5, with particular reference to the Redshank (Tringa totanus) , and the factors influencing the low tide feeding distribution and density of Redshank, Knot, Dunlin, and Shelduck are discussed in Section 3.6. In general, the density of each species increased with increasing prey abundance but environmental and behavioural factors influenced this relationship. The energy balance and winter survival of shorebirds, in particular the Redshank, are discussed in Section A together with the impact of Waders and Shelduck on the populations of invertebrates at Skinflats. Should large-scale reclamation plans be implemented on the Forth estuary it is concluded from this study that Skinflats could not support any large/ large populations of displaced birds. Since the Forth estuary is of national and international importance to several species of shorebirds in winter, it is recommended that the integrity of the major mudflats on the Forth estuary is maintained.