Tringa

Abstract: Present evidence suggests that a predator's response to increases in the density of its prey is an accelerated rate of feeding up to an asymptotic level where further increases in prey density result in no further change in feeding rate (Holling 1965). Hence when predators respond to local variations in prey density by aggregating in areas where the prey density is greatest, they are probably showing a preference for those localities where their feeding is most efficient (Hassell 1966). Very often the measurements necessary to demonstrate these responses in feeding efficiency and density are difficult to make under field conditions. On estuaries, however, the numbers and feeding rate of some birds are relatively easy to measure and the density of their prey often easy to assess. Preliminary studies on the Ythan estuary in Aberdeenshire (Goss-Custard 1966) revealed that these aspects of predation could be conveniently studied in the redshank (Tringa totanus (L.)), a wading bird which feeds on several species of small invertebrates. The aims of the present study, then, were to test the hypothesis that both the density of redshank and their feeding efficiency were positively correlated with prey density.

Abstract: Summary 1 Recent theoretical modelling has provided important insights into how habitat loss may affect local populations through impacts on individual fitness (survival, body condition, fecundity). Despite this, attempts to provide empirical evidence of such impacts on displaced individuals have been limited. Using a before-after-control-impact (BACI) approach, we report how a sudden loss of wintering habitat impacted on the body condition and survival of redshank Tringa totanus. 2 The intertidal mudflats of Cardiff Bay, UK, were inundated with freshwater in November 1999 following impoundment by a barrage, resulting in the displacement of c. 300 redshank to adjacent habitat on the Severn Estuary. Movements and the survival of these birds were monitored through observations of colour-marked individuals. Comparative survival rates were calculated for marked populations at the main recipient site, Rhymney, and a control site. 3 Displaced redshank had difficulty maintaining their mass in the first winter post-barrage closure: adults previously only recorded at Cardiff Bay were significantly lighter than those previously recorded at Rhymney. 4 Survival rates of displaced redshank also declined. The estimated annual survival of adult Cardiff Bay redshank fell from 0·846 in the 2 years pre-barrage closure to 0·778 in the 3 following years because of a significant decline in winter survival (P = 0·0006). In comparison, there was no significant change in the survival of adult Rhymney redshank, and adult survival at the control site was actually greater post-barrage closure than beforehand. The lack of decline in these rates and the similarity between those of Cardiff Bay adults pre-barrage closure and Rhymney adults indicate that the increase in winter mortality of Cardiff Bay birds resulted from their displacement. 5 Synthesis and applications. This study provides the first conclusive empirical evidence that habitat loss can impact individual fitness in a bird population. Adult redshank displaced from Cardiff Bay experienced poor body condition and a 44% increase in mortality rate. Without an increase in the recruitment of first-winter birds, such a change is likely to reduce substantially local population size. The results reported here should help to inform governments, planners and non-governmental organizations (NGOs) seeking to understand how developments might impact on animal populations.

Abstract: Habitat loss and degradation of wetland ecosystems, principally through large-scale drainage and conversion to arable farmland, have been implicated in the widespread, dramatic declines of breeding waders across Europe. Managing the remaining wetlands to reverse these declines will require a detailed understanding of their habitat requirements. In the UK, grazing marshes are key components of the remaining wetlands in both coastal and inland sites, and the structure of grazing marsh habitat can differ between these locations. Redshank Tringa totanus is a declining wader species that breeds in both marsh types. We quantified the habitat features that influence redshank selection of breeding and nest site locations, across coastal and inland marshes, in eastern England. On both marsh types, breeding location and breeding densities within fields were positively related to the lengths of pool edge and all wet features, respectively. Nest site location was principally influenced by vegetation characteristics, with soil penetrability also important on inland sites but proximity to wet features and vegetation type at the nest important on coastal sites. Hatching probability was higher when the surrounding soils were more penetrable. Synthesis and applications. The wet features of critical importance for breeding redshank are common on coastal marshes and can be deliberately established on inland sites. Coastal marshes are often rare and frequently threatened by dynamic coastal processes, whereas inland marshes are more abundant but largely unsuitable for breeding waders at present. These analyses highlight the scope for improving the management of inland marshes for breeding redshank. As habitat suitable for breeding redshank frequently supports a range of other wader species, this information can also direct management efforts to improve breeding wader populations in the wider countryside.

Abstract: The prey species mostly taken by the wading bird redshank, Tringa totanus (L.), on the shore belong to a number of taxa and include the amphipod crustacean Corophium volutator (Pallas), the decapod crustaceans Carcinus maenas (L.) and Crangon vulgaris (Fabricius), the gastropod mollusc Hydrobia ulvae (Pennant), the bivalve mollusc Macoma balthica (L.), and the polychaete worms Nereis diversicolor (O.F. Miller) and Nephthys hombergi (Lamarck) (Goss-Custard 1969; Prater 1970; Burton 1974; GossCustard & Jones 1976). The diet in a particular situation is affected by factors such as mud temperature and substrate which seem to affect the behaviour of the prey and thus their availability to the birds (Goss-Custard 1969, 1970a). This paper examines the influence of prey density on diet. The aims of the study were (1) to describe the diet at different prey densities, (2) to test whether the birds select between prey rather than simply take every available item they encounter and (3) if selection occurs, to test the hypothesis that the birds prefer the species which maximize the net rate at which they collect energy.