The feeding ecology and foraging behaviour of sanderling calidris alba and turnstone arenaria interpres at Teesmouth N. E. England

Abstract

The distributions of Sanderling and Turnstone were determined for the south side of the Tees Estuary. Location of roosting sites and the movement of the tide were the major factors affecting movement patterns of these two species. The invertebrate species Nerine, Bathyporeia and Eurydice, were observed to comprise virtually all of the Sanderling's open-beach diet. Extensive sampling of these three prey species showed a predictable occurrence along the beach with each species; most common at particular transect and distance below the High Water Mark, (e.g. Nerine was most abundant at 50 to 90 metres below the HWM). The times when these bands became available to 'foraging Sanderling helped to determine the movement patterns of the birds. Detailed studies of the feeding behaviour of Sanderling showed three main foraging techniques: probe feeding, water-column feeding and stitch feeding. The first two of these techniques have a visual component, (the Pause position). Switching occurred between these two techniques but was uncommon between the water column and stitch technique (which was a tactile feeding method). When feeding, Sanderling oriented themselves so that they could watch the progress of the waves. Colour-marked individuals of both Sanderling and Turnstone helped to determine movement, patterns, fidelity to site within a season and survival and fidelity between seasons. Mortality rates for Turnstone were especially low; fidelity was high for both species. Feeding observations on winter Turnstone showed both dispersed and concentrated situations. While aggression was seldom observed for Sanderling, it was common for Turnstone. Two main types of aggressive encounters were observed for the Turnstone and were determined mainly by the potential payoff of the encounter. The suggestion is advanced that aggressive patterns may help determine the dispersion of the Turnstone. Aggression may also help to determine the feeding location of the juveniles. Observations of breeding Turnstone (Finland) present, a picture of communal feeding (aiding in, predator awareness), high; nesting concentrations and numerous, interactions with the lafid species present. The latter include extensile robbing of larid eggs by Turnstone. Although the summer and winter Turnstone populations have different Wintering grounds, there are valuable comparisons to be made