The roosting and foraging ecology of turnstones Arenaria interpres and purple sandpipers Calidris maritima, in the pre-migratory period

Many bird species need to accumulate fat deposits prior to long distance migration. The surplus energy required to achieve this can be obtained by increasing food intake. There are two main ways of attaining an increased food intake; by increasing feeding day length or by an increase in the rate of feeding. The foraging and roosting behaviour of Turnstones, Arenaria interpres, and Purple Sandpipers, Calidris maritima, was studied in the spring pre-migratory period at Hartlepool, N.E. England. Adult Turnstone increase both their feeding day length and feeding rate. First year Turnstones show no lengthening of their feeding day and only a small increase in feeding rate, they do not undergo long distance migration so do not need to deposit fat. Purple Sandpipers do not exhibit an increase in their feeding day length, due to the availability of their feeding areas being strictly tidally controlled, and rely on an increased feeding rate alone to achieve fat deposition. Associated with the increased feeding rates is a reduction in time spent vigilant, suggesting a trade off occurs as increased time spent foraging becomes more beneficial. The possible conseqences of redevelopment of the West Harbour roost site are discussed and suggestions made for future study.