Migration strategies of shorebirds during the non-breeding season with particular reference to the sanderling (Calidris alba)
This study comprises two parts, one based at the Wash and one at Teesside, dye-marking of samples of oystercatcher, grey plover, knot, sanderling, dunlin, bar-tailed godwit, curlew, redshank and turnstone was undertaken to determine differences in the degree of mobility within the Wash. Most information relates to spring tide roosts. Wash Wader Ringing Group recaptures within the Wash, within a single season, were examined for sanderlings and dunlin. There were few results for grey plover, bar-tailed godwit, curlew or redshank. Results for other species indicate a range of mobility - in order of increasing mobility these are dunlin and turnstone, sanderling, oystercatcher, knot. Under lying reasons for mobility were associated with flights to spring tide roosts, increases in diurnal time spent feeding and, possibly, exploratory flights in search of unpredictable food resources. At Teesside, individually colour-ringed sanderlings were studied for differences in timing of use of Teesside and differences in degree of mobility. Generally, individuals display consistency in returning to Teesside each year and arrival and departure dates are similar from year to year for each individual. A continuum of sanderling mobility is apparent. There appears to be a balance between net advantages and disadvantages accruing from variations in mobility as estimates of survival rates indicate'. Heightened mobility was apparent by some individuals during severe winters and was interpreted as movement in search of better foraging conditions.