Within-year movements and site fidelity of Purple Sandpipers during the nonbreeding season

Abstract

ABSTRACT Although within-year site fidelity to specific wintering sites allows shorebirds to use prior knowledge of resources and microhabitats, such fidelity may also make populations more vulnerable to extirpation in the event of increased predation pressure, habitat loss, or disturbance. In the eastern Atlantic, Purple Sandpipers (Calidris maritima) have been found to be highly faithful to specific sites in wintering areas. However, little is known about the use of wintering areas by these sandpipers along the coast of Maine. We quantified movements of 60 radio-marked Purple Sandpipers in a bay near the mainland and on an offshore cluster of islands along the mid-coast of Maine during two winters (2005–2006 and 2006–2007). Birds marked in early- and mid-December remained until spring migration, with no evidence of onward migration. Mean maximum distances moved did not differ significantly between either males (8.6 ± 1.0 [SE] km; N= 30) and females (7.4 ± 0.8 km; N= 30) or juveniles (9.9 ± 1.6 km; N= 9) and adults (7.8 ± 1.1 km; N= 26). We also detected no monthly (January–May) differences in maximum distances moved. Sixty percent of marked individuals moved ≤5 km between the two most distant relocations and no birds moved >25 km during the 2- to 4-month tracking period. We attribute the high site fidelity primarily to the plentiful prey base in the study area. During a 2-d period with severe cold, feeding areas at locations protected from wave action became encased in ice and birds at these locations moved up to 10 km offshore to sites with less ice. Species with strong site fidelity, like wintering Purple Sandpipers, may be at higher risk in the event of large-scale changes in their food base, increased predation pressure, habitat loss, or disturbance. However, the short-distance movements made when intertidal feeding areas became encased in ice suggest that Purple Sandpipers could potentially move greater distances in response to changing conditions in their wintering areas.