No abstract

Timing and duration of primary moult in three populations of Purple Sandpipers Calidris maritima were described and discussed in relation to the birds’ need to complete moult before the onset of winter, when resources are required for survival. We predicted that moult would be completed earlier by birds wintering at higher latitudes. The south Norwegian breeding population, which moults and winters along the coast of east Britain (54–57°N) had a mean starting date of 21 July for primary moult (16 July for females and 24 July for males), a mean duration of 61 days, and completed on 20 September. Resident Icelandic (64–65°N) birds had a mean starting date of 22 July for primary moult (17 July for females and 25 July for males), a mean duration of 51 days, and completed on 11 September. Birds moulting in north Norway (70°N) arrived in north Norway in suspended primary moult or without having started moult, and completed it there. They had a mean completion date of 2 November for primary moult (31 October for females and 3 November for males). Starting date and duration could not be estimated because some suspended moult for an undetermined period, but it was thought that they started in late August. It is likely that most originated from Russia. The onset of moult appears to be set by the end of breeding and there is little overlap in these two events. The earlier start of moult by females in all three populations may be because they abandon the males when the chicks hatch, leaving the males to attend the chicks. Although the duration of primary moult followed the expected trend, being fastest in north Norway and slowest in Britain, the onset of moult was so late in north Norway that they had an unexpectedly late completion date, despite their rapid moult. The late completion of primary moult in north Norway suggests that wintering in the far north may not pose the energetic constraints on Purple Sandpipers that had previously been supposed.

No abstract

The masses of 3229 Purple Sandpipers Calidris maritima from Britain were analysed for differences related to age, season and size. First‐year birds were lighter by 2 g. There was only a slight increase in mass in mid‐winter, in contrast to other waders wintering in Britain, suggesting that Purple Sandpipers are less at risk to cold weather and food shortages. Their winter fat reserves were low but their breast muscles were relatively larger than other small waders wintering in Britain. Their plumage was slightly heavier and their breast and belly feathers were longer. There was a large increase in mass in May by first‐year and adult birds prior to migration. The ‘long‐billed’ population showed a greater relative increase in May, compared with the ‘short‐billed’ population, perhaps reflecting different migration distances.

Samples of Purple Sandpipers were captured around the coasts of Britain. Analysis of their bill‐length distributions enabled the sex ratios and percentages of ‘long‐billed’ and ‘short‐billed’ birds at each locality to be estimated. The sex ratio for the ‘long‐billed’ population was estimated to be one female to 2–11 males, and one female to 1 ‐34 males for the ‘short‐billed’ population. During winter, proportionately more ‘long‐billed’ birds occurred in northern and western Scotland, Wales and southern England, whilst ‘short‐billed’ birds predominated from Kincardine to Yorkshire. The total sizes of the ‘long‐’ and ‘short‐billed7’ populations were c. 15 000 and 4000, respectively. ‘Short‐billed’ birds started arriving from Norway in early July. ‘Long‐billed’ birds did not arrive until late October. Their origins are as yet unknown. No annual variations in the population structure were detected.