Southward migrating Red Knots (Calidris canutus) were surveyed on Cape Cod, Massachusetts. Unique markers, including ones applied to birds in wintering areas in North and South America, were found. Northern and southern-marked knots had different migration chronologies, plumage characteristics and flight feather molt. Knots from the two groups were found to have different foods and foraging habitats. Numbers of knots more than one year old were found to increase from mid-July to mid-August, decline during late August and then increase in September–October. As numbers declined in August, the proportion of knots from South America decreased and, by 1 September, all remaining marked birds had been tagged in North America. Average minimum stopover durations were found to vary according to original banding locations, e.g. 8.5 (±2.6) days for South America, 14.2 (±3.2) days for Delaware Bay, 16.1 (±3.5) days for the U.S. mid-Atlantic coast and 49.5 (±24.6) days for Florida. The proportion of knots with alternate plumage was higher in July–August than in September and by mid-October almost all had basic plumage. Also, low numbers (tens) of basic-plumaged knots—probably one-year-old subadults were found during July–August; most had active flight feather molt. First-arriving juvenile knots were seen beginning in the third week of August and their numbers peaked in mid-September. Differential uses of foraging and roosting habitats were found to be related to migration destinations. Vital habitats that should be managed for protection of threatened Red Knots at this key southward migration stopover area were identified.
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Vol. 33 • No. 3