Figure 1.
Primary molt start and end date (A, B), and molt duration (C), in free-living and captive red knots.
Symbols: closed symbols, males; open symbols, females. Group abbreviations: SYM, second-year males; SYF, second-year females; FAdM, free-living adult males; FAdF, free-living adult females; CAdM, captive adult males; CAdF, captive adult females.
Table 1.
Comparison of molt parameters between ages (within sex) or sex (within age) in free-living adult and second-year red knots.
Figure 2.
The average temporal distribution of primary molt in free-living adult and second-year red knots, and captive adult red knots (sexes combined, grey blocks).
The dashed vertical grey lines indicate when the knots had completed growth of primary 5. Also plotted are the estimated weekly maintenance costs for a red knot living in the Wadden Sea, calculated using the model of [63] (equation 5; using mudflat conductances) from daily wind, ambient temperature and solar radiation data obtained over the same period as the molt data (1998–2006; data from the Royal Netherlands Meteorological Institute (KNMI) weather station at Hoorn on the island Terschelling in the Dutch Wadden Sea, 52°23′N 5°21′E). Note that basal and thermoregulatory costs are included in maintenance costs, but molt costs (feather synthesis and increased thermoregulation) are not. Maintenance costs are indicated with circles; open circles indicate the period during which adult red knots are migrating or in the breeding areas [63]. In addition, daylength in the Wadden Sea is given (solid line, right Y-axis, data from KNMI, 2006). Arrows indicate the start of the rapid increase in number of peregrines in the Wadden Sea (P; [54]), and when the diet of free-living knots changes from shellfish to less profitable mudsnails (D; [56], [58]).