Duration and Phenology of Remigial Molt of Barrow's Goldeneye

We quantified the duration and phenology of remigial molt of Barrow’s Goldeneyes (Bucephala islandica) in northwestern Alberta, Canada. We estimated that the remiges’ average (± SE) growth rate was 3.94 ± 0.13 mm day–1, slightly slower than that of most waterfowl. Barrow’s Goldeneyes regained flight with the ninth primary 77% grown, a percentage similar to or greater than that of most waterfowl. By several metrics, remigial molt of Barrow’s Goldeneye was longer than that of most waterfowl. We estimated that it took 6.5 ± 1.2 days for a new ninth primary to become visible once the old primary was dropped (pre-emergence interval). The periods in which males and females were flightless were 30 ± 0.4 and 28 ± 0.5 days, respectively, and 36.5 ± 0.5 and 34.5 ± 0.8 days, respectively, including the pre-emergence interval. Complete maturation of primaries after emergence took 39 ± 0.5 and 36 ± 0.7 days for males and females, respectively, and 45.5 ± 0.6 and 42.5 ± 0.9 days, respectively, including the pre-emergence interval. These results suggest a lack of strong selective pressure to reduce the duration of remigial molt in this species. Initiated over a range of nearly 2 months, remigial molt was asynchronous both between and within age and sex cohorts, suggesting a lack of strong temporal optima for remigial molt of Barrow’s Goldeneyes at our study sites.