The Punctual Bufflehead, Bucephala albeola: Autumn Arrivals in Shoal Harbour Sanctuary, Vancouver Island, in Relation to Freeze-up

Abstract

Buffleheads are punctual in their return to wintering grounds on the Pacific coast. First arrivals appeared in Shoal Harbour Migratory Bird Sanctuary, southeastern Vancouver Island, on the 288th day of the year on average (± S.D. 2.3; n = 10), that is, 15 October. This vanguard preceded the first peak influx by about 15–20 days, and a second influx by about 24–26 days. First arrivals usually appeared by mid-morning, and included singles (females on two occasions) and small flocks of up to eight. First arrivals may represent a photoperiodic threshold, whereas subsequent peak influxes represent climatic thresholds associated with freeze-up. The phenology of Bufflehead autumn migrations is a good proxy indicator of the advance of the zero degree isotherm, and thus of climatic variability. The timing of their autumn migrations does not appear to have changed in the last half of the twentieth century, consistent with evidence that freeze-up has not advanced. Monitoring of their migrations, in conjunction with shore-based observations of freeze-up, would validate one-dimensional thermodynamic models of freeze-up, and provide a more ecologically meaningful index of climate change, at minimal cost.