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A study of the distribution of some members of the Nyrocinae wintering on the coastal waters of southern British Columbia. Mitchell, George Joseph

Abstract

From September, 1951, until March 1952, field work was carried on to determine the distribution of wintering diving ducks on the coastal waters of southern British Columbia, and an attempt was made to discover and evaluate the factors causing distribution and movement. Diving ducks are influenced by the availability of food and other factors related to this availability. These factors include salmon and herring spawning, grain elevators, sewer outfalls, and changing tides. Local movements result from courtship activity, diel periodicity and disturbing agencies. Mortality factors, including hunting, oiling, predation and lead poisoning did not cause serious Inroads in the wintering diving duck population during the study. Lake, and bay and estuarine habitats were found to be less important wintering areas than habitats along protected and unprotected coastline. All species of diving ducks showed preference for certain habitats and regions in the study area, and were absent or uncommon in others. During the winter, the drakes and hens of most species were distributed non-randomly because of the preponderance of males and their tendency to flock together. In early spring the sexes were distributed non-randomly due to pair formation and predominance of drakes. A differential sex migration was evident in most species of ducks during late fall and early spring. Only a small percentage of juveniles of all species were wintering on the study area, indicating that they possibly winter in other localities.

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