. The Canadian field-naturalist. 316 The Canadian Field-Naturalist Vol. 94. Figure L Location of II Glaucous-winged Gull breeding colonies and banding locations discussed in this study: I — Mitlenatch Island, 2—Lasqueti Island, 3 — Pam, Christie, and Passage Islands (Horseshoe Bay), 4—Westham Island, 5—Snake Island, 6—Ballingal Islet, 7—Mandarte Island, 8—Chain Islets, 9—Ucluelet, 10—Long Beach, 11—South- east Flores Island, all in British Columbia. Mandarte, and Mitlenatch) indicate that the breeding population of Glaucous-winged Gulls has increased about times between 1928 and 1974(data
. The Canadian field-naturalist. 316 The Canadian Field-Naturalist Vol. 94. Figure L Location of II Glaucous-winged Gull breeding colonies and banding locations discussed in this study: I — Mitlenatch Island, 2—Lasqueti Island, 3 — Pam, Christie, and Passage Islands (Horseshoe Bay), 4—Westham Island, 5—Snake Island, 6—Ballingal Islet, 7—Mandarte Island, 8—Chain Islets, 9—Ucluelet, 10—Long Beach, 11—South- east Flores Island, all in British Columbia. Mandarte, and Mitlenatch) indicate that the breeding population of Glaucous-winged Gulls has increased about times between 1928 and 1974(data in Drent and Guiguet 1961; Campbell 1975, 1976). Presumably most of this increase has occurred in the last 10-30 yr as shown in other species of gulls in the northern hemisphere (Kadlec and Drury 1968; Verbeek 1977c). We suggest that the dramatic forward shift in mortal- ity among first-year Glaucous-winged Gulls from December-February (birds banded in 1938-1940, Woodbury and Knight 1951) to September-No- vember (birds banded in 1963-1977, this study) may be the result of this increase in the population. In an environment saturated with gulls, competition for food with adults may result in many young dying shortly after dispersal from the colonies rather than later in the winter. Figure 3 shows the numbers of birds found belong- ing to the various age classes. The last banding year included in this study was 1977 and the last band recovery year was 1978. All banded gulls alive after 1978 are, therefore, older than 1 yr of age. To deter- mine accurately the age-specific mortality rate of all Glaucous-winged Gull age classes we should wait until all of the banded gulls have died; however, a few points can now be stated. Many Glaucous-winged Gulls appear to die in their first year (Figures 2, 3). Of 1002 banded recoveries, 581 were from first-year gulls, giving a mortality rate estimate of The remain- ing living gulls that will die after 1978 will lowe
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