Graduation Date
1988
Document Type
Thesis
Program
Other
Program
Science
Committee Chair Name
Dr. Stanley W. Harris
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Dr. David Kitchen
Third Committee Member Name
Dr. George Allen
Keywords
Science
Subject Categories
Natural Resources
Abstract
The breeding biology and food habits of mew gulls (Larus canus) in Anchorage, Alaska colonies were studied from 1979 to 1982. Three colonies were studied, two in the Port area of Anchorage (the "Port'1 and "Cement Yard" Colonies) and one on Gull Island in Lake Hood at the Anchorage Airport. During the study period mew gull numbers decreased at the Cement Yard colony, increased on Gull Island, and remained steady at the Port Colony. Nesting habitat was variable at the Cement Yard and Port Colonies, and nest site location seemed to depend on what was available in each area. Mew gulls nested on the ground, on soil, gravel, in meadows, on tidal flats, or on objects above the ground (i.e. vehicles, wooden objects, pipeline supports, and buildings). Nests on Gull Island were all found in short-grass meadow. Egg laying began between 7-15 May in all years, and all colonies studied, and generally was completed by the last week of May. First chicks hatched between the 2nd and 12th of June regardless of the year or colony location. All chicks were hatched by late June at most iii iv sites and most years, and young fledged from early July to mid-August. The incubation period for mew gulls in this study was 24.27 days (S. E. 1.4). At most sites and years, the average clutch sizes ranged from 2.5 to 2.9 eggs depending on the colony. Brood size averaged from 0-2.7 (range 0-3) chicks per nest. The greatest cause of egg loss was through unexplained gradual loss of eggs at the Cement Yard and Bort Colonies. Eggs were also lost from nest destruction by weather or tides or taken by humans (i.e., eggers). Most of the observed chick mortality occurred between hatching and one week of age. Mew gull chicks gained an overall average of 14.1 grams per day. After five days old, growth accelerated and chicks gained an average of 18.3 grams per day, slowing at 19 days of age. The heaviest weight was recorded approximately 25 days after hatching. Chicks began to fledge at 25 days of age. Mew gull diets varied between 1980 and 1981 as judged from analysis of pellets and regurgetations. Significant changes in numbers of samples containing fish, birds and voles were observed between 1980 and 1981. Small birds appeared to be the most common food item in 1980 and fish were most common in 1981. A plan to control gull numbers on Gull Island, was implemented in 1981. I destroyed most of the eggs there in 1981 and reproductive success was severely altered.
Recommended Citation
Adamson, Charlotte I., "The Breeding Biology and Food Habits of Mew Gulls (Larus Canus) Nesting in Anchorage, Alaska" (1988). Cal Poly Humboldt theses and projects. 2351.
https://digitalcommons.humboldt.edu/etd/2351