Title: The Canadian field-naturalist
Identifier: canadianfieldnat1973otta (find matches)
Year: 1973 (1970s)
Authors: Ottawa Field-Naturalists' Club
Subjects:
Publisher: Ottawa, Ottawa Field-Naturalists' Club
Contributing Library: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library
Digitizing Sponsor: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library

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1973 Nettleship and Lock: Tenth Census of Seabirds 397
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Figure 1. Sketch map showing approximate locations of the sanctuaries of the north shore of the Gulf of St. Lawrence. and line-transect procedures (Nettleship 1972a, b; Grant and Nettleship 1971). These methods are comparable with those of other years, al- though the determination of burrow number and status (active or inactive) at puffin colo- nies was more detailed in 1972, as were esti- mates of murres on inaccessible ledges. Although the 1972 survey appears to be comparable with censuses made previously be- cause of similar census techniques, there are at least three differences which can be identi- fied even if the methods used in the censuses are assumed to be identical (which, of course, they are not): first, and perhaps most impor- tant, is the fact that previous census teams had a relatively shorter time period available to census any single sanctuary (because of the R.C.M.P.'s boat schedule), which would of necessity result in less thorough counts being performed; second, the unknown effect on bird numbers of different weather conditions (local differences between years and either an early or late summer season) at time of census; and third, the time at which the censuses were made. The significance of these factors to ob- served differences in bird numbers is difficult to assess, but even with this Umitation it does seem important to compare the 1972 popula- tion figures with those recorded in 1965 in an attempt to detect major differences which may seem unlikely to be due to any change in methodology alone. Results and Discussion The results given in Table 1 show that the total number of birds has apparently declined by about one-third since 1965. Of the 13 species censused, eight appear to have declined (Herring Gull, Common and Arctic Terns, Caspian Tern, Razorbill, Common Murre, Black Guillemot, Common Puffin), four in- creased (Great Cormorant, Double-crested Cormorant, Ring-billed Gull, Black-legged Kit- tiwake), and one remained about the same

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