File:The Canadian field-naturalist (1935) (19898743643).jpg

Title: The Canadian field-naturalist
Identifier: canadianfieldnat1935otta (find matches)
Year: 1935 (1930s)
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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May. 19351 The Canadian Field-Naiuralist 81 logical interests of the National Parks Branch. The same questionnaire is used as a base for the Newfoundland, Anticosti and Alaska enquiries. In all instances the main comparisons of abund- ance are on a year-to-year basis, in order to reduce to a minimum errors of memory and of personal opinion. Absolute estimates such as "very abundant" or "very scarce" are recorded but not mapped. A mass of valuable records about habitats, epidemics, symptoms of disease, parasites, pred- ators, remains to be worked up. The mapping is done on an area basis plotted first on large- scale maps as the areas covered by individual observers, and then transferred to a grid of 30 X 30 mile squares on a map of Canada. The planimeter measurements discussed in the last report showed that the original areas are exaggerated (about doubled) by the grid method. This method is the only one, however, which enables records for the different provinces (which mostly have different scales of map) to be transferred onto a common map. Although the method has drawbacks, these drawbacks ajre known and their extent can be measured, and they do not greatly afifect the general conclusions that are drawn about relative increase and de- crease of snowshoe rabbits. The great advan- tages of this system of mapping are that it re- duces to a minimum personal bias in plotting the questionnaire results, and it makes allowance for the different sizes of area covered by observers. In one matter, however, personal judgement has to be used: some observers re- port about very large areas. The conventional circle used for people who do not give a detailed description of their area, is one of twenty-miles diameter. This is a very cautious figure, and a great many areas are larger. Anything more than a hundred miles across is considered as doubtful unless there is good reason to suppose that the observations are reliable. It is a fairly simple matter to decide these cases without bias- ing the result. Each Hudson's Bay Compaany post is given a circle with a fifty mile radius (100 mile dia- meter). This has been checked by sample re- ports of the exact districts covered and found to be an approximate limit. Where posts lie closer together than this a simple division is
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Figure 2.—State of the snowshoe rabbit population in 1933-34. Vertically hatched areas are groups of squares overlapped by areas of observers reporting relative decrease in 1933-34 over 1932-33. Horizontally hatched areas, no change. Larger dots are Hudson's Bay Company posts, etc. Broken lines show main vegetation zones.

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