File:The Canadian field-naturalist (1930) (20331487230).jpg

Title: Some Natural Factors governing the Fluctuations of Grouse in Manitoba. The Canadian field-naturalist
Identifier: canadianfieldnat1930otta (find matches)
Year: 1930 (1930s)
Authors: Norman Criddle
Subjects: Graph showing fluctuations in grouse and grasshoppers at Aweme, Manitoba. Upper lines represent Sharp-tailed grouse, the lower ones Ruffed Grouse and the broken ones grasshoppers. The lower columns show rainfall for the five months May-September the amount indicated by short projections on the left, each of which represents two inches.
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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April, 1930) The Canadian Field-Naturalist 7& and me for some years but that the birds are apparently dependent to such a marked degree upon these insects will come to most people as a revelation. Indeed it seems wise to accept the apparent fact with reservation until it can be verified or disproved by further studies. The study, indeed might be enlarged to include other forms, and we suspect that, when it is completed, more will be thought of the value of insects in preserving birds and less of birds as destroyers of insects. The following graph speaks for itself; the infor- mation upon which it is based has been taken from the journals of my father, Percy Griddle, and my own, supplemented by observations of Messrs. E. and S. Griddle. I have also consulted the Reports of the Dominion Entomologist, Dr. James Fletcher, covering the period of 1895-1907. My personal association with grasshopper control work has enabled me to keep a fairly accurate record of the fluctuation of those insects, while the almost continuous residence at Aweme, Manitoba, of my brothers and myself since 1882 has ensured a reasonable appraisement of the comparative numbers of grouse present from year to year. That the records are only approxi- mate is obvious and it is hardly necessary to add that the curves shown on the graph are based on approximations rather than actual numbers. One interesting point brought out by this graph is that rainfall seems to be of far less in- fluence in accounting for grouse fluctuation than is generally supposed. It will be noted, however, that the beginning of a grasshopper rise is nearly always preceded or accompanied by abnormally dry seasons but that having once risen well above their minimum numbers the further multiplica- tion of these insects is then so rapid that precipi- tation becomes a minor factor in controlling them. The grouse, on the other hand, being able, in times of grasshopper abundance, to procure a sufliciency of food under any weather condition, rear the maximum number of young and so become plentiful in spite of excessive rainfall. The question might be asked, by those unfa- miliar with insect habits: If grasshoppers multiply irrespective of meteorological adversities, why do they ever sink to insignificance? To this we reply that most insect pests rise to importance
Text Appearing After Image:
Graph showing fluctuations in grouse and grasshoppers at Aweme, Manitoba. Upper lin£s represent Sharp-tailed Grouse, the lower ones Ruffed Grouse ana the broken ones grass- hoppers. The lower columns show rainfall for the five months May-September the amount indicated by short projections on the left, each of which represents two inches.

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