Population Fluctuations in Some Northern Hemisphere Game Birds (Tetraonidae)

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Abstract
A well-marked cycle in the numbers of tetraonid game birds occurs throughout most of the northern part of North America. Although in any one district the length of the cycle may vary within fairly wide limits, there is a strong tendency over great areas for crashes to occur in synchrony every 9-10 years. In most of Canada and in the northern U. S. one main cycle appears to operate; however, in the Canadian Maritime Provinces the cycle seems to be advanced in its corresponding stages by about 3 years over the "main" cycle, whereas in Alaska the cycle appears to be retarded by about the same interval. In Britain and northwestern Europe snorter general cycles prevail[long dash]with a mean length of about 5 years in Britain and 3-4 years in Finland and Scandinavia. Although the British and Scandinavian cycles have many peak years in common it is impossible to decide, on present data, whether or not these coincidences are random. Fluctuations in the abundance of tetraonid game birds also occur in Greenland, Iceland, the northwestern U. S. S. R. and Spitsbergen. The Icelandic cycle seems to be predominantly a long one, showing resemblances to the North American pattern; whereas the U. S. S. R. and Spitsbergen cycles are almost certainly short cycles of the British and Scandinavian type. More information is needed to characterize the Greenland fluctuations. In North America the tetraonid fluctuations almost certainly occur in close synchrony with those of the snow-shoe rabbit; in Scandinavia they appear to be connected with the lemming cycle. When populations of many very different species of animals fluctuate together the most likely synchronizing agent would seem to be a common weather system. There is no evidence in support of the hypothesis that an extra-terrestrial factor is responsible.

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