ANNUAL FLUCTUATIONS IN A POPULATION OF MALLARD DUCK

J. D. Macdonald, Derek Goodwin, and Helmut E. Adler, Curiosities of Bird Life, Castle Books, 1962.

One point that may strike you is that there are far more birds at the end of the breeding season than there were at the beginning—the parents plus the young which survive from one or more broods—and yet at the beginning of the next breeding season you will find again only one pair, often the same birds, in approximately the same territory. Annual increase and decrease in the numbers of a species, of many mammals as well as birds, is a feature which is unusual to us.