On the Analysis of Productivity in Populations of Higher Vertebrates

Abstract

this work, but investigators, by assuming (or by leaving reader to infer) that loss of a clutch of eggs or a litter of young necessarily means that much net loss in productivity, may introduce errors of such magnitude that critics could, in many instances, appropriately ask whether conclusions were not as misleading as instructive. It may be conceded that various species for reasons of latitude, climate, rarity, inherent shortness and lack of synchrony of sex rhythm (Allen, 1934) physiology, psychology, etc., may have distinctly limited opportunities to reproduce. Late young--even of species that readily renest throughout a long breeding season-may be, moreover, few in number, subject to pronounced if not lethal handicaps, or undesirable special human viewpoints. Nevertheless, calculations of so-called life equations that ignore, for example, renesting when its compensatory value is substantial can lead pretty wide of truth; and common sense reasoning of administrators and sportsmen to effect that every game bird e g that fails to hatch is equivalent of one les hunting season pheasant (or quail or duck or something else) should hardly be surprising as long as comparable assumptions continue to be made by those whose studies are accepted as technical background. We have only to consider standard pract ces in poultry management to see how immense numbers of eggs would never be laid in first place were it not for timulus resulting removal of ggs laying hens. Among wildliving birds, flicker (Colaptes auratus) has long been known for its propensity for continuing to lay after egg losses (Bent, 1939: 272). Recognition of some of fallacies of misplaced concreteness (Whitehead, 1925; Henderson, 1941) that are so prevalent in life history analyses should be possible without unduly minimizing loss types of real importance. My own endeavors to evaluate renestings and related phenomena were inspired by Stoddard's (1931) classic investigation of bobwhite (Colinus virginianus) in Georgia and Florida, which clearly distinguishes between percentage and significance of nesting losses. On pages 224 and 225 of his book, we may not only read that from 60 to 80 per cent of unsuccessful nesting attempts may normally be expected at large over Southeastern quail territory but also that, in course of a season, the majority of pairs sooner or later are successful in hatching I Journal Paper No. J-674 of Iowa Agricultural Experiment Station, Ames, Iowa, Project No. 498. Fish and Wildlife Service (U. S. Department of Interior), Iowa State College, Iowa State Conservatioa Commission, and American Wildlife Institute cooperating.