PRODUCTIVITY ESTIMATES OF MOOSE POPULATIONS: A REVIEW AND RE-EVALUATION

Abstract

Estimates of moose population productivity in North America are often obtained from herd composition surveys done with the aid of light aircraft. Timing of the surveys may be adjusted to estimate gross productivity through neonate:cow ratios, or net productivity expressed as ratios between cows and 6-month-old calves, short yearlings or long yearlings. All of these estimates are biased by numerous variables, some of them ecological. Neonate surveys must be timed to achieve an optimum balance between the progression of parturition and early calf mortality. Calf:cow ratios in November are affected by search and effort during the surveys and by the aggregation behavior of cows without calves. Pre-parturition surveys tend to overestimate the occurrence of short yearlings due to group size differences in spring between cows with calves and those without. Long yearlings are often misidentified because of their variable antler characteristics. Productivity data are often used to monitor population welfare, but such data do not necessarily forecast population trends. The long-lived nature of moose allows previous reproductive performance to determine the trajectory of a population after productivity statistics change.