The co-occurrence of moose, white-tailed deer, and Parelaphostrongylus tenuis in Ontario

Abstract

Moose (Alces alces) populations were studied in parts of Ontario where they cohabit with white-tailed deer (Odocoileus virginianus) infected with Parelaphostrongylus tenuis. Trend data on changes in cervid numbers for the period 1980–1992, current population density estimates, and records of moose sickness were obtained from Ontario Ministry of Natural Resources managers; presence and abundance of P. tenuis were determined by examining winter deer feces for dorsal-spined larvae. Moose and deer coexist in 45 of 83 Ontario Wildlife Management Units (WMUs) surveyed and have persisted there for at least the past 12 years. Cervid populations in most of these WMUs are presently believed to be stable or increasing. Moose density was inversely related to deer density and was greatest where the latter was <4/km2. In addition, moose densities were lowest in areas with the highest mean intensity of P. tenuis larvae in deer feces. Nonetheless, the documented persistence of moose in numerous areas with infected deer, and case studies of recent moose declines, suggest that the effect of this parasite on moose populations is more subtle than was previously believed, and further study is required to separate and measure its importance relative to other mortality factors known to act on moose populations.