DENSITY-DEPENDENT RESPONSES OF GRAY-TAILED VOLES TO MOWING

Voles (Microtus spp.) commonly inhabit forage crops and may cause exce ssive damage to these crops. However, cover removal by mowing or hayin g may cause vole populations to decline. To determine if gray-tailed v oles (M. canicaudus) responded to mowing of alfalfa in a density-depen dent manner, we livetrapped 4 populations in each of low- (<30 voles), medium- (50-70), and high-density (>90) 0.2-ha enclosures before and after mowing in 1992. Survival rates of both sexes, population size an d growth rates, and proportion of total captures that were recruits de clined (P < 0.05) following mowing in all enclosures. The proportion o f animals captured in border traps, an index of dispersers, increased (P = 0.08) following mowing. Sex, age, and reproductive condition of d ispersing individuals did not differ from nondispersers (P > 0.22). Gr eater than 50% of dispersing adult females were pregnant, and we sugge st that mowing disrupted social organization of voles causing some ani mals to abandon home ranges or territories. Although mowing reduces po pulations of gray-tailed voles and disrupts social organization, the h igh reproductive potential of the species enables populations to recov er rapidly to premowing levels.