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.