The vole population at Arastradero Preserve is presently at a high level of it's cycle which may mean several hundred voles per acre.

From: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7439.html (UC Davis - Statewide Integrated Pest Management Program)

Vole numbers fluctuate from year to year, and under favorable conditions, their populations can increase rapidly. In some areas their numbers are cyclical, reaching peak numbers every 3 to 6 years before dropping back to low levels. Voles can breed any time of year, but the peak breeding period is spring. Voles are extremely prolific, with females maturing in 35 to 40 days and having 5 to 10 litters per year. Litter size ranges from 3 to 6 young. However, voles seldom live longer than 12 months.

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