Gray-Tailed Voles in the Willamette Valley

Gray-tailed voles (Microtus canicaudus) are endemic to the Willamette Valley up into Clark County, Washington. This species inhabits grasslands and has adapted to the agricultural landscape that has replaced the original prairie and oak savannah habitat. In fact, voles can be significant pests in grass seed fields. Although their population dynamics are not well-studied, they do appear to undergo population irruptions at irregular intervals of 5 to 8 years, with varying peak densities. In 2005, a phenomenal population explosion caused widespread economic damage to the grass seed industry, vineyards, orchards, and even greenhouse plants.

Despite widespread interest in vole population dynamics, relatively little work has been done regarding vole impacts on ecosystem dynamics and ecological processes. Their intermittent irruptions lead to tunnel networks that then decay, and their herbivory greatly impacts plant recruitment and survival for a brief time every few years. Irruptions also lead to pulses of organic matter in soil, associated with the voles dragging vegetation into burrows and other detritus in burrow systems. The burrows themselves offer shelter to other rodents and invertebrates. The physical structure of the burrows and the surface runways affect water runoff and soil saturation, and may help degrade some pesticides that flow into these organically rich, microbially active regions of soil. We know that small rodent irruptions have important implications for may species of raptors and their reproductive success. How do voles affect other members of the ecological community?With a team of collaborators from the Department of Crop and Soil Science at Oregon State University and from the US Department of Agriculture's Agricultural Research Service, I am beginning initial studies of the impacts of voles on soil. I am also interested in the interaction between vole dynamics and the bacterial disease tularemia, which is hypothesized to be a factor in populations crashes. In addition, in collaboration with scientists from The Institute of Applied Ecology and The Nature Conservancy, vole impacts on native grassland plant recruitment and survival will be studied.Finally, voles are a native player in the Willamette Valley ecosystem, but their negative economic impacts can be severe. Development of efficient population monitoring tools that can evaluate densities in crop fields, and better integrated pest management strategies, will greatly aid the continued coexistence of farming and native wildlife within the Willamette Valley.