To develop our trapping protocols, we did some preliminary field work in the fall of 2021. In a dairy pasture with signs of vole activity (holes, runs, fresh feces in runs) and even some vole sightings, we investigated burrow structure and timed ourselves identifying good candidate holes and deploying our trapping equipment. The general plan was to set traps in the runs around one hole and block nearby entrances to that burrow.
Trap Setting
To get a better sense of how many entrances a vole burrow might have, we used an insecticide fogger (heating vegetable oil). We inserted the smoke-emitting tube into one hole and observed how many other holes the smoke escaped from. The most we saw was about 40 holes in a network spanning about 11 feet. We got a sense of how close holes from one burrow are to each other, so we would know what our “block-the-holes” radius should be.
In this preliminary work, we configured our trap sets. A “trap set” consists of a numbered flag, 2 snap mouse traps in each run (trail) going to/from the flagged hole (usually 2 runs), burlap stuffed in neighboring holes to block them, and milk carton “roofs” to shelter the traps from other animals. Traps are checked ~24 hours later and removed.
Dog Training
To train our collaborating dogs and dog handlers, we set up a system where the dogs could practice detecting live voles. Six live voles were caught earlier and housed at an on-campus small animal facility (see photo of vole in a jar—temporarily; their homes were much bigger than that). We dug some holes and trenches where we could put live voles contained in PVC tubes like those used to keep rats safe in competition barn hunts. Several training sessions with the dogs and live voles were run. However, we discovered that at least some of the voles were positive for leptospirosis, a bacterial disease that can be transmitted to humans and dogs. Biosafety protocols were followed throughout our training sessions. (Health advisory: vaccinate your dog[s] against leptospirosis. It is in our environment.) The voles were subsequently euthanized by veterinary personnel.
Once the dogs had been trained on the vole scent, dogs and handlers tackled some “real” pastures with vole problems. Each dog/handler pair was assigned a search area, where the handler flagged holes that their dog alerted on. At each of those holes a trap set was installed and checked the next day. The more successful dogs (who identified holes where we caught voles) were invited to participate in the data-collection trials that ran in March.
