Optimizing vole trapping strategies in annual and perennial cropping systems

Progress report for OW21-364

Project Type: Professional + Producer
Funds awarded in 2021: $74,364.00
Projected End Date: 12/31/2024
Host Institution Award ID: G341-21-W8614
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Principal Investigator:
Nick Andrews
Oregon State University
Dr. Dana Sanchez
Oregon State University
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Project Information


Farmers managing different cropping systems lack detailed research-based information about vole management strategies other than rodenticides. For the educational component, we are providing current information about integrated vole management strategies including predators, habitat management and trapping. Our research focusses on innovative trapping strategies in the winter to interrupt spring reproduction and exponential population growth. We are investigating trap site identification methods (canine assisted trapping and human visual cue detection). We hypothesize that canine assistance can increase trapping efficiency and efficacy, strengthening vole management. We are  also investigating burrow architecture and underground vole activity.

Synthetic rodenticides are hazardous to non-target wildlife, including threatened or endangered species. They can be effective tools but—like other pesticides—are best used as part of an integrated management approach. This project will provide new insight into vole behavior, tunnel architecture, and trapping strategies that will enhance vole management on organic and conventional farms.

We will publish research findings in a peer-refereed journal, write a new Extension Publication on ecological vole management, and establish training guidelines for canine-assisted trapping. We will host on-farm field days and present our findings at farmer conferences. We are maintaining a project blog and writing newsletter articles to engage a wider audience.

Current research-based information about ecological vole management is lacking for Oregon farmers. We hope this project will be the first of many to fill this gap.

Project Objectives:
  1. Investigate canine vole scent detection and trapping strategies
  2. Study vole burrow architecture and behavior
  3. Disseminate results and evaluate adoption and impact


Click linked name(s) to expand/collapse or show everyone's info
  • Steven Burger - Producer
  • Dr. Jenifer Cruickshank
  • Sharon Gakstatter - Technical Advisor
  • Ian Gallacher - Producer
  • Jimmy Lee - Producer
  • Laura Masterson - Producer
  • Vanessa Blackstone (Researcher)
  • Stephen Pierson - Producer
  • Tim Stock
  • Kody Transue
  • Dr. Stephen Vantassel - Technical Advisor
  • Conner Voss - Producer
  • Dr. Nik Wiman
  • Jon Bansen


Materials and methods:

Preliminary Work

We received final approval (IACUC-2021-0187) to work with voles and detection dogs on August 31, 2021; the approval expires August 30, 2024. We started recruiting dog and handler teams (canine teams) in May 2021, and by late August we had recruited seven teams for our first year of vole detection training. In July and August 2021, we developed vole detection and trapping protocols and determined plot size by incorporating what we learned by timing ourselves doing these tasks in dairy pasture, vegetable farm, and hazelnut orchard settings. We also forced smoke down vole holes using vegetable oil in an insecticide fogger to assess tunnel connectivity.

Dog Training

In September and October 2021, we constructed a vole detection training arena at OSU’s Fairplay Farm in Corvallis using a trench design adapted from Earthdog training tunnels and with discrete holes drilled in the plywood covering the network. We purchased twelve PVC Barn Hunt rat tubes to contain live voles during nose work training; the design adapted was from the 2019 Barn Hunt Association rule book. Nose work training workshops with seven nose work dog-and-handler teams and our professional dog trainer started in November 2021. Training started with a lie-down alert to an object with no odor.  We transferred this lie-down alert to voles in tubes and empty tubes above the ground. Next, we placed the tubes with and without voles in the covered trenches and discrete holes in the training arena and reinforced the lie-down alert.

The voles used for nose work training of the dogs were captured in late October and early November. We used Sherman folding traps to catch live voles at a dairy in Corvallis. Six captured voles were subsequently housed at OSU’s Research Animal Isolation Laboratory (RAIL) for use during canine detection training. Two voles were found dead in the Sherman traps.  Dr. J. Sargent, DVM, Director of the OSU Laboratory Animal Resources Center and OSU attending veterinarian, conducted necropsies and testing that identified leptospirosis infection in the dead voles. Pooled urine samples from the six live voles housed at RAIL also tested positive for leptospirosis, so our training with live voles was discontinued pending revision of our vole handling procedures. After consulting with OSU physicians and veterinarians, the voles were labeled as biohazards and new standard operating procedures (SOPs) for vole handling were developed and implemented for all aspects of housing, transportation, handling, and exposure to dogs and dog handlers. The SOPs included education of dog handlers and strong encouragement to complete leptospirosis vaccination for those dogs not already vaccinated. Dr. Sargent attended one of our nose work sessions to observe our vole handling and dog interaction procedures.

One of the animal caretakers at RAIL became ill with a presumed but unconfirmed case of leptospirosis, at which point Dr. Sargent and the OSU medical advisors terminated our work with live voles, which were subsequently euthanized with isoflurane on January 19, 2022. Blood samples from each vole showed that three were positive for leptospirosis. Based on consultations with canine detection experts around the U.S. we adapted our nose work training using three new approaches that avoided live vole handling: 1) we transferred vole scent to cotton swabs, 2) we freeze-dried voles, and 3) we trained dogs in suspected vole hot spots.

We transferred vole scent to cotton swabs in two ways: 1) swabs placed in metal strainers were hung in the cages for about 72 hours before euthanizing the voles, and 2) at the time of death, the voles were rubbed with cotton swabs. Swabs used for these two types of scent transfer were stored separately for potential use later in scent training. After the voles were euthanized, they were immediately placed in coolers on dry ice to prevent formation of decomposition compounds. Within two hours they were placed in a -80°F freezer to await preservation by freeze drying on a unit equipped with a HEPA filter on the exhaust, per OSU’s Biological Safety Officer. On January 25, we transferred the voles from the freezer to the freeze dryer. On January 27 after approximately 48 hours the freeze dryer automatically shut off, and the voles were removed and stored in amber glass jars with desiccant for use in scent training.

Cotton swabs that had been hung from vole cages elicited a slightly greater response from the dogs. We placed the freeze-dried voles in shallow mason jars with perforated lids and then placed those in shallow holes in a field at Fairplay Farm, which also had active vole colonies. The dogs did not give a reliable alert to the freeze-dried voles, but some dogs alerted on apparently active voles holes. Therefore, we decided to conduct canine training workshops at suspected vole hotspots. First, we returned to the Corvallis dairy where we had caught the live voles for training. Although a few dogs alerted on some holes, we didn’t catch any voles. Then we moved to a Corvallis-area sheep pasture that reported high vole damage. More of the dogs alerted on voles there, and we caught 9 voles and 3 shrews at the first field training at that location and 3 voles at the second. Finally, we moved to a collaborating dairy near Monmouth with heavy vole pressure and caught 15 voles. At each location, we recorded the number of holes identified as active (“sets”) by the canine teams, and we used the number of voles caught per set to select four dog and handler teams for the 2022 field work; three teams (dogs Daphne, Sierra and Bijou) were available for the trials.

The approach of training dogs in vole hotspots appeared to be the most successful; however we noticed during the early winter that apparent vole abundance (via sign and sightings) had declined at some locations, suggesting that the population may have dropped after two-to-three successive years of extremely high vole populations and crop damage. This fits the "boom and bust" irruptive pattern that vole populations are known for. The multiple delays due to the complications described above caused us to be out of sync with our system's prime population-reduction season (January–February), but we conducted field trials in each cropping system to further refine our methodology.

In 2023, dog Reacher replaced Bijou for the research trial. Reacher and his handler are a trained conservation detection team, therefore they bring a different training and working approach than competition nose work teams. Reacher was introduced to vole scent by following Daphne and Sierra during vole searches and being awarded for alerts that were consistent with Daphne and Sierra’s alerts. Reacher’s handler supplemented this training by transferring vole scent from the freeze-dried voles to the interior of foam tubes typically used to insulate pipes. The foam tubes were placed in cinder blocks for introductory scent discrimination training using an approach developed by Working Dogs for Conservation. When Reacher was alerting reliably on vole scent in this setting, his handler used the foam tubes as hides for field training. Blank decoys (foam tubes with no vole scent) and hides with vole scent were placed in small holes in the ground, mimicking a natural vole hole with fresh vole odor. Reacher was rewarded when he alerted by sitting next to the hides with vole scent. This training continued until Reacher was reliably alerting on hides with vole scent but not decoys, and his handler was confident that they were ready to start field work.

In 2024 we received a no-cost extension until December 31, 2024. We continued the field research at one location with larger plot sizes (1/2 acre) searched solely by the professional canine team.

Trapping and crop damage

Our first on-farm trapping season started on March 14, 2022 and ended on March 25, 2022. Five farm locations were surveyed for vole activity with a pair of treatment plots (canine assisted and human searching) on each farm for a total of ten quarter-acre plots. Plot corners were marked with wood stakes. For each treatment pair of plots, one plot was surveyed by a canine-handler team and the other plot was searched by a person alone. The same person served as the human-alone searcher for all plots. During canine searches, 300-foot long tape measures or rope were laid around the perimeter of the plot to help dog handlers keep their dogs within the plots. Holes identified as occupied during canine-assisted and unassisted-human searching were marked with flags. Trap placement began within 30 minutes of the end of the survey. Two to four traps (a “trap set”) were set around most of the holes identified. The number of traps varied according to the number of runways at each hole, with a few holes getting five to eight traps. Burlap squares approximately 6”x6” were used to plug holes (presumed alternative burrow entrances) within a 1 m diameter of each hole with trap sets, based on preliminary observations with forced smoke. Milk carton roofs were installed above trap sets to reduce non-target catches and false triggers from wind, rain, or larger animals. Trap sets were left overnight and then checked and removed approximately 24 hours after initial trap setting. Preliminary trapping during the dog training phase indicated that few voles were caught in traps reset for a second day and more non-target species, especially shrews, were caught.

During the 2022 trials, it became apparent that different cropping systems had pros and cons for the field trials. Regular tillage in vegetable production fields disrupts vole tunnels; after tillage, voles gradually move into the production fields and can cause substantial damage. This disturbance and subsequent vole migration confounds our main research question. Operators of conventional hazelnut orchards spray hazelnut suckers, use rodenticides and sometimes apply residual herbicides to maintain a bare orchard floor. These practices posed safety concerns for our search teams and can impact vole populations. One vegetable farm and the hazelnut orchard had relatively high populations of deer mice (Peromyscus maniculatus) during the 2022 trapping season, this is a non-target species in this project.

During the summer of 2022 we scouted several organic or low input pasture, hay and hazelnut sites and found sporadic evidence of recent vole activity. Pasture and hay fields appeared to have the most consistent signs, and farmer reports of recent vole activity at the sites we visited. For these reasons (vole disturbance from tillage, high incidence of non-target species at some sites, pesticide safety concerns, and signs and reports of recent vole activity) we decided to conduct the 2023 field trials in pastures or hay fields that had not recently been reseeded. Regional vole populations crashed prior to the 2023 season. We surveyed several sites from July to December 2022 and identified sites that still had apparently high levels of vole activity. Heavy rain and ponding at some sites further limited our options, and in December 2022 we selected three sites for the 2023 field trials. We set up two pairs of three plots (one canine assisted, one human searching, one untrapped control) on each of three dairy farms.

Each site was trapped approximate every 14 days from early January until the first juvenile voles were trapped in mid-March, using the same searching and trapping methods described above.

Forage damage assessment protocols include visual assessments of ground cover using the Daubenmire Method described in Coulloudon et al. 1999 (pp 55-63) and the number of vole holes in eight 50 x 50cm quadrats, and collecting dry matter samples from 50 x 25cm quadrats:  eight along the transects and two additional quadrats visually identified with severe vole. We conducted spring damage assessments of all treatment plots from March 28 to April 3 and again from June 20 to 23, 2023.  

We decided to conduct one more year of field work in early 2024 with larger ½ acre plots in the organic hay field with highest vole incidence in 2023. We set up three replicates of two treatments: canine assisted trapping (with the professional team) and an untrapped control. Traps were set approximately every two weeks—except one week when ice-storms caused delays—from January 3 to March 15, 2024, using the same searching and trapping methods as previously described. The sampling method was consistent, but rather than sampling along transects and at sites of severe damage, 10 quadrats were randomly placed in the plots. We also conducted a pre-trapping forage assessment. Vole damage assessments and forage samples were collected on December 14 (before trapping) and March 29 (after trapping). Our final damage assessment will be a few weeks after the hay is cut (anticipated for late May).

Research results and discussion:

The 2022 pilot season was extremely valuable for refining our protocols, testing our datasheets, and developing our database. Voles were trapped at all five sites, with the greatest numbers in the pastures. Deer mice were caught at NWREC (hazelnuts) and 47th Avenue Farm (vegetables). Two shrews each were caught at Sar-Ben Farms (pasture) and at Diggin’ Roots Farm (vegetables), and one was caught at 47th Ave. Farm (vegetables).

Although vole trapping rate (voles per trap set) was essentially the same between canine and human searching (0.40 and 0.41 voles/trap set, respectively1), canine teams were far more time efficient (0.48 vs. 0.33 voles/minute of searching, respectively). Across all sites, canine assisted trapping took about half as long as human detection. The human searcher chose more sets for trapping (168 vs. 116), which added to the time required. Canine teams sometimes alerted on more than one hole in close proximity to connecting tunnels (linked trap sets); all of these holes were trapped and counted separately. When they were combined, the canine trap rates improved slightly when calculated as voles/trap set.

Two of the canine-identified holes/trap-sets caught deer mice; at one of these sites the human-identified hole/trap-set also caught deer mice. They are known to use vole (and other species’) burrow systems, and as seed eaters they are less likely than voles to damage crops. Canine detection rates improved slightly when deer mice were included in total rodent trap counts (voles and mice).

Vole populations tend to be lower over the winter and stay relatively low until breeding starts, so winter trapping (i.e., January through March when the first juveniles are trapped) is more likely to reduce crop damage by reducing a population’s reproductive capacity than trapping later in the season. The IACUC approval process with its multiple revisions and the leptospirosis infection issues delayed our dog training, and subsequently delayed our 2022 field work until mid-March. At that time, we caught juvenile voles along with adults, so we decided to conduct only one round of field trapping at all farms retained for the season in order to inform adjustments to our protocols for 2023.

During the single-bout pilot in March 2022, a total of 284 trap sets were made after a total of 273 minutes of search time, across team types. Across the 3 canine teams, a total of 116 trap sets were located by canine-assistance in 97 minutes of search time, resulting in 47 vole captures, 10 non-target captures, and a vole trap rate (voles/trap set) of 0.41 with 0.48 voles trapped per minute search time. There was notable variation in efficiency among the 3 dog teams, ranging from 0.29 to 0.65 voles trapped/minute of search time. The unassisted human trapper set 168 trap sets after 232 minutes of search time, caught 67 voles and 9 non-target animals, for a vole trap rate of 0.40 with 0.29 voles trapped per minute search time. The non-target captures consisted of deer mice and shrews.

Vole populations crashed in the winter of 2022-23. Over the entire season, canine-assisted teams searched a total of 593 minutes and placed 2,141 trap sets, killing 0.029 voles/trap set with an efficiency of 0.108 voles/minute searched. The unassisted human searched 1,207 minutes and placed 1,276 trap sets, killing 0.047 voles/trap set with an efficiency of 0.049 voles/minute searched. Across team type, 124 voles and 19 non-target animals were removed.

Spring 2023 (March 28 to April 3) crop damage estimates showed statistically significant difference between treatments despite relatively high standard deviations, with the canine assisted trapping plots showing greater dry crop biomass (3,768 lb/ac) compared to the human trapped and control plots (2,912 lb/ac and 2,947 lb/ac respectively). This difference did not persist to the summer (June 20-23) damage assessment, when all treatments were essentially the same, with 4,516, 4,481, and 4,574 lb/ac dry matter for the canine-assisted, human, and control plots respectively.

The 2024 trapping data and the spring crop damage data has been collected and entered but not yet interpreted.

Participation Summary
5 Producers participating in research

Research Outcomes

No research outcomes

Education and Outreach

25 Consultations
12 On-farm demonstrations
12 Published press articles, newsletters
6 Workshop field days
1 Other educational activities: We convened the new OSU Rodent Management Working Group

Participation Summary:

186 Farmers participated
53 Ag professionals participated
Education and outreach methods and analyses:

The OSU Rodent Management Extension working group was formed in 2021 with Nik Wiman (co-PI) as Chair and 12 other members including all OSU project collaborators on this grant. During our first working group meeting in March 2021, we identified three new vole related projects at OSU including this one. Since then, we have collaborated with an OSU colleague (Dr. Christy Tanner) who is using drones to assess vole damage. She has presented her research and demonstrated the drone during our project workshops and is collaborating in our 2024 field trials. We have also collaborated with the OSU Veterinary Teaching Hospital by donated voles caught during our project to their study of Leptospirosis in voles.

We have created a project blog (https://blogs.oregonstate.edu/voles) and have so far published six posts using photos from our training and field trials. In late 2022 and early 2023, we published four newsletter articles about the project. “Canine detection and vole management on organic farms: new project update” in Oregon Small Farm News; “Dogging your voles” in Digger Magazine, “Dogs sniff out destructive voles to help farmers with control” in OSU Extension Service News, and “Can dogs help in the annual struggle with voles?” in Pacific Nut Producers’ Magazine. Dana Sanchez presented this research at the 31st Vertebrate Pest Conference (March 2024) and submitted “Canine-assistance to increase vole-trapping efficiency and effectiveness” by D.M. Sanchez, N. Andrews, J. Cruickshank, N. Wiman and T. Stock to the Conference Proceedings. In collaboration with Alan Dennis (OSU Extension), we have filmed video footage that illustrates crop damage, human and canine-assisted trapping, and interviews with a farmer with vole management experience and an experienced dog handler, and are continuing to work on this in 2023-2024.

On November 9, 2021 we held our first field day for project collaborators at OSU's North Willamette Research & Extension Center from 2:30-5:30. Representatives from Oregon Department of Agriculture’s Pesticide Division discussed their interest in alternative rodent management and pesticide risk reduction. Sanchez and Andrews described the research and Extension objectives for the project, and the group discussed how to communicate during the project. Sanchez also described current knowledge on vole ecology. Cruickshank, Wiman, and Andrews facilitated a farmer-to-farmer discussion about vole management and trapping strategies. Two experienced dog handlers conducted a nose work demonstration using competition nose work scents (birch, anise, and clove oil) in a challenging outdoor windy environment with many competing odors of interest. Their successful search demonstrated that dogs can have strong “odor-obedience” and specificity. 

2022-23 Workshops: On December 1, 2022 we held our second workshop at Chemeketa Community College in Salem that was open to a wider audience: “Voles, Drones and Dogs”. 35 people attended the 3.5 hour workshop including 17 farmers and 18 other agricultural professionals. Participating farmers reported high levels of vole damage in vineyards, pastures, orchards, grass seed, vegetables and flowers. Andrews discussed recent vole damage observations and described how to correctly identify common rodents; Matthew Bucy from Oregon Department of Agriculture gave a regulatory update; Sanchez described vole ecology as it relates to vole management; and Christy Tanner from OSU Extension described her work using drones to detect and quantify vole damage in large grass seed fields. Radio interference made a drone demonstration impossible so Tanner described the drone and its features during the break. Sanchez and Andrews then described this project, 2022 results and 2023 plans in detail, and presented videos and photos of canine-assisted and human vole trapping. Cruickshank and Andrews then facilitated a group discussion for the final 40 minutes of the workshop.

On February 18, 2023 Andrews and Sanchez hosted a 1 hour and 45 minute workshop at the OSU Small Farms Conference in Corvallis: “Voles: their ecology, tales from the field, and can dogs help trap them?”, approximately 100 people attended. Of the 55 evaluations completed, 91% were farmers and 9% were other agricultural professionals. Sanchez and Andrews presented information and videos from the project, and adapted other content from the December 1 workshop for this audience and venue. Due to the larger audience, we facilitated a 45-minute panel discussion with Jon Bansen and Laura Masterson, dairy and vegetable farmers, respectively, who have experience with vole management and are collaborators in this project.

2023-24 Workshops: On November 1, 2023 we hosted a “Voles, Drones and Dogs” field day at OSU’s North Willamette Research and Extension Center in Aurora, OR. About 20 people attended and seven completed evaluations. This event included information on rodent identification and vole ecology. Research updates on crop damage assessment using drones, bait boxes, and canine assisted trapping were also presented. Field demonstrations included demonstrations of human- and canine assisted trapping and of the aerial drone. Farmer-to-farmer discussion was encouraged throughout the event.

On February 23, 2024, Andrews and Evie Smith (OSU Small Farms program) hosted a 2 hour and 30 minute workshop and trapping demonstration on a farm near Yachats, Oregon with about 17 in attendance. This event was requested by the local Extension agent because clients in her area could not attend that November 1 event in Aurora. Andrews presented information on rodent identification and vole ecology with research updates from the canine-assisted trapping project. Then human- and canine-assisted trapping was demonstrated in the field.

Sanchez, Bobo-Shisler and Andrews organized an on-farm “Voles, Dogs and Raptors” field day on April 11, 2024, with about 44 people attending. The host farmer also provided the site of our 2024 field trial. Over several years, he had invested in wildlife habitat and owl boxes and was interested in installing raptor perches to enhance vole predation. We installed six perches in one field (four were 9ft tall on t-posts; two were about 17ft tall on oak posts), and we recruited a biologist specializing in raptor ecology as a co-presenter. This event included information on vole ecology, raptor ecology and hunting techniques, and a canine -assisted trapping research update. Field demonstrations included human- and canine assisted-trapping demonstrations and raptor pole production, placement, and use. We installed motion-activated game cameras below each perch 1 week before the event and recorded raptor visitations with still photographs and short video. Over 45 camera days (images from one camera over 24 hours) 32 visitations were recorded, including 11 red-tailed hawks, 19 kestrels and two Great Horned owls. The hawks seemed to prefer the taller perches, kestrels regularly visited both, and the owls visited the shorter perches.

Evaluation questions were generally consistent within each topic at all events. Participants were asked to identify their role in agriculture and evaluate their learning using a yes / no response and a 5-point Likert scale with 5 representing the most learning. Some also responded to open-ended questions.

Education and outreach results:

A combined 77 participants responded to the surveys at the December 1, 2022 and February 18, 2023 workshops (approximately 135 participants), and most responses were similar at both events. Every respondent said the workshops were useful with an average rating of 4.47/5. All but one respondent thought canine assisted trapping could be useful for locating and controlling voles (4.25/5), and everyone said they learned to set snap traps more effectively (4.19/5). 75 of the 77 respondents improved their ability to recognize voles and vole damage (4.25/5) and the same number improved their ability to prevent vole damage early in the year (4.36/5). Everyone reported learning about canine-assisted trapping (4.56/5) and said the workshops improved their knowledge of vole ecology and the impact of vole damage on crops (4.65 and 4.26/5 respectively). 76 said they learned how other farmers are managing voles (4.26/5) and the panel format at the February 18 workshop appeared somewhat more effective in this regard with a 4.4 rating compared to the 3.83/5 rating for the group discussion on December 1. Based on these strong learning outcomes we estimate that about 50% of the farmers submitting evaluation forms at our events (38 farmers) are intending to change their practices. The venues provided limited opportunities for networking, likely because of their size and the workshop formats, only 62/77 said they could network well with other farmers with an overall rating of 3/5. The quality of networking opportunities was somewhat higher at the smaller December 1 event (3.39/5) than at the February 18 event (2.85/5).

About 81 people total attended the 2023-24 workshops with 40 completing evaluations. Everyone said the workshops were useful with an average rating of 4.45/5. Again, all but one participant thought canine-assisted trapping could be useful (4.2/5) with everyone reporting they improved their ability to identify active tunnels and set traps (4.1/5). 38 of 40 respondents said they improved their ability to recognize voles and vole damage (3.75/5), with 37 saying they planned to focus on early-season control to prevent damage (3.84/5). Again, everyone reported learning about canine-assisted trapping (4.4/5) and vole ecology (4.54/5). This year, all 40 respondents said they learned how other farmers are managing voles (4.15/5), and 38 of 40 reported being able to network with other farmers (3.53/5). Ratings for networking were higher than the previous year, perhaps in part due to our focus on smaller events with more time for informal interaction.  

78 Farmers intend/plan to change their practice(s)
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.