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: 03/31/2024
Host Institution Award ID: G341-21-W8614
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Principal Investigator:
Nick Andrews
Oregon State University
Co-Investigators:
Dr. Dana Sanchez
Oregon State University
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Project Information

Abstract:

Farmers managing different cropping systems lack detailed research-based information about vole management strategies other than rodenticides. For the educational component, we will provide current information about integrated vole management strategies including predators, habitat management and trapping. Research will focus on innovative trapping strategies early in the season to interrupt spring reproduction and exponential population growth. Specifically, we will investigate trap types (single- and multi-catch traps) and trap placement methods (canine scent detection and human visual cue detection). We hypothesize that canine scent detection can increase trapping efficiency and efficacy, strengthening vole management. We will also investigate burrow architecture and underground vole activity using infrared imaging and other techniques.

Synthetic rodenticides are hazardous to non-target wildlife and 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 article, write a new Extension Publication on ecological vole management, and establish canine vole scent detection training guidelines. We will host on-farm field days, and present our findings at farmer conferences. We will maintain a project blog and write 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

Cooperators

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

Research

Materials and methods:

Preliminary Work

Shortly after we were notified that our proposal was accepted for funding, we started the application process with the OSU Institutional Animal Care and Use Committee (IACUC). 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, and by late August we had recruited seven teams for our first year of vole detection training. In July and August, 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 tunnels using vegetable oil in an insecticide fogger to observe connectivity.

Dog Training

In September and October, we constructed the 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 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.

We purchased twelve PVC Barn Hunt rat tubes to contain individual live voles during nose work training, the design was adapted from the 2019 Barn Hunt Association rule book. In September and October we constructed the vole detection training arena at OSU’s Fairplay Farm in Corvallis using a covered trench design adapted from Earthdog training tunnels, and drilled holes in the plywood covering the network. We also dug individual holes that were separate from the trenches for vole placement during training. The trench network and individual holes are large enough for the rat tubes with the live voles. In late October and early November, we used Sherman folding traps to catch eight voles at a dairy in Corvallis. Six of these voles were housed at OSU’s Research Animal Isolation Laboratory (RAIL) for use during canine detection training. The other 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 appropriate 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 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 detection 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 were available for the trials.

The third approach 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 (Jan-Feb), but we conducted field trials in each cropping system to further refine our methodology.

Trapping

Our pilot 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 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 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.

 

Research results and discussion:

We have summarized our pilot 2022 results by crop type and farm (Table 1). Although neither the timing nor the extent of trapping matched our initial plan, we found the pilot season extremely valuable for refining our protocols, testing our datasheets, and developing our database. It is premature to draw any conclusions based on the limited number of trapping sessions this year, but early trends are promising. 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 shrew 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, respectively; Table 1), canine teams were far more time efficient (0.48 and 0.33 voles/minute of searching, respectively). Across all sites, canine detection 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. Although they are among non-vole species known to use vole (and other species’) burrow systems, it is unknown whether deer mice pose a significant source of damage to crops in the Willamette Valley. Canine detection rates also improved slightly when deer mice were included in total rodent trap counts (voles and mice).

Table 1. March 2022 data summary by crop type and farm.

Crop

Farm

Detection

team

Total trap sets

Search time (min)

Voles caught1

Mice caught1

Shrews caught1

Voles/ trap set

Voles/ search minute

Hazelnut

NWREC

Canine Bijou

12

17

5

5

0

0.42

0.29

Human

23

34

11

4

0

0.48

0.32

NWREC Total

35

51

16

9

0

   

Hazelnut Total

35

51

16

9

0

   

Pasture

Double J Jerseys

Canine Daphne

39

24

12

0

0

0.31

0.50

Human

36

53

14

0

0

0.39

0.26

Double J Total

75

77

26

0

0

   

Sar-Ben Farms

Canine Sierra

24

20

18

0

0

0.75

0.90

Human

56

60

28

0

2

0.50

0.47

Sar-Ben Total

80

80

46

0

2

   

Pasture Total

155

157

72

0

2

   

Vegetable

Diggin’ Roots Farm

Canine Sierra

11

21

0

0

0

0

0

Human

28

20

6

0

2

0.21

0.30

Diggin’ Roots Total

39

41

6

0

2

   

47th Ave. Farm

Canine Daphne

30

15

12

5

0

0.40

0.80

Human

25

35

8

0

1

0.32

0.23

47th Ave. Total

55

50

20

5

1

   

Vegetables Total

94

91

26

5

3

   

Canine Total2

116

97

47

10

0

0.41

0.48

Human Total2

168

202

67

4

5

0.40

0.33

Canine percent of human

69%

48%

70%

250%

0%

102%

146%

Grand Total

284

299

114

14

5

   

1 Trapped animals were identified to genus or species: voles are Microtus species; mice are Peromyscus maniculatus (deer mice); shrews are Sorex species.

2 "Voles / trap set" and "voles / search minute" totals are the sum of voles caught per sum of trap sets and time spent searching with canine and human searching methods.

Based on our 2022 results, we have made some adaptations from the proposal. We originally planned to use one-acre plots, however our preliminary time trials across all three crop types showed that to be beyond the project’s capacity. We set plots at one-quarter acre for each treatment and a control on each farm.  We switched one of the pasture sites, so we are now working with Double J Jerseys. We had planned to conduct trapping at Third Knight Farms (hazelnut orchard), but initial scouting showed little sign of vole activity. Additionally, the farm was broadcasting rodenticide, so we dropped this site out of concern for dog and human safety.

Vole populations tend to be lower over the winter and stay relatively low until breeding starts, so winter trapping (i.e., January through February) is more likely to reduce crop damage by reducing a population’s reproductive capacity. The IACUC approval process with its multiple revisions and the leptospirosis infection issues delayed our dog training, and subsequently delayed our in-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.

Additionally, at the vegetable farms voles were mainly detected in headlands and non-cropped areas with few active signs of vole use in the tilled production fields. Therefore, we are planning to focus our future work on pastures and hazelnut orchards, with three sites in each cropping system. This will improve our potential to detect a measurable effect on crop damage. We will continue to include collaborating vegetable farmers in the project although their fields won’t host field research, and they have agreed to this change. We will identify a new pasture and hazelnut orchard this year.

Participation Summary
5 Farmers participating in research

Educational & Outreach Activities

8 Consultations
5 On-farm demonstrations
1 Workshop field days
1 Other educational activities: We convened the new OSU Rodent Management Working Group

Participation Summary:

7 Farmers
16 Ag professionals participated
Education/outreach description:

The OSU Rodent Management Extension working group was formed in 2021 with Nik Wiman 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. We have created a project blog (https://blogs.oregonstate.edu/voles) and will publish our first posts soon using photos from our training and 2022 field trials. 

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. 

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.