Development, validation and application of enhanced-welfare technology for wild small mammal research

Lead Research Organisation: Royal Veterinary College
Department Name: Pathology and Pathogen Biology


Wild small mammals such as mice and voles are common study subjects in many fields of research including ecology, conservation, evolutionary biology and land management. However, current methods for studying these animals usually involve either the repeated setting of live-traps (a capture-mark-recapture approach), or radio-tracking. Both methods raise concerns for animal welfare. Small mammals can lose weight and sometimes die during trap confinement, and radio-tracking involves the attachment of a transmitter to small animals, which can impede their natural behaviour and reduce survival. Importantly, live-trapping is also indiscriminate, such that many captured animals are not required for research, including non-target species or animals that have already been captured and do not need to be captured again.

These traditional approaches are based on simple technology (metal traps or radio-transmitters), yet the technological foundations are available to develop more sophisticated solutions than improve both animal welfare and the quality of scientific data obtained. In particular, microchips (PIT tags) are frequently used to identify individuals with a handheld scanner. However, PIT tag technology has potential far beyond this role. In this proposal, we will tap into this, and develop, validate and apply two novel devices based on PIT tag technology that will reduce unnecessary captures and refine welfare in small mammal studies.

The first is an "intelligent trap", which is capable of making decisions about whether to trap a given animal based on its PIT tag and weight. This will allow species outside a particular size range to be excluded (e.g. shrews that are common by-catch in rodent studies) and prevent unnecessary recapture of tagged animals. It will also have an auto-release feature, allowing collection of faecal samples (commonly required in epidemiological studies) without animals having to stay a full night in traps and be handled for release.

The second device is a "spatial logger" that can monitor the whereabouts of tagged animals. When a tagged animal passes within 30cm of the logger, it's presence is recorded. By placing a set of these across a field site, researchers can monitor individual animal movements and survival without the need to repeatedly capture them or attach radio-transmitters and actively follow them.

We will develop both devices from our current prototypes, validate their performance in the field, and apply them in a study on wild wood mice and bank voles to demonstrate their scientific value and how they improve animal welfare. This study will also show how they facilitate completely novel science that cannot be approached using traditional methods. Specifically, we will use them to ask how social interactions affect the spread of gut bacteria among wild mice. Social interactions are hard to measure, particularly for animals that are small, nocturnal and nest underground. We will use spatial loggers to monitor wood mouse social interactions by placing them across our field site and at burrow entrances, to record who nests with whom and how their home ranges overlap. We will compare this to data on which gut microbes are present in each mouse (using molecular methods applied to faecal samples from traps) to assess how sharing of gut microbes, and which ones in particular, is predicted by patterns of social interaction.

We aim for these two devices to achieve maximum impact through eventual widespread uptake in small mammal research. To achieve this, dissemination and commercialisation plans feature in our proposal, including trialling of devices by four other research groups, a workshop, and communication of findings at a variety of meetings targeting scientists, policymakers and the general public.

Technical Summary

Wild small mammals are studied in many research fields, including microbiome ecology, disease ecology, demography and conservation. Two key methods for monitoring these animals are the capture-mark-recapture approach (CMR, i.e. repeat live-trapping) and radio-tracking to monitor movements. Live traps capture many animals not required for research objectives, including non-target species and recaptures. Spending time in traps can significantly reduce animal welfare, causing weight loss and a risk of mortality. Handling before manual release is also stressful. In this proposal, we will develop, optimise and apply two novel devices based on PIT tag technology that will reduce the number of animals used in this type of research, refine their experience, and enable higher quality scientific data to be collected from the animals involved. The first is an intelligent trap, which will allow researchers to selectively trap only those individuals required according to both body mass and ID. This device will also collect body mass data and allow for faecal sample collection without human handling and without animals being in traps overnight, via an auto-release feature. The second is a spatial logger, which records the presence of a PIT tagged animal when it passes a detector. These loggers have low power consumption and can be left in the field for c. 1-2 months, collecting high resolution data on individual whereabouts without human interference. Both devices have remote programming and data retrieval capability. We will apply these devices in our long-term study of wood mice, in order to quantify the 3Rs impact they can achieve and demonstrate their scientific value by using them to ask a novel scientific question about gut microbiome ecology, that has been out of reach with standard techniques. We will support four other research groups to trial these devices, both in the UK and mainland Europe, to establish their use in other species and systems.

Planned Impact

Through uptake of the devices we will develop and validate, the proposed work can achieve direct 3Rs impact in any research where small mammals are trapped or tracked.

Most obviously, our devices can significantly reduce the number of small mammals unnecessarily trapped for research, by allowing researchers to exclude non-target animals and monitor traits like survival and movement (after initial tagging) with non-invasive loggers rather than repeated trapping. They will also lead to refinement as with intelligent traps (i) one can program traps to deactivate if weather conditions deteriorate (ii) the trap records how long an animal has been inside so researchers can process animals trapped for longest first and (iii) the auto-release feature reduces trap time and avoids handling stress. The spatial logger will also lead to refinement when used instead of more invasive radio-tracking methods.

In our study system, we will quantify 3Rs impact by calculating the reduction in animal captures and refinement in three metrics (trap-mortality, trap weight loss and scores on the mouse Grimace Scale upon release), when these devices are used instead of standard traps. Below we outline the expected magnitude of reduction and refinement with wider uptake.

In our research, we made 451 small mammal captures in the last year. Around half of these involved non-target species (244 vole and 5 shrew captures), and 64% were recaptures. We estimate we could reduce the number of overnight captures by ~300/year (64%) by using intelligent traps. Despite insulating traps, providing warm, non-absorbent bedding and food, all 5 shrews died in traps as well as 16 voles and 3 mice - a 5% mortality rate. Through the refinements outlined above, we estimate these devices could reduce accidental mortality in our research from 5% to <0.5% (22 fewer per year). With our research funded for at least the next 3 years, this equates to a reduction of ~900 animal captures, and ~72 accidental deaths during that time.
We know of 14 other UK-based groups using CMR of small rodents. Assuming similar capture, recapture and mortality rates to us, with 50% uptake we estimate we could reduce the number of small mammals trapped in the UK by ~2400/year, and accidental mortalities by ~176/year. Given that trapping projects often run for many years, the ongoing benefits could be very large.
Using Scopus and Web of Science searches, we found 200 rodent studies published in 2011-2016 using CMR (33.3/year on average). Assuming each study requires 3 years of data (this is fairly typical) and has similar levels of recapture and mortality to our project, with 50% uptake of our devices we estimate we could reduce the number of small mammal captures globally by ~15,000/year and accidental trap mortalities by ~1100/year.
To assess the potential for spatial loggers to replace radio-tracking, we performed Scopus and Web of Science searches and found 62 studies published in 2011-2016 reporting small mammal radio-tracking (10/year). Assuming each tracked 40 animals, we estimate that with 50% uptake, spatial loggers could reduce the number of radio-tracked animals by ~200/year.

These estimates are likely to be conservative since (i) studies in applied fields (conservation and agriculture/industry) are often not published in standard journals and (ii) intelligent traps could be used for non-rodent species, which were not included in search terms. Moreover, 3Rs impact in the longer-term could be even greater if devices for larger species (e.g. squirrels, chipmunks, rats) are subsequently developed, or if this work stimulates the use of similar approaches in lab animal research. We are already considering how use of similar technology could be used to obtain handling-free, individual mass measurements for lab mice. As outlined in our Pathways to Impact, we will present results at conferences that target both wild animal and lab animal researchers for this reason.


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