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Capture and Maintenance of Bank voles.
Capture of wild living Bank voles.
The live traps used for this purpose is either of the "closed" type (Sherman, Longworth) or the more "open" type (Ugglan).
The Sherman trap.
By pushing the entrance door down until it clicks into a holding position by a locking mechanism activated this trap. This locking mechanism is simple and can be bent a bit so it can be adjusted regarding the pressure an animal must exert on the little platform immediately behind the opened door in order to release the locking mechanism. Toss some muesli (serials), nuts or grains into the trap and make sure the bait does not get under the platform and by doing that prevent the trap from being released. Now place the trap a suitable place and once an animal enters the trap its weight will release the locking mechanism and a spring will click the door shut. The size of the trap is roughly 9 x 9 x 25 cm.
Price: Probably around 200 DKK (35 USD) including VAT. Manufactory: H. B. Sherman Traps.
Advantages using this trap: Protects the animal against the wind and rain and (importantly) against other animals. The activation pressure can easily be adjusted and it is easy to see if there is a catch since the door in such cases will be completely shut. If a trap is lost - typically because the trapper cannot find it again, rarely because of theft - only the captive animal will die.
Back draws using this type: If it is to be used in an habitat housing many slugs (the long "house-less" types) they will typically trigger the trap and "slime" the bait so it has to be replaced. If the trap is slightly pushed while being placed, or afterwards, the bait can shift place and interfere with the release mechanism, thereby render it useless. If the trap is not protected against the sun in hot summers a trapped animal can overheat causing dehydration and death. This trap captures anything small enough to get into the 9 x 9 cm opening and short enough to be inside while the door slams shut. During my stay in USA I used this type to catch local Bank voles and accidentally caught three flying squirrels.
The Ugglan trap.
This trap is my preferred type. It is a mesh-wire construction with a semi-roof made of aluminium and a platform device with a contra-weight, which the animal lowers into the trap while sitting on it. The dimensions is roughly 7 x 8 x 25 cm; a bit smaller than the Sherman trap. Once the platform lowers the animal can go to the bait and when leaving the platform it goes up and the animal is trapped.
Price: roughly 150 SEK (25 USD) plus the price for the semi-roof and transport. Manufactory: Grahnab (Sweden).
Advantages using this trap: Slugs and snails cannot block the entrance door, or the platform, for a longer period of time. The access hole to this trap is typically 3 cm (for voles - other diameters is available) meaning in effect that one does not risk catching rats or mustelid predators trying to get a bite of ones catch. The trap is operative as long as the platform is not blocked meaning it can capture more than one Bank vole in one "sitting". I once caught five medium-sized Bank voles in the same trap.
Back draws using this type: The trap is operative as long as the platform is not blocked so if the trap is lost it will continue to capture animals until it is either found or rust away. Dead animals might block the platform for a while but when they have decayed enough the trap is ready again. The trap typically has to be lifted for a satisfying inspection or alternatively the semi-roof has to be removed. These Ugglan traps comes with full coverage roofs which protects well against the weather, but makes it necessary each time to lift up the trap and remove the roof for inspection. If a Bank voles is so unfortunate to be caught immediately after the trap is placed, and it then starts to rain, it will most likely have died of hypothermia next time the trapper comes by. Slugs often enter these traps due to their keen sense of smell and once they decide to leave it will be through the wire-mesh (diameter 0.7-0.8 cm). Slugs appear to have something inside their body that get stuck after a third has gone through the wire-mesh so there they hang. The only way to get rid of the slug is to cut it in half, which of course is not so good for the slug. Wood-mice (A. sylvaticus) and Yellow necked field-mice (A. flavicullis) is typically both a bit larger than the Bank vole and can kill them if they are in the same trap for long. The common shrew (Sorex araneus) is a real wild beast which certainly will kill any smaller Bank vole or other rodent if caught together - luckily the shrew usually dies quickly of stress, hunger or dehydration (my guess is within a couple of hours) but they can be a real nuisance specially if the abundance of Bank voles is low.
The Longworth trap.
I have only limited experience with this type of trap but it seemed too heavy, complicated and un-reliably. On the bright side, it was solid so if one happened to step on it by accident it was not damaged.
Taken together - the Sherman and the Ugglan:
These two types of traps seemed equally efficient in capturing rodents in the Danish forests. The Sherman typically only captures one at a time, although I once managed to capture three simultaneously. The Ugglan can capture many in the same session, which, considering the habit of Bank voles to live in colonies, all in all makes the Ugglan trap, my favourite. For the special interested in this subject I can refer to Ylonen et al., 2003 which have compared the efficiencies of Sherman, Ugglan and Longworth traps in arid and moist areas.
Placing the traps:
It is a good idea to camouflage the traps with ferns, leaves little twigs etc, both to make them seen more "natural" to the rodents and to prevent other visitors in the Forest from stealing them. It his highly recommended to draw a map to tell precisely how many traps is in place and where they are. Note special fix-points (tree's, rocks) for every 5-10 trap and place maybe 25 traps at a promising locality. Place other smaller groups of traps in adjacent localities provided they seem promising. The reason for this is that Bank voles is distributed in a lumped way and even though you may not catch one in this locality, you can easily be lucky in the adjacent plot, 30 meters away. It all depends in the locality, so forget about placing traps with e.g. 10 meters apart in straight lines - that you will only do if you are studying the distribution of Bank voles. For this purpose it is better to have 6 traps placed the right places than 100 traps in open country.
I believe a single trapper should not operate more than around 125 traps. Place them in 3-5 groups, preferable a bit apart, and only in habitats you imagine will be preferred by Bank voles. They want protection against airborne predators, they like ferns, fallen down tree-trunks and it is generally a waste of time to trap in stands of pinewood and other conifers. Beech woods with brushwood and ditches with scrubs are good hunting grounds.
Checking the traps:
Traps should be looked after at least twice a day. In the summertime/autumn typically between 0800-0900 and 1900-2000. Bring 8-10 traps and some bait (grain products, raisins, corn etc. - no cheese) and in case you have a catch replace the trap with a fresh one. Count all traps carefully each time you make a sweep and if one is missing you either look to find it or become convinced it is stolen. Note that deer's can sometimes push traps around with their anthers in which case it will normally be within a radius of 5-10 meters. It can sometimes be hard to locate a trap if it is too well camouflaged; I once searched for 15 minutes just to find it 1 meter from where it was supposed to be.
Housing in stable:
As far as I am informed there is no law against housing Bank voles in the same stable as ordinary research-rodents. Nevertheless it is a fact that wildcaught Bank voles can harbour a variety of different vira, parasites and bacteria's of which some are suspected zoonoses. Use of latex gloves and some kind of protection against dust particles is therefore probably a good idea. I have personally maintained Bank voles in the same room as mice and rats for years without problems for any of the parties, which is just a fact - nothing more than that.
Weaning:
Bank voles start to be more of less self-sustaining after 2-2.5 weeks and weaning them at the age of three weeks is therefore appropriate. However, one has to take a look at the weight, which should not be below 10 grams at weaning. The normal weight of my Danish Bank voles have typically been 11-13 grams at age three weeks so if a pup only weighs e.g. 7 grams it should not be isolated/weaned before after one more week or so.
Number per cage:
Bank voles can be maintained isolated or in minor groups. Pups and young adults (siblings) can be put together without bigger problems, but it is my feeling that one ought not to keep more than 4-5 Bank voles in the same cage (cage size typical 14 x 16 x 23 cm for isolated Bank voles; 15 x 21 x 38 for group housing). When a group is formed for the first time this should be in a fresh cage provided with possibilities of taking cover (tubes of card board, toilet paper and a thick layer of bedding). Usually there will be some fights in the start and if these have not been terminated within a couple of days it is best to remove the subordinate. If the fighting's results in open wounds one might just as well remove the injured vole at once since it most often will end being killed or die of stress/trauma. There are in my experience not a pronounced gender difference when it comes to being aggressive in a cage - the Bank vole that have been there longest will normally attack what it probably perceives as intruders in its homecage (hence the wisdom in using fresh cages for new groups).
Best type of cage and enrichment.
The cage should in my opinion be transparent so they can keep oriented (and the researcher can observe the animals) and Bank voles do fine on woodcuttings as bedding and a toilet paper roll. The roll serves the purpose of providing a rest place when they want to be a little private and maybe have something different to chew upon. The females use toilet paper if present as nesting material no matter if they are together with a male or not (the males practically never makes something that resembles a nest). Especially in the breeding pairs there should be at least one paper roll. Avoid tubes of metal with a closed end. It has occurred more than once that I have had to cut free a bank vole, which had gnawed a hole in the back wall of such a closed tube, and when it puts its head through it is not always it can retract the head. A few times have I found a dead bank vole with its head sticking out such a hole it had gnawed and on one memorable occasion I found a dead Bank vole that had managed to entangle some toilet paper around its neck and thereafter choked.
Food:
Bank voles do fine on standard rat chow and water ad lib. I usually gave them a handful of a mixture of grains (for birds) once a week and they liked cucumbers, apples etc. In the literature one can read that they eat insects in the autumn, but considering beetles and lazy flies sometimes climbed down their cages and survived fine, I kind of doubt their desire for animal supplements. Cannibalism does occur, but rarely among adults. Usually it is because a female has had a stillbirth.
Diurnal activity:
Danish Bank voles (in Denmark), maintained in a stable will typically exhibit a period of increased activity lasting 3-4 hours and centred around 1000-1200 hours. A relatively more intense period of activity, lasting again around 3-4 hours, is centred around 2200-2400 hours (Schoenecker & Heller, 2001). Between these periods the overall activity decrease steadily. There will typically be brief periods in between, lasting from 15 minutes to a half hour, where the Bank voles seem to synchronize their activity. This is not necessarily related to outside disturbances from e.g. a vole-keeper, loud noises from bypassing truck or other like that.
Last updated the 26. July 2007