Winter breeding in three rodent species, the bank vole Clethrionomys glareolus, the yellow-necked mouse Apodemus flavicollis and the wood mouse Apodemus sylvaticus in southern Sweden

Winter breeding, as judged from heavy reproductive organs in both males and females, was observed in bank voles, yellow-necked mice and wood mice in south Sweden during the winter of 1976–1977. The breeding was probably a result of unusually favourable feeding conditions created by an extremely rich beech mast crop.     

Haemoglobin polymorphism in the Bank vole, Clethrionomys glareolus, in Britain

Three hundred and twenty-two Clethrionomys glareolus from 17 localities in England, Wales and southern Scotland were typed for haemoglobin and two phenotypes were discovered. They have been designated HbS and HbF. The latter is more electronegative at physiological pH. The nature of the molecular difference between the phenotypes was examined and it was concluded that HbF polymerises more readily than does HbS. Haematological investigations showed that although the red cells of animals with HbF contain more potassium, thereby ensuring electrostatic neutrality, there has not been concomitant dilution of the cell contents. It is suggested that the osmotic stress imposed by this high concentration of particles might be reduced by in vivo polymerisation of haemoglobin. HbS was found to predominate in the north of Britain and HbF in the south. As none of the populations sampled contained animals of both types, it is not yet known whether there is a north-south cline in haemoglobin type, or a sharp disjunction.     

The spread of the Bank vole Clethrionomys glareolus in Ireland

The discovery of the Bank vole Clethrionomys glareolus in Ireland and the published information on its spread are reviewed, and the results of a complete resurvey of its distribution, in 1 982 , presented. The rate of spread is extremely variable and somewhat unpredictable. Over suitable habitat—agricultural land with hedges and other cover (and sometimes mountain valleys)—spread may average 2–4.5 kmyr^-1 but can sometimes be very much slower. This might be influenced by the type and extent of hedges and of permanent pasture. High ground and moorland usually prevent spread but there have been dramatic exceptions. In 1982 Bank voles occupied probably the whole of Co. Limerick; most of Co. Kerry, with the exception of substantial parts of the mountainous peninsulas in the southwest and contiguous interior; a large part of Co. Cork, though not the south-east and again excepting portions of the mountainous south-west, together with a substantial strip of east Co. Tipperary, and the south-east quarter of Co. Clare.     

Predation by Tawny owls (Strix aluco) on Bank voles (Clethrionomys glareolus) and Wood mice (Apodemus sylvaticus)

During 1954–56 we made a study of the numerical relationships between a population of Tawny owls ( Strix aluco ) and populations of their main prey species, the Bank vole ( Clethrionomys glareolus ) and the Wood mouse ( Apodemus sylvaticus ), in a 48.6-ha area of mainly deciduous woodland near Oxford. The owls were censused by plotting their territorial challenges (hooting), the rodents by the capture-mark-recapture technique. Since the rodents were marked with numbered monel metal leg rings, we were able to recover a proportion of these in the pellets of undigested material cast by the owls.
The results for Bank voles, which were the more numerous of the two prey species, indicated that 20–30% of the standing crop was removed by owls in any two-month period. We also made an independent estimate of predation rate from the number of rings recovered from owl pellets in relation to the number of ringed rodents released into the population each two months. This coincided with the limits indicated by the first method for voles (20-30% removed of the standing crop each 2 months).
Wood mice were scarcer than Bank voles and were not amenable to satisfactory capturemark-recapture analysis but, when treated on the system of recovery of rings in owl pellets, we found that they were preyed upon relatively more heavily than were the voles. Of the latter 18–46% of the marked animals were recovered in the owl pellets compared with 28–70% of the marked mice. Either the mice were preferred prey or they were more vulnerable to owl predation by reason of their preference for more open habitats.     

Changes in home range size during growth and maturation of the wood mouse (Apodemus sylvaticus) and the bank vole (Clethrionomys glareolus)

Summary A field study was carried out during winter and spring of 1982/83 to determine changes in home range size with increasing body weight and maturation in the wood mouse (Apodemus sylvaticus) and the bank vole (Clethrionomys glareolus). Individual home range sizes in males increased and in females decreased with increasing body weight. Relating these changes to changed energetic requirements failed. In these species behavioral aspects seem to be a more important determinant of home range size than body weight.     

Plasma esterase polymorphism in the Bank vole, Clethrionomys glareolus, in Britain

Three hundred and eighty-three Clethrionomys glareolus from 20 localities in England, Wales and Scotland were typed for plasma esterase and a genetic polymorphism was discovered. The esterase was named Es-1. Breeding tests suggested that three alleles were segregating: Es-1^o when homozygous results in complete absence of enzyme activity. The active alleles Es-1^f and Es-1^s code for enzyme variants which migrate more rapidly and less rapidly, respectively, under starch gel electrophoresis. Of these active alleles, Es-1^f is morc common in the north of Britain and Es-1⁸ in the south. A 23-month field study on two areas at Wicken Fen, Cambridgeshire, suggested that animals possessing Es-1^s survived less well at high population densities, perhaps through their being more likely to emigrate.     

Woodland small mammal population ecology in Britain: a preliminary review of the Mammal Society survey of Wood Mice Apodemus sylvaticus and Bank Voles Clethrionomys glareolus, 1982–87

The Mammal Society has co-ordinated a population survey of Wood Mice Apodemus sylvaticus and Bank Voles Clethrionomys glareolus in 13 0.81 -hectare sites in Britain. Numbers of mice and voles live-trapped using standard methods were collated every May/June and November/December from 1982 to 1987. The data were analysed with results from four independent studies in England and the corresponding assessments of tree seed crop size. Wood Mouse numbers are usually higher in winter than in summer but Bank Vole fluctuations are less regular. In deciduous woodland, Wood Mouse mean relative densities are significantly greater in the winter and the following summer after a good seed crop than after a poor one; rates of population change from summer to winter are significantly higher when a good seed crop falls. Bank Vole relative densities are significantly greater in the summer following a good seed crop than after a poor one, and rates of change from winter to summer are significantly higher. In Wood Mouse populations, tests for density dependence suggest that it is strong from summer to winter but absent from winter to summer; in Bank Voles weaker density dependence is present in both halves of the year. Thus, Wood Mouse numbers are regulated in autumn but are also influenced by seed crop size in winter and the following summer; Bank Vole numbers are less strongly regulated during both autumn and spring and are influenced by seed crop size in the following summer. Evidence is presented suggesting that populations of each species in deciduous woodlands are synchronized over the country in summer and that Wood Mice are also synchronized in winter; highs and lows tend to coincide between different sites. The yield of tree seed is shown to vary significantly from year to year and may be the cause of the synchrony, but weather effects may also be involved.     

The dynamics of Wood mouse (Apodemus sylvaticus) populations in the Camargue

The ecology of two monospecific populations of Wood mice ( Apodemus sylvaticus ) was studied using mark-recapture techniques in a high grassland and a low grassland of the Camargue. Annual changes in population size resembled the classical pattern of variation for European Wood mice. Numbers were low in summer, and peaks in numbers occurred in autumn and decreased sharply in early spring. However, the densities of the populations in winter were higher than many other European Wood mouse populations. The Wood mouse population in the high grassland area was dense and showed regular variations throughout the year. In the low grassland area, the population was lower and showed less regular variations, especially in winter, coinciding with soil flooding. Reproduction-related differences between the demographic parameters of the two sexes pointed to the use of differential space use strategies by males and females.     

Structure of the plantar sweat glands of the Bank vole Clethrionomys glareolus

The plantar pads of the hind feet of 15 male and female, young and old Clethrionomys glareolus (Rodentia–family Muridae) were examined for the presence of tubular glands. Groups of eight or nine coiled glands were found in all of the 11 plantar pads. The secretory portion of the gland lies deep in the fatty hypodermis and communicates with the plantar surface by a coiled duct whose lining cells merge with those of the stratum basale of the undersurface of the foot. Groups of shallow depressions mark the site of the duct openings. They are not associated with any hairs.
Although light microscopy shows only one cell type, electron microscopy reveals two morphologically different cell types. Neither conform directly to the light and dark secretory cells of the human sweat glands although similarities exist. Myoepithelial cells surround the secretory cells, but do not appear to be present around the duct cells.     

Evidence for different bottom-up mechanisms in wood mouse ( Apodemus sylvaticus ) and bank vole ( Myodes glareolus ) population fluctuations in Southern Norway

Animals that feed on forest tree seeds, such as Apodemus mice, increase in number after a mast year. At high latitudes, there is a similar delayed response by Myodes voles to high seed crops of bilberry (Vaccinium myrtillus), but here the mechanism is hypothesised to be increased forage quality, caused by a trade-off between reproduction and defence in the plants. Both Apodemus mice and Myodes voles eat berries, but only the latter feed on bilberry plants. Hence, only Myodes voles are predicted to respond to bilberry peak years. A second prediction is that the effect should last longer than any possible direct impacts of bilberries, because the plants would not be able to rebuild their defence until the succeeding summer. During a 21-year snap-trapping study of small rodents in Southern Norway, the spring population of bank vole (Myodes glareolus) was positively related to a bilberry seed index of the previous year, indicating increased winter survival, whereas the wood mouse (Apodemus sylvaticus) was not affected. Also the succeeding autumn population index of the bank vole was positively related to the bilberry index of the previous year, even when controlling for spring population levels. The wood mouse population responded to mast years of sessile oak (Quercus petraea), whereas seeds of Norway spruce (Picea abies) seemed to have some impact on both species. It is concluded that these rodents are mainly limited from below, but by different mechanisms for the granivorous and the herbivorous species.