Growth in field and laboratory populations of Wood mice (Apodemus sylvaticus)

Intrinsic growth rate and asymptotic body weight parameters were estimated for two laboratory and three field populations of the Wood mouse, Apodemus sylvaticus , using a logistic model fitted by an ordinary least squares method. The data upon which the growth equations were based were differences in body weight for individual animals between sampling occasions. Suckling mice in one of the laboratory studies suffered high mortalities and poor body growth which was related to disturbance to the mothers and their young during examination. Growth in weaned mice appeared normal and was compared with growth in autumn and winter populations of wild mice with poor and good natural seed supplies. Males tended to have higher growth rates, and to a lesser extent, higher body weight asymptotes than females in all groups. Growth rates were highest in the autumn field population with a good seed supply; differences between the other groups were less marked. These results are discussed and it is suggested that, despite the approximations inherent in the method, the method will be a useful tool for studying the the productivity of wild populations of small mammals.     

The ecology of Wood mice (Apodemus sylvaticus) on arable farmland

The ecology of Wood mice ( Apodemus sylvaticus ) was studied by live trapping and by examining the stomach contents of killed animals on an arable farm in West Suffolk. The study area included several fields but only a short length of hedgerow and was distant from other hedges and woods. Wood mice were trapped in the open fields throughout the year and their burrows were also found there. Population densities were comparable with those reported from deciduous woodland and seasonal population changes, ranging behaviour and timing of the breeding season were also broadly similar. The survival rate of juvenile mice varied greatly within and between breeding seasons tending to improve when young of the year replaced overwintered animals in the adult breeding population. Wood mice showed no marked preference for fields with different crops in winter when the main foods were grain, waste sugar beet roots, weed seeds and soil invertebrates. In spring and early summer they preferred winter wheat fields where seeding weeds provided most of their food.     

Epigenetic polymorphism in populations of Apodemus sylvaticus and Apodemus flavicollis (Rodentia, Muridae)

The main object of this study was to use discontinuous variation as a means of measuring divergence between populations of A. sylvaticus (L.) and A. flavicollis (Melchior) from Britain and Eurasia. Samples from 17 populations (671 skulls) were each classified for 20 discontinuous morphological variants. The investigation has shown that certain epigenetic variants have a characteristic incidence in populations of the two species and that the relative incidence of the variants could be used as an aid to specific separation. The calculation of degree of divergence between the populations has made it possible to suggest the order in which populations are related to each other.     

Observations on trap response in confined populations of Wood mice, Apodemus sylvaticus

Three laboratory studies of trap response in confined Wood mouse populations at various densities and using various densities of traps are described. Individual variation in trap response and whether captures were made at random are examined, and factors which affect trap response in confined populations of mice are discussed.     

Population structure and dynamics of wood mouse Apodemus sylvaticus in Iceland

Five-year-studies of two wood mouse populations (Apodemus sylvaticus L.) were carried out outside the village Vík. S. Iceland, and in a birch forest close to the lake Mývatn, N. Iceland. The population at Vík was studied on a 1.10 ha grid on a slope covered with Angelica archangelica L., the seeds of which constituted a major food resource for the mice. Altogether 948 individuals were caught, marked and followed during 1973–1978. No other free-living small mammals occur in Iceland, and predator pressure is low and considered non-existent on the Angelica slope. The population density was extremely high; highest autumn density recorded was 150 ind ha^?1. Like other Apodemus populations, the one at Vík showed a typical seasonal pattern in numbers: a winter decrease, relatively stable numbers in late summer, and an autumn peak. Breeding started in late April or early May and ended in late September; no winter breeding was observed. Three or four litters were produced, and the last litter(s) of the season greatly contributed to the autumn increase. The output of young per reproductive female throughout the year was negatively correlated with spring density, and autumn peak density with the number of females in August. Also overwinter success and weight changes appeared to be associated with population density (and weather). Survival rates did not vary much between years and seasons and were consistently rather high. Autumn survival of juveniles was positively correlated with mean minimum temperatures. Juvenile survival was, at least at times, negatively affected by the presence of adult males. Trapping outside the main grid did not indicate any marked dispersal, though some immigration to the grid must have occurred, especially in spring and early summer. Among the factors governing the population density and dynamics of wood mouse at Vík we emphasize the absence of interspecific competition and predation, the rich and dependable food resources (mainly Angelica seeds), the mild (though moist and windy) climate, the shelter of dense Angelica stands, the abundance of crevices (e.g. nest-sites), and the social interactions. The birch forest in northern Iceland was low productive and the wood mouse population differed from the Vík population by exhibiting low density, short breeding season, and high vagility; characteristics we consider to be representative for most Apodemus populations in Iceland.     

Some population dynamics of the Bank vole, Clethrionomys glareolus and the Wood mouse, Apodemus sylvaticus in mixed woodland

The population dynamics of Clethrionomys glareolus Schr.and Apodemus sylvaticus (L.) in mixed woodland in County Durham, were studied from March 1963 to January 1965. Two areas of 0.9 ha (2.25 acres) each were trapped monthly and information was obtained on population size, reproduction, survival and growth from marked animals.
Clethrionomys populations increased from June to an autumn peak; then declined, at first rapidly, but then more slowly in winter, before reaching a spring trough. The breeding season of Clethrionomys was from May to December; juveniles were caught from mid-June to December. Survival was in general poor during the breeding season but good at other times. Survival of young born early in the summer was particularly good on one of the areas and some individuals lived long enough to breed in two successive years. On both areas young born early in the year matured rapidly and bred in the year of their birth. Young born in late summer and early autumn ceased growing at a weight of about 14.5 g, remained immature, and formed the bulk of the overwintering population. Growth was completed at the time of sexual maturation the following spring.
Trapping failed to provide adequate samples of juvenile Apodemus in summer to account for subsequent recruitment. The possibility that a substantial proportion of the adult population of this species was also either trap shy or had emigrated temporarily is discussed. Breeding occurred from April until the following January, but the numbers trapped remained very low throughout the early months of the breeding season. Large scale recruitment of young fecund animals into the trap-revealed population occurred during the autumn. Apodemus males continued to grow rapidly during the winter.     

On the interpretation of host-parasite ecology: Heligmosomoides polygyrus (Nematoda) in wild wood mouse (Apodemus sylvaticus) populations

This paper describes epidemiological and seasonal patterns in the interaction between wood mice, Apodemus sylvaticus and Heligmosomoides polygyrus. Data used in the analysis were collected by C. S. Elton and co-workers at Bagley Wood, Oxfordshire in the late 1920s. Heligmosomoides polygyrus was by far the most common helminth parasite with 70% of all wood mice infected and average intensity around 12 worms per mouse. Male and female mice were shown to harbour similar parasite burdens. Parasite numbers per host were highly overdispersed and were well described by the negative binomial distribution. There was little evidence for convexity in age (= weight)-intensity curves, either within or across sexes.
Host and parasite numbers showed predictable seasonal patterns, with mouse populations at their largest at the end of the breeding season, in August and September, and parasite populations at their largest in the late spring, around May. Results are discussed in relation to the ecology of H. polygyrus in wood and laboratory mice, and tentative comparison is made with human helminth infection. The interpretation of epidemiological patterns in these data was problematic. Of particular importance was the statistical distribution of parasites within the host population, and possible differences between mouse sexes in relation to growth, survival and trapping. Such difficulties are relevant to a range of similar field data.     

Population dynamics of the wood mouse Apodemus sylvaticus (Rodentia: Muridae) in a Sitka spruce successional mosaic

A population of wood mice, Apodemus sylvaticus (L.), was studied by capture-mark-recapture, in five 0.81 ha grids within a habitat mosaic produced by the felling of a plantation of mature Sitka spruce ( Picea sitchensis Carriere). From May 1990 to June 1992, we estimated population sizes, survival (total and by weight classes), recruitment, and home-range sizes, usually at monthly intervals, for the study area taken as a whole. Inter-grid movements were frequent for both sexes, supporting the assumption that the population could be analysed in this way. Wood mice were more abundant in 1991 than in 1990, associated with increased seed supply. In both years, numbers were low in spring and increased gradually towards an autumn peak, which was of similar size in both years. Male home-range areas varied seasonally, and were negatively correlated with population sizes, while female home ranges showed little seasonal variation. Survival and recruitment both declined sharply in late autumn, apparently in a densitydependent way. Except for this latter result, the population dynamics in a heterogeneous coniferous woodland were consistent with those described previously for this species in more homogeneous deciduous woodlands, suggesting that the same regulatory processes are operating in both habitats.     

Home range sizes in the Wood mouse Apodemus sylvaticus: habitat, sex and seasonal differences

This paper investigates home range sizes in the Wood mouse Apodemus sylvaticus in two habitats of differing productivity; deciduous woodland and sand-dunes. The ranges were measured by radio-telemetry. The home ranges in the sand-dunes were approximately circular whilst those in the woodland were much more complex in shape. At all seasons, the ranges in the sand-dunes were much larger than those in the woodland. Male ranges were larger than female ranges, especially so in the breeding season. In the non-breeding season, sexual differences in range sizes could be accounted for by the greater energy requirements of the larger males. During the breeding season, males expanded their ranges, probably in an attempt to find receptive females.     

Seasonal variations in infestations of parasites in a Wood mouse Apodemus sylvaticus population in the West of Ireland

Seasonal variation in most of the metazoan parasites of a Wood mouse population was investigated by a statistical analysis of their frequencies in 11 samples of about 30 mice trapped regularly over one year. Numbers of the flea Ctenophthalmus nobilis , most mesostigmatid mites and the beetle Leptinus testaceus were correlated with breeding in the mouse population and may have been directly linked with it as all ofthese arthropods are common in Wood mouse nests. The tick Ixodes ricinus was abundant over the summer but scarce in winter. Its preponderance on male hosts is doubtless because they cover more ground than females. Flukes were commonest in summer, probably as a result ofthe period of intensive feeding on invertebrates by the mice which usually occurs in early summer. Female mice were more heavily infected, perhaps because of their increased food requirements in the breeding season. Abundance of flukes declined with the turnover in the mouse population in autumn. The infestation pattern of the nematode Capillaria muris sylvatici is similar and the possibility of an invertebrate vector is discussed. While older mice were generally more heavily infected with helminths than were young, this was least marked in the tapeworm Cataenotaenia lobata (which most likely has a mite as an intermediate host and may be picked up as soon as juveniles start grooming) and the roundworm Syphacia stroma (eggs of which are almost certainly transferred by body contact between hosts)     

The diet of the wood mouse Apodemus sylvaticus on set-aside land

The diet of wood mice on set-aside consisted of 87% plant material, 65% of which was green leaf materials. This diet contains very much less seed or animal material than does that of wood mice studied in other habitats. The poor diet reflected what was available in the area.     

Cyclic and non-cyclic dynamics in populations of the helminth parasites of wood mice, Apodemus sylvaticus

Two populations of Apodemus sylvaticus, one in deciduous woodland and another in coniferous forest in Co. Down, Northern Ireland, were trapped at monthly intervals over 33 months. The dynamics, reproduction and age structure of the mouse populations differed between years with over a 40 fold range of population size. Nine species of helminths were recovered from the alimentary tract and associated organs of the mice. The prevalence and mean worm burden of the cestodes, Catenotaenia lobata, Hymenolepis hibernia and Taenia taeniaeformis varied erratically. The trematodes, Corrigia vitta and to a lesser degree Brachylaima recurva, had seasonal changes in abundance. The nematodes Capillaria murissylvatici and Nematospiroides dubius had strongly seasonal cycles of abundance associated with the onset of host reproduction. Trichuris muris was the rarest helminth. Despite protracted periods of absence this species maintained a seasonal increase in mean worm burden in late winter. The nematode, Syphacia stroma, had a weakly seasonal pattern of dynamics. The bases of these cyclical and non-cyclical dynamics of the helminths of A. sylvaticus are discussed.     

Sex-chromosome heterochromatin variation in the wood mouse,Apodemus sylvaticus

Variation in heterochromatin content, as revealed by G- and C-banding, was studied in the sex chromosomes of the wood mouse, Apodemus sylvaticus. The sex-chromosome heterochromatin was also characterized by DAPI staining. Variation in sex chromatin was recorded in extremely large (giant) sex chromosomes in certain individuals and populations. In some individuals, the Y chromosome was the largest element of the complement. Different variants of both the X and Y chromosomes were found within a single population. The variation is therefore a type of population polymorphism and should not be used for taxonomic discrimination.