Pitfall Trapping of Microtus townsendii
A field population of Microtus townsendii was trapped concurrently with live-traps and pitfall traps throughout the spring and summer of 1975. The population was at peak densities, with a maximum of 519 voles per acre. The number enumerated by pitfalls was up to two times larger than the number enumerated by live-traps. Capture of a large number of young in pitfalls indicated that mortality was higher among post-weanlings than among any other age group. Recruitment to live-traps was largely restricted to animals over 40 g, whereas in pitfalls animals were generally lighter. Over half of the 1,100 animals captured first by pitfalls were never caught by live-traps. Among those subsequently entering live-traps, many stayed away for 6 to 10 weeks, and some of the smaller ones stayed away even longer. Few animals dispersed to other nearby trapping grids. Pitfall trapping and live-trapping sample different subpopulations, young animals and transient adults being a large fraction of the individuals caught in pitfalls.
Population dynamics and trappability of four rodent species in a forest habitat
: Trappings were carried out in a forest (Querco robori-Carpinetum) habitat on the Dráva Lowlands in two periods, using the capture-mark-recapture method. The sampling grid in the 1 ha study area contained 9 by 9 trap stations for 15 months in 1995-1996, and 11 by 11 sta­ tions for 10 months in 1997. A total of 10910 trap nights were recorded in the two periods, dur­ ing which 71 wood mice (Apodemus sylvaticus), 448 yellow-necked wood mice (Apodemus flav- icollis), 568 striped field mice (Apodemus agrárius) and 382 bank voles (Clethrionomys glareolus) were marked. Changes in the numbers of rodent populations were characterized using MNA="minimum number alive" and abundance values obtained by the Jolly-Seber estimator. The latter yielded higher values than MNA in the four-trap-night periods and lower values than MNA in the five-trap-night sessions. For the ratio of morning mean number of captures vs. recap­ tures by species, significantly better results were obtained in the five-night periods. species: Carpinus betulus, Ulmus minor, Fraximus angustifolia and Robinia pseudoacacia. The shrub layer of 1-4 m height and 25-90 % cover consists of young indi­ viduals of Cornus sanguinea, Ligustrum vulgare, Crategus monogyna, Sambucus nigra and Robinia pseudoacacia. Characteristic species of the high herb layer with 90-100 % cover are Corydalis cava, Anemone nemoralis, Stellaria holostea, Galium aparine, Veronica hederifolia, Lamium purpureum, Alliaria petiolata, Urtica dioica. In a smaller spot the herb layer is shorter and not very dense (40-70 % cover), and a thick litter of fallen leaves is present. Dominant species are: Dentaria bulbifera shoots, Ficaria verna, Hedera helix, Asperula odorata, Ajuga reptans, Stellaria holostea, Rubus sp. In patch­ es where the undergrowth is scarce (0-30 % cover) and small, leaf cover is dominant or the surface is bare, with scattered specimens of Circaea lutetiana, Hedera helix, Pulmonaria officinalis, Asperula odorata. Since no forestry activity has been carried out in the area for three years, the extent of the lat­ ter has decreased parallel with the regeneration of the vegetation.
The Regulation of Wood Mouse (Apodemus sylvaticus) Numbers in Wytham Woods, Berkshire
The wood mouse (Apodemus sylvaticus (L.)) is one of the commonest small mammals in English woodland and has been frequently studied. But, apart from the early study of Elton et al. (1931), little attention has been given to the problems of whether and how its numbers are regulated. This paper is an attempt to answer these questions using data collected from one woodland area over 18 years by workers at the Bureau of Animal Population, Oxford.