We report experimental results showing that, under both laboratory conditions as well as in outdoor enclosures, the fossorial vole Arvicola terrestris preferentially feeds on acyanogenic white clover (Trifolium repens) when offered the choice between two varieties (Ladino and Aran) differing highly in their content in cyanogenic glycosides. We also observed that the voles adapted their diet and reduced their relative consumption of the cyanogenic variety during experiments conducted for two to three weeks in outdoor enclosures as compared to shorter tests conducted for 48 hr in laboratory cages. In addition, we report a similar preference for the acyanogenic Ladino variety for the slugs Arion ater and A. subfuscus.

We investigated how territory quality, settlement date and morphometry affected several components of yearly breeding success of a Swiss population of Savi's Warblers Locustella luscinioides. Territories occupied by males differed from unoccupied sites of similar size and location by having higher and denser reeds, a more extensive straw litter, and a thicker cover of dead sedge leaves. Territories with these characteristics were the ones first chosen by males upon spring arrival. These males, however, did not differ in morphometry from those that arrived later. Availability of suitable nesting sites, rather than food availability, appears to be an important choice criterion for territories. Early arriving males had higher breeding success than late males because of a higher mating success and more successful clutches. The positive correlation between male breeding success and territory quality was thus mediated through their common dependence on occupancy date. Female breeding success decreased with the date of first-clutch laying, mainly because late-nesting females fledged fewer broods. Breeding success in either sex did not correlate with morphometry. Our results provide clear support for territory choice by males, but not for mate or territory choice by females, and show the crucial role played by individual settlement date on many aspects of the breeding cycle of both sexes. We propose a lottery model of mate choice: arriving females obtain the best available territories even without choosing mates or territories; since males occupy territories sequentially and in order of decreasing quality, the few unpaired males available at any moment also occupy the best available territories.

Numbers and distribution of Capercaillie Tetrao urogallus in Switzerland 2001 and their changes in the 19th and 20th century. - Male Capercaillie were censused at their leks in spring 2001 in most parts of their range in Switzerland. A large part in the canton of Grisons was not censused with the same method but by a stratified sampling of tracks, droppings and feathers. The Capercaillie is distributed in the Jura mountains, along the northern slopes of the Alps and in the central Alps of the canton of Grisons. On 147 leks, 252 Ca- percaillie were counted. The total number of Capercaillie males in Switzerland is estimated to be between 450 and 500. In 196 8/ 1971 and in 1985 two censuses had been carried out with the same method. The first revealed an estimated number of Capercaillie males of at least 1100, the second of 55 0- 650. Since 1985, the range has shrunk, too. Capercaillie has almost completely disappeared from the northwestern slopes of the Alps. The main reasons for the long-term negative trend in population numbers of Capercaillie seem to be changes in forest structure and human disturbances. Meteorological data suggest that between 1985 and 2001 the decline has been overlayed by population fluctuation caused by changing weather conditions.