No abstract

The effect of summer feeding on juvenile arctic fox survival -a field experiment -Ecography 17 88-96The arctic fox Alopex lagopus L population in Sweden is small and its numbers fluctuate widely with food availability, l e rodent populations This fluctuation is mediated through differences in recruitment rales between years The recruitment can be divided into three phases number of litters bom, number of cubs per litter and cub survival rates The number of litters and their sizes have been shown to depend on food availability dunng winter and spnng To examine cub survival dunng the summer and how It relates to food availability, we conducted a feeding expenment m northem Sweden during 1990, a year of low rodent density, involving six occupied arctic fox dens Feeding at dens lowered cub mortality rates However, condition and growth rates of juveniles were not influenced by supplementary feeding at dens, nor were they related to the probability of survival for an individual Thus arctic foxes seem to minimize risks rather than maximize growth The juvenile mortality from weaning and over the next 6 wk was 21%, mostly due to starvation Only 82% survived from weaning to the first breeding season Of the one-year-old foxes, 50% survived their second year Supplementary feeding of juveniles had no effect on the final survival rates over these two years However, the immediate, positive effect on cub survival could be used in a long-term, extensive management programme if combined with wmter feeding M Tannerfeldt, A Angerbjom and B An'idSon,

The breeding sex ratio of Willow Warblers Phylloscopus trochilus in a subalpine birch forest was strongly female biased. Very few territorial males remained unmated and most became polygynous. Bigyny was the rule, but some males probably had three females. Male assistance at secondary nests varied and was probably dependent on temporal distance between the females' nests. There was no significant reduction in reproductive output for these females. Variation in the sex ratio of breeding birds can be explained, at least partly, by variation in the timing of male settlement.