1. Section of Ecology, Dept of Biology; Univ. of Turku; Finland
2. Dept of Animal Ecology; Netherlands Inst. of Ecology (NIOO-KNAW); PO Box 50, 6700 AB Wageningen the Netherlands
3. Laboratory of Comparative Endocrinology; Biology Dept; KU Leuven Belgium
4. Behavioural Biology, Groningen Inst. for Evolutionary Life Sciences, Univ. of Groningen; the Netherlands