Biology of the Wood Warbler Phylloscopus sibilatrix (Bechst.) in the taiga zone of north-western Russia
© Nikolay V. Lapshin. Biology of the Wood Warbler Phylloscopus sibilatrix (Bechst.) in the taiga zone of north-western Russia. // Avian Ecol. Behav. 13, 2005: 25-46.
Institute of Biology, Karelian Scientific Center, Russian Academy of Sciences, Petrozavodsk 185610, Russia
The study was carried out in Karelia and Leningrad Region in 1968-2003 by (1) trapping full-grown birds by tape lure and automatic traps when feeding the nestlings); (2) colourringing and subsequent observation of marked birds; (3) territory, nest, and dispersed brood mapping. In the province of Karelia the Wood Warbler Phylloscopus sibilatrix prefers medium to mature managed forests of mixed species composition. Breeding density decreases from south (8.4-36.4 pairs•km-2) to north (0.2-1.3 pairs•km-2) in Karelia. In Leningrad Region it may reach 60-80 pairs•km-2 in good years in optimal habitats, which is much lower than in the core part of the range. Long-term data reveal fluctuations in numbers with long periods of low numbers. The first males arrive in April, on average on 5 May, females on average on 12 May. Juveniles start to leave their natal territories on fledging from mid July. The last transient hatching-year individuals were captured on 9 and 17 September, the last adults on 11 and 12 August. The period of stay in the study area varied from 93-140 days in different years, on average 119 days which is much shorter than in the Chiffchaff Phylloscopus collybita and Willow Warbler Ph. trochilus. Wood Warbler males are polyterritorial. The spread of the first laying dates was 24 days, and the mean first laying date was 30 May. The earliest laying date was 19 May in 1968 and 1975, the latest one – 13 July 1979. Spread of clutch initiation was 17-43 days, on average 29.3 days. The overall mean date of laying the first egg was 11 June (n = 151). The Wood Warbler is single-brooded in the study area. Complete clutch size was on average 5.3 and declined with the season. Brood size is on average 3.7 (n = 151), 24.5% of nests failed completely. Survival of offspring is lower than in the Willow and Greenish Warblers Phtrochiloides but higher than in the Chiffchaff: 92.4% during incubation, 75.4% at nestling stage, 69.5% overall. Juveniles and adults undergo a partial moult in the breeding area in NW Russia. Some adults moult one or two tertials along with body feathers. Individuals which are feeding the young in late July to early August overlap breeding and moult.