Characteristics of pre-nesting behavior of <em>Phylloscopus</em> warblers in the northern part of distribution area

Abstract

On the basis of field studies conducted in 1973–2000 it was found for four species of Phylloscopus warblers breeding in the taiga zone of NW Russia that their northern marginal populations, more remote from wintering grounds, have considerably shorter period of staying in the breeding region as compared with southern populations (because of later arrival and earlier departure), shorter interval between male and female arrival and lower population densities. It determines the regional features of their behavior during pre-nesting period: reduction of time of its first phase (before female’s arrival) and more “peaceful” delimiting of nesting territories. The “companionship” stage (according to D. May) is absent as the warblers from northern populations arrive in the nesting sites being physiologically readier for breeding. Although socially monogamous pairs dominate, the cases of facultative polygamy occur, especially in Willow Warbler. The molecular-genetic analysis has shown that in this species the frequency of polygyny (5–17 %) is much lower than the frequency of polyandry (68,4 %), i.e. in majority of Willow Warbler’s nests the bastard nestlings (15,3 % of total nestling number) are found. This is obviously conditioned by the excess of adult males, which is quite typical for all Phylloscopus species. Refs 31.