Lost hotspots and passive female preference: the dynamic process of lek formation in capercaillie Tetrao urogallus

The evolutionary processes behind the polygynous mating system known as lek s are difficult to document. One approach is to study the behaviour that dr ives the formation of new leks today. Several hypotheses have been put forw ard to explain the formation of leks, and they can roughly be divided into two groups; one which advocates that the males are the driving force and on e which argues that the females are the driving force. In this study we use data from a long-term study (1979-1998) of a capercaillie population at Va raldskogen in southeast Norway to develop a model describing how new leks a re formed in this species. By using data on spacing pattern and behaviour o f radio-marked young and adult birds of both sexes we demonstrate how the s ituation develops from winter towards mating in spring. Furthermore, we rep ort on a few cases of new leks that have arisen in the area during the 20 y ears of study. We argue that both female mate choice, male territoriality a nd male attraction to locations with high densities of females are involved in a dynamic process of lek formation. We present results which indicate t hat new leks are mainly founded by young birds. Finally, we shaw that when new leks are formed the spacing patterns of the individuals involved change . This questions the method of using comparisons between the position of fe male home ranges and established leks to infer how leks are formed.