Correlates of male mating success on black grouse (Tetrao tetrix L.) leks

Sexual selection in black grouse was studied through multivariate analyses of possible correlates of mating success using data from an eight year stud y of 10 different leks. Body size was weakly correlated with mating status (0 or greater than or equal to 1 mating) and tail length was significantly correlated with mating success (total number of copulations) even after con trolling for the effects of age and body size. Among several behavioural va riables, having a high attendance, being more active and having the tail ly re feathers erected more often were significantly related to high mating su ccess also when age and the other factors were controlled for. In addition, there were strong relationship between a combined measure of territorial c entrality and territory size and their interaction such that males that hel d relatively large central territories had higher mating success. Males tha t spent more time rookooing (display) had lower mating success. This last s omewhat counter-intuitive result could be explained by a significant intera ction between rookoo and centrality; central and successful males were enga ged in more interactions with neighbours, and therefore were not allowed to display as often as peripheral unsuccessful males. Display activity indeed turned out to be a significant factor of mating success when we controlled for territory position. All of the significant variables are likely to ref lect male motivation and/or competence. Tile results thus indicate that suc cessful males are signified by being healthy, active and capable to defend relatively large central territories on the leks. We conclude that sexual s election in black grouse is most likely mediated both by male-male competit ion and female preference.