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 study 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 controlling for the effects of age and body size. Among several behavioural variables, having a high attendance, being more active and having the tail lyre feathers erected more often were significantly related to high mating success also when age and the other factors were controlled for. In addition, there were strong relationship between a combined measure of territorial centrality and territory size and their interaction such that males that held relatively large central territories had higher mating success. Males that spent more time rookooing (display) had lower mating success. This last somewhat counter-intuitive result could be explained by a significant interaction between rookoo and centrality; central and successful males were engaged 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 reflect male motivation and/or competence. The results thus indicate that successful males are signified by being healthy, active and capable to defend relatively large central territories on the leks. We conclude that sexual selection in black grouse is most likely mediated both by male-male competition and female preference.