BEHAVIORALLY MEDIATED SEXUAL SELECTION - CHARACTERISTICS OF SUCCESSFUL MALE BLACK GROUSE

Recent studies of lekking animals suggest that a suite of characters m ay be favoured by sexual selection. Examples of such traits are high s urvival, increased androgen levels, territory features and morphologic al characters including exaggerated morphological ornaments. Here we a rgue that such selection is often mediated by behavioural differences and we use results from a field study of lekking black grouse, Tetrao tetrix, as an example of our argument. In the absence of females, male s display a range of stereotyped behaviours including vocalizations, v isual displays and fighting. When females attend the lek, the behaviou ral repertoire of the males becomes more limited. Time budget analyses reveal that in the vast majority of cases, males in the presence of f emales perform only three types of behaviour: a vocal display called r ookooing; a courtship behaviour called circling; and fighting. This su ggests that female preference could be based on male courtship and fig hting behaviour while females visit individual male territories and th at displays not used in the presence of females could be ruled out as important for female preference. Sexual selection in black grouse, how ever, is a complex interplay between male-male competition and female choice and therefore female preference is not the only determinant of male success. Successful males were more often involved in fights in t he absence of females on the lek and defended territories that were la rger than expected. Therefore, we hypothesize that differences in male fighting ability result in some males occupying relatively large terr itories at the centre of the leks. Relatively large territories seem t o be needed for successful courtship. Therefore behavioural difference s mediate differences in male copulation success both through female p reference and male-male competition. (C) 1997 The Association for the Study of Animal Behaviour.