Combs and sexual selection in black grouse (Tetrao tetrix)

We studied supra-orbital combs in lekking black grouse (Telrao tetrix) in r elation to sexual selection at five leks in Finland 1991-1998 and four leks in Sweden 1992-1995. Comb size was estimated in two ways: by observing its natural size in the field at different behaviors ("observed comb size"), a nd by measuring the comb size from captured birds ("measured comb size"). T he size of combs is highly variable, and individuals can change it within s econds. Males express their larger combs during display, as compared to oth er behaviors. Observed mean comb sizes were larger on leks with a higher nu mber of males and a higher number of copulations. Measured and observed com b sizes and copulatory success did not significantly correlate when all mal es where analyzed, but a positive and significant relationship between obse rved comb size and copulatory success was found within males that achieved copulations. Measured comb length correlated positively with the amount of testosterone. While females were present on the lek, displaying and success ful males showed the largest observed comb size. When we compared observed comb size during fighting between successful and unsuccessful males and cor related comb size of pairs of fighting males with their fighting activity, no significant differences in comb size were found. The result that comb si ze correlated significantly with an increase in testosterone level and that larger comb size, within successful males, predicted higher copulatory suc cess suggests that combs may be a cue for females to assess male quality. T he lack of a significant relationship between observed comb size and fighti ng behavior suggests that comb size either has minor importance in male-mal e signaling on the lek or that males may express similar-sized combs during fighting to avoid serious fights and thus risk of comb injuries.