Behavioral Ecology Vol. 11 No. 5: 465-471
© 2000 International Society for Behavioral Ecology
Combs and sexual selection in black grouse (Tetrao tetrix)
a Department of Population Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18 D SE-75236 Uppsala, Sweden b Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18 D SE-75236 Uppsala, Sweden c University of Jyväskylä, Department of Biological and Environmental Sciences, PO Box 35, FIN-40351, Jyväskylä, Finland d Arctic Centre, University of Lapland, PO Box 122, FIN-96101 Rovaniemi, Finland
Address correspondence to P. T.Rintamäki. E-mail: pekka.rintamaki{at}ebc.uu.se .
We studied supra-orbital combs in lekking black grouse (Tetrao tetrix) in relation 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"), and by measuring the comb size from captured birds ("measured comb size"). The size of combs is highly variable, and individuals can change it within seconds. Males express their larger combs during display, as compared to other behaviors. Observed mean comb sizes were larger on leks with a higher number of males and a higher number of copulations. Measured and observed comb sizes and copulatory success did not significantly correlate when all males where analyzed, but a positive and significant relationship between observed 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 successful males showed the largest observed comb size. When we compared observed comb size during fighting between successful and unsuccessful males and correlated comb size of pairs of fighting males with their fighting activity, no significant differences in comb size were found. The result that comb size correlated significantly with an increase in testosterone level and that larger comb size, within successful males, predicted higher copulatory success suggests that combs may be a cue for females to assess male quality. The lack of a significant relationship between observed comb size and fighting behavior suggests that comb size either has minor importance in male-male signaling on the lek or that males may express similar-sized combs during fighting to avoid serious fights and thus risk of comb injuries.
Key words: black grouse, combs, copulatory success, sexual selection, Tetrao tetrix.