Why do Black Grouse males perform on lek sites outside the breeding season?

Studies of sexual selection have focused mainly on explanations of how male characteristics influence mating success during the breeding season. By co ntrast, few studies have investigated how behaviours prior to the breeding season influence mate choice during the mating period. Males in many specie s of birds exhibit behaviours that resemble mating behaviours typically per formed during the breeding season, even though environmental conditions are then not suitable for breeding. In one such species, the lekking Black Gro use Tetrao tetrix, both males and females visit leks regularly in autumn. B etween 1988 and 1994 we studied autumn lekking and its relation to the perf ormance of males and females in spring in a Black Grouse population in cent ral Finland. We found that virtually all males. regardless of their previou s copulation success, joined the lek in autumn, and that territory defence, in terms of fighting behaviour, was as intense in autumn as in spring. Fur thermore; males that did not establish their territories until spring were less successful in obtaining copulations than males that established their territories in the previous autumn or earlier. In addition, males possessin g central territories in autumn had higher copulation success in the follow ing spring, probably because Females visited the same male territories in a utumn and in the following spring. Our results suggest that males lek in au tumn to increase. their copulation success in the following spring. Consequ ently, this behaviour may provide females with an opportunity to assess mal es prior to the breeding season.