Biology
Sexual Selection and Lekking Behavior in Black Grouse
Quick fact
At a black grouse lek, a single central dominant male may perform over 90% of the copulations, despite dozens of competing males displaying around him.
Why this is interesting
Every spring, male black grouse gather on the same patch of ground to perform spectacular displays, but only a few ever get the chance to mate. What makes these arenas so special, and why do females flock to them?
Read the full explanation
Understanding Sexual Selection and Lekking Behavior in Black Grouse
Black grouse are a classic example of a lekking species. In early spring, before sunrise, males gather on traditional open areas called leks. These arenas are not territories with resources; they are purely for show. Each male defends a small area within the lek, and the most dominant males occupy the center. Females visit these leks to choose a mate. They walk through the arena, inspecting males, and typically mate with the one that appears most vigorous and attractive. This central male, often the most dominant and highest in the pecking order, achieves the vast majority of matings. The males' elaborate displays—ruffling their lyre-shaped tail feathers, making a distinctive bubbling coo, and leaping into the air—are all signals of their quality. The whole spectacle is a stark demonstration of sexual selection: the traits that make a male successful are not those that help him survive, or even fight, but those that females find most appealing.
A deeper explanation
The evolutionary engine behind lekking is a positive feedback loop between female preference and male trait expression. Females tend to be attracted to exaggerated characters—such as the black grouse's bright red comb and curved tail feathers—because these traits are honest signals of health and dominance. Strong, well-nourished males can afford to produce these handicaps, and their displays also reflect their hormonal state, particularly testosterone, which is linked to both immune function and aggressive success. In a lek, males also sort themselves by status: the dominant male is at the center because he can out-compete others. Females, by mating with him, likely gain indirect genetic benefits for their offspring. This overwhelming preference for the top male creates intense skew in reproductive success, which drives the evolution of ever more elaborate courtship displays. In turn, such extreme discrimination by females can lead to runaway selection, where the preference and the trait escalate together, sometimes even creating costs to survival that are outweighed by the reproductive advantage. Understanding lekking in black grouse reveals not just an oddity of nature, but a window into the powerful and often paradoxical forces of sexual selection.