Only two polygamous birds regularly perform lekking behaviour in Britain – the other is the capercaillie. Male black grouse, called blackcocks, gather at their leks all year, with the peak period in April and May. This is when females, ‘greyhens’, attend the display sites to select mates. The males assemble at dawn and display by fanning out their white undertail feathers and lyre-shaped outer-tail feathers, while posturing, flutter-jumping and uttering continual bubbling sounds. ‘Lek’ comes from the Old Norse for ‘play’ but it is a serious business, with males battling for territory and to secure matings.
Dominant adult males take the central locations; subordinates and juveniles occupy the outside. Today, British leks usually have fewer than 10 males, though up to 30 is possible, with larger leks attracting more female visits and subsequent matings. First-year males seldom mate, but their presence increases the mating success of the adults.
After 150 years of decline, there are now at most 5,100 UK males, restricted to Scotland and northern England and Wales.
5 FACTS YOU NEED TO KNOW
1 Lek sites Leks are situated in open areas away from woodland, which provide good acoustics and visibility. They are located on areas of short vegetation, such as grass or on tracks. In Scandinavia some leks even take place on frozen lakes.
2 Mid-air fights Only a handful of males at a lek manage to copulate. Fighting is a prerequisite for success, because that is how males defend their territory – they face off and leap into the air on whirring wings.
3 Tail fanning Competing males spread their long, curving, black tail feathers into a wide fan. They contrast strongly with the brilliant white undertail covert feathers, raised vertically in the centre.
4 Wattles Males have a bright red wattle above each eye, which becomes engorged with blood and swollen when displaying. The size of the wattle is linked to testosterone levels, and may be a visual signal by which females can assess male quality.
5 Courtship calls Two distinct calls are made. The first is a bubbling or ‘rookooing’ sound – a continuous vocalisation produced with the aid of air sacs in the neck. The second is a guttural hiss. On clear, still mornings black grouse leks can be heard from up to 4km away.
3 KEY STAGES OF A LEK
1 Arrival In spring blackcocks fly into their traditional arenas just before first light, and take up their positions arranged by rank.
2 Display They perform energetic displays – fanning tails, posturing, jumping and sometimes making short flights over the lek.
3 Mating Females choose the fittest male occupying a central position in the arena. There is no pair bond – males do not help rear the chicks.