Sven Zacek / Black Grouse (Tetrao tetrix) two males facing off on a lekking site, Varumaa county, Southern Estonia. April.

SCOTLAND: The Big Picture / RF - Black Grouse (Tetrao tetrix), two males fighting on lek , Scotland, UK.April (This image may be licensed either as rights managed or royalty free.)

Nick Garbutt / Andean cock-of-the-rock (Rupicola peruvianus), male displaying at lek in tree. Manu Biosphere Reserve, Amazonia, Peru.

Sergey Gorshkov / Black Grouse (Tetrao tetrix) males fighting at lek in the snow, Tver, Russia. April

Gerrit Vyn / Greater sage-grouse (Centrocercus urophasianus) male displaying on a lek in snow, Sublette County, Wyoming, USA. April.

Sven Zacek / Black grouse (Tetrao tetrix) males lekking at sunrise, Southern Estonia, April.

SCOTLAND: The Big Picture / Two male Black grouse (Tetrao tetrix) displaying at a lek, Cairngorms National Park, Scotland, UK, April.

Andy Trowbridge / Capercaillie (Tetrao urogallus) male displaying in Scots pine tree (Pinus sylvestris) Southern Norway. May.

Erlend Haarberg / Male Great snipe (Gallinago media) displaying, Norway, June

Erlend Haarberg / Male Great snipe (Gallinago media) calling during display, Sor-Trondelag, Norway, May

Sven Zacek / Two Black Grouse (Tetrao tetrix) fighting at a lek. Virumaa, Estonia, Europe, April.

Tim Laman / Red Bird-of-Paradise (Paradisaea rubra) male performing practice display at tree-top lek, Raja Ampat, Indonesia. *Medium repro only.

Konrad Wothe / Three male Six plumed birds of paradise (Parotia lawesii) displaying to nearby females, hopping on display ground in a rainforest, Papua New Guinea.

Konrad Wothe / Two male Six plumed birds of paradise (Parotia lawesii) displaying, hopping on display ground in a rainforest, Papua New Guinea.

Konrad Wothe / Male Six plumed bird of paradise (Parotia lawesii) displaying, Papua New Guinea.

Konrad Wothe / Male Six plumed bird of paradise (Parotia lawesii) preening and displaying, with a female watching nearby, Papua New Guinea.

Konrad Wothe / Male Superb bird-of-paradise (Lophorina superba) displaying, Papua New Guinea.

Konrad Wothe / Male Superb bird-of-paradise (Lophorina superba) displaying, Papua New Guinea.

Konrad Wothe / Tracking shot of two male Six plumed bird of paradise (Parotia lawesii) hopping on display ground in a rainforest, Papua New Guinea.

Sven Zacek / Black grouse (Tetrao tetrix) male jumping in a lekking site at dawn. Varumaa county, Southern Estonia. April.

Sven Zacek / Black grouse (Tetrao tetrix) males displaying at lek in frozen bog, Varumaa county, Estonia. April.

Sven Zacek / Black grouse (Tetrao tetrix) on lekking site on a cold and frosty morning, Värumaa county, Estonia.

Nick Garbutt / RF - Black Grouse (Tetrao tetrix) - males fighting on frozen lake at sunrise. Kuhmo, Finland, April. (This image may be licensed either as rights managed or royalty free.)

Danny Green / RF - Capercaillie (Tetrao urogallus) male displaying, Finland, March. (This image may be licensed either as rights managed or royalty free.)

Danny Green / RF - Black Grouse (Lyrurus tetrix) displaying. Finland. March. (This image may be licensed either as rights managed or royalty free.)

Danny Green / Black Grouse (Lyrurus tetrix) fighting on icem Finland. March.

Danny Green / Black Grouse (Lyrurus tetrix) displaying. Finland. March.

Danny Green / Black Grouse (Lyrurus tetrix) displaying. Finland. March.

Danny Green / Black Grouse (Lyrurus tetrix) displaying. Finland. March.

Andy Sands / Black grouse (Tetrao tetrix) male displaying at lek in dawn light, Upper Teesdale, Durham, England, UK. May

Andy Sands / Black grouse (Tetrao tetrix) female overlooking lek, Upper Teesdale, Durham, England, UK. May

Loic Poidevin / Ruff (Philomachus pugnax) territorial male fighting with satellite males during lek, Varanger, Norway, May

Loic Poidevin / Ruff (Philomachus pugnax) displaying territorial male, Varanger, Norway, May

Loic Poidevin / Ruff (Philomachus pugnax) male, Varanger, Norway, May

Markus Varesvuo / Black Grouse (Lyrurus tetrix) male with group of females, Suomussalmi Finland, January. Commended in Bird Photographer of the Year competition 2020.

Loic Poidevin / Ruff (Philomachus pugnax) males displaying and fighting each other at a lek, Finland. May.

Jussi Murtosaari / Western capercaillie (Tetrao urogallus), male displaying at lek, Finland, April.

Jussi Murtosaari / Western capercaillie (Tetrao urogallus), male displaying at lek, Finland, April.

Jussi Murtosaari / Western capercaillie (Tetrao urogallus), male displaying at lek, Finland, April.

Jussi Murtosaari / Western capercaillie (Tetrao urogallus), male displaying at lek, Finland, April.

SCOTLAND: The Big Picture / RF - Black Grouse (Tetrao tetrix), two males fighting on lek , Scotland, UK.April (This image may be licensed either as rights managed or royalty free.)

SCOTLAND: The Big Picture / Black grouse (Tetrao tetrix), male taking off from ground, Cairngorms National Park, Scotland, UK, April.

SCOTLAND: The Big Picture / Black Grouse (Tetrao tetrix), two males fighting on lek , Scotland, UK. April.

SCOTLAND: The Big Picture / Black Grouse (Tetrao tetrix), two males fighting on lek , Scotland, UK. April.

SCOTLAND: The Big Picture / Black Grouse (Tetrao tetrix), two males fighting on lek , Scotland, UK. April.

SCOTLAND: The Big Picture / Black Grouse (Tetrao tetrix), close up of male displaying on lek , Scotland, UK. April.

SCOTLAND: The Big Picture / Black Grouse (Tetrao tetrix), two males fighting on lek , Scotland, UK. April.

SCOTLAND: The Big Picture / Black Grouse (Tetrao tetrix), close-up of male in breeding plumage , Scotland, UK. April.