Birds
Western Capercaillie
Tetrao urogallus · also called capercaillie, wood grouse, cock of the woods
On a cold spring morning in an old pine forest, a sound carries between the trunks that is unlike any other bird — a quickening series of clicks and clops that ends in a noise like a cork pulled from a bottle. It comes from a male western capercaillie, tail fanned and beard raised, displaying at a lek his ancestors have used for generations.
Overview
Tetrao urogallus is the largest grouse in the world. The male is a dark, iridescent, turkey-sized bird weighing 4 to 6.5 kg; the hen is a mottled brown bird half his size or less. Capercaillies are birds of mature conifer and mixed forest with a rich understorey of bilberry, and they range across the northern forests of Europe and Asia from Scotland to Lake Baikal.
Needles and berries
The capercaillie’s diet shifts hard with the seasons. Through the snow-bound months it eats little but conifer needles, mostly pine, a low-quality food it processes with an enormous gut and a muscular gizzard full of swallowed grit. In the warm half of the year it turns to bilberry, buds, shoots, and flowers. Chicks, however, need insects in their first weeks, which ties breeding success to warm, dry spring weather.
The lek
Males breed by lekking. Before dawn in spring they gather at a traditional forest clearing, hold small neighbouring territories, and display with strutting, leaping, and wing-fencing. The dominant few males do nearly all the mating; hens visit only to choose. During the climax of his song the male is briefly deaf, a quirk long used by hunters to close the distance a few steps at a time.
Status
Globally the capercaillie is Least Concern, on the strength of its vast boreal population, but the trend is downward and the birds at the western and southern edge of the range are in serious trouble. The Scottish population has fallen to a few hundred despite being rebuilt from Swedish stock in the 1830s, and faces a possible second national extinction from forest loss, predation, fencing collisions, and disturbance at leks.
Western Capercaillie: common questions
How big is a western capercaillie?
The male is the size of a small turkey. He can stand around 60 to 75 cm tall in display, spans roughly 90 cm to well over a metre across the wings, and weighs between 4 and 6.5 kg. The hen is a completely different-looking bird, mottled brown for camouflage on the nest, and weighs about 1.5 to 2.5 kg, so a large male can be twice her mass. This gap between the sexes, called sexual dimorphism, is among the most extreme of any bird and reflects the intense competition among males for mating rights at the lek.
Why does the male capercaillie go deaf during his display?
In the last part of his song, a rapid series of clicks that speeds up into a sound often likened to a popping cork and a knife being sharpened, a fold of tissue in the bird's outer ear canal swells and seals it. For a few seconds he cannot hear his surroundings. The likely trade-off is that closing the ear protects it from the volume of his own call, or that the same muscular effort that produces the song also drives the swelling. Whatever the cause, hunters have exploited it for centuries, timing each few steps toward a calling bird to coincide with the deaf phase.
What is a capercaillie lek?
A lek is a traditional patch of open forest where males assemble before dawn each spring to display communally. Individual cocks hold small adjoining territories within the lek, and through the early morning they strut with fanned tails and raised beards, leap into the air, and clash with neighbours. Hens walk through, watch, and mate with one or two of the most dominant males before leaving to nest and raise the brood entirely alone. The same lek sites are used year after year, sometimes for decades, which makes them a focus of conservation because disturbance at a lek can cause males to abandon it.
Why is the capercaillie declining in western Europe?
The core boreal population remains large, but the birds at the southern and western edge of the range are in trouble. The main pressures are the loss and fragmentation of old, structurally rich conifer forest with a bilberry understorey, which the birds need for food and cover; higher numbers of predators such as foxes and crows in human-altered landscapes; collisions with deer fences; disturbance from forestry, recreation, and skiing near leks; and cooler, wetter springs that kill chicks. In Scotland the population has dropped to a few hundred birds and a second national extinction is considered a real possibility.