In winter, their plumage is pure white, except for their black tail, which is present in both sexes throughout the year. The legs are strong and their claws spread acting as ‘snowshoes’, which help them walk in the snow. In summer, both sexes are streaked with black and brown spots on their upper body. The abdomen and the outer edge of the wings are whitish. Females are more marked than males. Males loose their white winter plumage later on, before changing to their courting plumage. This has an unexpected effect: a larger number of males are hunted by birds of prey as they become more noticeable with their lack of camouflage, while females are almost invisible. The males have a black streak from the beak to the eye and red wattles that hang over the iris. In autumn, the whole plumage changes to greyish white on top, the abdomen remains white. This plumage is the briefest.
The winter habitat is formed by the scrubby slopes near the tree line in places where vegetation is apparent in the snow. Males continue to frequent this alpine environment, while females tend to shelter under the canopy. In spring and autumn, grouse choose open landscape with sparse vegetation, males opting for territories with rocky outcrops providing opportunities that enable them to guard over the females and the rest of the flock. The chicks live in the crags where they can be sheltered in case of danger.
Ptarmigan migrate in flocks over short distances. They abandon the higher ground in winter to nest in the valleys and low lands, males and females in separate flocks. These flocks then disintegrate in the early spring. The male then select their territories that they defend with great cries and loud energetic aerial displays. The ceremony to defend territory is marked by a series of elaborate songs and flights intended to deter potential intruders. During courtship, the male initiates circular manoeuvres around the female, spreading out the fanned tail and leaving a wing dragging on the ground. At the same time, he expands the red wattles located above the eye.
The females nest on the ground in a shallow hollow, lining the nest with a few feathers and plant materials. This is usually placed on a bare rocky outcrop with a little vegetation. While she searches for some security against possible preditors from the sky, the female builds the nest directly against the rock. The clutch is composed of 7 to 10 eggs. The incubation by only the female lasts 21 days. The downy chicks start to venture outside the nest immediately after hatching. They are able to feed and fly after 10 days. They are fledged within 10 to 12 weeks.
The adults are almost exclusively vegetarian, only including insects, spiders, snails for the benefit of the chicks. The principle diet is a mixture of plants as diverse as blueberries, berries, heads of rushes or reeds or specific plants of high altitude. The winter diet consists mostly of buds, catkins of dwarf birch, twigs and buds of willow.
The "endemic subspecies Hispano-French" is mainly threatened by the development of winter tourism, construction of infrastructure such as ski resorts and ski lifts, creation of paths and trails, as well as by poaching.