Pyrenean ostrich differs from the ancestor in more thickset constitution – it is an adaptation to reduction of heat emitting in winter. Growth of an adult bird is up to 1.5 m; weight is about 110 kg. This ostrich has heavier constitution comparatively to ancestor: short thick neck and thick legs. Head of this species also seems larger and more massive. The lateral toe on legs is reduced in great degree, almost useless and only slightly touches the ground. Despite of this feature, characteristic for quickly running birds, Pyrenean ostrich can accelerate momentum only about 50 kms per hour. Possible, it descends from quickly running ancestors, but has lost a part of speed due to development of northern habitats of colder climate.
The plumage of Pyrenean ostrich is rich and resembles wool more. In feather colouring the sexual dimorphism is expressed: male is dark grey, but its neck keeps reddish shade; female is colored lighter – it is brownish with grey spots on plumage. Male lacks white feathers in wings characteristic for the African species. The neck of these birds in bottom part is covered with large feathers like on body – approximately the half of its general length from shoulders. The top part of neck and head are covered with thin hairlike feathers.
Beak of this bird is thick and deep. Pyrenean ostrich eats fruits, roots and grass. With the help of strong hoof-like claws it is capable to dig bulbs out of the ground. Occasionally this bird tramples and pecks lizards and small snakes, and also may eat any rodent.
Similarly to African ostriches prior to the beginning of their extermination, these birds are monogamous and live in permanently existing pairs or in groups of three birds; in the south of area male may form family with two females at once, and they hatch eggs alternately and look after chicks together. If the herd is larger, it means two or three parents lead the grown up chicks.
The breeding season at this species begins in early spring. The female lays up to eight eggs, and all members of family incubate the clutch alternately: male at night, and female in day time. In hot weather female only protects clutch from the sun. The hatching proceeds till 45 days. Breeding rate at these birds is rather slow: chicks follow parents more than year and for this time they reach approximately 70% of weight of adult individual. Nesting and rearing of posterity takes away many efforts from adult birds; therefore nesting at these ostriches repeats once in two years. Young birds become sexually mature at the third year of life. Life expectancy reaches 25 – 28 years.