Castile and León presents a great diversity of fauna. There are numerous species and some of them are of special interest because of their uniqueness, such as some endemic species, or because of their scarcity, such as the brown bear. There have been counted 418 species of vertebrates, which make up 63% of all vertebrates that live in Spain. Animals adapted to life in the high mountains, inhabitants of rocky places, inhabitants of fluvial courses, species of plains and forest residents form the mosaic of the Castilian-Leonese fauna.
The isolation to which the high summits are subject leads to the existence of abundant endemisms such as the Spanish ibex, which in Gredos constitutes a unique subspecies in the Peninsula. The European snow vole is a graceful small mammal of grayish brown color and long tail that lives in open spaces over the limit of the trees.
Small and large mammals such as squirrel, dormouse, talpids, European pine marten, Beech marten, fox, wildcat, wolf, quite abundant in some areas, boar, deer, roe deer and, only in the Cantabrian Mountains, some specimens of brown bear tend to frequent the deciduous forests, although some species also extend to coniferous forests and scrubland. The wildcat is slightly larger than a domestic cat, has a short and stout tail, with dark rings and striped fur. The Iberian lynx, however, lives almost exclusively in areas of Mediterranean scrubland.
Small reptiles such as the ladder snake, the coronella girondica and the aesculapian snake are also found in this environment. The smooth snake can be found from sea level to 1,800 m in height and in the community it tends to live on the heights. Further up, in the rocky areas of the subalpine floor at about 2,400 m altitude the Iberian rock lizard lives, one of the few reptiles adapted at this point.
In the mountain rivers live the otter and desman and in its waters the trout, anguillidae, the common minnows and some of the increasingly scarce autochthonous river crabs. The otter and the desman are two mammals with aquatic habits and very good swimmers. The otter feeds mainly on fish, while the desman seeks its food among the aquatic invertebrates that inhabit the riverbed. In lower sections of calmer waters swim barbel s and carps. Among the amphibians, the salamanders and as remarkable species: the Almanzor salamander (Salamandra salamandra almanzoris) and the Gredos toad (Bufo bufo gredosicola), which are two endemic subspecies to the Sistema Central.
Where the rivers are encased forming sickles and canyons, rock-dwelling birds such as griffon vulture, cinereous vulture, Egyptian vulture, golden eagle or peregrine falcon. The Egyptian vulture, a small vulture, is black and white with a yellow head. Downstream and on its banks between the lush vegetation form their colonies the black-crowned night heron and the grey heron and the goldcrest, the eurasian penduline tit, the eurasian hoopoe and the common kingfisher.
Among the birds that populate the open Mediterranean forests live two endangered species: the black stork and the Spanish imperial eagle. The black stork, much rarer than its congener the white stork, is of solitary habits and lives far from man. The Spanish imperial eagle nests in the trees and feeds mainly on rabbits, but also birds, reptiles and carrion.
In the coniferous forests live among others the short-toed treecreeper, the coal tit and the eurasian nuthatch, a bird of gray back and flanks reddish-orange that it nests in holes to which it narrows the entrance with mud. The western capercaillie is a very dark and large rooster that lives in forest environments, so it is very difficult to observe. Among the forest raptors are the accipiter, the eurasian sparrowhawk or the tawny owl, which frequently attack other smaller birds such as eurasian jay, european green woodpecker, fringilla, great spotted woodpecker and typical warbler.
The bustard frequents the open plains with rain-fed crops; It is large and has a grayish head and neck and a brown back. In the Castilian-Leonese wetlands during the winter many specimens of greylag goose, which breeds in northern Europe and visits the area in winter, are concentrated.
The naturalist Félix Rodríguez de la Fuente (1928 – 1980), natural from Poza de la Sal, stands out in the scientific study and its dissemination. He had a great research and made the leap to fame with the television series El hombre y la Tierra (TVE).
In the Montaña Palentina, in the municipality of San Cebrián de Mudá, a program of reintroduction of the European bison, animal that had been a thousand years without presence in the Iberian Peninsula, in order to avoid the extinction of the species.