Pastures concentrate the largest number of herbivores. The Black Vulture, which nests in the steep mountain ranges, uses them as a food resource, feeding on the occasional casualties among the cows, pigs and sheep that graze freely in the fields. The dehesas are open forests of holm oak, cork oak and oak, created by human activity over centuries. It is the ecosystem that occupies the largest area in the Iberian West. Huge extensions border the main and most emblematic sites of the area.