Those who have ventured to scale the rugged heights and steep precipices frequented by these birds, are often startled by the sound of their clear, sweet voices, as they suddenly salute the ear in situations apparently destitute of animal life, whilst those whose patience will permit them to follow the sound until they come to the spot upon which a pair have taken up their abode, will behold a performance that richly repays the trouble of a tedious climb. Upon a ledge or platform of rock he will see the male bird either tripping lightly around the open space, or executing a regular dance, with wings and tail outspread, accompanying the movements of his feet and body with a continuous flow of song, and bowing his head repeatedly: this entertainment being varied by rising suddenly into the air, and sinking again rapidly, with open pinions, to the ground. Upon one occasion, whilst journeying over the Sierra de los Anches, we came upon a pair of these birds, seated near to a nest containing their unfledged young. The terrified female immediately began flitting from rock to rock, while her mate at once commenced dancing, tripping gracefully about, and singing with all his power, as though with the idea of riveting our attention on himself, and thus averting danger from his little family. We could not find it in our hearts to render the wily stratagem abortive, so contented ourselves with a hasty glance at the nest, and left the spot, followed by a loud song of triumph and rejoicing from the anxious father. The nest, which is placed in holes in the rock, is not commenced until the end of April or beginning of May. The exterior is formed of fibres and grass, woven firmly together, the interior being carefully lined with a layer of goats' hair. The eggs are of a pale greenish blue, marked violet or reddish, but their pattern is very variable; they are from four to six in number: in Spain we have occasionally found as many as seven in a brood. The young are reared upon insects, and are no sooner fledged than they may be seen perching upon the rocks or stones, watching their parents as they pursue flies or other insects destined to fill their craving beaks. Meanwhile, should any unusual sight or sound attract the attention of the vigilant father, he instantly warns his brood by a peculiar cry that they must at once seek shelter in the neighbouring holes and fissures, and recalls them with the same note when they may again venture forth. It is only after the moulting season, which continues throughout July, August, and September, that the young withdraw themselves from the protection of their parents, in order to seek a mate and begin life on their own account. [Illustration: THE STONE THRUSH, OR ROCK WAGTAIL (_Petrocincla-Turdus-saxatilis_).] * * * * *