Page:Bird Life Throughout the Year (Salter, 1913).djvu/118

88 ing bleak ranges of hills, as shown by the fact that those which land in South Devon diverge to either side to avoid having to cross Dartmoor. It may seem that inherited instinct has done enough in guiding the migrants back to English shores, but she has still a more wonderful task, that of enabling each bird to find its way to its native district, in many cases to the very spot where it was reared or which it frequented the previous year. This seems to the writer the real and inner mystery of migration. That birds are not guided merely by the experience of their elders is conclusively proved by the case of the cuckoo, where the young birds of the year remain with us long after the adult cuckoos have left.

Who that sees the Swallows at the moment of arrival make straight for the shed where they nested last year, or the House Martin fly direct to the eaves, can doubt that they are the identical birds whose departure he watched in the autumn? A pair of Wood Wrens nested year after year within a yard of the same spot. Over hundreds of leagues of land and sea the memory of that shady bank deep in blue bells drew them with the magnetic influence of home. Birds of the previous year making for the spot where they were reared and finding this occupied, or being perhaps driven off by their elders, seek homes of their own. This tends to a general dispersal, and, where the species is increasing in numbers, to an extension of range into