root of the migration of birds. The advantages of the power of flight, to which also it owes its development, include the ability to avoid active and passive enemies, and to remove from one feeding ground to another undeterred by the barriers which restrict the terrestrial animal. A natural sequence of this ability to take advantage of aerial locomotion is the habit of wandering in search of food, more or less noticeable in all birds. The habit of wandering led to the discovery of feeding grounds and suitable nesting places; where these nesting places, probably at first, only removed a short distance from the parents' nesting site, were suitable, dispersal and an extension of the distributional area or range of the species followed; but where the feeding area was unsuited or not so well suited to the needs of the species, hereditary attachment to the original home and memory of the direction of this home, or even in some cases accidental wandering back to the more suitable locality, would originate a migration. Coupled with this are two important factors which would tend to make the habit periodical and regular both as regards time and locality. The memory of the bird, call it instinctive memory if we like, would limit the wanderings in search of food to a certain number of places where food was most abundantly found, and the passage between feeding area and breeding area become regular
