Surely the question of original home, at anyrate of the home in pre-Glacial days, may be entirely left out of the question. No one can ever prove that this wonderful memory did or could exist. Post-Glacial dispersal northwards, and the foundation of migratory habits of advancing to the new food-producing areas, suitable also for the rearing of young, was doubtless a fact, but would have taken place in any case. The congestion due to the increased numbers driven to a restricted area, would involve a rebound outwards, and the uninhabited areas northward of the refuge would be the natural bourn towards which the birds would travel. The seasonal return of cold would drive them southwards in winter, and the periodical migration habit would thus be originated.
The intense love of home during the spread of glacial conditions would tend rather towards extinction than the formation of any new habits. The birds which possessed the greatest attachment to the particular district would be less likely to fly from adverse conditions, and the reduction of their numbers through the ordinary physiological changes in habit—reduction of the number of young produced, and possibly disinclination to pair—would inevitably end in extinction. The stronger the attachment to home the more likely the bird to remain to the bitter end, and if driven away by
