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When a migrant bird has reached the southern shores of England, it is nearly " home." What exactly does " home " mean to the returning migrant after its spring journey ? Does it mean any spot in these islands where there is suitable cover for its nest and a suitable food supply for the rearing of a family, or does it mean, as if often does to us, one particular spot near to where we were born and bred ? Since the advent of the practice of ringing birds with marked bands round their legs, it has been possible to prove conclusively a fact that had long been suspected, namely that birds normally return each year to the identical area in which they were born, and this applies equally to young and old birds alike. The swallow returns to the barn in which it nested last year, or to one close to it; the willow-warbler sings in the same coppice, or if not he, then one of his brood from last year ; all come as near to " home " as they can. There arises at once the age-old question of how birds, even those that are returning for the first time, find their way unerringly to this one wished-for spot. The sentimentalists would have us believe that the old birds show the young ones the way, as Tennyson's " Many wintered crow, that led the clanging rookery home ! " Nothing could be further from the truth, and we know, again as the result of careful experimentation, that wild birds possess, in a remarkable degree, the ability to orientate themselves towards a particular spot on the earth's surface, especially when that spot contains their nest and eggs or young. Such an ability is called, for want of a better phrase, the " homing instinct." In considering the reasons for this ability in birds to " home " from great distances, people are apt to be influenced too much by the example of the homing pigeon. This domesticated bird is trained by regular and increasing jumps over the route which will finally be taken in the race, and hence the conclusion is often reached that the homing ability is bound up solely with the fine visual memory which birds are known to possess, the birds recognising at once tracts of country over which they have already passed. In support of this thesis, it is pointed out that in fog, pigeons become hopelessly lost,'and that if overtaken by dark, they immediately lie up until daybreak, when they resume their journey. Therefore, it is argued that unless the pigeons can see recognisable landmarks, they cannot home. Yet this scarcely does justice even to the domesticated homing pigeon, for the |
