Page:Popular Science Monthly Volume 60.djvu/343

Rh magnetic pole, the migrating bird knows the location of this point and is enabled to direct its course accordingly. It is perhaps needless to say that this theory is not only unsupported by any serious facts but, as has been shown by Baird, is opposed to the facts of migration in North America.

If during the migrations the older and stronger birds always led the way, it might be said with plausibility that this faculty is due in large measure to experience, but here again the facts are either conflicting or directly opposed to such a view, for it seems to have been demonstrated with reasonable certainty that in Europe the young birds not only precede the old, during the fall movement, but often travel by a wholly different route. In this country, however, observations on this point are limited and authorities differ, but the tendency is to believe that the old birds do actually lead. Observation is much needed to settle this question.

In the case of birds migrating over land areas, sight is supposed by some to have an all-important function, especially when it is recalled that a bird two miles above the earth is surrounded by a horizon line of 90 miles on either side. As already shown, they have been observed at a height of three miles, which would easily keep them within sight of prominent landmarks, and would even permit them to cross considerable bodies of water without entirely losing themselves. That they depend to some extent on such landmarks to guide them on their course seems to be shown by the fact that they migrate mainly on clear nights and are obliged to seek the earth on the approach of cloudiness and storms. But in the case of birds migrating over hundreds or even thousands of miles of open water, vision must play an unimportant part. Möbius ('Das Ausland,' Aug., 1882) suggests that in such cases they may be guided by observing the roll of the waves, but while this may be true in a few instances, it cannot possibly be so in the majority of cases. We, therefore, seem inevitably led to the conclusion that birds are possessed of a 'sense of direction.' This homing' faculty or power of orientation which is, for example, so strongly developed in the carrier pigeon, is by no means unique among birds. It is possessed in a greater or less degree by many animals, by most savage races of men and, not infrequently by individuals among civilized races, more especially those accustomed to life away from centers of civilization, in forest and on plain—just how it is to be explained is difficult to say. Some would give it the dignity of a sixth sense and would fix its seat in the semi-circular canals of the ear.