Birds and Birding's Guide to:

Watching THE MIGRATIONS OF BIRDS

Further Bird Migrational Theories

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. Mobius (Das Ausland, August, 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. As an example of this power of orientation it may be mentioned that the members of the Harriman Alaska Expedition went by steamer from the island of Unalaska to Bogoslof Island, a distance of some 60 miles.

”A dense fog had shut out every object beyond a hundred yards. When the steamer was halfway across, flocks of Murres, returning to Bogoslof after long quests for food, began to break through the fog-wall astern, fly parallel with the vessel, and disappear in the mists ahead. By chart and compass the ship was heading straight for the island; but its course was no more exact than that taken by the birds."—Cooke.

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 semicircular canals of the ear.

 

 

 

 

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