Sense of Direction in Birds 43 



The great group of Warblers, of which some 70 species are found in the United 

 States, has been mentioned before. They are all strongly migratory and mainly 

 pass beyond our southern borders in winter, although a few individuals of a 

 single species the Yellow-rumped Warbler have been known to winter on 

 Cape Cod. Some of them visit the West Indies, but the larger number, after 

 rearing their young in the dense coniferous forests of the Hudson Bay region or 

 even in Alaska, spend the winter in Mexico, Central America, or northern South 

 America. 



The Sparrows as a group are also strictly migratory. Quite a number, such as 

 the Tree Sparrow (Spizella monticola), Snowflake (Plectra phenax nivalis), and 

 Longspur (Cakarius lapponicus], breed far to the north of the United States in 

 Arctic districts, and come down in winter into the Northern States or irregularly 

 farther south. Many species which breed mainly north of the United States only 

 go into the Middle and Southern States during the winter, while a few may reach 

 the West Indies, Mexico, Central America, or northern South America. The 

 Nighthawk is another example, some individuals spending the summer in Alaska 

 and the winter in Patagonia, points separated by over five thousand miles, over 

 which they must travel in spring and fall. 



But after having described these migration routes and the wonderful journeys 

 over continents and vast oceans, the mystery of mysteries How is it possible 

 for the birds to find their way so unerringly ? still remains without a wholly 

 satisfactory answer. As in the case of theories propounded to account for the 

 origin of migration, so numerous suggestions have been made to explain this 

 wonderful faculty. Thus Dr. Von Middendorff, a distinguished naturalist who 

 studied exhaustively the migrations in the Russian Empire, suggests that because 

 all the spring movements in that country are toward the magnetic pole, the migrat- 

 ing bird knows the location of this point and is enabled to direct its course accord- 

 ingly. It is perhaps needless to say that this theory is not only unsupported by 

 any serious data, 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 experi- 

 ence, 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 



