OVERSEAS MIGRATION 



themselves give evidence of land. J. Donald Smith, who traveled about the 

 archipelago a great deal in his light aircraft, writes me that "Kauai Island, 

 the northernmost of the main islands, is covered by clouds at one point most 

 of the year. In fact, Mt. Waielele is supposed to be the wettest spot on earth. 

 I have no idea how far this can been seen, but I have noted the cloud cover 

 of Kauai from a distance of 100 miles when flying at 3,000 feet. I would not 

 consider it reliable for precise navigation, but usable as a general indicator 

 of land." 



In long overseas journeys there is no physical advantage to be gained by 

 high-altitude flying, and it seems to hold for waterfowl as well as for many 

 other sea travelers that passages are made at low elevations. The Mallards 

 and Pintails that Buss observed were 150 to 200 feet above the water; and 

 since his original observation, he writes (letter) that he has watched the 

 ocean travel of many more ducks on the open Pacific and their flights have 

 always been below 400 feet. J. Donald Smith has written me of a flock of 

 about two hundred and fifty Pintails which he watched depart in northward 

 migration from Oahu, in January 1951. The birds, bunched and swimming 

 nervously in close formation, "arose in a mass, circled the pond once, and 

 took out over the ocean which is separated from the pond only by a beach 

 ridge. They established a north course and continued on it until I lost them 

 from sight. They flew just above the water and sometimes disappeared from 

 sight in the trough." Yocom (1947) presents an interesting account of Pin- 

 tails on the Pacific, and, while he does not give the actual elevations of the 

 birds, they apparently were flying much lower than is the rule for overland 

 migrations. 



In their trans-Pacific migrations, then, waterfowl sometimes, perhaps 

 usually, travel slower and lower than is their custom when moving over 

 land; but even so, we seriously distort the problem by stating it in terms 

 of absolute miles. The application of the relativity of motion to such pas- 

 sages renders the long overseas journeys somewhat less amazing, as the 

 complexities are appraised by the mind of the human observer. 



Besides distance, of course, directional cues are an aspect of the mystery 

 of overseas migration. What do these birds follow as guides to orientation 

 in a perceptual space that holds only sky and water? Many writers on bird 

 navigation have considered the sea to be "trackless," without "landmarks"; 

 and their readers, often without ocean experience, are easily led to accept 

 this point uncritically. "The sea has no landmarks," so the reasoning goes ; 

 "hence birds must have some yet unknown sense that guides them over the 



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