The horizon is always at eye level. 



into view. This phenomenon is so common to human experience that it 

 needs no further elaboration except to emphasize the point that at higher 

 elevations the eyes see farther because the relative values of the components 

 of space become smaller. Thus all parts of the landscape — rivers, hills, fields, 

 villages, and marshes — are seen in reduction as the eye climbs higher. 



As the elevation of travel increases, the complexity of the visual field for 

 the human air traveler undergoes little change, and, granting differences in 

 acuity, I believe the same must hold for waterfowl. The details that con- 

 cern the eye at ground level become reduced as the altitude is increased, 

 and they are in the field of vision for a longer period of time. Flying at an 

 elevation of 200 feet, one briefly sees individual trees standing out conspicu- 

 ously, but at 2,000 feet each tree is lost in the arboreal pattern of the whole 

 forest, which is viewed with leisure. This relativity of awareness was made 

 clear to me in a flight with Robert H. Smith from The Pas, Manitoba, to 

 Delta, in the "Grumman Widgeon" of the U.S. Fish and Wildlife Service. 

 We left The Pas early on a bright August afternoon and followed the same 

 course as taken by migrant waterfowl, southeast to the Delta Marsh. Com- 

 ing down the maze of waterways of the Saskatchewan River, Bob flew at 



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