MIGRATIONS OF WATERFOWL 



200 feet, where we identified all species of ducks easily, as well as Crows, 

 Coots, and Canada Jays. We could see the eyes of each Moose. Meadow 

 and muskeg, spruce tree and waterfowl, were all perceived clearly. Aware- 

 ness was of details within a limited landscape, each scene viewed for only 

 an instant. We were lost, however, as regards exact geographical location. 

 Bob then climbed to 2,000 feet, where we became precisely oriented. Now 

 spruce trees were not seen individually; we were no longer aware of each 

 duck, although there were many hundreds below. The plane drifted slowly 

 over a world of green and blue, of forest and water, the patterns of which 

 could be examined with leisure despite a ground speed of 120 m.p.h. 



The cues or "landmarks" of aerial travel must be relative to height. In 

 flying from The Pas to Delta at an altitude of 200 feet, there are perhaps 

 a hundred or more key points in the landscape, identification of which is 

 important to oriented travel. Miss two or three of these when flying low and 

 the way is lost. At 2,000 feet, however, there are at most six landmarks 

 that guide flight for the human pilot flying in reasonably good weather 

 (Figure 22). Each new cue appears in the distance before the last one has 

 receded from view behind, so that at this elevation the pilot is never beyond 

 sight of such guiding features. It follows, then, that the number of cues 

 required for memory is relative to the height of travel. It is much easier 

 for the pilot to remember his way across Manitoba's lake country at 2,000 

 feet than at lower elevations. Were this not so, swift air travel would be 

 impossible; no pilot (lacking instruments) could fly from Winnipeg to 

 New Orleans if he had to obey as many cues to orientation as are followed 

 by a man driving the same course in an automobile. Their behavior sug- 

 gests that this same relation between height and landscape holds for ducks, 

 for they precisely follow the patterns of creeks and channels, points and 

 sloughs, in local movement at low altitude. In higher flights, these details, 

 so important on the native area, are insignificant segments of the mosaic 

 of the whole marsh, which the migrant, crossing at 2,000 feet, sees in its 

 entirety as a single landmark along the way. I suspect that the cues to 

 oriented travel about the Delta Marsh are no less numerous for the bird 

 on its home range than are the landmarks required by a migrant during a 

 day's journey at 2,000 feet. 



The perceptual space of the traveler includes not only the surrounding 

 world, but the sky above, with its sun, moon, and stars. These celestial 

 bodies are so far from the eye that the traveler does not perceive them as 



156 



