TRAVELS OF WATERFOWL 



with constant light intensity day and night, the sleeping time nevertheless 

 remains on the whole unchanged for some time." He concludes that sleep 

 "behaves as an autonomous periodical function, although largely controlled 

 by the light conditions." Armstrong (1954) and Cullen (1954), presenting 

 careful reviews of the literature and reports of their own original observations 

 of birds living under continuous daylight, conclude that little is known re- 

 garding the "factors which may modify the length of a bird's working day" 

 (Armstrong), and that "there is still a virtually untouched field of investiga- 

 tion of diurnal rhythm in the Arctic" ( Cullen ) . 



There is a similar regularity in the activities of mammals. A doe White- 

 tailed Deer and her fawn passed down a trail within sight of my office each 

 afternoon for a week, the two reaching this spot within a few moments of 

 four o'clock. Those who live on the western prairies know the sunset song 

 of the coyote. Along the edge of the Delta Marsh skunks begin to wander 

 along the road at the same hour of twilight each evening. At Cornell Uni- 

 versity my Pointer dog Nelly had a routine of classes which she attended 

 more precisely than some students. She always entered a classroom quietly, 

 walked to her usual corner, and flopped down to endure the lecture hour. 

 The Library bell was the usual announcement ending class, but Nelly in- 

 variably became restless a moment or two before the bell rang. In one room, 

 where she had a conspicuous position up front, her pre-bell rise and yawn 

 was the students' mark for the end of the hour. I presume that some cue 

 which I could not perceive was her signal of the end of the period. Similar 

 behavior on the part of animals in a zoo is well known; lions and bears 

 follow the actions of their keepers that identify feeding or pen-cleaning 

 time. We know that cattle wend homeward at evening, beckoned by their 

 distended udders as well as by twilight. 



We recognize both sun time and metabolic time in our own lives, awak- 

 ening earlier with the vernal increase in the length of the day. Through the 

 course of the day, many of us find ourselves checking the sun's position. It 

 is a rule with some gunners to walk outward until the sun attains a point 

 halfway between the horizon and its position at the start; then the turn is 

 made toward home, which is reached at sundown. The office worker and 

 the farm hand both recognize the metabolic cues that signal lunch hour. 

 The time of the daily bowel movement obeys metabolic rhythm. Perhaps 

 the most precise response to metabolic time is found in the human infant 

 which is fed on schedule ; if this is not met, the baby cries. Woodrow ( 1951 ) 

 suggests that "time is always judged indirectly by means of some process 



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