THE AERIAL ENVIRONMENT 



winged Teal set free in a 25-30 m.p.h. wind made distinct into-wind loops 

 such as those characteristic of the sparrows ( Figure 8, F ) . 



This downwind drift of the blindfolded birds finds an interesting analogy 

 in the behavior of the fry of Chum Salmon, Oncorhynchus keta, as described 

 by Hoar (1953). "Chum Salmon fry emerging from gravel of the lower 

 reaches of coastal streams swim vigorously into currents and maintain their 

 position during the day — even in quite rapid water. They are lively little 

 fish and do not behave in any way like floating plankton. ... As the light 

 intensity falls, rheotactic responses, which are to a large degree dependent 

 on vision, fail, and these fish pass downstream in shoals. The fact that such 

 mass movements occur during a rather precise period of the night is prob- 

 ably due to the dark adaptation of the eye and a period of night blindness. 

 It is not necessary to assume that fish transported in this way will move at 

 the same rate as floating objects. They are active fish and as they dart to 

 and fro will move most easily and farthest with the current, and will, at 

 night, go downstream rapidly until they can again see to maintain position 

 with respect to fixed objects." For the salmon fry in darkness or the bird 

 flying blindly, the total of any movement, regardless of whether the pattern 

 is circling or otherwise, must add up to a down-current drift when the 

 eyes cannot see some stable part of the environment. 



Wing-stroke and other flight actions of the hooded birds varied accord- 

 ing to the species. In those, such as ducks, with a heavy wing load the beat 

 was rapid, strong, and deliberate. * Once a hooded duck was in flight, there 

 often was no characteristic of action distinguishing it from another flying 

 naturally with full sight. Such rapid travel was a necessity for these birds 

 if they were to remain aloft, just as the jet aircraft with its heavy wing load 

 must fly faster than the broad-winged "cub" type. In sparrows and others 

 with light wing loadings, there was a wide variation in flight action. Some 

 hooded blackbirds and sparrows flew in a natural manner; but many, es- 

 pecially among the English Sparrows, adopted a hovering flight like that 

 used by free-flying birds when alighting. 



Most of the birds in these tests were young-of-the-year taken in banding 

 traps and flown shortly after their capture. Many of the English Sparrows 

 and Yellow-headed Blackbirds still showed the yellow gape as evidence of 

 their recent departure from the nest. I was able to detect no difference be- 



* "Wing load" is the ratio between wing area and body weight. Poole (1938) has com- 

 puted wing loadings of many wild birds, showing, for example, that the English Sparrow has 

 a wing load of 3.78 centimeters per gram of body weight while the Blue-winged Teal has a 

 wing load of 1.10. 



