THE AERIAL ENVIRONMENT 



tween juveniles and adults in the hooded flights. Of twenty juvenile English 

 Sparrows flown in 1951 and 1952, none crashed and three remained on the 

 wing until they had circled out of sight (Table 2). 



The hooded birds generally spiraled upward to a certain elevation, then 

 leveled off to continue the downwind movement at that height. The opti- 

 mum flying level was approximately the same for all birds of a species on 

 a given day, but there were specific differences ; for example, Yellow-headed 

 Blackbirds always flew higher than English Sparrows. The flight level was 

 lowest for the English Sparrow, which mounted from twenty to fifty feet, 

 depending on the strength of the wind. In stiff winds there seldom was a 

 stable flight level; the subjects often spiraled upward until lost to sight. 

 William Carrick has suggested that this flight level depends on ground 

 turbulence, the depth of such disturbance being shallower in light winds. 



While these hooded birds were not able to orient their flight to the wind 

 when it blew without variation, they did show awareness of sudden, sharp 

 shifts in the air flow, as on a gusty day when they were met by a quick 

 change of wind from a new direction. The bird showed its awareness by 

 facing the gust. But, as after its initial thrust into the air, this moment of 

 orientation was fleeting and the circling flight was quickly resumed. 



Although unable to orient to the wind, hooded birds, especially the 

 passerines, often responded skillfully to auditory cues. When hooded English 

 Sparrows were released near a clump of willows in which wild companions 

 chirped, they flew directly toward these voices without circling. A Red- 

 winged Blackbird released near trees where wind whistled in the branches 

 flew directly toward this grove, crashing therein. If we talked loudly during 

 a hooded flight or whistled or made other noises, the hooded birds often 

 faced abruptly in our direction. 



Of birds which accomplished successful 

 flight, only 20 per cent of those we saw 

 come to earth descended with a hard crash. 

 Most of the birds either spiraled down 

 gently at a shallow angle, or "parachuted" 

 with hovering wings. If parachuting, the 

 bird showed its awareness of descent by 

 thrusting its legs forward in landing atti- 



Figure 9. Direction of landings relative to the 

 wind as observed in 51 hooded flights, 1950 



