RED-TAILED BUZZARD. 13 



South America generally, take when surveying 

 their prey, has led me to trouble you with the 

 following remarks on the flight of raptorial birds. 



" Raptorial birds that take their quarry on the 

 ground, as we very well know, before they seize 

 their prey, attentively survey it ; keeping it in 

 view by sailing round and round it. In these 

 circumgyratory evolutions they leisurely gaze down 

 on their intended victim, and then descend circle 

 by circle, to pounce on it with a swoop. 



" The attention of birds in ordinary or direct 

 flight is immediately fixed on the objects before 

 them. The swiftness with which they shoot through 

 the air makes every visual impression indistinct 

 and evanescent on either side of them. If they 

 take wing for a distance, they rise at once high, 

 that they may command a view of the place which 

 they intend to visit ; and if they proceed to an 

 object that is near, they elevate themselves to such 

 a height only as is necessary to give them a clear 

 and direct course to where they are speeding. The 

 circular flight of raptorial birds, is therefore the 

 result of their directing their vision to the centre 

 of the gyrations they describe in examining their 

 prey, or descending upon their victims. 



" The eye of all birds is large and prominent. 

 The prominence widens the field of vision. The 

 width of the circle which the several kinds of 

 raptorial birds variously describe, I think, as a rule, 

 vdll be found to be determined by the size of 

 the head and position of the eyes, or increased 

 with the rotundity of the head of the bird. The 



