142 CORVUS AFFIXIS 



altogether. Often durino- this performance they would join, 

 or be joined l)y, Vultures, Eagles or Hawks, and then the 

 entire company would sail along, circling as they went, the 

 Crows cutting across the paths of their larger companions in 

 utter disregard of their movements, or without, apparently, 

 fear of a collision. While thus soaring I never noticed 

 any movement 'of the wing, the birds propelling themselves 

 onward and upward in the same mysterious manner as 

 is observed of the birds of prey, when similarly engaged." 

 This phenomenon of rising without effort, in the air, is, 

 I believe, due, to a great extent, to the bones of birds 

 being hollow and not air-tight, at least when the wings are 

 expanded, and consequently the air becomes more rarefied 

 in their bodies as they ascend, and this being warmed bj' the 

 peculiarly rapid circulation of the blood in birds, diminishes 

 their weight as they ascend. 



The species is equally abundant throughout Shoa, 

 A.b3'ssinia and Arabia, but gradually dwindles in number 

 towards Palestine, Egypt and Kordofan, where it can hardly 

 be regarded as more tlian a straggler. The types were dis- 

 covered by Riippell at Massawah and Shondi, where he 

 records them as abundant. Heuglin writes : "I once saw 

 it at Thebes, afterwards in Southern Xubia, in the oasis of 

 El Kab, at Kordofan, through the whole of Abyssinia up to 

 an altitude of 10,000 to 12,000 feet ; on the Danakil and 

 Somali coasts in large flocks in October. In general it is 

 much more gregarious in its habits than C. umhrinus and 

 C. scapulatus ; in the plains, in the mountains, and on the 

 coast it is not unfrequently seen, as also near human habita- 

 tions. In the highland it appears to breed in colonies in the 

 cliffs, and I saw large flocks circling round like Jackdaws. 

 In the flat country it is rarer, usually occurring in pairs ; and 

 it sometimes inhabits the most sterile deserts, frequenting the 

 caravan halting-places and the wells." 



