306 



ZOOLOGY. 



years, as proved by Spallanzani) return, young and old. sue - 

 naively to the place where they were produced, the young 

 building their nests in tin- vicinity of those of their parents. 

 Spallanzani removed a couple of swallows in a cage from the 

 nrst whnv they \\viv hatching from Pavia to Milan ; on being 

 let loose they returned in thirteen minutes to their young. 



445. The instinct of sociability has also been alluded 

 to ( 329, 330, 339), an instinct, however, which prevails 

 mostly with insectivorous or granivorous birds. Birds of 

 prey are generally solitary or live only in pairs. 



446. Birds differ also in the manner in which they pro- 

 cure their food : some search for it by day, others by night, 

 and some by twilight; and of these latter, it is sufficiently 

 remarkable that they are of a sombre colour, with downy 

 pinions, so that they strike the air without any noise. To 



Fig. 255. GypaSte, or the Lamb-Slaying Vulture. 



this class belong the owl and goat-suckers, &c. ; their habits 

 and structure are strictly in unison. 



447. The species known to naturalists amount to seven 

 thousand, and their classification is difficult by reason of the 

 great uniformity of their structure. Their distinguishing 

 characters, as being in relation with their rfyime, have been 

 taken chiefly from the conformation of the bill and legs. 

 Cuvier, whom we follow, divided them into six orders, 

 namely, rapacious birds, passerines, climbers, gallinaceous 

 birds, waders, and palmipeds. 



J448. The rapacious birds or birds of prey are recog- 

 by their claws, their robust, short, and powerful hills. 

 and the strength of their legs. Their aspect denotes tln-ir 



