that connect the Orders and Families of Birds. 427 



§ 1. FiSSIROSTRES. 



The families which compose the first tribe are distinguished 

 from those of all the others, except the Tenuirostres, by their habit 

 of feeding on the wing. From the latter, or the Suctorial Birds, 

 which meet them at one of the extremes of the tribe, and of which 

 the typical families feed also on the wing, they are distinguished 

 by their animal food, which they take by their bills, or in the 

 gape of their mouths; while the Tenuirostres live chiefly upon 

 vegetable juices, which they extract with their tongue. The Fis- 

 sirostres, depending so much on the powers of their wings, exhi- 

 bit a proportional deficiency in the strength of their legs. These 

 members are not only shorter and weaker than in the other Perch- 

 ers, (the typical families of the Tenuirostres here again being ex- 

 cepted, which correspond with them in this particular also,) but 

 they have their external toes in general to such a degree united 

 with the internal, — for the most part as far as to the second pha- 

 lanx, — that they are deprived of the free play of the joint : and 

 the bird is thus rendered nearly incapable of using its legs in walk- 

 ing, or for any purpose besides that of mere perching. But even 

 in this particular a group of the typical family appears deficient : 

 for the toes of the genus Cypselus being all placed in front, seem 

 to assist the bird only in suspending itself, where other birds would 

 perch. All the families of the tribe are again united by a striking 

 conformity in their mode of nidification. They deviate from the 

 manners of the Perchers in general, in forming their nests on the 

 ground; or if, like some of the Hirumlinida, they choose elevated 

 situations for that purpose, they build up the exterior of their 

 nests with earth cemented into a solid substance, and thus pre- 

 serve a similarity in their construction to those nests which are 

 actually formed on the ground. The two typical groups of this 

 tribe may be observed to be separated from the other three 

 by the shortness of their bills and the wider gape of the mouth. 



VOL. XIV. 3 K Their 



