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 T'enuirostres, 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 Hirundinide, 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. 
Their 
VOL. XIV. 2X 
