FRIGATE-BIRDS. 



183 



on its head, to draw out the long tail-feathers. It resents this insult by screaming and 

 snapping, but never tries to escape by flying or shuffling along the ground ; in fact, 

 like all birds which have their legs placed so far behind, they cannot rise off a flat 

 surface, but require a drop of a few feet to give them an impetus." Where rocks are 

 wanting, however, the tropic-bird breeds in trees. The same gentleman, during a 

 mountain ascent on one of the Seychelles, observed a yellow-billed tropic-bird (P. 

 flavirostris) enter a hole in the stump of a dead tree. " On returning," he says, " I 

 made for it. After a scramble over dead wood and granite boulders, I got to it. The 

 hole was about fifteen feet from the ground, and my man soon ascended, not, however, 

 without fears on my part that the rotten old stem would come down with his weight. 

 Unfortunately there was only a young bird inside it. This I took home and endeav- 

 ored to rear, but it only lived four days." The young is cov- 

 ered with pure white down, and consequently is very unlike the 

 downy youngs of the Laridas. The chick, like that of all the 

 members of the order, is reared in the nest, or rather on the spot 

 where the egg was hatched, until able to fly. 



Only three species are known, the two above mentioned, 

 and the red-billed, white-tailed P. cethereus, which is the species 

 represented in our wood-cut. 



In Fig. 89 is shown one of the more obvious characters of the 

 FREGATOIDE^E, namely, the remarkably short tarsus, the short- 

 ness and breadth of which is absolutely unique amongst the Euor- 

 nithes. It is only equalled by the corresponding bone of the pen- 

 guins, in which, however, the three component metatarsals are 

 nearly separated, and equally well developed. On the whole, the 

 foot of the frigate-bird is short, and abnormally developed, for 

 the " webs " are so deeply excised that they hardly deserve their 

 name, and the tarsus is feathered to the legs and feathered to the 

 toes, a very extraordinary feature in a " water-bird," it being, in 

 fact, the only one among all the birds so designated that exhibits 

 this character. The abnormal ratio of the phalanges of the middle 

 toe has already been mentioned. 



The wings are hardly less remarkable, since the cubitus is 

 longer than the upper arm bone by one third of its length ; and 

 as the humerus itself is very long, the stretch of the wings becomes quite excessive in 

 proportion to the size of the body. In regard to the breast-bone we remark that the 

 hind border is described as truncate, without any notches or lateral processes. Peculiar 

 to Fregata is also the fact that there is no interval between the lumbar and caudal ver- 

 tebrae, as the transverse processes are continuously developed throughout these verte- 

 bras. As to the pelvis, it may be remarked that the ilia do not meet together medianly in 

 front of the acetabula at all, as they do in both the other super-families. The caudal 

 vertebrae have very strong transverse processes, and the external tail is long and very 

 forked. In many other external characters the frigate-birds show affinities to the 

 cormorants ; for instance, in the shape of the bill, which is composed of several pieces 

 separated by grooves, ending in a strongly-hooked nail, in the naked gular pouch, and 

 also in the pectination of the claw of the third toe. The pterylosis approaches that of 

 the cormorants, but is peculiar on account of the remarkable sparse arrangement of the 

 contour feathers. 



FIG. 89. Leg bones of 

 Fregata aqu'ila, from 

 the knee, tb, tibia ; 

 mts, tarso-metatarsus. 



