Vol. xxixn 



1912 



J Gross, The YeUow-biUed Tropic-bird. 67 



feathers by running its beak through its plumage. When I chanced 

 to make a noise in the observation box, the bird would suddenly 

 squat down and with an excited look peer out towards the opening 

 of the nest to see Avhat was going on. 



At night the young bird slept most of the time, but when day- 

 break came, it was all alert and very attentive to every noise which 

 in any way suggested the coming of the parent with the customary 

 breakfast.' The adult bird when it appeared uttered a peculiar 

 and characteristic "click" as it flew back and forth above the nest 

 before alighting. This call note never failed to excite the little 

 creature to the utmost. As the adult alighted at the edge of the 

 nest the young bird produced a series of guttural chirps, and braced 

 itself back on its legs and tail in preparation for receiving the long 

 expected breakfast. 



The food is transferred from the pouch-like gullet of the adult 

 to that of the young by a process of regurgitation. This transfer 

 of food is accompanied by a series of gulps, strains, and wrigglings 

 of the head and neck on the part of both birds. 



By the 40th day the young is completely feathered, but down 

 still shows about the region of the head and rump. The tail 

 feathers are now prominent and each shows a black spot near the 

 end of the vein. Ten days later the down is frayed away and the 

 plumage assumes the typical markings of the immature phase of 

 plumage. The black markings are most evident on the wing 

 coverts, scapulars, and inner secondaries, the regions which are 

 destined to become black in the adult. The bill now has a dis- 

 tinctly yellowish color, which continues to deepen to reddish- 

 orange in the older adult birds. From the 50th day (Plate XI, 

 fig. 19) to the 60th day (Plate XI, fig. 20) the black areas of the 

 coverts and secondaries become more continuous, while the black 

 barring of the crown and back become diminished, or rather ob- 

 scured, by the white tips of the growing feathers. The relative 

 proportions between the wings and the tail have undergone a 

 great change and now approach those of the adult. 



The young birds are unable to fly well when they leave the nest, 

 although the wings have been exercised very frequently for some 

 weeks. Those which I observed leaped into the water from the 

 edge of the nest and then made their way out to sea by paddling. 



