1912 J Gross, The Ydlow-hiUed Tropic-bird. 71 



The feathers of the head are beginning to show through the skin. The 

 white hair-hke feathers of the auricular region now measure about 0.8 cm. 

 in length, but are hidden from view by the mass of down on the sides of 

 the head. 



Fig. 18. Young Tropic-bird. Age about 37 days; length 31.5 cm.; 

 tail 4.5 cm.; extent 60.2 cm.; wing 13.1 cm.; bill 38 cm.; foot 6.2 cm.; 

 weight 377 grams. Except for a slight advance in development of plumage, 

 the description of the bird shown in fig. 17 will also apply to this 

 one. This figure, however, shows the plumage of the head and breast to 

 much better advantage. Feathers now completely hide the black skin 

 at the base of the upper mandible, and lores, which were devoid of feathers 

 and down until the 20th day of development. The black loral spot, 

 which is present in the adult, is here distinctly differentiated from the 

 white and its appearance forms an important epoch in the development 

 of the plumage. 



Plate XI. 



Fig. 19. Immature Tropic-bird. Age about 52 days; length 40.6 

 cm.; tail 11.2 cm.; extent 82.4 cm.; wing 22.2 cm.; bill 4.4 cm.; foot 6.5 

 cm.; weight 497 grams. The primarj' covering of down is completely 

 replaced by the plumage of the advanced immature bird when the young 

 attains the age of 50 days. This view was taken to show the black mark- 

 ings of the feathers of the flanks, back, and head. The bill now has a pale 

 yellowish color. 



Fig. 20. Immature Tropic-bird. Age about 60 days; length 42.6" 

 cm.; tail 13.7 cm.; extent 86.1 cm.; wing 24.6 cm.; bill 4.6 cm.; foot 6.6 

 cm.; weight 467 grams. This figure shows the bird in the final and splen- 

 did development of body and plumage which it attains before leaving the 

 nest. To acquire the plumage of the adult only slight modifications are 

 necessary, viz. : the disappearance of the black bars of the crown and upper 

 parts of the body and the condensation of the black areas in the region of 

 the wing coverts and secondaries. Two days later, at 62 days of age, 

 this bird left the nest. 



