A CONTRIBUTIOX TO THE ECOLOGY OF THE ADUI.T 



HOATZIN.i 



[With 7 plates.] 



By C. William Beebe. 



INTRODUCTION. 



The strangeness of life and structure of this bird have made it 

 classic in the annals of ornithology, and because of this claim upon 

 our interest I offer the present article as a resume of our present 

 knowledge of the habits of the adult hoatzin. We are still ignorant 

 of a considerable part of its life history, although there is small 

 excuse for this, as the bird is sedentary, abundant wherever found, 

 and tame to an absurd degree. 



I have had two brief opportunities for observing this species in 

 life, once in March, 1908, on the (xuarapiche Eiver in northeastern 

 Venezuela, and again in April, 1909, on the Abary River, British 

 Guiana. On neither occasion were young birds to be found, so my 

 notes refer solely to the adults. 



Although it is not my intention to discuss the anatomy of the 

 hoatzin, mention may be made of certain peculiarities which exert 

 an important influence upon its habits and activities. 



The crop of this bird is unique in having assumed the structure 

 and importance of the gizzard in other birds. It has increased greatly 

 in size, measuring, when well filled with food, about 2^ inches in 

 diameter. The walls, instead of being flabb}^ and glandular, are 

 thick and muscular. This increase in the size of an organ situated 

 far forward in the body has resulted in a reduction of the front 

 part of the keel of the sternum, a condition unique among birds. In 

 reducing the area of attachment for the pectoral muscles this change 

 has radicallj^ affected the power of flight. 



In spite of this specialization, there is no doubt that the hoatzin 

 is an extremely ancient and isolated type, and it has very properly 

 been set aside in a separate order by itself — Opisthocomi formes (43). 

 Combining, as it does, the characters of several orders, it is impos- 



1 Reprinted by permission, after author's revision, from Zoologica ; Scientific Contri- 

 butions of the New Yorlc Zoological Society, Vol. I, Nos. 2, 3, Dec. 28, 1909, pp. 45-66. 



527 



