WHITE-FACED TREE DUCK 123 



so large that from ten to eighteen could be brought down at a shot. Recent investiga- 

 tors in the same region have made similar remarks (F. P. and A. P. Penard, 1908-10). 

 Swynnerton (1908) says he has seen flocks of one hundred and fifty in the air at a 

 time in Gazaland. In Paraguay Azara (1805) met with flocks of two hundred and 

 over. A. E. Brehm (1857) speaks of "veritable clouds" as occurring in the Sudan. 

 There is, however, no indication that any such numbers are ever met with on the 

 coast. They seem to be more plentiful on inland waters. 



Association with other Species. For the most part the type of country in- 

 habited by this species is not rich in true ducks, but Holub and von Pelzeln (1882) 

 saw the White-face together with Anas erythrorhyncha, on the Zambesi, and von 

 Heuglin (1873) reports it mixing with flocks of Spur-wings and Comb Ducks, in 

 northeast Africa. In Guiana, according to the Penards (1908-10), it lives in harmony 

 with the Blue-winged Teal {Anas discors). In aviary life it has little to do with 

 other ducks, and Tree Ducks of several different species may be seen standing 

 closely together, and holding disdainfully aloof from all other aquatic birds. 



Voice. In the males of this species, as with other members of the genus, there is a 

 swelling of the windpipe, representing a primitive bulla ossea, which attains its full 

 development in the males of the true ducks. In this species it is very small and 

 symmetrical. Heinroth (1918, p. 241) notes that in the female, there is, in the place 

 of the tracheal dilatation a slit covered with a membrane. At any rate, as far as 

 known the note is identical in both sexes. It consists of a clear whistle, sometimes 

 double or even triple. The note is frequently repeated while the flock is on the wing, 

 and there seems to be no variation in its character. This whistle is probably a flock- 

 call, and it is worthy of note that small numbers of birds in aviaries or ponds where 

 they cannot fly, are extremely silent. The actual sound of the voice has been variously 

 described, as follows: two whistling notes, rarely three, frequently uttered by the 

 whole flock when on the wing (Swynnerton, 1908); -pyswy, pyswy, a piercing whistle, 

 uttered constantly when on the wing (Sibree, 1892) ; three long clear whistling notes 

 different from those of Dendrocygna bicolor (P. L. Sclater and Hudson, 1889). In 

 Madagascar the native name "Tsiriry " is said to be onomatopoetic (Milne-Edwards 

 and Grandidier, 1876-81), and it is interesting to compare this with the Spanish 

 name "Quiriri." 



Food. I have been unable in the literature to find any scientific analysis of stom- 

 ach-contents, but the birds are omnivorous, and not only feed on insects, mollusks, 

 and crustaceans, but also occasionally on fish, or even prey on the rice-fields (Hart- 

 laub, 1877; Layard, 1875-84; Swynnerton, 1908). Buttikofer (1885) noted them 

 feeding on small salt-water crustaceans and mollusks on the flats left by the receding 

 tide off the coast of Liberia. They are equally fond of various vegetable seeds. 



