144 DENDROCYGNA ARCUATA 



In spite of its being a grazing bird, it seems to be, if one may judge from Rogeron's 

 remarks, more fond of the water than Dendrocygna viduata or Dendrocygna autum- 

 nalis, and spends at least a part of its time on that element. 



Perching. On this point also, our information is very meager. This species prob- 

 ably perches no more than do the other Tree Ducks, though Hall (Emu, vol. 9, p. 78, 

 1909) says he used to see them perching on the dead limbs of gum trees along the 

 Murray River. Doubtless they seek the shelter of trees either to roost or to nest, or 

 only when there is some definite necessity. 



Association with other Species. Although in Australia they apparently feed 

 in company with other ducks, at the approach of man or at the report of a gun they 

 are said, on rising, to separate from the others, and form into a distinct flock (Gould, 

 1865). Keartland (North, 1913) recalls having shot numbers of Dendrocygna eytoni 

 and Dendrocygna arcuata at one shot, and it is certainly true that wherever more 

 than one species of Dendrocygna occur, they are usually found closely associated. 

 Even in confinement it was noticed to prefer the company of its congeners to that of 

 other ducks (Rogeron, 1903). 



Voice. Like other Tree Ducks this species is silent except on the wing, when it 

 emits a note described by various writers as a "peculiar whistle." So far as is known, 

 the note is the same in both sexes. Rogeron's (1903) tame birds emitted what he 

 describes as a twittering note, which is probably quite different from the flocking- 

 call heard in the field. 



Heinroth (1911) describes the voice of all Tree Ducks as a peculiar "twittering 

 whistle." As has been remarked before, this genus represents the beginning stage in 

 the development of the peculiar syringeal box which reaches its highest stage in the 

 bulla ossea of the male in the true ducks. In the male of Dendrocygna arcuata the last 

 twelve tracheal rings are widened and enclose a spacious chamber about twice the 

 diameter of the rest of the trachea. In the female eleven of the tracheal rings are 

 imperfect posteriorly, being closed by a membrane, forming a modified region in 

 the trachea (Beddard, 1898). This very possibly may result in a slight difference in 

 the notes of the sexes, a difference which, however, it would be very difficult to 

 determine, on account of the similarity in plumage and size between the male and 

 the female. 



Food. Described as being primarily grass-feeders, they may, occasionally, pro- 

 cure fish, as noted by Gould (1865). In northwest Australia it was found to have 

 native millet seed, grass-seed, and grit in the crop (Mathews, Emu, vol. 10, p. 106, 

 1910). 



