LIFE HISTORIES OF NORTH AMERICAN WILD FOWL 273 



southern Uruguay and Argentina, and also in South Africa and in India — 

 a very striking case of what is known as interrupted or discontinuous dis- 

 tribution. In North America the chief breeding ground of the species is in 

 Mexico, but a considerable number of birds breed in the southwestern United 

 States. The latter contingent is migratory, moving south for the winter 

 season. 



S'pring. — Col. A. J. Grayson, in his notes quoted by Mr. George 

 IS". Lawrence (1874), says: 



Although its geographical range is confined within the limits of the Tropics, 

 yet this species has its seasons of periodical migrations from one part of the 

 <?ountry to the other ; during the month of April their well-known and peculiar 

 whistle may be heard nightly as they are passing over Mazatlan in apparently 

 large flocks, going northward. At first this phenomenon puzzled me not a 

 little, as I well knew that they are not often found far north of the Tropics, 

 ■except an occasional straggler. But I was at length enlightened as to their 

 point of destination ; by frequent inquiries of the natives, I was satisfied that 

 they went no farther north than the Mayo and Yaqui Rivers, in Sonora, and 

 the adjacent lakes and lagoons, where they breed. Some, however, remain 

 and breed in the State of Sinaloa, and the adjoining localities. 



Referring to the migration in South America, W. H. Hudson 

 (1920) writes: 



Tliis duck, the well-known Pato silvon (whistling duck) of the eastern 

 Argentine country, is found abundantly along the Plata and the great streams 

 flowing into it, and northwards to Paraguay. Along this great waterway it 

 is to some extent a migratory species, appearing in spring in Buenos Aires 

 in very large numbers, to breed in the littoral marshes and also on the pampas. 

 They migrate principally by night, and do not fly in long trains and phalanxes 

 like other ducks, but in a cloud ; and when they migrate in spring and autumn 

 the shrill confused clangor of their many voices is heard from the darkness 

 overhead by dwellers in the Argentine capital ; for the ducks, following the 

 eastern shore of the sealike river, pass over that city on their journey. 



Nesting. — One of the best accounts of the nesting habits of the 

 fulvous tree duck in California is given by A. M. Shields (1899), 

 as follows : 



Starting early next morning to search a different locality, the place selected 

 was an extensive strip of high grass growing in the damp swampy ground and 

 sometimes in several inches of water. The grass was from 2 to 3 feet high, 

 of a variety commonly known as " sword " or " wire " grass, and covered an 

 area of perhaps 100 acres of low land between the deep water and the higher 

 ground a few hundred yards back. Just as we were alighting from the wagon 

 on the edge of the swampy area I saw a fulvous tree duck flying from the 

 swamp. After a few circles she dropped down among the dense grass not 

 300 yards distant, and I, not stopping to put -on my wading boots but keeping 

 my eye on the spot where she had settled, quickly approached and when with- 

 in a few yards I was delightfully shocked by a flutter of wings and the sight 

 of the old bird rising and winging a hasty retreat. I reached the nest and 

 what a thrill at the sight, there in the midst of a little vacant square of 

 4 or 5 feet was a beautifully built nest, composed entirely of grass, about 6 

 inches in height and containing 19 beautiful white eggs. I immediately saw by 

 comparison that my surmise as to the identity of the strange parasite eggs 

 found the day before was correct. 



