102 
BIRDS OF NEW MEXICO 
without a moment's pause, and with thrilling speed, they dived earth¬ 
ward. Sometimes they went together as one bird, at others each bird 
steered its own course, when the air seemed full of plunging, darting, 
crazy Ibises. When about fifty feet from the ground, their reckless 
dash was checked and, on bowed wings, they turned abruptly and shot 
upward. Shortly after, like the rush of a gust of wind, we heard the 
humming sound caused by the swift passage through the air of their 
stiffened pinions" (1908a, p. 292). 
In South America near Buenos Aires, on November 16, 1920, it is 
gratifying to learn, Doctor Wetmore found nearly a thousand of the 
Ibises scattered through the flooded fields. 
Additional Literature.—Bent, A. C., U. S. Nat. Mus. Bull. 135, 52-57, 
1926.— Willett, George, and Antonin Jay, Condor, XIII, 158 and 159, 1911 
(nest). 
DUCKS, etc.: Order Anseriformes 
DUCKS, GEESE, and SWANS: Family Anatidae 
The large bills of the waterfowl are peculiarly adapted to their 
feeding habits, having flutings or teeth-like projections along the edges 
of both mandibles, which enable them to strain out their food from the 
water. Their feet are palmate or webbed in front, and their legs placed 
far to the sides of their broad bodies, making them waddling walkers 
but free swimmers. Their plumage is soft and dense with a copious 
under covering of down. The nest is on the ground, or in hollow 
stumps or trees, and the young, which hatch covered with down, follow 
the mother at once. The family is one of great economic importance 
from the food and feathers supplied by it, especially in the arctic regions 
where many of its members nest. 
References.—Bent, A. C., U. S. Nat. Mus. Bull. 126, 1923; Bull. 130, 1925 
(courtship, nesting, eggs, sequence of plumages, etc.).— Brewster, William, Bull. 
Mus. Comp. ZooL, LXVI, Part 1, 67-189, 1924.— Brooks, Allan, Auk, XXXVII, 
353-367, 1920.— Bryant, II. C., Condor, XVI, 217-239, 1914.— Cooke, W. W., 
Bull. 26, Biol. Surv., U. S. Dept. Agr., 1906 (migration).— Cory, C. B., How to 
Know the Ducks, Geese, and Swans, 1897.— Forbtjsh, E. II., Birds of Massachusetts, 
I, 173-307, 1925.— Grinnell, Bryant, and Stoker, The Game Birds of California, 
79-262, 1918.— Griscom, Ludlow, Auk, XXXIX, 31-41, 517-530, 1922; XL, 
69-80, 1923 (field identification).— Job, H. K., Among the Water Fowl, 1902.— 
Leopold, Aldo, Condor, XXI, 122, 128-129, 1919; XXIII, 85-86, 1921 (weights 
and plumages); XXVII, 8-11, 1925 (duck census); McAtee, W. L., Bull. 205, U. S. 
Dept. Agr., 1915 (duck foods); Bull. 465, U. S. Dept. Agr., 1917 (duck foods); 
Millais, J. C»., The Natural History of British Surface-feeding Ducks, 1902; Brit¬ 
ish Diving Ducks, 1913 (habits, plumage changes, etc.).— Phillips, J. C., A Natural 
History of the Ducks, 1922-26.— Saunders, A. A., Auk, XL, 526-527, 1923.— 
Taverner, P. A., Birds of Western Canada, 75-79, 1926.— Thayer, G. H., Conceal- 
ing-Coloration in the Animal Kingdom, 62-66, 1909.— Wetmore, Alexander, Bull. 
217, U. S. Dept. Agr., 1915 (mortality); Bull. 672, U. S. Dept. Agr., 1918 (duck 
sickness).— Witherby, II. F., A Practical Handbook of British Birds, 1920-1924 
(sequence of plumages, etc.).— Woodruff, F. M., Wilson Bull. XXXV, 4-20, 1923. 
