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Food Habits North American Ducks

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Food Habits North American Ducks i% mf'ii'àMfem»^,'-' ■ APRIL 1939 />^'-c^ \>'- . FOOD HABITS NCVl NORTH AMERICAN DUCKS By CLARENCE COTTAM Senior Biologist, in Charge Section of Food Habits Division of Wildlife Research, Bureau of Biological Survey UNITED STATES DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C. For sale by the Superintendent of Documents, Washington, D. C. ----------____ Price 30 cents TECHNICAL BULLETIN NO. 643 APRIL 1939 UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. FOOD HABITS OF NORTH AMERICAN DIVING DUCKS ^ By CLARENCE COTTAM Senior Mologist, in charge Section of Food HaMts, Division of Wildlife Research Bureau of Biological Survey CONTENTS Page Page Introduction __ 1 Predominantly animal feeders—Continued, Economic importance of ducks Clangula, Histrionicus, and Camptorhyn- Purpose and method of the study chus 73 Systematic position and description of Old squaw ( Clangula hyemalis) 73 ducks Harlequin duck (Histrionicushistrionicus). 80 Predominantly plant feeders Labrador duck (Camptorhynchus labrado- Nyroca rius) Redhead (Nyroca americana) Eiders 87 Ring-necked duck (Nyroca collar is) Steiler's eider (Polysticta steileri) Canvasback (Nyroca valisineria) Northern eider (Somateria mollissima Greater scaup duck (Nyroca marila) borealis) Lesser scaup duck (Nyroca affinis) American eider (Somateria mollissima Erismaturinae.- dresseri) 95 Ruddy duck (Erismatura jamaicensis Pacific eider (Somateria v-nigra)... 101 rubida) King eider (Somateria spectabilis) .._ 105 Masked duck (Nomonyx dominicus) Spectacled eider (Arctonetta fischeri) 110 Summary of food of inland divers Scoters 113 Propagation of preferred plants White-winged scoter (Melanitta deglandi). 114 Predominantly animal feeders 56 Surf scoter (Melanitta perspicillata) 121 Goldeneyes and buflBehead 56 American scoter (Oidemia americana) 127 American goldeneye (Glaucionetta clangula Summary of food of sea ducks 131 americana) 56 Summary 133 Barrow's goldeneye (Glaucionetta islán- Literature cited — 135 dica) -_ 65 Buflaebead ( Charitonetta albeola) 68 INTRODUCTION ECONOMIC IMPORTANCE OF DUCKS It is difficult to overrate the economic importance of ducks, and undoubtedly their esthetic and recreational worth is fully as great. The mergansers are sometimes condemned because of their fish-eating proclivities and are not highly prized as game, but most of the other species are of great economic value. As game birds, they help main- tain trade in guns, ammunition, and sporting goods and bring custom or trade to country hotels and boarding houses as well. In the devel- opment and maintenance of duck clubs and shooting preserves, com- merce and industry are stimulated, so that directly and indirectly the hunting of these birds affords worthwhile employment. In certain sections of the country the gathering and preparation of the down of the eiders is an important industry. During the pioneer and settle- 1 Submitted for publication June 27, 1938. 102231°—39 1 1 2 TECHNICAL BULLETIN 643, U. S. DEFT. OF AGRICULTURE ment days of our country waterfowl afforded an important source of food, and they still contribute to the sustentation of the aborigines of far northern regions. Formerly the food value of waterfowl taken in the United States reached several million dollars annually. The recent precipitous decline in the abundance of waterfowl has been alarming. Drought, encroachment of man into their nesting territory, drainage, reclamation, overshooting, and perhaps the in- crease of crows on their nesting grounds are some of the factors responsible. It is hoped that the present efforts toward restoration and conservation will halt this decline and cause a return of the birds to more satisfactory numbers. One of the fundamentals of any restoration and game-management plan is to shape the environment to fit the needs of the animals con- sidered. Food and cover are the primary essentials. The fallibility of field observation alone in determining what is taken as food by various forms of wildlife has been demonstrated innumerable times to workers in economic biology. The only safe guide in ascertaining the food requirements of any species is to find out, by stomach analy- ses, what is actually eaten by that species under varying circumstances and in different localities. PURPOSE AND METHOD OF THE STUDY The Biological Survey has been engaged in food-habits studies for more than half a century. In its Food Habits laboratory it has accumulated great numbers of stomachs, including gizzards and gul- lets, of birds of many groups, many of which have been examined. An appreciable number of diving duck stomachs have been analyzed by W. L. McAtee, W. F. Kubichek, D. C. Mabbott, and the writer. Reports on food habits of North American shoal-water, or river, ducks by McAtee {57, S8)^ and Mabbott (SS) and on ducks of the genus Nyroca by Kubichek (^7) have been published. The present bulletin ^ deals with a study of the food habits of North American diving ducks, exclusive of mergansers. It is based both on field studies and on the analyses of the stomach contents (including both gizzard and gullet) of 6,665 adults and 140 juveniles. In accordance with the standard followed for many years, the food percentages in this bulletin have been computed by the volumetric method, described by the writer * as follows : When the individual stomach examination is completed, the results are tab- ulated on a card and filed systematically. While the numbers of occurrences of individuals of each specific item in the stomach are recorded, the final results are expressed in percentages of volume. In general, bulk or volume percentages have been found to be much more reliable and more rapidly computed than those based on weight. Where the items in a stomach are of sufficient volume, the 2 Italic numbers in parentheses refer to Literature Cited, p. 135. ^ ^ ^ 3 Grateful acknowledgment is made to officials of the National Museum of Canada, particularly to P. A. Taverner, for submitting good series of stomachs of juvenile birds and of the more northern diving ducks, without which this study would have been very Incomplete; to members of the U. S. National Museum, especially to Paul Bartsch and William B. Marshall, of the Division of Mollusks and Cenozoic Invertebrates, and to Waldo L. Schmitt, Clarence Shoemaker, Mary J. Rathbun, and James O. Maloney, of the Division of Marine Invertebrates, for expert service in identifying questionable mollusks and crustaceans ; and to Phoebe Knappen, Lois E. Graham, and other members of Food Habits staff for willing and efficient assistance in compiling tabulations and computing percentages. 4 COTTAM, CLARENCE.—ECONOMIC ORNITHOLOGY AND THE CORRELATION OF LABORATORY AND FIELD METHODS. U. S. Bur. Biol. Survey Wildlife Research and Mangt. Leaflet BS-30. January 1936. [Mimeographed.] FOOD HABITS OF NORTH AMERICAN DIVING DUCKS 3 components are usually measured in a vial of appropriate size and computed on the basis of 100 percent. If, for example, the stomach contents consisted of but four items and measured 5, 10, 15, and 20 mm, respectively, they would obviously represent 10, 20, 30, and 40 percent, respectively of the food content of the par- ticular stomach. Gravel is frequently found, and among certain species of waterfowl it is usually greater both by weight and volume than the food. It is therefore, first computed as a percentage of the total stomach content, then' the food proper, after excluding the gravel, is computed also on the basis of 100 percent. In fio-uring the percentages, each month was considered as a unit to prevent undue emphasis being placed on a larger series of stomachs taken at any one period of the year. A given month Avas ignored it too few stomachs were taken to make the figure representative. For marsh and aquatic plants the nomenclature adopted by Hotch- kiss ^ has been followed. SYSTEMATIC POSITION AND DESCRIPTION OF DUCKS North American ducks are members of the family Anatidae of the order Anseriformes. This order includes about 230 species and varie- ties of birds that inhabit all parts of the world, of which North American species, including 17 extralimital ones, number 77. The ducks have lamellate bills, that is, the edges of both mandibles have toothlike projections that alternate above and below, interlocking when closed to form an effective sieve that enables the birds to strain out from the water the necessary food items, often including rather minute plants and animals. The bill has a distinct nail, or clertruin, at the end and is more or less flattened except m mergansers, m which it is rather slender and rounded and toothed. The tongue is thick and fleshy, with a naillike or horny tip, and is fringed along the edges. The three front toes are fully webbed, but the hmd toe, or hallux, which is slightly elevated, is free and reduced m size. Most species of ducks go through an incomplete postnuptial molt in midsummer. All flight feathers (except the inner secondaries) and all tail feathers are lost almost simultaneously, during which time—a period of 3 or 4 weeks—the birds are flightless and the males are said to be in eclipse plumage, as they lose their brightly colored dress and approximate the plumage of the females. There is considerable diversity in the nesting habits of the various species. Although most of them build their nests hi marshes or on the adjacent uplands, a few nest in stumps or holes in trees. The eggs are plain white, buffy, or olive in color and oval in shape. The young are eminently precocious, leaving the nest as soon as hatched. Most of our ducks, including all the more highly prized game spe- cies, are more or less migratory, although individuals of certain spe- cies may be found in a given locality at all periods of the year. Evi- dence indicates that in their flight the birds adhere more or less to their ancestral fly ways. In distribution they are found from the ice- bound arctic regions to tropical Mexico and Central America, and even to South America, where three species occur.
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