1.0 1.0 1.1 1.1 111111.25 ""'~ .4 111111.6 111111.25 1111,1.4 111111.6 MICROCOPY RESOLUTION TEST CI-'ART MICROCOPY RESOLUTION TEST CHART N~TlONAL SURE:'!! or STANDARDS·1953·" NATIONAL aU~E"U OF STANDARDS·1963·A ,:," ~~~~~!!!!!!!!!!~!!!!!!!!!!!!~= '~N'~BU"ll=NO.""~~ .APRIL 1939 UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. '~OOD HABITS OF NORTH AMERICAN DIVING DUCKS 1 By CLARENCE COTTAM 1ior biologist, in chame Section of Pood.llubits, DiL'ision of Wildlife Research Bureau of Bio7o[li<'al S/(,'rvey CONTENTS Page Page oduction_______________________________ _ Predominantly nnimalfeeders-Contlnued, ::onomic Importance of ducks____________ _ C langula,chus. ____________________________llistrlonlcus, and Camptorhyn·• ____ _ lrpose nnd method 01 the stud,_________ _ i3 'stomaticdticks_________________________________ position and description • __01 Old squl\\\' (Olungula hVemali.) __________ _ 73 3 llarlequin duck (l:lislrionicuJ hi.lriollicu.L 80 lomlnnntly plant leeders_________________ yrocn...__________________________________ 4 Labrador duck (Camptorhvnchu.labrado­ 4 rius) ....______ ._.•__________ ••__ ....__ __ 86 Redheud (Ngroca americana) ____________ _ 6 Eiders__ .....________ • ____ •___________ ...___ 87 Ring-necked duck (Nvroca collari&) ______ _ 14 Steller's eider (Polv.ticta slelleri) __ ._._.___ 88 Canvasback (Nvroca "alisinerial _________ 23 Northern eider (Somalcria molli..ima Greater SC.1UP duck (Nvroca marila) ____ 30 borealis) _____..__.......__ ..._...__ ...._ 93 -lsmalunna6J;.esser s9up_____________________________ duck (Xvrora affi,nisl _______ _ 38 Americnn eider (Somaleria molli..ima 46 dresseri) ___.._._______ ....____.......__ _ 95 Ruddy duck (Erismatura jamaiumi. Pacillc eider (Somaleria t~,.igra) .._______ __ 101 Tubida) ___ •__ . ______ •• ____ •_________ •___ 40 King eider (Somaltria .pectabili.) _.._..___ 105 Masked duck (Nomonvx dominicus) ______ 52 Spectacled cider (Arclonelta Ji.lChtril __ ..__ 110 tmmury 01 food 01 inland divers._________ 53 Scotors•. ___________ ..______ •__ ..........._. 113 'opagation 01 preferred plants_____________ 55 \"hite·winged scoter pIe/anitta deglantlil_ 114 lominantly animal feeders ________________ 56 Surf seoter pItlaJlitta per.picillala) _ •• ___• 12.1 )ldeneyes and bufflehead________________ _ 56 American scoter (Oidtmia americana) ..__ _ 127 American goldeneye (Glauciondla clangula 56 Summary of food of sea ducks..________ __ 131 amr.ricana) _.. ____ .... __________ .......... ______ _ Summary______________________________ ...... 133 tl5 Literature cited._____.._________•_______..__ Barrow'sdica) ________ goldenoye•_________________________ (G/aucior.dta i.lan· _ 135 Buillehead (CllaTitondta albeola) _________ 58 INTRODUCTION ECONOMIC IMPORTANCE OF DUCKS :t is difficult to owrrate the economic importance of ducks, and ioubtedly their esthetic and recreational worth is fully as great. e mergansers are sometimes conuemlled because of their fish-eating lclivities and are not hi.ghly prized as game, but most of the other cies are of great economic value. As game birds, they help main­ 1 trade in guns, ammunition, and sporting goods and bring custom trade to country hotels and boarding hOllses as ~\-el1. In the devel­ nent and maintenance of dnck clubs and shootmg preserves, com­ rce and industry are stimulated, so tllllt directly and indirectly the lting of these bi.rds affords ,Yorthwhile employment. In certai.n :ions of the country the gathering and preparation of the down of eiders is an :'}portant industry, During the pioneer und settle­ lubmlttcd for publication June 27, 1938, 1022:31o_3fl__l 1 2 TECJL'\ICAL BULLETIN 643, U. S. DEPT. OF AGRICULTURE ment days of our country waterfowl afforded an important source of fond, and they still contribute to the sust~ntation 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 (If man into their nesting territory, dralllage, 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 ~lan is to shape the environment to fit the needs of the animals con­ sidered. Food and covel' 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 "':)ecief' is to find out, by stomach analy­ ses, what is actually eaten by that species under varying circumstances and in different localities. PURPOSE Al'Io'D METHOD OF THE STUDY The Biological Survey has been engaged in food-habits studies for more than half a· century. In its Food Habits laborat.ory 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 stomacb co have been analyzed by W. L. McAtee, 'V. F. Kubichek, D. C. M.(bbOlt, ancl the writer. Reports on food habits of North American shoal-water, or river, ducks by McA.tee (57, 58) 2 and Mabbott 153) and on ducks of the genus NY?'oca by Kubichek (4-7) have bee]l published. The present bulletin 3 deals with a study of the food 1; abits of North American diving ducks, exclusive of mergansers. It is :1ased both on field studies and on the analyses of the stomach contents (including both gizzar<l and gullet) of 6,665 adults and 140 juveniles. In accordance with the standard followed for many years, the food percentages in this bulletin haye 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 or individuals of each specific item ill the stomach are recurded, the final results are expressed in percentages of volume. In general, bulk or volume per('entages have been found to bl:' much more reliable und more rapidly computed than those hased on weight. Where the items in a stomach are of sufficient volume, the "Italic numbers in parentheses refer to LltHatnre Cited, p. ]35. S Grateful acknowledgment Is made fO officials of the National Museum of Cllnada. particularly to 1'. A. Ta,erne.·. for suhmlttin; good serleR of stomachs of jun~nlle birds and of the more northern diving durkH. without which this study would have been very Incomplete; to members of the C. S. National Museum, espednlly to Panl Bartsch and William B. Marshall, of the Division of Mollusks and Cen(1zol~ ID\'ertel)ratcs, .wd to Waldo L. Schmitt. Clarence Shoemaker. "Iary .T. Rath.bul). and ,~umes O. Malonry, of tht! Division of lIIarine Inv{'rtebrates. for pX(J('rt service 10 IdentlfylO~ rlnestlonabJe mollusks and crustllcpans; and tn Phoebe Knappcn, Lois E. Grnham, and other members of F,?od Habits staff for wllllng and <,ffident assistance in compiling tabulations and comJlutlOg per~~~~~: CLARENCE.-E('ONO~!IC ORNITHOLOGY ANn TllF: CORRELATION OF' LABORATORY AND FIELD METHODS. U. S. Bur. Biol. Sun-ey Wildllfe Research and )tangt. Leallet BS-:-30. January 1936, [)Ull1eographed.] FOOD HABITS OF NOR1'H 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 or but four items and measured 5, 10, 15, and 20 mm, respecti"l"ely, they would obviously represent 10, 20, 30, and 40 percent, respectively of the food content of the par­ ticular stomach. Grayel 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 figuring the percentages, each month was considered as a unit to prevent lmdue emphasis being placed on a larger series of stomachs taken at anyone period of the year. A given month was ignored if too few stomachs were taken to make the figure representative. For marsh and aquatic plants the nomenclature adopted by Hotch­ kiss 5 has been followed. SYSTEMATIC POSITION AJ.~D DESCRIPTION OF DUCKS North American ducks are members of the family ~t\..natidae 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 11 extralimital ones, number 77. The ducks have lamellate bills, that is, the edges of both mandibles have toothlike projections that alternate above and below, interlocl-ing 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 dertrum, at the end and is more or less flattened except in mergansers, in 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 hind toe, or hallux, which is slightly elevated, is free and reduced in 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 lust almost simultaneously, during which time-a period of 3 or 4 weeks-the birds art. 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.