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Home , Canvasback, Chara (alga), Greater scaup, Lesser scaup, Redhead (bird)

FOOD HABITS OF , REDHEADS, AND IN

JAMES C. BARTONEK

Northern Prairie Wildlife Research Center Bureau of Sport Fisheries and Wildlife Jamestown, North Dakota 58401

AND

JOSEPH J. HICKEY

Department of Wildlife Ecology University of Wisconsin Madison, Wisconsin 53706

The purpose of this paper is to present in- Mum-o 1941: 135; Yocom 1951: 174; Collias and formation on food habits of 175 Canvasbacks C&as 1963:7). ( ualitin&u), 99 Redheads (A. urn&- Cottam ( 1939)) in his presentation of the cuna), and 71 Lesser Scaup (A. @finis) col- food habits of North American diving , lected in southwestern Manitoba during the summarized the data accumulated by the late spring, summer, and early fall, from 1959 Bureau of Biological Survey over many years, to lQ64. Primary emphasis is on juveniles and Much of the published information on food spring- and summer-collected adults. habits of Canvasbacks, Redheads, and Lesser Studies of food habits lead to a better under- Scaup has been based wholly or partly on standing of a species ’ environmental and nutri- these data (Phillips 1911, 1925; McAtee 1917, tional requirements, its diseases caused by 1939; Preble and McAtee 1923; Kubichek 1933; parasitic infestation and food poisoning, its Gabrielson and Jewett lQ40; Martin et al. role in the biological transportation or con- 1951) * centration of environmental contaminants, and its economic relationship with man. Relatively COLLECTING AREAS IN little waterfowl food-habit information is SOUTHWESTERN MANITOBA based upon juveniles and adults collected during the summer; most information of this The ducks used in this study were collected primarily is based upon collected during from the following areas in southwestern Manitoba. either the season, winter, or early Minnedosa-Erickson pothole area. Located mainly within the aspen parkland but extending into the spring. prairies, the Minnedosa-Erickson area with its numer- Information on the food habits of adult ous ootholes (kettle-hole oonds and ) and as- Canvasbacks, Redheads, and Lesser Scaup on sociated upland woods, pastures, and cereal crops their breeding grounds is very limited. Cottam provides some of the most productive, unmanaged, waterfowl nesting remaining in . ( 1939) summarized food habits of many Can- Canvasbacks. Redheads. and Lesser Scauo use this vasbacks, Redheads, and Lesser Scaup taken area primarily for breedmg and nesting. None of the throughout the year, but sexual, seasonal, and adults, both male and female, of these three species regional differences could not always be were known to have remained on the potholes during their postnuptial molt. Descriptions of this area and evaluated. Yocom (lQ51:172-176) and Keith its use by waterfowl were given by Evans et al. (X%1:34) examined a combined total of 2 (1952:216), Dzubin (1955:2&l), Kiel (1955: Canvasbacks, 12 Redheads, and 9 Lesser Scaup l&I-190), Rogers (1959:218), and Stoudt (1962- collected during the summer; however, they 64). The general ecology of the aspen parkland was lumped these data in with data from other described by ( 1961) . Delta- Francis . The two adjacent and species and, in doing so, obscured possible somewhat similar marshes of Delta and Lake Francis interspecific differences. Specific data on are located between Lake Manitoba and the fertile foods of adults during spring and summer are aericultural lands of the Portage la Prairie olain. The Delta is important to Canvasbacks,*Redheads, available for 6 Canvasbacks, 1 , and and Lesser Scaup as a breeding area and a stopover 51 Lesser Scaup (Pirnie 1935308, 310; Munro during spring and fall migration, but it is relatively 1941: 134-137; Erickson 19448:282; Rogers and unimoortant as a molting area ( Hochbaum 1959). Korschgen X%6:2.59-261). Published data on Hochbaum (1959:3-12)-and Olsen (1959:49-41) described the general ecology of the Delta marsh, juveniles are available for 9 Canvasbacks, 8 Love and Love ( 1954) described its emergent vegeta- Redheads, and 32 Lesser Scaup (Cottam 1939; tion, and C&as and Collias (1963:%13) presented

The Condor, 71:289-290,1969 [2801 FOOD HABITS OF CANVASBACKS, REDHEADS, AND SCAUP 281 data on some invertebrates that were potential foods adult males, which were high in for waterfowl. material (table 1). Indexes of Similarity Lake Winnipegosis. Lake Winnipegosis is a large ( Curtis 1959: 82-83) were used to compare (5200 km2), shallow (8-m mean depth), eutrophic lake lying within the southern edge of the boreal diets among the various groups of birds. An forest. This lake is important to Canvasbacks, Red- I S value of 1.00 would indicate that diets were heads, and Lesser Scaup as a stopover during the identical, while a value of 0.06 would indicate spring and as both a stopover and a staging area that diets had nothing in common. We com- during the fall; in July and August, Redheads use it as a molting area (Bartonek 1985:1&19). All pared “per cent of volume” of the items in three species nest here to a limited extent. The the esophageal material and obtained I S Manitoba Department of Mines and Natural Re- values of 0.32 for juveniles and female adults, sources, the Wildlife Management Institute, the U.S. 0.03 for juveniles and male adults, and 0.09 and Wildlife Service ( 1948), and McLeod and for female and male a,dults. Corresponding Bondar (1953:%4) described the lake; Bajkov ( 1930) listed its plankton and bottom fauna. values determined from esophagus-proventric- &s-gizzard contents were 0.52,0.13, and 0.25. METHODS I S values are highest in this latter group of comparisons because these food materials con- Of the 345 ducks used in our analyses, 331) were shot tained items common in most ducks, i.e., hard- and 15 were drowned in gill nets of commercial fish- ermen. Prior to 1983 we placed most of the birds, coated seeds that tend to be retained by the immediately after collecting, in ice until they were gizzard. autopsied or could be frozen. In 1963 and 1964 we Mostly immature aquatic and minimized the effects of post-mortem digestion of foods by either injecting digestive tracts with Formalin, various gastropods (Lymnaeidae, Physidae, or removing the tracts and placing them in Formalin and Planorbidae) formed 87 per cent of the immediately after collection. The various foods were volume of foods found in the esophagi of identified, segregated, and volumetrically measured juvenile Canvasbacks (table 1) . Trichoptera while wet by water-displacement. Grit was analyzed separately from foods. Because of biases resulting larvae and cases, Tendipedidae larvae, pupae from food digesting at different rates in certain parts and an occasional adult, and Ephemeroptera of the upper digestive tract, we analyzed the contents nymphs were the most abundant insects of the esophagus separately from that of the ac- companying proventriculus and gizzard. Dillon ( 1958: found in these young birds. Zygoptera and 114) recognized that “gullet material reflects recent Anisoptera nymphs, Corixidae nymphs and consumption and stomach material may distort the adults, Haliplidae and Dytiscidae larvae and importance of some hard seeded .” We noted adults, Stratomyidae larvae, and an adult Mal- that data on certain invertebrates are similarly dis- torted and that the composition of most foods found lophaga were the remaining insects, and in the esophagus is significantly different from the totaled only one per cent. Other invertebrates composition in either the proventriculus or gizzard. (Hirudinea, cladoceran ephippia, ostrocods, Because many of the earlier waterfowl food-habit studies included the proventriculus and gizzard in arachnids, etc. ) formed less than one per cent their analyses, the esophagus-proventriculus-gizzard volume. Consumption of Zannichelliu pa2uztri.v data and the preferred esophageal data are presented nutlets by two flying juveniles accounted for for comparative purposes. “Per cent of volume” (the “aggregate volume method” of Martin et al. 1946) and 62 per cent of the plants found in esophageal “per cent of occurrence” are used in presenting these material from the juvenile sample, and unduly data. “Percentage of bulk method” data (the “ag- influenced the values of both Zannichelliu and gregate percentage method” of Martin et al. 1946) the total plant material. Oogonia and vegeta- were used to compare our findings with those of others who had used this method of analvsis. tive branches of Cham, tubers and rootstalks of Potamogeton pectinatus, and seeds and vegeta- FOOD HABITS OF CANVASBACKS tive parts from numerous emergent and sub- emergent species formed the remainder of the The spring-summer food habits of Canvas- plant material in the esophagi. backs were determined from 120 juveniles col- lected between mid-June and the first of Sep- As juvenile Canvasbacks grow older, they tember and from 42 adults collected between rely less and less upon food. By fall May and the end of August. Fall food habits their diet and that of adults consist primarily were determined from 13 birds collected in the of plant material (table 2). The percentage last part of September and in October during (aggregate percentage method) of animal the hunting season. material found in the esophageal contents of During summer, food habits of juvenile birds aged 0 to 5 weeks was 99 * 1 (95% and adult female Canvasbacks were similar C.L.); at 5 to 9 weeks of age, 66 -‘ 11; and at in their high percentages of invertebrates flying time, but before the fall hunting season, and differed appreciably from those of only 38 f 22. 282 JAMES C. BARTONEK AND JOSEPH J. HICKEY

TABLE 1. Foods from Canvasbacks collected during the spring and summer in southwestern Manitoba.

% Occ”rrence % aggregatevol. Sourceof material Juve- Adult Adult Juve- Adult Adult Food item Common name (part of type) nil.3 female male nile female male

Esophageal contents (n) (86) (16) (13) (86) (16) (13) Zannichellia sp. Horned pondweed (nutlets) 8 spp. Muskgrass (oogonia, vegetative) : 6 2 tr. Pot0mogeton spp. Pondweeds (tubers) 12 44 62 1 7 95 Other plants Various seeds 45 25 46 2 tr. tr. Misc. vegetative parts 34 15 tr. 2 Total plant material 73 756 160 : 8 98

Trichoptera Caddis flies ( larvae, cases ) 53 44 59 10 snails 38 18 66 Tendipedidae Midges (larvae, pupae) :? 31 31 8 2 2 Ephemeroptera Mayflies (nymphs) 6 6 1 13 Misc. Insecta Misc. aquatic insects 26 12 1 tr. Other Other aquatic invertebrates Total animal material :: 88 92 2

Esophagus-proventriculus-gizzard contents (n) (23) (IQ) Potamogetonspp. Pondweeds ( tubers. winter buds) 13 81 Pondweeds ( nutlets ) 52 87 79 2 6 4 Zannichellia sp. Horned pondweed (nutlets) 2 4 Chara spp. Muskgrass (oogonia, vegetative) 8 9 4 2 Scirpus spp. Bulrushes (achenes) 83 87 79 3 4 3 Ceratophyllum.sp. Coontail (nutlets) 11 17 16 3 tr. tr. Carex spp. Sedges (achenes, perigynia) 32 35 63 1 : tr. 2 M yriophyllum sp. Water milfoil (nutlets) 43 87 79 tr. 1 Chenepodium sp. Lambs-quarter ( utricles) 5 9 21 tr. tr. : Miscellaneous Various seeds 31 52 58 1 1 tr. Vegetation 33 17 32 Total plant material 98 100 100 g g &

Trichoptera Caddis flies ( larvae, cases) 72 61 37 61 24 1 Gastropoda Pond snails 22 30 10 33 Tendipedidae Midges (larvae, pupae) 34 44 37 4 5 3 Odonata Damselflies, Dragonflies ( nymphs ) 16 17 1 tr. Ephemeroptera Mayflies ( nymphs ) 8 4 1 8 Other animals Misc. aquatic invertebrates 39 9 11 1 1 tr. Unidentified animal material 12 17 Total animal material 91 91 58 7; 732 4

Cottam (19.39:30) examined eight juveniles per cent was animal (table 1). Lymnaeidae from Alberta and . Three older snails formed 99 per cent of the gastropods. birds, taken in September but still flightless, Immature forms of Trichoptera, Ten,dipedidae, had fed almost entirely upon Potumogeton and Ephemeroptera, and Zygoptera comprised the [email protected], while animal material comprised 56 remainder of the animal food and 26 per cent per cent of the food found in the five younger of the esophageal contents. Ephippia of ducklings. Percentages of the more important cladocerans, corixids, Haliplidae adults and food items found by Cottam were: Potumoge- larvae, and arachnids were the “miscellaneous ton, 37; Scirpus, 5; Sparganium, 7; Myriophyl- invertebrates” found in the esophagus-proven- lum and Hippuris, 4; Trichoptera, 19; Corixi- triculus-gizzard contents. Potamogeton pectin- dae, 8; Coleoptera, 4; and Tendipedidae atus tubers were utilized by the females, but larvae, 2. In comparing our data with Cottams’ not as extensively as by the adult males. Mis- but excluding both miscellaneous and un- cellaneous plant items included Lemma identified materials in the comparison, we ob- trkulca, segments of Myriophyllum ex- tained an I S value of 0.47. Yocom ( 1951:174) albescens, and the seeds of Sparganium,, reported that a juvenile collected Hordeurn, Eleocharis, Rumex, and Ranunculus. at the end of July in Washington had fed Apparently, animal material forms the bulk entirely upon Ruppiu ma&ma and Potamoge- of the adult females ’ diets during nesting, in- ton spp. cubation, and brood-rearing, but plant material Of food found in the esophagi of adult later increases in importance. female Canvasbacks during spring-summer, 92 Adult male Canvasbacks consumed pri- FOOD HABITS OF CANVASBACKS, REDHEADS, AND SCAUP 283

TABLE 2. Foods from Canvasbacks collected in late September and early October during the hunting season in southwestern Manitoba.

Yo source of material % aggregate Food item Common name (part or type) occurrence VOl.

Esophageal contents (n) (7) Potamogeton spp. Pondweeds (tubers) (;il) 71 Chara spp. Muskgrass (vegetative) 14 5 Myriophyllum sp. Water milfoil (nutlets) 14 1 Other plants Misc. vegetative parts and seeds 14 1 Total plant material 100 78

Ephemeroptera Mayflies (nymphs) 14 18 Zygoptera Damselflies (nymphs) 14 3 Other animals Misc. aquatic invertebrates 29 1 Total animal material 29 22 Esophagus-proventriculus-gizzard contents ( n ) y 0; ’ Potamogeton spp. Pondweeds (tubers, winter buds) Pondweeds (nutlets) 92 20 Scirpus spp. Bulrushes ( achenes ) 62 4 Charu spp. Muskgrass (vegetative) 15 4 Myriophyllum sp. Water milfoil (nutlets, vegetative) 38 1 Other plants Various seeds 23 1 Unidentified vegetative parts 8 5 Total plant material 199 86

Ephemeroptera Mayflies (nymphs) 8 12 Zygoptera Damselflies ( nymphs ) 8 1 Other animals Misc. aquatic invertebrates 15 1 Total animal material 15 14 marily ( Q7 per cent) the vegetative parts and larvae and cases, were taken primarily during nutlets of Potamogeton, the tubers being summer; mollusks were taken primarily during mainly utilized (table 1) . Although animal winter. Najadaceae (pondweeds) formed 33 matter was found in four males, it comprised per cent of the summer foods. Preble and only two ’ per cent of the esophageal food items. McAtee ( 1923:47) reported that an adult male Sexual differences in food habits, as ob- Canvasback, collected in the Pribilof Islands served between adult male and female Can- in May, had fed exclusively upon Trichoptera vasbacks during summer, have not previously larvae and cases. Erickson ( 1948:282) ex- been reported. Only once before has this amined six spring migrants that died from lead aspect of waterfowl food habits been ex- poisoning and found Scirpw acutus and amined, i.e. for the , ATULSpbyrhyn- Potamogeton pectinatus fruits in limited quan- chos (Perret X%2:36-39). Although the rea- tities. son for this difference is unknown, a high If todays’ information on the food habits of protein diet simply may not be a necessity for Canvasbacks throughout their range had been the adult males. available to Alexander Wilson, he might well The food found in Canvasbacks collected have named them Anas‘ potamogeton” in- during the hunting season was similar to that stead of “A. disineriu.” The published reports, in adult males collected during the spring and which are either reviewed subsequently or summer (I S = 0.71; table 2). Vegetative listed in table 3, indicate that potamogetons parts of aquatic plants, especially tubers of and other Najadaceae are more important to Potamogeton pectinatuz, formed 77 per cent Canvasbacks than is the much acclaimed Vab of the esophageal material. One juvenile male lisneria americana. Stewart (1962:51, 17& Canvasback, shot’ in late September on the 173) reported the food habits of 86 Canvas- Delta Marsh, contributed 21 of the total 22 per backs taken from the Chesapeake region of cent of animal material for esophageal con- Delaware and between October and tents and 13 of the 14 per cent of esophagus- March. Combining Stewarts’ findings from proventriculus-gizzard contents. four different areas, the “percentages of OC- Cottam (lQ39:24-29) found that animal currence” for Najadaceae species were: matter comprised 21 per cent of the food con- Potamogeton vegetative parts, 28, and fruit, sumed by birds collected during April, May, 31; Zostera marina vegetative parts, 13; Rup- June, and September (48 “stomachs”). Insects, piu ma&ma vegetative parts, 6, and fruit, nearly two-thirds of which were Trichoptera 8; and Naia.s vegetative parts, 1. Vallisneriu 284 JAMES C. BARTONEK AND JOSEPH J. HICKEY

TABLE 3. Quantities of Potumogeton.spp., other Najadaceae, V&.m&a americcmta, and total plant material found in Canvasbacks (esophagus-proventriculus-gizzard content), as presented in reports involving 10 or more birds.

% vol. or (% occurrence) Other Reference Potamo- Naja- VtZUis- Total Location N Season geton daceae neria plants 26 states, 5 provinces 427 Sept.-June 18 1 9 81 Cottam (1939:25) Mostly southern states 381” Winter-Spring -18-- 11 85 Phillips (1925:136-131) Northeastern U. S. 71” Fall-Spring 19-2.5 tr.-2 25-2.0 Martin et al. ( 1951: 68 ) Southeastern U. S. 64” Winter lo-25 tr.-2 Martin et al. (195168) Western U. S. 199” All seasons 2-5 Martin et al. ( 195168) Oregon 12” Fall? (& (8) 60 Gabrielson and Jewett ( 1940: 157) Minnesota 88 Fall? (95) tr. Smith (1946:74) Tennessee 38 Fall 38 74 Rawls ( [19581:65-66) Illinois 28 Oct.-Dec. 46 65 Anderson ( 1959:320) 17 Oct.-April 16 3 19 Yocom and Keller ( 1961: 48-49) Missouri 10 Oct.-Dec. 45 1 95 Korschgen ( 1955: 16) Manitoba 175 April-Ott. 23 3 37 this study

* These data are also incmporated into Cottams’ ( 1939:25) data based upon 427 birds.

americana was found in 24 per cent of the partakes of more animal food, for wild celery birds. In four birds from Maryland, Warren does not grow in this state.” (189043) found only vegetable substances The succulent , stems, rootstalks, that he “judged” to be “remains of Vallisneria.” tubers, and to a lesser extent the fruits, of H. L. Skavlem found Potamogeton tubers to Potamogeton spp., Ruppiu muritima, Zostera form 80 to 80 per cent of the Canvasbacks ’ marina, Va&neti americana, and Sagittana’ food on Lake Koshkonong ( McAtee 1917: 14 ) . spp. appear to be the plant foods most utilized He discredited the importance of ValEisneria by Canvasbacks. While the extent to which as a food in Wisconsin by taking some of the “preference” in the wild determines their alleged “wild-celery” buds from esophagi of relative utilization has not been studied, plant Canvasbacks and growing them; in reality, distribution provides a partial explanation for they proved to be a Potamogeton (Kumlien differences noted in utilization. Potamogeton, and Hollister 1903:22). Zimmerman ( 1953: being more widely distributed in continental 172) indicated that Potamogeton and VaL range than Vallisneriu (Martin and Uhler li.sn.eria were among the foods eaten by six 1939:25-35, 43), logically should form a birds examined in Wisconsin. Seven of eight greater proportion of Canvasbacks ’ diets, as it birds collected by Pimie ( 1935:307-398) in apparently does. Michigan contained, in addition to other items, Most of the previously mentioned references either the tubers, winter buds, or nutlets of on Canvasback food habits indicate that con- potamogetons. Longcore and Cornwell ( 1984) sumption of animal material is not uncommon. Additional references reporting Canvasbacks successfully maintained Canvasbacks and feeding extensively upon animal material are Lesser Scaups in Michigan by feeding them those of Dawson and Bowles (1909:793) in “natural foods” which included 84 per cent Washington, Trautman ( 1940:192) in Ohio, (oven-dried weight) Vallisneria. and Saunders (1964:257) in the coastal waters Additional references indicate that plants of . other than Vallisneria are extensively utilized by Canvasbacks. Nuttall (1834:431) claimed FOOD HABITS OF REDHEADS that in Massachusetts Bay the Canvasbacks ’ The spring-summer food habits of Redheads principal foods were Zostera marina and were determined from 59 juveniles, collected Ruppiu maritima instead of Vallisnerk. Mc- between the end of June and the first week of Atee (1X7:21) reported that the tubers of September, and 24 adults collected between Sagittark platyphyllu were important in at- mid-May and late August. Information on fall tracting large numbers of Canvasbacks into the food habits was provided by 2 juveniles and Mississippi Delta in Louisiana. Grinnell et al. 14 adults shot during the hunting season. ( 1918: 154)) not mentioning any Najadaceae, Differences between the food habits of reasoned that “in California the Canvasback juveniles and adult females and those of adult FOOD HABITS OF CANVASBACKS, REDHEADS, AND SCAUP 285

TABLE 4. Foods from Redheads collected during the spring and summer in southwestern Manitoba.

% Occurrence % aggregatevol.

Source of material Juve- Adult Adult JUV.3 Adult Adult Food item Common name (part or type) nile female male nile female male

Esophageal contents (n) (37) (6) (6) (37) (6) (6) Chum spp. Muskgrass ( oogonia ) 8 16 Muskgrass (vegetative) 11 Scolochloasp. Whitetop grass (grains) 16 17 17 I? tr. tr. Chlorophyceae Green 19 17 8 tr. Ranunculus spp. Buttercups (achenes) 5 5 Scirpus spp. Bulrushes ( achenes ) 51 50 33 3 4 Potamogeton spp. Pondweeds (winter-buds) 11 33 17 3 15 : Lemna spp. Duckweeds (vegetative) 11 17 17 2 tr. tr. Other plants Misc. plants (seeds) 32 67 50 2 Total plant material 81 106 83 5: : 14 Trichoptera Caddis flies ( larvae, cases ) 41 50 50 18 86 62 Gastropoda Pond snails 11 11 Cladocera Water fleas (adults, ephippia) 16 7 Tendipedidae Midges ( larvae, pupae ) 24 17 17 tr. 22 Other animals Invertebrate eggs 11 : Misc. aquatic invertebrates 30 33 33 1 tr. 2 Total animal material 50 43 81 86 Esophagus-proventriculus-gizzard contents ( n) (2) ($ (14) (E) (IO) (14) Chara spp. Muskgrass (oiigonia) 5 Muskgrass (vegetative) 10 Potamogetonspp. Pondweeds (winter buds) 8 30 43 : 19 50 Pondweeds (nutlets) 44 60 33 3 1 tr. Scolochloa sp. Whitetop grass ( grains ) 10 10 7 7 9 s&pus spp. Bulrushes (achenes ) 95 60 57 6 : 2 Ranutudus spp. Buttercups ( achenes) 19 7 5 tr. Chlorophyceae 17 10 7 5 tr. tr. Misc. Various seeds and vegetative parts 51 80 57 2 Total plant material 97 100 100 426 ; 64 Trichoptera Caddis flies ( larvae, cases ) 64 50 50 36 72 33 Cladocera Waterfleas (adults, ephippia) 14 5 Gastropoda Pond snails 7 10 4 tr. Tendipedidae Midges (larvae, pupae) 24 20 7 1 1 3 Corixidae Water boatmen (adults, nymphs) 20 10 tr. Other animals Invertebrate eggs 7 : Misc. aquatic invertebrates 44 30 29 tr. Total animal material 85 70 57 54 :3 & males were not as great among Redheads as nymphs, and eggs of various invertebrates among Canvasbacks (table 4). I S values formed the “miscellaneous invertebrates” in for esophageal contents were 0.21 for juveniles the esophagus. and female adults, 0.24 for juveniles and male The only other references on juvenile Red- adults, and 0.74 for female and male adults. heads reported plant material to form the Corresponding values determined from esoph- bulk of the foods. Cottams’ ( 1939:13-14) agus-proventriculus-gizzard data were 0.52, three downy Redheads contained primarily 0.52, and 0.57, respectively. Potamogeton (33 per cent), Scirpus (31 per Various foods were consumed by juvenile cent), and animal material ( 31 per cent) ; Redheads and no particular item was utilized of the latter group, Corixidae, Coleoptera, extensively by the entire group (table 4). The Orthoptera, and Odonata were most important. algae, Characeae and Chlorophyceae, com- Collias and Collias (1963:7) reported that prised 26 per cent of the esophageal contents five one-week-old Redheads collected on the and were found in I2 of the 37 esophagi ex- Delta marshes had eaten primarily the nut- amined. Hard-coated seeds and Trichoptera lets of Potamogeton. larvae with their cases comprised a greater Animal material found in our small samples percentage of the foods in the esophagus- of adult males and females comprised 86 and proventriculus-gizzard contents than in the 81 per cent, respectively, of esophageal esophageal contents. Zygoptera nymphs, volumes (table 4). Trichoptera larvae and Haliplidae and Dytiscidae adults and larvae, cases and Tendipedidae larvae and pupae Hydracarina, Chonchostraca, Ephemeroptera comprised the bulk of animal foods consumed 280 JAMES C. BARTONEK AND JOSEPH J. HICKEY

TABLE 5. Foods from Redheads collected in late September and early October during the hunting season in southwestern Manitoba. : .I

Soure of material Food item Common name (part or type) Esophageal contents (n) Chara spp. Muskgrass (vegetative) Hordeum sp. Squirrel-tail grass (grain) Total plant material

Esophagus-proventriculus-gizzardcontents (n) (16) Chara spp. Muskgrass (vegetative) 96 Potamogeton spp. Pondweeds (vegetative, nutlets) 12 1 Misc. Various seeds 12 2 Unidentified vegetative parts 6 1 Total plant material 100 100

by these adults. Zygoptera nymphs, Haliplidae and suggested that Chara serves as a natural and Dytiscidae adults and larvae, amphipods, means to deworm the birds either mechanically and Sphaeridae were the “miscellaneous or chemically. animal” foods eaten. Winter buds of Potamoge- Cottam (1939:7-13) considered Redheads ton were almost the exclusive item eaten by to be predominantly vegetarians; plant ma- a group of 11 flightless adults drowned in gill terial comprised 91) per cent of the “stomach” nets during late August on Lake Winmpegosis. contents found in his 364 adults. Najadaceae In addition to those plant items listed in table ( 32 per cent ) and Characeae ( 21 per cent) 4, fruits from the following plants were found were the most important plant families repre- in small quantities: Myriophyllum, Chene- sented in the foods consumed. Insects, includ- podium, Eleocharis, Sparganium, Ruppiu, ing Orthoptera, Tendipedidae, and Trichop- Hordeum, and Echinochloa. tera, and mollusks, including Gastropoda and Chara, with its musky odor and limy in- Pelecypoda, comprised six and four per cent, crustation, is at times an important food of respectively, of the total foods consumed. Redheads. Vegetative branches of Chara were Animal material comprised 24 per cent of the found in all I4 birds shot on Lake Winni- food in June and 26 per cent in July; no adults pegosis during the hunting season (table 5). were collected during May or August. Both oogonia and, to a lesser extent, vegetative parts from these plants were eaten by six FOOD HABITS OF LESSER SCAUP juveniles (table 4). Kubichek ( 1933: 108 ) Data on spring and summer food habits of reported that Chara comprised 91 per cent of Lesser Scaup are based upon 47 juveniles col- the food found in the “stomachs” of 83 Red- lected during July, August, and the first week heads collected at Okanagan Landing, British in September, and 24 adults collected in each Columbia, during the winter. We disagree month from May through August. We did not with Kubicheks’ conclusion that Redheads collect scaup during the hunting season. resort to Chara because other foods are scarce. Animal matter was more important than Eleven Canvasbacks, also collected with the plants to duckling and adult Lesser Scaup; Redheads during the hunting season on Lake and, as was expected, animal food decreased Winnipegosis, had fed primarily upon Pota- in importance when material from proven- mogeton tubers and nutlets, suggesting to US triculi and gizzards were included with the that, although Potamogeton was available as a contents of the esophagi’ (table 6). I S values notential food for Redheads, Chara was pre- for esophageal data were 0.61 for juveniles ferred. Cottam ( lQ39: 10) also considered and female adults, 0.20 for juveniles and male Chara to be an acceptable food in many areas adults, and 0.22 for female and male adults; where other excellent foods were avail- corresponding values determined from esopha- able. At Swan Lake, , Munro gus-proventriculus-gizzard contents were 0.50, ( 1939: 183)) found Charas’ vegetative branches 0.34, and 0.46, respectively. and o&pores to comprise 31 and 17 per cent, Amphipods, gastropods, and Tendipedidae respectively, of the foods found in eight Red- larvae formed 96 per cent of the esophageal heads collected in the fall. Cornwell and material found in 25 juvenile Lesser Scaup. Cowan ( lQ63: 186)) examining the same 14 The esophagus-proventriculus-gizzard contents birds from Lake Winnipegosis used in this of 47 juveniles increased the importance of study, noted a paucity of intestinal parasites such plants as Myriophyllum and Sci~pus. FOOD HABITS OF CANVASBACKS, REDHEADS, AND SCAUP 287

TABLE 6. Foods from Lesser Scaup collected during the spring and summer in southwestern Manitoba.

% OccuIrence % aggregatevol. Source of material JW3 Adult Adult Juve- Adult Adult Food item Common name (part or type) nile female male nile female male

Esophageal contents (n) (25) (7) (7) (25) (7) (7) Misc. plants. Various seeds 16 29 29 tr. tr. tr. Misc. vegetative 32 43 29 tr. 1 tr. Total plant material 40 57 57 tr. 2 tr. Amphipoda Scuds 52 43 29 49 46 8 Gastropoda Pond snails 4 14 43 39 4 4 Tendipedidae Midges ( larvae, pupae ) 20 43 29 8 41 6 Corixidae Water boatmen (adults, nymphs) 40 14 2 2 1 Coleoptera Aquatic beetles (adults, larvae) 8 :: tr. 2 Hirudinea Leeches 4 14 tr. 61 Trichoptera Caddis flies ( larvae, cases ) 8 14 29 tr. 2 16 Other animals Misc. aquatic invertebrates 16 29 14 1 1 1 Total animal material 80 86 100 99 98 99

Esophagus-proventriculus-gizzard contents (n) (4477) (12)92 (12)92 (47)12 (12)7 (1;) Myriophyllum sp. Water milfoil (nutlets) scirpus spp. Bulrushes ( achenes ) 92 190 100 6 4 7 Other plants Various seeds 51 17 75 1 2 2 Misc. vegetative parts 15 25 25 tr. tr. tr. Total plant material 96 100 100 19 13 14 Amphipoda Scuds 32 25 17 39 19 7 Gastropoda Pond snails 2 17 33 20 2, 3 ’ Tendipedidae Midges (larvae, pupae) 17 25 25 9 34 12 Corixidae Water boatmen (adults, nymphs) 38 17 25 4 1 tr. Coleoptera Aquatic beetles (adult, larvae) 6 8 25 1 tr. 2 Trichoptera Caddis flies (larvae, cases) 6 25 25 tr. 5 24 Hirudinea Leeches 2 8 8 tr. 2 31 Misc. Crustacea Misc. 13 25 8 tr. 2 tr. Misc. Insecta Misc. aquatic insects 4 25 8 tr. 2 1 Unident. animals Unidentified animal material 32 17 17 7 20 6 Total animal material 68 58 64 81 87 86

Chlorophyceae, Potamogeton vegetation and same area. An I S value of 0.39 was obtained. nutlets, and the fruits of , Sparganium., In spite of using esophagus-proventriculus- Scolochloa, Horakum, Eleocharis, Carex, gizzard contents which usually greatly inflate Rumex, Ceratophyllum, Ranunculus, and the importance of plant material, the percent- S0nchu.s were among the group of “miscel- ages of animal material in both studies were laneous plants” that formed only one per cent high-86 per cent for ours and 91 per cent of the total foods. Ephippia of cladocerans, for theirs. Three of Rogers and Korschgens’ ostracods, nymphs of Ephemeroptera and birds ate Daphnia, which amounted to eight Zygoptera, and the larvae of Culicidae formed per cent of the foods. None of our scaup con- the “miscellaneous invertebrates.” tained these mature cladocerans, but 7 of the Eighty-nine per cent of the “stomach” con- 71 birds (47 juveniles and 24 adults ) did con- tents of I.7 juvenile Lesser Scaup collected in tain trace amounts of their ephippia. Leeches the Prairie Provinces was animal material ( Cot- were eaten by birds in both studies. tam 1939:45-46). Aquatic beetles, Tendipedi- The amphipods, Gammarus and Hyalellu, dae larvae, Corixidae, and Odonata nymphs are important foods for many adult and were the most important groups of animals juvenile Lesser Scaup in potholes and marshes eaten by this group. In spite of a preponder- of southwestern Manitoba. Of 71 scaup we ance of Dytiscidae beetles eaten by Cottams’ examined, 20 contained these crustaceans birds and amphipods by ours, and I S value of (table 6). Rogers and Korschgen ( 1966:259- 0.24 was obtained in a comparison of esopha- 261) found 21 of 39 adults had eaten amphi- gus-proventriculus-gizzard data from the two nods. Amphipods composed most of the food groups. found by Munro ( 1941:lW137) in 10 juve- We compared our findings based upon 20 niles and 9 adults taken during the summer in adult Lesser Scaup collected in the pothole British Columbia. Cottam (1939:40-46), how- area with those of Rogers and Korschgen ever, found them relatively unimportant in (1966:260) who collected 39 adults in the birds that he examined. 288 JAMES C. BARTONEK AND JOSEPH J. HICKEY

DISCUSSION Curex, Myriqvhyllum, Hippuris, Rununculus, Cottam (1939:5, 53), whose information was Chenepodium, and Rumex, and the oijgonia of based upon specimens collected largely from Chara, and the vegetative parts of Myriophyl- fall to spring, was probably justified in con- lum, Cerutophyllum, and Lemnu were fre- cluding that the food habits of AZ&U, except- quently incorporated into the larval cases of ing those of the (A. marila), Trichoptera, and were therefore incidentally are predominantly vegetarian. The present ingested by those birds that fed upon the study during the spring and summer, however, larvae, Of course seeds are eaten as a food shows that Canvasbacks (excepting adult or as a substitute for grit, but their importance males), Redheads, and Lesser Scaup in south- as a summer food is often overrated. western Manitoba consumed chiefly animal Aquatic invertebrates formed the bulk of material. Other investigations tend to cor-’ foods eaten by the Canvasbacks, Redheads, and roborate the importance of animal foods for Lesser Scaup during the spring and summer diving ducks during summer. Martin et al. months in southwestern Manitoba. Trichoptera ( 1!%1:66, S&69) reported percentages of larvae with cases, Tendipedidae larvae, and animal material among summer-collected birds gastropods were important items for all three to be 37 for Canvasbacks, 21 for Redheads, and species; amphipods were additionally im- 52 for Lesser Scaup. Keiths’ (1961:34) data portant to scaup. Immature rather than adult from Redheads, Lesser Scaup, Ruddy Ducks insects were most frequently consumed. Al- ( Oxyuru jumuicensis), and Canvasbacks taken though juvenile birds were occasionally seen during the spring and summer in Alberta chasing flying insects across the water, flying showed that animal material comprised 59 per- forms of insects were rarely encountered in the cent of the foods found in 24 “stomachs.” examination of food contents. Rogers and Korschgen (1966:26%263), who Potarrwgeton, with its tubers, winter buds, presented seasonal data and reviewed studies rootstalks, and nutlets, was the most important following Cottams’ ( 1939)) concluded that the vlant . Chura was often consumed in food habits of Lesser Scaup were more akin large quantities by particular groups of birds, to those of Greater Scaup in that both con- but it was not found in a majority. Scirpus and sisted mainly of animal material. Muriophyllum were found in most birds, but During the summer, Canvasback and Red- seldom in large quantities. With the possible head juveniles ate progressively less animal exception of two birds feeding upon caryopses material as they became older. Lesser Scaup of Scolochloa that were still attached to this juveniles, however, maintained diets high in emergent, seeds were taken from the bottom animal material. Chura ( 1961: 124-126) noted of the pond. that juvenile also consumed progres- There were greater similarities in food habits sively less animal material as they became between ducks of all three species collected older. Perret ( X62:61-62), however, did not from potholes and marshes (I S = 0.34) than find a similar change in the diets of the ducks frosm either potholes and lakes (0.13) juvenile Mallards he examined. Mendall or marshes and lakes (0.13). The fruits of ( 1958: 187) believed the diets of half-grown upland and emergent vegetation such as juvenile Ring-necked Ducks ( Aythya co&~ri.s) S&pus, Curex, Eleocharis, Scolochba, HOT- were more similar to those of adults (more deum, Ranunculus, Rumex, Chenepodium, plant material) than to those of downy young Meliotus, and Senecio were more frequently ( more animal material). consumed by ducks from the potholes and Studies in which “stomachs” or “gullets and marshes than by those from the lakes. Con- gizzards” were used in analyses of food habits versely, aquatic vegetation such as the vegeta- have probably over-estimated the importance tive branches and tigonia of Chara and the of plant material because of the bias resulting winter buds of Potumogeton’ was more fre- from the inclusion of the proventriculus and quently found in birds from the lakes than in gizzard contents in with the more meaningful those from either potholes or marshes. These esophageal contents. Some plant foods found differences may in part reflect the higher ratios in the ducks were probably ingested inciden- of edge to open-water associated with potholes tally. Filamentous algae (Chlorophyceae) and marshs in comparison with lakes. were frequently ingested when ducks fed upon Use of foods, with respect to quantity and amphipods, corixids, Tendipedidae larvae, and availability and interspecific relations of the Trichoptera larvae, since these plants adhered food habits among diving ducks, will be dis- to the invertebrates that were being eaten by cussed in a separate paper (Bartonek and the birds. The seeds of Eleocharis, Scirpus, Hickey, unpublished). FOOD HABITS OF CANVASBACKS, REDHEADS, AND SCAUP 289

SUMMARY podium, and Carex were occasionally im- Among 162 summer-collected Canvasbacks, portant to ’ this group of birds. animal material formed the bulk of esophageal ACKNOWLEDGMENTS contents in both juveniles (87 per cent) and adult females (92 per cent), but it was less We wish to thank G. W. Cornwell, L. B. Keith, important to both adult males (2 per cent) R. A. McCabe, D. P. Olson, J. H. Stoudt, and and 13 fall-collected birds (22 per cent). P. Ward for advice and assistance received Trichoptera larvae with cases, Tendipedidae, during this study. We wish to acknowledge Ephemeroptera nymphs, and gastropods were N. G. Perrets ’ (unpublished M.S. thesis) work the animal items found in greatest quantities. on the food habits of Mallards in the Minne- Tubers of Potamogeton comprised 95 per cent dosa pothole area, which importantly in- of the esophageal contents of summer-collected fluenced the nature of this study. H. A. Hoch- adult males, and 71 per cent of the fall-col- baum is especially thanked for his guidance lected birds. A review of literature on food and assistance during this study. We received habits indicated that Potamugeton, probably financial support from the Wildlife Manage- because of its continent-wide distribution, is ment Institute, operating through the Delta a more important food of Canvasbacks than Waterfowl Research Station, Delta, Manitoba, the often acclaimed Vallisne&z americana. and from the University of Wisconsin. We The esophagi from 83 summer-collected gratefully acknowledge the time and assistance juvenile and adult female and male Redheads made available to us by the Bureau of Sport contained, respectively, 43,81, and 86 per cent Fisheries and Wildlife during the preparation animal material. Trichoptera larvae, Tendi- of this manuscript. pedidae, Cladocera, and gastropods were the LITERATURE CITED most abundant animal items. Chura oogonia and vegetative branches, Chlorophyceae, and ANDERSON, H. G. 1959. Food habits of migratory the fruits of Scolochloa, Ranunculus, Scirpus, ducks in Illinois. Illinois Nat. Hist. Serv. Bull. 27( 4) :28%344. and Potamogeton were among the more im- BAJICOV,A. 1939. Biological conditions of Manitoba portant plant items consumed by these sum- lakes. Contrib. Can. Biol. and Fish., N. S. 5: mer-collected birds. Vegetative branches of 381422. Chara were ahnost the only item found in 16 BARTONEK, J. C. 1985. Mortality of diving ducks on Lake Winnipegosis through commercial fish- fall-collected Redheads. ing. Can. Field-Naturalist 79: 15-20. Animal material formed 99, 98, and 99 per Bran, R. D. 1961. Ecology of the aspen parkland cent, respectively, of esophageal contents in of western Canada in relation to land use. Can. 71 summer-collected juvenile and adult female Dept. Agr., Res. Branch, Res. Sta. Contrib. 27. and male Lesser Scaup. Amphipods were 155 p. CHUFIA, N. J. 1981. Food availability and prefer- particularly important to these diving ducks, ences of juvenile Mallards. Trans. N. Amer. Wildl. but gastropods, Tendipedidae and Trichoptera and Nat. Resources Conf. 28:121-134. larvae, corixids, and leeches were also used. COLLIAS, N. E., AND E. C. COLLIAS. 1963. SeIec- With the possible exception of adult male tive feeding by wild ducklings of different species. Canvasbacks that fed mainly upon tubers of Wilson Bull. 75:8-14. CORNWELL, G. W., AND A. B. COWAN. 1983. Potamogeton, the three species of Aythya used Heliminth populations of the Canvasback ( Aythya animal material extensively throughout the valisineriu) and host-parasite-environmental inter- summer. By fall, however, plant material relationships. Trans. N. Amer. Wildl. and Nat. formed the bulk of the diets of Canvasbacks Resources Conf. 28: 173-199. and Redheads. Lesser Scaup probably main- CQTTAM, C. 1939. Food habits of North American diving ducks. U.S. Dept. Agr. Tech. Bull. 843. tain a diet high in animal material throughout 140 p. the year. Juvenile Canvasbacks and Redheads CURTIS, J. T. 1959. The vegetation of Wisconsin. consumed progressively greater quantities of Univ. Wisconsin Press, Madison. 857 p. plant material as they became older. DAWSON, W. L., AND J. H. BOWLES. 1909. The Trichoptera larvae with cases, Tendipedidae birds of Washington. Vol. 2. Occidental Publ. larvae, pupae, and adults, gastropods, amphi- Co., Seattle. p. 459-997. DILLON, 0. W., JR. 1958. Food habits of wild pods, Ephemeroptera and Odonata nymphs, ducks in the rice-marsh transition area of Louisi- and corixids were among the most important ana. Proc. Ann. Conf. Southeastern Assoc. animal items consumed by the three species of Fish Comm. 1l:llP119. birds. The vegetative parts and fruits of DZUBIN, A. 1955. Some evidences of home range Potamogeton and Chara were the most fre- in waterfowl. Trans. N. Amer. Wildl. Conf. 20: 278-298. quently consumed plant items; fruits of ERICKSON, R. C. 1948. Life history and ecology of S&pus, Myriophyllum, ScoEochloa, Chene- the Canvas-back, Nyrocu vuZtineria (Wilson), in 290 JAMES C. BARTONEK AND JOSEPH J. HICKEY

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