Underwater Foraging Behavior of Canvasbacks, Lesser Scaups, and Ruddy Ducks’

The Condor 90:16X-172 0 The Cooper Ornithological Society 1988

UNDERWATER FORAGING BEHAVIOR OF CANVASBACKS, LESSER SCAUPS, AND RUDDY DUCKS’

MICHAEL W. TOMES AND DALE A. WRUBLESKI~ Delta Waterfowl and WetlandsResearch Station, RR #I, Portage la Prairie, Manitoba RIN 3A1, Canada

Abstract. We observedthe underwater behavior of captive Canvasbacks(Aythyu valisineria), LesserScaups (A. u&is), and Ruddy Ducks (Oxyurajamaicensis) while they foraged on a variety of food items in a large aquarium. Canvasbacksprobed into the substratewith the bill and body oriented perpendicular to the bottom. Lesser Scaupsand Ruddy Ducks strained food items from the substratesurface by moving their bills in short, lateral arcs while rapidly opening and closing their mandibles; their bills and bodies were oriented at a 3.5 to 45” angle to the substrate.Scaup also fed by grasping prey in the water column, where they appeared to locate prey visually. Ruddy Ducks did not appear to select prey visually. The speciesalso differed in their underwater locomotory behavior and postures; these differencesprobably are related to the prey and conditions typically encounteredby each. Key words: Canvasback;Aythya valisineria; LesserScaup; Aythya affinis; Ruddy Duck; Oxyura jamaicensis;foraging behavior;diving behavior.

INTRODUCTION habitats and distributions of the three species Although the behavior of many speciesof diving overlap (Palmer 1976), but their diets differ ducks has been described,very little is known of markedly. During most of the year, Canvasbacks their underwater foraging and locomotory be- feed primarily on plant tubers or molluscs dis- havior. Diving behavior of some specieshas been tributed in wetland substrates,although prelay- observed in the wild from above the water sur- ing and laying females, and juveniles consume face (e.g., Brooks 1945; Humphrey 1957, 1958; large numbers of aquatic invertebrates (Bartonek Snell 1985) but turbid water hampered visibility and Hickey 1969). LesserScaups consume aquatic and the foraging actions of the birds were not invertebrates (primarily amphipods), both in the recorded.Only a few investigators have observed water column and on vegetation and substrate the underwater actions of captive waterfowl in surfaces(Bartonek and Hickey 1969, Hoppe et aquaria. Livezey and Humphrey (1984) ob- al. 1986). Ruddy Ducks feed almost exclusively served the underwater locomotory behavior of on benthic chironomid larvae during the breed- steamer-ducks(Tuchyeres spp.) and Suter (1982) ing season(Siegfried 1973, Tome 1981) and on briefly described some of the foraging behaviors oligochaetes(Stark 1978) or chironomid larvae of Common Goldeneyes (Bucephala clangula), (Hoppe et al. 1986) during the winter. Each of Common Pochards(Aythyaferina), Tufted Ducks these kinds of prey differs in mobility, antipred- (A. fi&z&z), and Eurasian Coots (IQ&u &-a). ator response,and the environmental conditions This paper describesthe underwater locomo- in which they are found; thus, we predicted that tory and foraging behavior of three species of the foraging behaviors of thesewaterfowl species diving ducks: the Canvasback (A. valisineriu), would vary accordingly. LesserScaup (A. a#%), and Ruddy Duck (Oxy- METHODS ura jamaicensis). The breeding and wintering During the summers of 1983 to 1985, we observed the foraging behavior of seven Ruddy Ducks (four males, three females), four Canvas- ’ ’ Received22 April 1987. Final acceptance8 August backs (two males, two females) and two male 1987. Lesser Scaup in a 5 x 2 x 2-m indoor concrete z Present address:Patuxent Wildlife ResearchCen- aquarium through four, 1 x 1-m plate-glasswin- ter, Laurel, MD 20708. 3Present address: Department of Entomology, Uni- dows. We photographed underwater behavior versity of Alberta, Edmonton, Alberta T6G 2E3, Can- using a 35-mm camera and both super-8 and 16- ada. mm movie cameras.

f1681 DIVING DUCK FORAGING BEHAVIOR 169

The bottom of the aquarium consisted of a the bird. The birds used simultaneous strokesof 4 x 4arrayof 1.0 x 0.5 x O.l-mwoodentrays the legsto propel themselves towards the aquar- filled with 6 cm ofsand that provided a substrate ium substrate. At the end of each power stroke, for the benthic prey. In 1985, we anchored into the feet convergedmedially, below the tail. Dur- the substrateone end of several 50-cm long, 0.6- ing the “recovery stroke” (the portion ofthe stroke cm diameter polypropyleneropes which had been when the leg is brought forward), the toes and separatedinto fine strands. The free end of the web were folded posteriorly, reducing resistance rope floated in the water column; this simulated to the water. All speciesswam to the bottom with submerged vegetation and provided a refuge for necks stretchedforward. None of the speciesex- benthic and pelagic invertebrates. tended their wings for propulsion or stabilization We attempted to observe each speciesforage while underwater. on prey that they normally consumed in the wild; Upon reaching the bottom, the birds main- however, in some instances we could not obtain tained their location with leg strokes directed numbers of natural prey necessaryto conduct our perpendicular to the water surface. The Lesser observations and, thus, we provided substitute Scaup and Ruddy Ducks always used simulta- prey. In some of the Ruddy Duck observations, neous leg strokes;the Canvasbacks,however, oc- we used wheat grains to simulate patchesof ben- casionally used alternate leg strokes. When for- thic prey. The grains were placed approximately aging,the birds positionedtheir bodies at an angle 1 cm below the surface of the sand in densities to the substratewhich varied among species(see of 500 to 1,000 grains/m2. For all Canvasback next section). When its body was angled away trials, we placed corn kernels in the sand in den- from perpendicular to the substrate, the power sities of 100 to 500 kernels/m2 to simulate plant stroke moved the bird forward and also pre- tubers distributed beneath the substrate surface. vented the bird from floating toward the water For all LesserScaup and some Ruddy Duck trials, surface.All speciesmoved forward along the bot- we releasedseveral thousand amphipods into the tom with the power stroke of the legs parallel to aquarium at least 4 hr before feeding trials began. the axis of the body. This provided time for the invertebrates to ac- To return to the water surface,the birds stopped climatize to the experimental habitat. The ma- moving their legs and briefly (< 1 set) floated jority of the amphipods attached to the substrate backwards, towards the water surface, until a or to the walls near the bottom of the aquarium. power stroke and an upward motion of the head At least 5 hr before each observation session, oriented the body towardsthe water surface.They we placed the birds in pens beside the aquarium floated to the water surfacewith little or no effort. and deprived them of food. We observed each The feet normally trailed behind the bird in a speciesseparately, but also observed the Lesser relaxed position with the webbing folded so that Scaupand Ruddy Ducks together. During all ob- the legsand feet provided little resistanceagainst servation sessionsat least two individuals of a the water. Occasionally, however, the birds specieswere in the aquarium. moved their feet to changedirection; e.g.,to swing to the right, the bird extended the right foot lat- RESULTS erally with its web spread open. As the birds GENERAL UNDERWATER LOCOMOTORY neared the water surface,they extended both legs BEHAVIOR laterally and spread the foot webbing, which de- All speciesinitiated dives similarly. Immediately creased their velocity. Occasionally, the birds before diving, the birds exhaled and brought both adopted this posture to slow their upward ve- feet forward, close to the body on each side of locity and maneuvered to grasp a food item. the mid-sternum region. Each dive began when The Ruddy Ducks floated to the water surface the bird swept both feet simultaneously in a ven- with the neck and bill slightly forward of the tral-posterior direction (“power stroke”) while posture adopted when sitting on the surface.The arching the neck forward into the water. The Lesser Scaup and Canvasback arched the neck head and neck entered the water when the feet so the distal end of the bill was near or against were approximately half-way through the power the upper chest or lower neck. These positions stroke. During the descent,the legs were rotated were maintained until the head broke the water laterally from the normal swimming posture to surface and the birds returned to the normal a position near or above the horizontal plane of swimming position. 170 MICHAEL W. TOME AND DALE A. WRUBLESIU

FORAGING BEHAVIOR consumed prey distributed on the artificial vege- Ruddy Duck. When foraging on prey distributed tation; but unlike them, they often pursued and in the substrate,the Ruddy Ducks inserted their consumed amphipods that would drop to the bills at a 35 to 45” angle into the substrate to a substratewhen the vegetation was disturbed. point slightly distal to the nares. The birds swam Canvasback. The body and bill of the Can- forward and rapidly opened and closedthe man- vasbackswere oriented perpendicular to the sub- dibles while also moving their heads in short, strate when they foraged on prey distributed in lateral arcs so that an area of about 1.5 times the the substrate. The Canvasback used the bill as a bill width was searchedfor food. This mandib- probe to locate and extract food items from the ular movement caused substrate and associated substrate. When searching for corn kernels dis- benthos to be drawn into the bird’s mouth when tributed beneath the substrate, Canvasbacks in- the mandibles were opened. Upon closing, sub- serted their bills into the substrate using slight, strate was forced out the sides of the bill while lateral head shaking motions. The bill remained the lamellae retained items that were consumed. in the substrate for 1 to 2 set; the birds then Often the birds stoppedtheir forward movement pulled the bill from the substrate and either in- and began very vigorous lateral head shaking sertedit somewhereelse or returned to the water movements in one spot. In these situations, the surface.When Canvasbacksencountered smaller birds also oriented the body more perpendicular food items, such as wheat grains, on or directly to the substrate. beneath the substrate surface, they held the bill The Ruddy Ducks did not appear to visually at a 50 to 75” angle and used rapid opening and select individual prey; they did not direct bill closingmovements of the mandibles to sieve food movements towards prey that we could see on items from the substrate; they rarely exhibited the bottom in the immediate vicinity of the feed- the rapid, lateral bill and head movements uti- ing birds. Ruddy Ducks, however, often swam lized by Ruddy Ducks and LesserScaup. We did directly towards large aggregationsof amphipods not conduct any observations of Canvasbacks which appeared as dark patches on the bottom foraging on invertebrate prey. or walls of the aquarium. Ruddy Ducks also did not direct bill movements towards individual DISCUSSION amphipods swimming in the water column. In- The legs of Canvasbacks, Lesser Scaups, and stead, where dense aggregationsof amphipods Ruddy Ducks are located on the posterior por- occurred, they strained them from the water col- tion of the body, an adaptation for efficient swim- umn using bill and head movements similar to ming and diving (Raikow 1970). During sub- those used when foraging in the substrate. mersion, the legs of each specieswere abducted Some amphipods aggregatedon the artificial to a position near or above the horizontal body vegetation. To consume these,the Ruddy Ducks plane. This is the most efficient position for div- grasped a piece of the vegetation between the ing and is also exhibited by other species(e.g., mandibles and then “dabbled” (rapid opening loons [Gaviiformes] and grebes [Podicipedi- and closing of the mandibles) along the vegeta- formes]) that are highly adapted for foraging un- tion, ingesting amphipods that remained on the derwater (Raikow 1970). vegetation. Several speciesof waterfowl, including steam- Lesser Scaup. The Lesser Scaup foraged in a er-ducks (Livezey and Humphrey 1984), Old- similar manner to the Ruddy Ducks with one squaws, Clangada hyemalis (Kelso 1922, Snell important difference: scaup appeared to visually 1985), scoters,Melanitta spp., eiders, Somateria locate both prey individuals and patches.When spp., and Harlequin Ducks, Histrionicus histri- diving, the scaupfrequently stoppedand directed on&s (Brooks 1945; Humphrey 1957, 1958), foraging movements of the bill towards amphi- use their wings for propulsion or stabilization pods that were swimming in the water column. during some portion of submergence. Canvas- When foraging on prey distributed beneath the backs, Lesser Scaups, and Ruddy Ducks, how- substrate surface, the behaviors of the Lesser ever, kept their wings folded against the body, Scaup (including bill movements, bill angle, and similar to the wing position of Greater Scaups, body angle) were the same as those describedfor Aythya marila, mergansers, Mergus spp., gold- the Ruddy Duck. Like Ruddy Ducks, scaupalso eneyes,Bucephala spp., and the Musk Duck, Bi- DIVING DUCK FORAGING BEHAVIOR 171 ziura lobata(Townsend 1909, Kelso 1922, Brooks backs, which consume large numbers of aquatic 1945, Frith 1967). invertebrates (Bartonek and Hickey 1969). All three speciesexhaled immediately prior to Lesser Scaups and Ruddy Ducks have a bill beginning a dive. This has been observed in morphology well adapted for straining food from another pochard, the Tufted Duck (Butler and the water column or soft substrate. Character- Woakes 1979) and in steamer-ducks(Livezey and istics of a bill adapted for straining include a Humphrey 1984). This action likely reducesthe spatulate bill shape with closely spaced, blade- buoyancy during submersion (Livezey and like lamellae (Goodman and Fisher 1962). In our Humphrey 1984). study, LesserScaup foraged in the water column The Canvasback and LesserScaup returned to and on the surface of the substrate and vegeta- the water surface with the tip of the bill held tion. This speciesfrequently consumes amphi- against the anterior sternum, a posture similar pods (Bartonek and Hickey 1969), which occur to that described for the Surf Scoter, Melanitta in any of these three sites and may differ in their perspicillata (Humphrey 1957), and the Com- visibility and availability to the foraging bird. mon Eider, Somateria mollissima (Humphrey LesserScaup foraging behavior varied according 1958). The Ruddy Duck returns to the water to prey location and visibility. In clear water, the surface in a posture that is similar to that de- scaup visually located and directed grasping scribed for the steamer-ducks (Livezey and movements of the bill towards amphipods en- Humphrey 1984) with the head and neck countered in the water column and individual stretched slightly forward of the position used prey in aggregations.This speciesalso employed when swimming on the surface. a foraging strategy that utilized only tactile lo- The Canvasbacks bill and skull shapeare well cation of a food item. LesserScaup used the bill adapted for probing the substrate for plant tu- to sieve through the substrate in search of food bers. As Goodman and Fisher (1962) note, “the using lateral movements of the head and bill bill and cranium are relatively long, narrow, and similar to those used by Ruddy Ducks. Depend- low; the bill narrows moderately from base to ing on the conditions presentin the wetland where tip which is unusual among the straining ducks. the scaupare foraging, any combination of these Thus, the skull is modified for probing, and the behaviors could be employed. jaws are capable of a powerful gaping action.” Although Ruddy Ducks and LesserScaup have In this study, Canvasbacks foraged by inserting similar underwater posturesand behaviors, their the bill into the substrate while the long axis of foraging behavior differs in one important as- the body and the power strokes of the legs were pect: the Ruddy Duck rarely directed grasping perpendicular to the water surface. In this po- movements of their bills towards prey. The most sition, the Canvasbacks maximized the force commonly consumed prey of the Ruddy Duck necessaryto insert the bill into the substrate to is benthic chironomid larvae, which are located find buried tubers and maintained their position in very fine bottom ooze. This type of substrate in the area that tubers were located. Pondweed clouds the water when disturbed, making visual tubers have a clumped distribution (Anderson detection of prey impossible; tactile location of and Jones 1976) and once a tuber has been lo- food is much more efficient in turbid water. cated a foraging bird should continue to search in that general area for more tubers. Canvasbacks ACKNOWLEDGMENTS also differed from the other speciesin this study We thank W. C. Alexander, D. H. Bnmton, B. C. Live- by occasionallyusing alternate foot strokeswhen zey, and an anonymous reviewer for helpful sugges- feeding. This has been observed in Canvasbacks tions which greatly improved an earlier version of the by other investigators(J. Takekawa, pers.comm.) manuscript. This research was funded by the North American Wildlife Foundation through Delta Water- and may permit the exertion of a more constant fowl and Wetlands ResearchStation. force with the bill while probing for tubers. Can- vasbacks exhibited flexibility in their foraging LITERATURE CITED behavior by also sieving epibenthic prey with ANDERSON,M. G., AND R. E. JONES. 1976. Sub- rapid opening and closing of the mandibles, a mergedaquatic vascular plants of EastDelta Marsh. behavior that is probably more efficient for ju- Manitoba Dept. RenewableResources and Trans. venile and prelaying and laying female Canvas- Serv., Winnipeg. 172 MICHAEL W. TOME AND DALE A. WRUBLESKI

BARTONEK,J. C., ANDJ. J. HICKEY. 1969. Food habits behaviour of steamer ducks Tachyeresspp. Ibis of Canvasbacks,Redheads, and Lesser Scaup in 1261257-260. Manitoba. Condor 71:280-290. PALMER,R. S. 1976. Handbook of North American BROOKS, A. 1945. The under-water actions of diving birds. Vol. 3. Yale Univ. Press, New Haven. ducks. Auk 62~517-523. RAIKOW,R. J. 1970. Evolution of diving adaptations BUTLER,P. J., ANDA. J. WOAKES. 1979. Changesin in the stifftail ducks. Univ. California Press, heart rate and respiratoryfrequency during natural Berkeley. behaviour of ducks, with particular reference to SIEGFRIED,W. R. 1973. Summer food and feeding of diving. J. Exp. Biol. 79:283-300. the Ruddy Duck in Manitoba. Can. J. Zool. 51: FRITH, H. J. 1967. Waterfowl in Australia. Angus 1293-1297. and Robertson, Sydney. SNELL,R. R. 1985. Underwater flight of Long-tailed GOODMAN, D. C., AND H. I. FISHER. 1962. Functional Duck (Oldsauaw)Clannula hvemalis. Ibis 1271267. anatomy of the feeding apparatus in waterfowl STARK,R. ‘T. 1978. ’ Foodhabiis of the Ruddy Duck Aves: Anatidae. Southern Illinois Univ. Press, (Oxyurajamaicensis) at the Tinicum National En- Carbondale. vironmentalCenter. M.S.thesis, Pennsylvania State HOPPE,R. T., L. M. SMITH,AND D. B. WEBSTER.1986. Univ., State College. Foods of wintering diving ducks in South Caro- SUTER,W. 1982. Vergleichende NahrungsGkologie lina. J. Field Omithol. 57:126-134. von iiberwintemden Tauchenten (Bucephala,Ay- HUMPHREY,P. S. 1957. Observations on the diving thya) und BllRhuhn (Fulica atra) am Untersee- of the Surf Scoter (Melanitta perspicillata).Auk Ende/Hochrhein (Bodensee).Der Ornithol. Beo- 74~392-394. bachter 791225-254. HUMPHREY.P. S. 1958. Diving of a captive Common TOME, M. W. 1981. Reproductive bioenergeticsof Eider. Condor 60:408-4 10: female Ruddy Ducks in Manitoba. M.S.thesis, KELSO.J.E.H. 1922. Birdsusine. their wingsas a means Univ. Maine, Orono. ofpropulsion under water-Auk 39:4>6428. TOWNSEND,C. W. 1909. The use of the wings and LIVEZEY,B. C., AND P. S. HUMPHREY. 1984. Diving feet by diving birds. Auk 261234-248.