[- Auk 424 LVoL76 INTERSPECIFIC INTOLERANCE OF THE AMERICAN COOT IN UTAH BY RONALD A. RYDER INTRODUCTION The American Coot (Fulica americana)is extremely territorial and vigorouslydefends its territoryagainst not only other cootsbut also a wide variety of vertebrates.The effectsof this interspecific intoleranceupon waterfowlproduction were investigated,with par- ticular emphasisupon comparativebehavior, nesting and young- rearingsuccess of cootsand ducks. The followingobservations con- cern primarily the first aspect. Nesting and young-rearingsuccess will be discussedin a later paper. This studywas financedthrough the Utah CooperativeWildlife Research Unit, with the U.S. Fish and Wildlife Service, Utah Fish and Game Department, Utah State University, and the Wildlife ManagementInstitute cooperating.Dr. JessopB. Low assistedin the direction and supervisionof the project. Observations were made at various marshes in northern Utah but primarily on Ogden Bay Refuge,one of six waterfowlmanagement areasdeveloped by the Utah Fish and GameDepartment. A detailed descriptionand history of this important waterfowl area has been publishedby Nelson (1954). Most findingsrelate to five studyareas, varyingin sizefrom 15 to 76 acres,three on OgdenBay Refugeand two on the Bay View Club, two miles west of Westpoint in Davis TABLE 1 GENERAL DESCRIPTION OF STUDY AREAS, WEBER AND DAVIS COUNTIF.•, UTAH PercentagesX Total Open Emer- Study Area AcreageX Water gents Upland Treatment Applied Unit 3 76.4 45 49 6 Control, no treatment Check Station N. Pond 17.• 21 48 •1 Control, no treatment S. Pond 14.8 16 46 •8 Coots reduced by shooting and trapping Westpoint N. Pond 48.0 38 1• 49 Cootsincreased by introduc- tion S. Pond 44.5 28 28 44 Coot hatch delayed by nest destruction x Basedon planimeteringcover maps prepared from aerial photosand ground inspection. THE Au•., VOL. 76 PLATE 90 A COOT[•TE•PECIFIC CONFLICTS. A. Patrolling coot "herding" a pair o[ Eedheads away ko• lh½ vicinily o[ lh½ cool's n½;l. B. •ot de[ending [o• source around Whistling Swan. C. Coot "sp]atterinp 31 Black-neckedStilt. D. Coot "sp]at- te•ng" at a male Cinnamon Tea]. E Coot "swanning" a• a G;•t Blue Heron F. Coo• "splattering"a• •Yhi•e-[afed 11)is. •050] RYDER,Intolerance o[ American Coot in Utah 425 County. Coots were reduced on the smallestarea by shooting and trapping,while their hatchwas delayed and reducedby systematicegg destructionon anotherarea. Unsuccessfulattempts were made to in- creasecoots on a third area by introduction of wild-caughtcoots. A generaldescription of thesestudy areas and the treatmentsapplied to each is given in Table 1. Weekly behavioralobservations of about four hours' duration were made from late March until mid-Augustduring both years. These observationswere from semipermanentblinds erectedon three of the areas (Unit 3, Check Station North Pond, and Westpoint North Pond). Weekly censuseswere made on all areas. Routine nesting surveyswere also conducted,followed by frequent brood counts. A few of the cootsdiscussed in this paper were marked with plastic neck tagssuch as usedby Gullion (1951), while most were identified by their location on the areasand by the shape and size of their frontal shields. Sex determinationwas basedupon voice differences, TABLE 2 ESTIMATED BREEDING PAIRS ON STUDY AREAS, 1956 AND 1957 Westpoint CheckStation Species Unit 3 N. Pond S. Pond N. Pond S. Pond Total Coot 1956 70 55 27 14 x 17 183 1957 65 48 29 12 2 9 163 Mallard 1956 8 2 1 4 2 17 1957 11 5 5 $ 2 26 Gadwall 1956 4 2 1 1 0 8 1957 $ 1 1 0 1 6 Pintail 1956 1 0 0 0 0 1 1957 1 0 0 1 0 2 G~w Teal 1956 1 1 0 0 0 2 1957 0 0 0 0 0 0 B-w Teal 1956 I 1 0 0 0 2 1957 1 1 0 0 0 2 Cin. Teal 1956 15 3 2 4 4 28 1957 14 2 2 2 1 21 Shoveler 1956 1 1 0 1 0 $ 1957 1 1 0 0 0 2 Redhead 1956 30 12 $ 9 0 54 1957 26 10 6 5 2 49 Ruddy Duck 1956 $ 5 5 2 2 17 1957 3 $ 2 2 1 I1 Coot population before control; after control 4 pairs estimatedin 1956. Coot population before control;after control 5 pairs estimatedin 1957. ]' Auk 426 RYDER,Intolerance o! AmericanCoot in Utah I.VoL 76 while agedetermination was based upon plumageand leg color. The terminologyused to describevarious coot displaysis, with few ex- ceptions,that usedby Gullion (1952). BREEDING POPULATIONS In addition to coots,the followingducks nested on the studyareas: Mallard (Anas platyrhynchos),Gadwall (Anas strepera), Pintail (Anas acuta), Green-wingedTeal (Anas carolinensis),Blue-winged Teal (Anas discors),Cinnamon Teal (Anas cyanoptera),Shoveler (Spatulaclypeata), Redhead (Aythyaamericana), and Ruddy Duck (Oxyura ]amaicensis). Table 2 summarizesthe numbersof these birds estimated to have nested on the areas. INTERSPECIFIC INTOLERANCE OF COOTS Numerousreferences in the literature describeinterspecific terri- torial displaysand aggressionsby both AmericanCoot and European Coot (Fulica atra) (Table 3). These include attacksupon a variety of water birds, especiallygrebes and ducks,and even upon turtles, garter snakesand muskrats. Boyd (in litt.), writing of the Wildfowl Trust in Great Britain, said, "a few cootsspend the winter with our captive waterfowl, and hold their own successfullywith almost all speciesirrespective of size." Someinvestigations have been conductedto determinethe impor- tance of this interspecificconflict. Munro (1937) concluded,"The sizeof duck broodsis not conspicuouslyinfluenced by the presence of coots." Later Munro 0939) reportedhe found no direct evidence of cootsattacking or molestingyoung ducks. R. Smith (1955), how- ever, felt that the belligerenceof territorial coots should not be overlookedasa factorpossibly limiting i0af spots for breedingducks. On his study areas at Ogden Bay Refuge, Smith found the coot dominant over all speciesof waterfowl with the exceptionof the Mallard and Canada Goose. He believedcoots can greatly reduce availablefeeding areas for waterfowl.Sooter (1945) believedcoot ter- ritoriality might be a factorin reducingthe area of suitablenesting territoriesfor other waterfowl,as well as limiting feedingof certain broods. Neither Hochbaum (1944) nor Low (1940 and 1941) re- ported any interferencebetween coots and Canvasbacks(Aythya valisineria),nor with Redheadsor Ruddy Ducks. Stevens(1947), referring to his Iowa studies,said, "There seemedto be no schism betweencoots and gallinuleson the onehand and the diving duckson theother." Harris (1954) however,believed that cootsmade small pot- Oct. Intolerance of American Coot in Utah 427 TABLE $ SvE½Irs AvrAc•o BY COOTS IN TEiattTor, txt• Dr•Ns• (Fulica americanain North America,F. atra in Europe and Asia) SpeciesAttacked by Coot Areasand Authorities Mud turtle California (Gullion, 1958) Garter snake California (Gullion, 1953) Eared Grebe New Mexico (Wetmore,1920); Germany (Kornow- ski, 1957) Red-necked Grebe Germany (Kornowski,1957) Great Crested Grebe Germany (Kornowski,1957, and Heyder, 1911); England (Witherby, et al., 1949) Pied-billed Grebe California (Gullion, 1953) Little Grebe England (HShn, 1949, and Brown, in liter.); Ger- many (Kornowski,1957) "Ducks" New Mexico (Wetmore, 1920); Scotland (Berry, 1939) "Ducklingos" Oregon? (Job, 1915); Washington (Jeffrey, 1948, and Harris, 1954); England (Witherby, et al., 1949) Mallard Oregon (Sooter,1945); Washington,D.C. (Collins, 1944); California (Gullion, 1958);England (Boyd, in litt., and Cramp, 1947); Germany (Kornowski, 1957,and Libbert, 1926) Gadwall Oregon (Sooter, 1945); Utah (R. Smith, 1955); Germany (Kornowski,1957) Pintail Utah (R. Smith, 1955) Common Teal Germany (Kornowski, 1957); England (Brown, in litt.) Blue-wingedTeal Utah (R. Smith, 1955) Cinnamon Teal Oregon (Sooter,1945); Utah (R. Smith, 1955) Shoveler Utah (R. Smith, 1955.);Germany (Kornowski,1957, and Libbert, 1926) Garganey Germany (Kornowski,1957) Redhead Oregon (Sooter, 1945) Common Pochard Finland (Nylund, 1945); England (Hfhn, 1949) Tufted Duck England (Cramp, 1947); Germany (Kornowski, 1957) Ruddy Duck Oregon (Sooter,1945); California (Gullion, 1955) Ruddy Shelduck England (Cramp, 1947) Whooper and Mute Swans England (Burkill, 1911) Moorhen England (H/Shn, 1949, and Brown, in litt.); Ger- many (Kornowski, 1957) "Long-leggedwaders and Utah (R. Smith, 1955) shore birds" "Small birds" California (Gullion, 1953) Yellow-headed Blackbird California (Gullion, 1953) "Other birds" (than coot) North America (Blanchan, 1904); India (Stuart- Baker, 1929) Muskrat California (Gullion, 1953); Washington (Harris, 1954) [' Auk 428 RYDw,Intolerance of AmericanCoot in Utah I.Vol. 76 holesin Washingtonless desirable to duck broodsand wrote, "It is suspectedthat the high breedingpopulation of cootsserved to partially limit duck populationsin the Potholes." Allen Smith (1956) has written in regard to his Alberta studies: "Sincethe start of this studyin 1952,general field observations of coots and waterfowl on the Lousana area have led us to be- lieve that the aggressivenature of the coot during all periodsof the breeding seasoncould not but adverselyaffect the duck populationin coot habitats. Nevertheless,we have been able to collect no data to prove that this is so." Apparently the coot territorial defenseis not alwaysimpenetrable. Various authorsdescribe finding coot nestsparasitized by other birds such as the Common Gallinule (Gallinula chloropus) (Attwood, 1948),Redhead (Bryant,1914) and Ruddy Duck (Low, 1941;Weller, 1956). Similarly, Delacour and Mayr (1946) and Goodall, et al., (1951) mention the Black-headedDuck (Heteranetta atricapilla) parasitizingthe nest of the Red-garteredCoot (Fulica armillata) in South America. Munro