290 Lr Vol.Auk 75 COURTSHIP, HOSTILE BEHAVIOR, NEST- ESTABLISHMENT AND EGG LAYING IN THE EARED GREBE (PODICEPS C.4SPICUS) TH• behaviorof North American grebesis little known. This is especiallytrue of their nestingbehavior. They are relativelysecretive and nest in marshesout of reach of most observers.This paper de- scribescourtship, hostile behavior, nest establishment,nest building, copulation,and egg layingof the Eared Grebe,and discussessome of the comparativeaspects of thesebehavior patterns. In addition, some problemsof clutchsize and layinginterval are considered. Simmons'work (1955) on the Great CrestedGrebe of Europe, Podicepscristatus, has been usedextensively for comparisonwith the Eared Grebe. TI-IE STUDY AREA The studyarea was near Williams Lake in the Carlboodistrict of British Columbia,52.00 ø North latitude, 122.00ø West longitude,and 1500 to 3000 feet above sea level. The Cariboo Parklands biotic area or biomeas describedby Munro and Cowan (194Y) is flat to rolling grasslandbroken by standsof lodgepolepine (P{nus conioria), Douglas fir (Pseudotsu#amen•iesii), and aspen (Populustremuloides). Fre- quently the bottomsof depressionsin the grasslandhold shallow lakes varyingin size from a few acresto twenty squaremiles. The Eared Grebeschose lakes about a mile by half a mile. The studylakes, Westwick and Sorensen,were once one but are now artificiallydivided by an unpavedroad. The lakesare carefully de- scribedby Munro (1941). The greatestdepth is twelvefeet, but more thanhalf the lakearea is lessthan five feet deep.These highly produc- tive lakes have at least a foot of thick black mud on the bottom. The clear water is filled with numerous small invertebrates, but no fish. The concentrationof invertebratesis such that food does not appear to limit the populationsof any of the birds using the lakes. By the middle of July, the bottom flora reachesto within two feet of the surfaceand extendsover ninety percentof the bottomarea. In addition densemats of floatingalgae cover one fourth of the surfaceby the end of July. The bottomplants are Scirpus,Ruppia, Ceratophyllum, Myrio- phillum, and Potarno#eton,and the floating forms are principally ./Iphanizomenonand Cladophora. WestwickLake had a colonyof two hundredand ten pairs of Eared Grebes,and SorensenLake a colonyof forty pairs. This study was July•9•83'1 MCALLISTER,Courtship, etc.,in Eared Grebe 291 made during the summersof 1955 and 1956, using ordinary observa- tional methods. Sex of the birds could often, but not always, be told. The maleshad larger crestsand sometimesappeared to be larger in total body size. Diagrammaticdrawings of someof the patternsde- scribedare shownin figures,and the courtshippatterns of the Eared Grebeand the Great Crested Grebe are comparedin Table 1. Dr. I. McT. Cowandeserves my greatestthanks for his valuablesug- gestionsand enthusiastic support. I alsowish to thankall theothers who helpedwith the manuscript.Financial support came from the National Research Council of Canada. COURTSHIP DISPLAYS Courtshipdisplay was seenas soonas the Eared Grebesarrived at the breedinglakes. In 1955the first grebesarrived on May 1; in 1956 a few were on the lakeswhen I arrived on May 2. In both yearsmost of the grebeshad arrivedby the end of the first weekof May. Courtshipwas mutual; all patternsnoted were performedby either sex. The courtshipdisplays were all doneon openwater in the center of the breedinglakes. There wasno territoryof any kind involved,and each bird made use of the whole lake area. The Great Crested Grebe (Simmons,1955) courtedon territory and usedthe defenseof terri- tory boundariesas part of its courtship. Courtshipdisplay tapered off abruptly as nestingbehavior began. The colony,stimulated by courtship,acted as a unit in the total change in behavior. Simmons(1955) describeda similar abrupt changeof behaviorin the territorial Great CrestedGrebe, but each pair had its own change-overtime. The increaseduse of advertisingbehavior seemedto serveto synchronizecourtship in the Eared Grebeand create a true colonial situation. .4dvertisingBehavior Advertisingbehavior was seenwhere an unpairedbird was in search of a mate, or when a paired bird had temporarilylost touch with its mate. The advertisingbird swam up and down approachingother grebeswith a characteristicattitude (fig. 1) and call. The feathersof the wholebody were fluffed out makingthe posturingbird seemlarger than its fellows. Both crest and neck feathers were raised, the neck was erect, and the bill was directedstraight forward and closedduring the call. The call wasa three-notedpoo-eee-chk, but the endingchk couldonly be .heardat very closerange. It may be produced,as Simmons(1955) suggestedfor the Great CrestedGrebe, by the effort of producingthe first two notes. The first two notes were plaintive and slurred, about 292 McALLISTER,Courtship, etc., in EaredGrebe I.• VoL Auk7• threat advertising cat attitude penguin dance alarm resting FIGUREl. Some behavior patterns of the Eared Grebe. a musicalfifth apart. They soundedmuch as if playedon a flute. The third note was on the samepitch as the first but much quieterand very gutteral. Eared Grebesgave the appearanceof beingpaired on arrival in the spring. More than half were swimmingin pairs on the day of their arrival at Westwick Lake. When a single bird approacheda pair, situationssuch as the following occurred:"One of the pair swam to- ward the advertisingintruder, and it turned away and left them." "Intruder appearedand swam between the paired birds and around them. The male of the pair ignoredthe intruder for a while and then rushed at him from a distance of four feet in a threat attitude. Then the pair moved off while the intruder moved into the reeds." Such incidentsas theseled Munro (1941) to say that the birds were paired July•õ58A'] MCALLISTER,Courtship, etc., in EaredGrebe 293 on their arrival, and my judgmentoriginally followed his. Closerstudy of individualpairs, however, showed that noneof the Eared Grebeswere paireddefinitively at this stage. Partnershipslasted from threehours to five minutes. An advertisingsingle bird of either sex swamup to the pair and took oneof the pair away. The otherof the pair then went off and advertised.The numberof changesof partnersseen dropped off rapidly until pairs were definitivea few days before nestingbehavior was first seen. The advertisingposition of the Great CrestedGrebe describedby Simmons(1955) seemsthe sameas that of the Eared exceptthat the crest of the larger speciesis depressed.The elementsof the Great CrestedGrebe advertisingcall seemto be the sameas those of the EaredGrebe call. The Great CrestedGrebe remained stationary while advertising,which may be relatedto the territorial nature of its court- ship. The Eared Grebemight be either stationaryor swimming.It might evenswim up to other grebes,but it was not seento be aggressive. Habit Preening Courtinggrebes floated along in pairsand preenedvigorously. This behaviordid not differin aspectfrom ordinarycomfort preening and I saw nothingto indicatethat it was a courtshipactivity. However, be- tween thesebouts of comfort preening,a different kind of preening was seen. The two birds drifted within a foot of each other and preenedtogether; either bird might lead, but the other repeatedthe movementsexactly. The timing was so closethat it was often difficult to tell whichbird wasleading. There wasno definitesequence of move- ments,but both birds preenedthe samefeathers at the sametime. The movementswere a little quickerand not quite so thoroughas those of comfortpreening. The participantswere most frequently side by side but mightend up facingeach other. ! have not seenthis patternexcept duringthe courtshipperiod, and ! think it musthave a courtshipfunc- tion. Habit preeningis by far the mostcommon courtship pattern in the Eared Grebe. It is also reportedfor the Great CrestedGrebe (Sim- mons,1955), but in that specieshead shaking was the more common courtshipmovement. Head Shaking Head shakingwas seenboth as a separateceremony and as part of the penguindance. As a separateceremony the two birds swamalong rapidly,one in front and slightlyto the sideof the other. Their body featherswere raised,and their positionwas very high on the water. Their neckswere stretchedup higherthan in the advertisingbehavior 294 MCALLISTER,Courtship, etc., in EaredGrebe LVol.[ Auk75 with crestraised and neck feathersdepressed. The generaleffect was taller, higheron the water, and thinner than in the advertisingattitude. The headwas turned smartly left and right,all in the horizontalplane. The tempowas military, precisebut not hurried. Six to twelveturns constituteda ceremony;then both birds usuallydove. The timing of both the turns and dive was generallyquite preciseas the following bird apparentlycopied the leader. Either sex might lead, and oncehead shakingwas seen done by an unpairedbird. After advertisingto a pair, the odd bird did severalhead shakes,and the female of the pair swam off with him. The headshaking ceremony was as commonas the cat attitude (fig. 1), but not as commonas the penguindance (fig. 1). In about half the instancesrecorded, head shakingwas directedtoward other grebes, pairedor singlebirds, as a threat. Once the shakingpair were riding so high on the water that white breastfeathers were visible. In the Great CrestedGrebe (Simmons,1955) head shakingalmost replacedhabit preening and the penguindance. In additionto courtship, it is usedto cementthe pair bond duringand after territory-boundary disputes.The use of shakingas threat toward