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Home , Anatidae, Galliformes, Great crested grebe, Least grebe, Little grebe

290 Lr Vol.Auk 75

COURTSHIP, HOSTILE BEHAVIOR, NEST- ESTABLISHMENT AND LAYING IN THE EARED ( 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, ,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 , 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 , but no . The concentrationof invertebratesis such that food does not appear to limit the populationsof any of the 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 ,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 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 . 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 thebreeding lakes. There wasno territoryof any kind involved,and each 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 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 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 muchquieter and 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 thoseof 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 sohigh 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 an intruder was the onlyEared Grebe counterpart of this. The attitudeof the GreatCrested Grebewas basicallythe sameas that of the Eared Grebe,but the birds usuallyfaced each other and were alwaysstationary. Often, too, their bills were below horizontal. Faster turns were alternatedirregularly with slower ones in the Great Crest, while the tempo was even in the Eared Grebe. The Great CrestedGrebe had a specialhead-shaking call. Huxley (1914) describedGreat CrestedGrebes head shakingwhile back to back, but Simmons (1955) had never seen this variation. Wetmore (1920) cited the samefor the Eared Grebe,but I havenot seenit. Kilham (1954) describeda pair of Pied-billedGrebes (Podi- lyrnbuspodiceps) head shaking while they swamnear eachother. Pen#uin Dance The penguindance is that peculiardisplay in which grebesstand up like penguinswhile treadingwater. The penguindance (fig. 1) was more commonthan the cat attitude or head shaking,but less common than advertisingbehavior and courtshippreening. Both birds would tread water face to face raisingtheir white breastfeathers out of the waterand seemingly stood on their tails. Their bellieswere only a few inchesapart, and they paddledtheir feet alternatelyand so rapidly that they sometimessplashed. As they stoodup they uttereda shrill chit- tering call and shooktheir headsviolently from side to side. There were from six to twenty headshakes, but the pacewas so fast that the birds were usuallyout of phase. Droppingto the water, they slowed July•õ.•8.1-[ McALLISTER,Courtship, etc., in EaredGrebe 295 headmovements to the paceof the headshaking ceremony, and eight to twenty turns were made from the swimmingposition facing each other. Only oncewere Eared Grebesseen shaking face to face with- out first going throughthe dance. Sometimesthe birds turned during this last head shakingand continuedas in a normal shakingceremony, swimmingtogether down the lake. Sometimesthey simply stopped headshaking, drifted apart, and comfortpreened. Habit preeningwas a part of the post-danceceremony about a third of the time. The was dippedeight to sixteen times to the breast feathersor primaries eitherbefore or duringthe headturns. The preeningmovements were here evenmore ritualized than wasseen in the usualhead shaking. The featherswere touchedbut not stroked,and the rhythm of the ceremony was not broken. Very occasionallythe Eared Grebesturned while still standingand ran a short distanceon the water before settlingdown to head shake. Usuallythe birdsstood up actuallyfacing each other, but occasionally they stoodup facing the samedirection, but turned while standingto face eachother. This turningseemed to be the sameas that seenin the Great CrestedGrebe discoveryceremony (Simmons, 1955). In diving the Great Crested Grebe most often overshotits mate, came up facing away from it, and turned to face it. The mate was in a cat attitude, and the diving bird slowly droppedto the water, head shakingwith it. I have not consideredthe discoveryceremony under a separateheading, because I think that it is an incompleteform of the penguindance. This incompleteform is the more commonform for the GreatCrested Grebe, and the completeform wasrarely seen. When it did occur,Great CrestedGrebes dove and eachof the pair broughtto the surfacea bit of pond weed,swam toward its mate and rose in the penguindance. The Eared Grebemay beginits dancefrom a dive or from the surface; but the use of weed was not seen. The Great CrestedGrebes leaned against each other during the pen- guin dance (Simmons, 1955), but the Eared Grebesstood without leaning. The chitteringcall of the Eared Grebepenguin dance consisted of the two notesof the advertisingcall uttered more quickly and in wild excitement. In constructionit is the same as the threat call, but the quality seemedmore musical. Simmons(1955) did not describeany call for the penguindance of the Great CrestedGrebe. Perhaps,since headshaking was so closelyrelated to the dance,the headshaking call wasused. The EaredGrebe was not heardto call duringhead shaking. Occasionallyin the Eared Grebe an unmatedbird flappedin high intensitythreat at a pair doingthe penguindance. Often it camefrom 296 McALLISTER,Courtship, etc., in EaredGrebe ['LVol. Auk7.5 quite a distanceat the soundof the dance. This was more likely to happenlater in the seasonwhen the odd bird had been advertising for a long time. In the Eared GrebeI did not observethe penguindance after a pair had begunnest building. Lawrence(1950) said that the upright rush of the (,4echmophorusoccidentalis) was seenin reduced intensityall summer;but the uprightrush may not be homologousto the penguindance of other grebes. Cat •Ittitude In the cat attitude the head was drawn down on the breast with the crestand neckfeathers raised (fig. 1). The raisedbody feathers made the birdslook muchlarger than usual,and the wingswere away from the bodybut bent. The carpaljoint was tippedforward and down to almosttouch the water. The posturingbird exactlyfaced the bird elicit- ing the display,thus makingmore strikingthe orangecircle of plumes in the centerof the larger black circle of the wings and body. The attitude of the Great Crested Grebe seems to be the same. The cat attitude was quite rare comparedto the other courtship patterns.Apparently the Great CrestedGrebe (Simmons,1955) uses it more than the Eared Grebe. Its function is not clear. Both grebes usedthe cat attitude when an unmatedbird had beenadvertising. other grebe swam toward the advertisingbird and dove. The adver- tising grebe assumedthe cat attitude, and the approachingbird rose in the penguinattitude. Paired Eared Grebesused the sameceremony withoutprevious advertising. In the Eared Grebethe penguindance seemedalways to follow; in the Great Crested Grebe head shaking followed. Once a femaleEared Grebe assumedthe cat attitude facing an advertisingmale as he passed. Her mate immediatelydrove the odd bird away. Rarely in eitherspecies one bird flappedover the water a little way and did a cat attitudeturning to face its mate. Or it might just patter away and swim back without usingthe cat attitude. The penguindance or head shakingfollowed respectively as seenbefore. In addition the Great Crested Grebe unmated female used the attitude when threatenedby a matedmale. I have includedthis sectionunder courtshipand madeno mentionof it underthreat as Simmons(1955) did, becauseI think that it is not related to threat behavior.

I-IOSTILE BEHAVIOR Threat •Ittitudes Threat behaviorwas seenunder two setsof circumstances.During the courtshipperiod, advertising birds (fig. 1) swam up to courting July'[ 297 19,•8 .! MCALLISTER,Courtship, etc., in Eared Grebe

TABLE 1

COURTSHIP PATTERNS COMPAREI)

Advertising Behavior: Eared Grebe Great Crested Grebe neck erect, bill forward x x crest and neck feathers raised x crest down body feathers fluffed x x body high on water x x call: poo-eee-chk x tIrr-owp row-ah done while: moving x stationary done by lone bird mated or not x Habit Preening: precise, stereotyped movements x x primaries and breast used mostly x x preens whole body x ? seenalone or with head shaking x x Head Shaking: neck erect, medium stretched x x crest up x x neck feathers down, body feathers medium x x bill: forward x slightly down x facing: forward x each other x done swimming x done stationary x done between battles x used by pair as threat or courtship x x Penguin Dance: head turning x x crest up, bill forward x x neck medium stretched x x body and neck fluffed x x standingposition x x leaning x not leaning x chitter call x ? elicited: by diving for weed x by penguin x from surface x by cat attitude x turn forward while shaking x stay facing each other x x iollowed by head shaking x x 298 McALLxs•r,w,Courtship, etc., in Eared Grebe

Cat Attitude: head withdrawn, crest raised x body feathers raised x wings out, tipped forward x faced partner x elicitedby penguin x elicited by mate approachingon surface x female may do it when threatened followed by: penguin dance x head shaking

pairs and were either driven off or acceptedby one of the courting birdswhile the otherswam away. Later, duringnest establishment, the birdsowning and defendingnest platforms threatened and droveaway any EaredGrebes approaching within about two feet of the platforms. Throughoutthe nestingseason nests were defended in this way. But during courtshipand on open water during nesting,threat was rare. While thereis completeoverlap from the highestto the lowestintensi- ties of threat,three arbitrary divisions can be madeon the basisof the elementsincluded. The higherintensities were more characteristicof nestdefence, and the lower of courtship. At low intensitythe angleof the neck was forty-fivedegrees for- ward,the bill straightforward and open(fig. 1). The feathersof the neck were laid down and those of the crest raised. The threatened bird usuallyjust swamaway. At middleintensity the birds swam slowly towardthe threatenedbird in the low intensitythreat attitude. In high intensitythreat the low intensitythreat attitude was takenfirst. Then the wings were raised and the bird flappedover the water toward the otherbird. The threatenedbird escapedby diving, was sometimesfol- lowed a short distance,and might be struck or bitten before it had a chanceto get awayby diving. The strikingmotion involved drawing the head back and then thrustingit forward. The movementseemed to be the sameas that performedin diving,and the dive was sometimes actuallycompleted at the endof the rush. The threatenedbird turned away as the rushbegan and took the blow, or most frequentlythe bite, on the sideor wing. Threat seemedalways to be successfulin driving the intruderoff. The Eared Grebehad movingattack-escape sequences instead of the stationaryfighting and upright threat of the Great CrestedGrebe (Simmons,1955). The threat call was almostalways associated with the middleand high intensitythreat, rarely with the low. The call is a loud chitter,the two notesabout a musicalfifth apartand alternatedrapidly. In spiteof the speed,each syllableis individuallyaccented. •J•] McAI•I,IsTE•t,Courtship, etc.,in Eared Grebe 299

The forward threat and attackof the Eared Grebeappear to be the sameas thoseused by the Great CrestedGrebe (Simmons,1955), and the Great Crested'sbark call seemsto be homologouswith the chitter of the Eared. it is interestingthat Simmonsreported in the Great CrestedGrebe so many variationsof the threat call. This may be associatedwith its apparentlygreater use of threat behavior. ! have observedno uprightthreat posture in the Eared Grebe,perhaps because two Eared Grebesnever seem evenly matched. The Eared Grebehad no largeterritory boundary, for the onlyterritory defendedwas the nest itself, and there one pair was always dominant. In the fightingof the Great CrestedGrebe, Simmons said, "both grebesleap at each other and clashvertically breast to breast." It is not clearwhether this was the upright swimmingposture of the upright threat or the standingposture of the penguindance (fig. 1). This standingposition, I havenever seen in the Eared Grebe. Dubois(1918) describedthe , Podiceps auritus, as having a lunging attack similar to what I saw in the Eared Grebe. Wetmore (1920) spokeof a femalel•ied-billed Grebe, podiceps, with young as "rising threateninglyon the water, made a great boilingnoise by treadingrapidly with her feet." As the presenceor absenceof the stand- ing fightingor threatbehavior may haveimportance in tracingthe evo- lutionof someof the courtshippatterns, it shouldbe morethoroughly investigated. During the courtshipperiod a pair of Eared Grebesmay use the headshaking courtship pattern as threat. Escape,dttitudes The alarm posture (fig. 1) was seen during courtshipwhen the birds were disturbedby man. No other animalor naturalphenomenon was seen to produceit. During nestingthe alarm attitude was the usualone for birds on openwater. They were shy and constantlyalert duringthis time. When the eggswere hatched,the grebesreturned to the former restingposture. In the alarm attitude the feathers of the body, neck, and crest were all laid down. The neck was extendedvertically, and the bill was straightforward. The wingswere tightly closed.The grebewas ready to escapeby diving, submarinediving, or flappingacross the water. The alarm attitude is probablypart of the intentionmovements of escape.The postureseems to be the sameas that of the Great Crested Grebe (Simmons,1955) but I do not find it describedfor any other . I have heardno call in alarm or escapebehavior. This is particularly •00 MCALLISTER,Courtship, etc., in EaredGrebe FtVol. Auk noticeablein the nesting colony, where, even with the naost silent approach,I seldomsaw and never heard a grebe; only the empty nests were found. Simmons(1955) did not mentionwhether or not the Great Crested Grebe had an alarm call. Gross (1949) describedthe , Podiceps dominicus,male as having an excited call, yeep-yeep-yeep, followedby a rattledye-ye-ye-ye-ye-e-e-e-e-e-e. The femaleand young all dove "in a wild splashat this signal." Deusing (1943) said that the Pied-billed Grebe had a hu,hu,hu,hucall continued for several sec- onds,which he said might be an alarm call. When a person or boat or other strange object appearedclose to a grebe, it first assumedthe alarm posture, and then escaped. When anothergrebe attacked it, however,it escapedwithout using the alarm posture.Escape may be madeby patteringover the surface,by diving, or by the submarinedive. The crashdive was only seen in extreme circumstances,and was a •ombinationof divingand patteringover the water. The wings were raisedas if for flight, but the bird dived and usedits wings a short distanceunder water. The submarinedive was almostas commonas the ordinary escapedive and pattering. Unlike these, it was never seen except in an alarm situation. In this pattern the grebe sank out of sight from the alarm attitude, body first, then neck, then head. NESTinG Bet7innln#of Nest Establishment In the courseof one week, the behaviorof the grebeschanged abruptly. Late arrivals were conspicuousexceptions, keeping apart in a little group until they finishedtheir courtship.When they began nest establishmentbehavior, these late arrivals were absorbedinto the larger group. Before May 16, 1956 none of the elementsof nest establishmentwas seen; after May 20 none of the courtshippatterns was seen. The situation was the same and the dates were almost identical in 1955. '1'hechange is evidenteven to the casualobserver. In the first periodfeeding and restingare closelyintermingled with courtship;there is almost always a pair courting somewherein sight. The birds are scatteredall over the open water. The number of calls of the adver- tising courtshippattern makesthe lake seemnoisy all day, and the birds are very tame when approached. In contrast,nest establishmentbehavior is seeneach day for short periodsonly, and the whole colonyis usuallyinvolved. Thesemating partiesare always in the reedsor floating vegetation,and show plat- form building, platform defense,soliciting, and copulation. Between July1õ,•8']j •IcALLISTER,Courtship, etc., in EaredGrebe 301 partiesthe birds spendmost of their time restingin large groupsnear the reed area where they last built nest platforms. They scatterto feed periodicallybut alwaysreturn to the group. While on openwater they are silentand increasinglyshy. The changefrom courtshipto nestestablishment depends on the date the ice goesout and the temperaturein the early part of May. The birds almostall arrive in the first three days after the ice breaks up on the breedinglakes. The warmer and sunnierit is in May (it sel- dom exceeds85 ø F.) the greaterthe degreeof courtingactivity. Pre- sumablya certain amount of courtshipmust be done before the birds beginto changeto nestingbehavior. This is suggestedby the observa- tion that late flockscontinue to courtafter the early flockshave already startednesting activities.

Solicitin# Solicitingis the first behaviorpattern of nestestablishment seen each spring. In a solicitinggrebe, the bodyis low in the water, neck forward, and head and bill laid straight out on the surface of the water. The neck is not unduly extended,and the crest is down. Both sexes may solicitand both call. This positionis the sameas the positionof the femalein copulationexcept that in copulationher bill is usuallypointed slightlydown. One call is associatedwith both solicitingand copula- tion. It is an eerienote somewhatsimilar in quality to the screamof the Red-shoulderedHawk, lineatus. It doesnot, however,change in pitch. The solicitingbird may be answeredby its matewith the same call. Later in the seasonboth birds solicit on the nest platform and copulationfollows. Simmons(1955) statesthat the Great CrestedGrebe rarely solicits on the water, and doesnot start solicitinguntil the platform is at least partly built. The positiontaken is the sameas that of the Eared Grebe, exceptthat the neckis somewhatstretched. Simmons does not mention that any call accompaniesthis patternas in the Eared Grebe. The Great Crested Grebe has another soliciting display in which it stands on the nest and archesits headas thoughto peer at its feet. Simmons(1955) refers to this as rearing. Hosking (1949) describesa similar pattern in the Horned Grebe, Podicepsauritus. Buddie (1939) gives a photographof the New Zealand Dabchick, Podiceps rufopectus, in the rearing attitude. I have not seen this in the Eared Grebe, although it may occur. Perhaps rearing is the ritualized inten- tion movementof sitting down on the nest. Motion picturesof both rearing and sitting down on the nest would be helpful in decidingthis question.Rearing also resemblesthe copulation posture of the male and the posture of both birds in turning the . 302 MCALLISTER,Courtship, etc., in EaredGrebe I.FVol. Auk75

Developmento[ Plat[otto Building Nest or platform buildingbegins at a very low intensitya few days after the first soliciting.The birds beginto drift all togetherinto the reeds.Almost any place may be chosen,but somefloating algae or reeds must be present. Isolatedtufts and sparsefloating pondweeds totally unsuitablefor finishednests may be usedfor theseearly platforms. As the birdsswim slowly around in the chosenarea, a singlefemale may pull a brokenreed over and lay it acrossanother reed caught between two upright stalks. Then the whole group swimsaway and resumes feeding. With eachoccasion of group activity the intensityof the behavior increasesand morepairs becomeinvolved. On SorensenLake the eve- ning of June9, 1955,this sequencewas seen:At sunsetthe birds were all feeding on open water. A pair drifted into the entranceto the marsh, and the birds swam to oppositesides of a reed tuft in the middle of the channel. This tuft was one of a group of three each containingless than a dozenreed stalks. The femalepulled at a long floatingreed and addedsome floating algae to that alreadycaught in the reedtuft. Severalpairs swam by andwere driven off, the areadefended beingonly a foot or two aroundthe platform. This pair held the tuft until dark at eleven•,.M. and copulatedon it abouta dozentimes. Sev- eral otherpairs could be heardsimilarly occupied in the marsh,but the majorityof the birdshad not yet chosentufts and troupedup and down in a body, headsdown in restingposture. These early platformsare shown in Plate 13. More and more pairs becameinvolved, until on May 18, 1955 an activeparty was seenon WestwickLake. The day was warm and sunny,and the grebeswere feedingall over the lake. At four •'.M. a disturbanceon the far shore causedthe grebes to drift toward me. In the next half hour they were all in the reed fringe in front of my canoe.The eerietrilling of the copulationcall beganand increasedas pair after pair joinedin. Six pairs solicitedand copulatedon old nests. Pairs rushedat eachother, wings raisedand beaksopen in threat. A dozensmall battles raged at onceand the threatcalls of fifty individuals were so continuousthat I could not distinguishthe birds which were calling. Six singlebirds tried to attractmates but were dealt with vio- lentlyby bothmembers of eachpair theyapproached. American (Fulicaamericana) and RuddyDucks (O•yura ]amaicensis)swam by and were not botheredby the grebes. These partiesstart spontaneouslyand may take placein a different area eachtime. There is a tendencyto useone reed bed for several daysand thento moveto another.The movestook placeboth on the THE AUK, VOL. 75 PLATE 13

Eared Grebe. Above:An areaof sparsereeds showing five unfinished nests used for copulation. Below:An earlyunfinished nest used for copulation. TI-•E Av•, VOL. 75 PLATE 14 !

.•...-...,.,.,,•::. ,- ,.:,•.... •

•ests of Eared Grebe. •bove: A n•t not yet complete. Below: A finished nest with abandonedegg. The egghas been peckedby a grebe. July19•8-1'] MCALLISTER,Courtship, etc., in EaredGrebe •03 lake that I was watchingfrom the canoeand on the lake which I watchedonly from a distanthillside. I doubt,then, that my presence disturbedthe birds and causedthem to move. The movesmay have beenconnected with the increasingmaturity of the nestingpatterns. In each of the two summersthe grebesat one time chosean area of reedsfar too sparseto supportnests. On June21, 1955 the grebes were in an area of new reeds in the center of Westwick Lake. The tufts each contained less than a dozen stalks and were several feet apart. I couldsee in this openarea the beginningsof nearly fifty nests. The grebeswere alternatelysoliciting on the new platformsand adding new materialto them. Five nestshad one egg; one nest had two. A thundershoweraccompanied by strongwinds the next night destroyed the nests,and activity switchedto a new area. Nest Building Patterns All the buildingseemed to be doneby the female. The malefollowed the female but was not seen to handle nest material. Since it was diffi- cult to tell the sexesapart, someerrors may have beenmade here. If only the female builds, this is the only pattern besidescopulation in which the roles of the sexes are not the same. The female dives near the nest site and comesup about two feet from it with a large beakful of algae,lays it on the edgeof the heap with a quick reachingmove- ment, and divesagain. The nestis set on a foundationof severalbent- over reeds. It may be in the center of a small clump of reeds or at the sideof a largeclump. The heapof debrisfinally makesa more or lesspyramid-shaped pile reachingfrom a foot or two from the bottom of the lake to slightlyabove the surface. Three hoursis sufficienttime for the constructionof a nest. Additionalmaterial may be addedto the sidesof the nest during the egg-layingperiod. The centerof the nest is cupped,but the rim is never more than an inchabove the center.The wholenest is soggy,and the centermay be slightlybelow water level even when the adult is not on it. The lower half of eachegg is alwayswet. The nest material dependson the lake bottom in the immediate vicinity of the nest. Nestsbuilt in a new reed bed were bright green, completelyconstructed of living algae; those in old reed beds were nearly black with rotting reedsand algae. All the nestshad the appear- ance of being moldedof wet clay, smoothand soft. The colonieswere compactunits in the densestpart of the reed bed and visibleneither from the shore nor from open water. The final nestson other lakes, however, are often built much more in the open. Nests are from one foot to three feet apart and are in water one to three and a half feet deep. Placeswhere there are surfacealgae are 304 MGALLISltlI,Courtship, etc., in EaredGrebe LVol.F Auk7• avoided.The first nestsin the final colonyare in a groupand form a nucleusfor the developmentof the colony. Darling (1938) suggested that a centralnucleus and concentricrings is the usualcolony form in . The colonyis compact,using every availablereed tuft in the area. When nestbuilding, the femalesassume a shy attitude that continues throughegg-laying and incubation.Their crestsand neckfeathers are sleekeddown in a low intensityalarm attitude. The malesdo not seem to adoptthe alarm attitudeuntil the middle of egg laying. Nest material was never seen used ritually in courtshipor as an invitation to nest.

Copulation Copulationoccurs frequently from the time the first platformsare madeuntil the end of egglaying. The femalehops up on the platform with a thrustof her legs,wings closed. She standson it with her legs out like props for a few secondsand then drops down on her belly. She stretchesher neck forward and holds her bill pointed down at a forty-fivedegree angle. Her headand neckfeathers are flattened.The male swimsaround behindthe nest and hops up on her back without openinghis wings. He standsat an angle slightly forward of vertical with crest and neck feathers down. His neck is curved and his bill pointeddown. Both birdsare motionless.The malegives the copulation call. The femaledoes not join in the calland may even threaten passing birds. After about half a minute the male slides into the water over the head of the female. There is no post-copulatorydisplay. The femaleGreat CrestedGrebe (Simmons,1955) holdsher head and beak straightout, probablybecause of her long neck. The male takesthe sameposition as seenin the male Eared Grebe,but the closed wingsare quiveredas in the rearingsoliciting attitude. The call is a harshrattle "soundinglike a creakingee eee" (Simmons,1955, quota- tion of Hanzak). As the male slidesoff the nest, he takesthe escape bathingposition except with the crestand headup. He settlesand be- ginshead shaking with his backto the female.The femaleraises her head to head shake with him. "Escape bathing" was so named by Simmons(1955) becausehe thoughtit was a real escapepattern. It is a particularlyviolent version of the bathingbehavior which ends with a peculiarattitude. The body is heldupright but half submerged,that is, half the white breastfeathers are showingabove the water. The neckis archedand the crestdown; the chin is on the breast. I have seen this only three times in the Eared Grebe,and Simmons(1955) only five in the Great Crested July•958-1'l MCALLISTER,Courtship, etc., in EaredGrebe 305

Grebe.In all of my EaredGrebe records the patternfollowed defeat in a nestestablishing encounter. in three of Simmons'records, escape bathingfollowed aggressive encounters with other grebes;in the other two, it followedan escapedive. Followingescape bathing, the Great CrestedGrebe puts its headunder water and looks around as if looking for something;I did not see Eared Grebesdo this. Simmonsfelt that the grebeswere lookingfor fish predatorsand that the wholepattern was oneof escape.He saysthat the assumptionof this attitudeafter copulationis a return to escapebehavior after this unusuallyclose con- tact with anotherbird. I do not doubt that post-copulatoryattitude and the escapebathing posture are related. ]gut the upright posture, the archedneck, and the loweredbill are neverseen, even separately, in escapebehavior. Escapebathing may be derived from the male copulationposture or from the rearing solicitingattitude, but it is probablya carry-overof sexualmotivation. ,'lbandonedEggs Whenmost of the pairswere involved in nestestablishment, eggs be- ganto appear.At first they werenot broodedbut simplyabandoned on flimsyplatforms. These were "yard eggs"in the samesense as those of galliformsand showreadiness of the gonadsbefore maturation of the incubation behavior. The hormonal basis of maturation of incuba- tion behaviorin grebesis not known,but it may well be relatedto increasedproduction of the anteriorpituitary hormone prolactin which is knownto stimulatebroodiness in pigeonsand (reviewed in Sturkie, 1954). The first few days theseeggs were not pecked,but after this all eggsfound had a holepecked in the top. Presumablya grebe pair may fightfor andgain a platformwith an egg,peck the egg,and push it off the nest. Just beforefinal clutcheswere startedon Westwick Lake in 1956 there was a brokenegg undernearly every platform,and two undersome. I neversaw the grebespeck an egg,but the peckswere clearlythose of smallbills, and peckingwas donewhen no otherbirds were around the area. The contents were not eaten. As the season progressed,the birdsbecame more and morevigorous in guardingtheir platforms,and they beganto incubatethe eggsas they laid them. Theseincubated eggs were the eggsof the final . Two clutchesof peckedeggs were found in the last week of incuba- tion. One bird of eachpair may have died or desertedthe nest. Plate .... showsan abandonedegg that has beenpecked. Nest-establishmentbehavior begins about the sametime, but it may end as early as May 20 or as late as July 16. On Westwickand Soren- 306 MCALLISTER,Courtship, etc., in EaredGrebe [Vol.F Auk75 sen lakes in 1955 clutcheswere not begun until June 27 and June 22 respectively.1956 was similar. If June is warm, the tempo of nest establishmentrises graduallyto a culminationin the laying of final clutchesin the early part of June. But usuallyJune is coldand rainy in the studyarea, and the birds stopall reproductiveactivity and rest and feed until good weatherin July. When good weatherreturns, a burst of nest establishmentactivity leadsto incubation. Lack (1933) and Kendeigh(1934) give a numberof examplesof delayin nestingwith unusually cold or wetweather. These delays may bein nestbuilding, laying, or beginningincubation. They are apparently causedby inhibitionof nervousmechanisms, because the changesare too suddento be explainedby changesin hormonebalance. The selectivemechanism presumably works in sucha way that young are hatchedwhen food is abundant,according to Kendeigh (1934). Cold weatherdid not seemto affectthe supplyof food for the Eared Grebe or its young,as the grebesfed on plentifulinsect larvae in the water. But manyyoung died of exposureduring the first few daysafter hatch- ing. If the birdsstarted to incubateduring inclement weather, these losseswould probablyincrease. Clutch Size Full clutchesvaried from one to six eggs,but clutchesof one, two, five, and six were relativelyrare. The meanclutch size for all nests observed,except those robbed experimentally, was 3.48. Table2 gives data for all nests where sufficient observations were made to ascertain full clutch size. TABLE 2

ACTUAL FULL CLUTCH SIZE

Total of Clutches c/1 c/2 c/3 c/4 c/5 c/6 Mean

Westwick Lake, 1955 113 1 8 47 45 9 3 3.48 (Marsh colony) SorensenLake, 1955 37 0 0 13 22 2 0 3.70

Total 150 1 8 60 67 11 3 3.59

Westwick Lake, 1956 106 0 0 69 33 2 2 3.40 (Marsh colony, undisturbednests) Westwick Lake, 1956 15 0 0 14 0 0 1 3.42 (Willows colony) SorensenLake, 1956 22 0 1 16 4 1 0 3.22 Total 143 0 1 99 37 3 3 3.36 July,9•8J'1 McALLxS•R,Courtship, etc., in EaredGrebe 307

There is a significantdifference (P: .01) betweenthe distribution of clutch sizes for all nests observed in 1955 and for nests observed in 1956. SorensenLake, when the two are compared,shows a less significantdifference (P -- .05). Westwick Marsh 1956 when com- pared with Westwick Marsh 1955, shows a significantdifference (P -- .01). The Westwick colonieshad many more neststhan the Sorensencolonies, so the total figure for the approachesthat for the comparisonof the two large Westwick colonies. Significantdiffer- encesbetween the clutch sizes of one lake from year to year are indi- cated. When two coloniesare comparedin the sameyear, there is less dif- ferencebetween them. Westwickcompared to Sorensenin 1955 shows no significantdifference (P -- .30). Westwick Marsh 1956 when comparedto Sorensen1956 and to Westwick Willows 1956 showsa slightdifference (P -- .05). Two coloniesof birds underthe same environmentalconditions may, then, have clutchsizes which are signifi- cantly different, but the differencesare not as great as thosebetween twoyears. of thesame colony. The marsh colony was higher in mean clutch size than Sorensen Lake in 1955 and lower in 1956. Indeterminate Clutch Size One fresh egg was taken from each of thirty-two nests within the WestwickMarsh colony in 1956.The environmental conditions (except for the robbing) were exactly the same for robbed and undisturbed nests. Clutch sizes for the robbed nests are shown in Table 3.

TABLE 3.

Im)uc• CLugc•[ S•zE (BY ROBm•G) Westwick Lake 1956 No. of (Marsh colony) Clutches c/1 c/2 c/3 c/4 c/5 c/6 c/7 Mea• Secondegg removed 15 0 5 7 2 1 0 0 2.93 Third egg removed 14 0 5 7 1 0 1 0 2.92 Fourth egg removed 3 0 0 2 1 0 0 0 Total eggs in robbed nests 32 0 10 16 4 1 1 0 2.97

Total eggs laid 32 0 0 10 16 4 1 1 3.97

The total numberof eggslaid in the experimentalclutches is signifi- cantlydifferent (P -- .01) from the controlclutches in the samecolony. In the absenceof environmentaldifferences the birds respondedto the 1,ossof an egg by replacingit, making up fifty percent of the loss. The samepercentage of losswas made up whetherthe third or the 308 McALL•STZR,Courtship, etc., in EaredGrebe [I_Vol. Auk7.• secondegg was taken. The first egg could not be taken becausethe nest would have been abandoned, and the data for the fourth egg removedare too few for analysis.Lack (1947) and Davis (1955) reviewedthe incidenceof determinateand indeterminatelaying in birds. ,some , and many Charadriiformesare strictly determinate.Only the fixed numberof oocytesare formedand these are laid whethereggs are taken from the nestor addedto it. Many pas- serines,, and are indeterminatelayers and keep laying until a predeterminednumber of eggsare in the nest. In these birds laying may not be suppressedby the additionof eggsto the nest. All indeterminatelayers and the determinatepasserines are to a certain extent variable in their clutch sizes. The Eared Grebe fits into the in- determinategroup with thoseof the passerineswhich replaceonly a limited numberof lost eggs. The mechanismfor controllingthe end of laying in indeterminatelayers which have not beenrobbed is appar- ently not known fo.rany species. Synchronizationof and Intervals betweenEt7t7 Layint7 Clutchesof one colonywere all startedvery closetogether in time. In the Westwick Willows colony 1956, the first eggsfor all 22 clutches startedwere laid within a four day period. (Only 15 of theselend themselvesto clutch size analysis.) Laying o.f first eggsin the larger colonieswas more spreadout; in 180 clutchesstarted in Westwick Marsh 1956,all first eggswere laid in a thirteenday period. Darling (1938) foundthat in gullslarger colonies had a smallerspan of first egg dates than smaller colonies. He felt that the greater the number of birds, the greater the stimulatingeffect of the group courtship,and thereforethe greaterthe synchronizationof egg laying. Nest establish- ment activitiesmust be highly stimulatingand those birds which are not yet involved swim back and forth watching. Also egg pecking would seemto hold back the first birds to lay until the whole group is ready. The resultingsynchrony, while striking, is not so striking as that seenin Darling'sgulls. Perhapslate migrantslaid late in the large colony,o.r possiblythe large colonyhad more youngbirds which laid late. The clutch size averageof late layers was the same as that of early layers. Darling showedthat synchronizationin gulls reducedthe percentage lossof youngby predation.The EaredGrebe seemed to haveno preda- tors in the lakes studied,and therefore colonialismand synchronized laying for them servesno. purpose in protectionof eggsand young. Data on the interval betweeneggs in a singleclutch are diffi'cultto obtain. In orderto get largenumbers of records,work wasconcentrated in the Westwick Marsh colony. Countstook nearly two hours and July1958J-[ I•,{CALLISTER,Courtship, etc., in EaredGrebe 309 couldnot be mademore than oncea day for fear of disturbingincuba- tion too much. On coldrainy daysthey had to be omittedaltogether be- causeof thedanger of the eggsbeing chilled. Further studies should in- cludemore intensive study of fewer nests.In one four-dayperiod before clutchesin thesenests were complete,fourteen nestsheld four fresh eggs,fifteen three, and three nests five. I have three records of two daysskipped between eggs and two of three daysbetween eggs. If the normal laying is every day, as it is in most passerines,skipped days occurredin 50% of the clutches.Lunk (1955 unpub.) showedthat while Rough-wingedSwallows (Stelgidopteryx ruficollis) regularlylay every day, 20% of the clutchesshowed skipped days. In one instanceI made countsin the evening,and the morning and eveningof the next day. The fol}owingwere noted: 1 egg laid between: no. nests 8:00 •'.M. and 10:00 A.M. 15 10:00 A.M. and 8:00 •'.M. 13 no eggswhole 22 hours 21 All of thesebirds laid at least one more egg after this period. Skutch (1952) showedthat most of the passerineshe studiedlaid shortly after dawn. A few laid in late morningor very early afternoon.A capri- mulgid laid in the afternoon. More detaileddata on fewer nestswould clarify the situationfor the grebes. SUMMARY The behavior of the Eared Grebe was studied in 1955 and 1956 in the CaribooRegion of British Columbia. The Eared Grebehas five courtshippatterns: an advertisingdisplay, habit preening,head shaking,the standingpenguin dance, and the peculiarcat attitude. Comparisonis madewith the courtshippatterns of the EuropeanGreat CrestedGrebe, as reportedby Simmons.Both sexeshave the samedisplays. Threat and escapeattitudes are described. Eared Grebesare colonialbirds, with remarkablesynchronization in the transitionof the colonyfrom courtshipbehavior in early May to nestingbehavior in the latter part of the month. When nest-building beginscourtship 'ceases. During nest establishmentgroups of birds frequentareas with reeds and floating vegetation,there is a soliciting display, and temporary platformsare made and abandoned.The femalesappear to do the actual nest building, but the lack of any striking sexual dimorhpism leaves room for error. The nest is a floating heap of debris, on a 310 MCALLISTER,Courtship, etc., in EaredGrebe tVol.F Auk75 foundationof reeds,with the slightlyrimmed cup risingonly an inch or two abovethe water, so that the eggsare constantlydamp. Nests are from one to three feet apart, in water one to three and a half feet deep. Copulationoccurs on the nest from the time the first platformsare made until the end of egg laying. Eggs are laid and abandonedbefore the nest is fully built. Full clutchesvaried from one to six, three or four beingusual; mean clutch size was 3.48. Experimentsin the removalof eggsindicate that the Eared Grebeis an indeterminatelayer, but replacesonly a limitednumber of losteggs. There is considerablesynchronization in the beginningof egglaying amongbirds of a colony,particularly in the smallercolonies. The usual intervalbetween egg laying was not definitelyestablished, but in about 50 per cent of the clutchesthere was one day skipped,and in some casestwo or eventhree dayselapsed between eggs.

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