MATING BEHAVIOR OF THE COMMON LOON

D. JEAN TATE AND JAMES TATE, JR.

HUXLEY (1923) describescopulation and somedisplays for the Red- throated Loon (Gavia stellata), and Zedlitz (1913) gives similar informa- tion for the Arctic Loon (Gavia arctica). A variety of displayshave been described(Roberts, 1932; Munro, 1945; Yeates, 1950) for the Common Loon (Gavia iramet), but their sequenceand significanceare not clear. Other than Southern's(1961) singlereport of an apparentmidsummer copulationby two CommonLoons, no descriptionof copulationseems to have been reported for this species. In their detailed study of the Common Loon on its nesting grounds,Olson and Marshall (1952) never observedcopulation and suggestit possiblyoccurs at night. We watchedtwo CommonLoons attempt to copulateon the water of French' Farm Lake, Emmet County, Michigan, at about 17:30 on 19 April 1968. By this date the lake had been free of ice for only a week to 10 days; thus our observationof the pair was soonafter their arrival. We returned on 20 and 21 April (a weekend), but found the loons so disturbedby fishermenthat observationwas difficult. On 22 April from 16:30 to 19:00, we were able to watch the pair without interruption through a 15-60X telescope,and 8 X 40 binoculars. The birds were unawareof our presenceduring this time, and we saw them copulateon land. Initially, our attentionwas attractedon 19 April by a loon poisedup- right on the water, splashingand flappingits wingsjust beyondmarsh vegetationmore than 200 yards away from us. We then saw two loons swim out into open water, apparently fishing. Some 10 or 15 minutes later one loon swamup to the other, which had turned on its left side in a normal rolling preenposition (Olson and Marshall, 1952: 16, Figure 6) with its breast and belly exposedand head clear of th.ewater. The male (sexesassumed from copulatoryrole) swamup onto the female'sexposed belly at nearly a right angleto her. Contactwas very brief; the female submergedand the male rolled off to his left. The male faced away from the female and engagedin a wing-flappingact (cf. Johnsgard,1964), which exposedan expanseof white belly and breast visible for some distance. Each of the severalwing flaps sprayedwater, and the rapid return of his breast to the water also produceda splash. He then sub- merged in front of the female until only his head and neck were visible. Meanwhilethe femaleemerged to nearly a normallevel. Unlike this hasty encounter,about 30 minutesof relaxed swimming, •A contributionfrom the University of Michigan BiologicalStation.

125 The Auk, 87: 125-130. January 1970 126 TAt• ANDTATE [Auk, Vol. 87

c

Figure1. Threeprecopulatory displays of the CommonLoon. A, bill-dipping,a mutualdisplay; B, head-rubbing;C, head-tossing,a mutual display. feeding,and a distinctbout of displayingpreceded the two attemptsat copulationon 22 April. The actionswe watchedon this date are described below in approximateorder of occurrence.

PRELIMINARY DISPLAYS Bill-dipping.--Whenthe two birdsfirst cametogether, both engaged in bill-dipping (Figure 1A). Incliningtheir headsforward on stiffly archednecks, first at random then in unison,both birds raisedtheir bills out of the water, then immersedthem to eyelevel. The birdskept 1-2 feet apart and closelysynchronized their movements. They performedfrom 10-20 mutual dips during each session.The black-and-white flutedcollar flashed prominently at the backof the neckduring this display. The stiflened neck and stylized motions, as well as the mutual nature of this displaydistinguish it from peering(Olson and Marshall,1952: 16, Figure 6). Jan. 1970] CommonLoon Mating Behavior 127

Huxley (1923: 256) refers to bill-dippingin the Red-throatedLoon as the snake- ceremony,and he also notesits similarity to peering. Simultaneous-dive.--On the two occasions when this occurred, it immediately followed mutual bill-dipping. At the height of bill-dipping, as if on a signal, both birds threw their headsup, forward, and dove quickly. On one occasionthey faced in the same direction; on the other they faced each other when they dove. The flowing, gracefuldive and the perfect synchronizationof this display impressedus. Immediately upon emergencethey engagedin a bill-dipping ceremony. A period of vigorouspreening followed. Both birds preened,but the actionswere not synchronizednor were all the movementsclearly display elements.During this period,we interpretedtwo actsas displays,largely because of their stereotypedform. Head-rubbing.--Asin Figure lB, both sexespointed the bill vertically upward so that the head lay on the back betweenthe shouldersof the closedwings. Each bird rubbed its head on its back in a movement similar to that of oiling. The fluted black-and-white anterior throat patch was prominent during this display. Headqtossing.--Thethroat patch was also prominent during head-tossing(Figure 1C). The performingbird raisedits bill abovethe horizontalplane quickly,returning to horizontal more slowly. On some occasionsthis was done mutually but not synchronously;at other times it was an individual display. From three to seven head-tosseswere involved in a sequence.

COPULATION The extendedperiods of preeninglasted about 5 and 7 minutes respectively.One or the other bird interruptedits preeningand began a long surfaceswim that endedat a placesuitable for copulation. We found we could differentiate between the two birds consistentlyby their body posture. One bird (male, based on later role in copulation) rode higherin the water, its neck pulled back farther with more white breast exposed,its neck more curved (exposingmore prominentlythe necklaceon th'eback of the neck), and its bill tilted abovethe horizontal (Figure 2A). The otherbird (female) with its breastdeeper in the water, straighterneck, and slightly downward-tiltedbill, seemedsubmissive (Figure2B). Its plumageappeared duller (probablyfrom sleekingof the feathers)at thesetimes. In contrast,the two were equallybright when they were fishingseparately. The differentialposturing began only after th'ebirds came together,dove simultaneously,and beganinteracting as a pair. When swimmingtoward the northeast,the male was first, but about halfway along a channelon the east shore he slowedand the female passedhim. She alternatelymoved ahead and was caughtup to by the male. About 300 yards up th'echannel she climbedout of the water onto a wet platform of aquatic vegetationon a small island and turned onto her left side with her head at least partially erect and facing anteriorly. The male followedimmediately and slid up againsther, his feet under her and his cloacapressed against hers. The entire contactlasted about 9 128 TATs At•) TATE [Auk, Vol. 87

Figure 2. A, erect swimming posture of the Common Loon; B, swimming posture of the fenhale Common Loon when sexually interacting with her mate. seconds,after which the male pivotedoff behindthe femaleand returned to the water in the same direction from which he had come. There he held his neckand head stiffly and dippedhis bill. The femalelay quietly for about 60 secondsand then joined the male. During the next 30-40 minutesthe birds remainedconstantly together, diving and swimming. They pulled plant materialsfrom shallowwater and placed them on a nest platform some distancefrom the copulation platform. They did considerablemutual bill-dipping and head-shaking, but no rolling preeningor head-tossing.Both birds spent some time in peeringwith the head partially submerged. Bill-dipping,a simultaneous-dive,head-rubbing, head-tossing, and preen- ing precededanother attempt at copulation.In this casethe female led the way to the northeastup a channelalong the far shore. We lost sight of them for about 2 minutesbehind a low hummockof vegetation.Copula- tion probably did not occurbehind this hummockbecause we would have seen the male mount the female. After coming back into view the male attempted to copulate. The female ran aground against a hummock, but was unable to climb up becauseof dense shrubs. The male approached Jan. 1970] Common Loon Mating Behavior 129 her threetimes but eachtime backedoff. Beforebacking off, he immersed his bill and threw water laterally upwardin an apparentdisplacement act. The movementwas similar to the head-shakeof waterfowl (Mc- Kinney, 1965: 135) exceptthat the bill was in the water when the head was thrown to the side. Becauseof the tangledvegetation the female did not turn on her sideand the male couldnot approachher: he grounded himselfagainst the tangleseveral feet away from her. Within lessthan a minute both birds swamoff togetherdipping their bills. It seemedas if the female missedthe copulationplatform and was unable to find a suitable place to turn on her side in solicitation.

DISCUSSION Before the male attempted to copulate,the female first exposedher white belly in solicitation.In the copulationattempt on 19 April, the femalewas engagedin a normal rolling preen on the water, a common maintenancemovement, when the male attempted to mount her. In the completecopulation we watchedon land 2 dayslater, the female'ssolicita- tion act was very similarto the rollingpreen. On 19 April the threshold of the male's responseto solicitationmight have been so low that the similarrolling preen act elicitedthe copulatoryresponse. The swimmingposture of the malewhen with the female,as well as the mutualdisplays of bill-dippingand head-rubbing,appear to enhancethe prominenceof the necklaceposteriorly and anteriorly,and/or the promi- nenceof the white breast. Thus ritualized preening,comfort movements, and foragingbehavior serve direct display functions.We saw no display that resembledthe emergenceceremony in the Red-throatedLoon (Huxley, 1923: 256, Figure3). Nor did we seeany overwaterchases such as Olsonand Marshall report in their discussionof copulation-directedbehavior. Their observations, as well as thoseof Southern(1961), occurredduring late May or early June and may not have representedattempts at copulation,but served merely to strengthenthe pair bond. Olson and Marshall (1952: 27) commonlynoted bouts of displaysvery similar to the precopulatory sequencewe have described. These bouts, seen until mid-July, "invariably" endedin a chase. Thus the chaseappears to replacecopulation later in the breedingseason. The chasesthey observedincreased in frequencyin July,often involving three or sometimesmore birds, and fromtheir descrip- tion greatlyresemble the rushingceremony of the WesternGrebe (Aechmo- phorus occidentalis).As in the rushing ceremony(Storer, 1963), the chasein the CommonLoon probably contains both displayand aggressive elements. Prominentvocalizations accompanied the overwaterchases that Olson 130 TA• ANmTA•E [Auk, Vol. 87 and Marshall (1952: 23) describe;none were associatedwith the pre- copulatorydisplays we saw. A pair of CommonLoons we watched in Lincoln County, Maine, were not vocal early in July, but becamevery much so during the period they were caring for young in late July and early August. Such vocalizations apparently function in pair bond maintenanceand not as a part of precopulatorydisplay per se. Olson and Marshall (1952: 29-30) stressthe late summeroccurrence of aerial displays, which often involved several birds. We saw no aerial displaysin Michigan, but they were very frequentduring late August in Maine wh'en the Common Loons were leaving their freshwater breeding areas to feed in the saltwaterbays. In our experienceaerial displaysare not a part of precopulatorydisplay. The secretivebehavior and unobtrusivedisplays associated with effec- tive copulationearly in the springare in marked contrastto the later obviousand often dramatic displaysapparently associated with pair bond maintenanceor servingaggressive and territorial functions. The use of a copulation platform, not previously reported in this species,agrees with the usageZedlitz (1913) and Huxley (1923) describe for the Arctic and Red-throatedLoons respectively. We wish to thank R. W. Storer for making severalvaluable suggestions duringthe preparationof this manuscript.

LXT•P. ATUPm CXT•I) HUXLEY, J. S. 1923. Courtship activities in the Red-throated Diver. J. Linnean Soc. London, 23: 253-292. JO•NSGARI), P. A. 1964. Comparative behavior and relationships of the eiders. Condor, 66: 113-129. McKZNNEY, F. 1965. The comfort movements of anatidae. Behavior, 25: 120-220. Mu•rRo, J. A. 1945. Observations of the loon in the Caribou Parklands, British Columbia. Auk, 62: 339-344. OLSON, S. T., AND W. H. MARSI-IAI,I,. 1952. The Common Loon in Minnesota. Minneapolis, Univ. Minnesota Press. ROBErtS, T. S. 1932. Birds of Minnesota. Minneapolis, Univ. Minnesota Press. SOU•aERN, W.E. 1961. Copulatory behavior of the Common Loon. Wilson Bull., 73: 280. S•o•, R. W. 1963. Courtship and mating behavior and the phylogeny of the grebes. Proe. 13th Intern. Ornithol. Congr., 1: 562-569. YE^•ES, G.K. 1950. Field notes on the nesting habits of the Great Northern Diver. Brit. Birds, 63: 5-8. ZEDL•TZ,O. G. yoN. 1913. Ein Beitrag zur Biologie des Polartauchers,Urinator arcticus. J. Ornithol., 61: 179-188.

Laboratoryof Ornithology,Cornell University, Ithaca, New York 14850.