Sexual Behavior in the Northern Elephant Seal Mirounga angustirostris Author(s): Burney J. Leboeuf Reviewed work(s): Source: Behaviour, Vol. 41, No. 1/2 (1972), pp. 1-26 Published by: BRILL Stable URL: http://www.jstor.org/stable/4533425 . Accessed: 19/02/2013 19:16 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. BRILL is collaborating with JSTOR to digitize, preserve and extend access to Behaviour. http://www.jstor.org This content downloaded on Tue, 19 Feb 2013 19:16:23 PM All use subject to JSTOR Terms and Conditions SEXUAL BEHAVIOR IN THE NORTHERN ELEPHANT SEAL MIROUNGA ANGUSTIROSTRIS by BURNEY J. LEBOEUF 1) (Crown College, University of California, Santa Cruz, Calif., U.S.A.) (With 12 Figures) (Rec. 25-I-1971) To understand mammalian reproductive behavior, systematic data repre- senting all species is needed. Investigations must be carried out both in the laboratory, where rigid controls can be effected, and in nature, where ques- tions concerning the evolution and adaptive value of the behavior are ap- plicable. In the past, the focus of study has been overwhelming in favor of laboratory and domestic animals such as: mice, rats, guinea pigs, rabbits, cats, dogs, monkeys, chickens, pigs, sheep, cattle, and horses. With few exceptions, little is known about the behavior of these animals in their natural habitats; indeed, since most of them are domesticated, the question has little meaning. There are even greater gaps in our knowledge of reproductive behavior in wild animals that are not amenable to study in the laboratory or cannot be observed within the confines of an outdoor enclosure. This is hardly sur- prising since dugongs, sperm whales, black-footed ferrets, ant eaters, and rock hyraxes, to name a few, are difficult to locate, let alone observe at the right time and long enough to record mating behavior. However, some wild animals, such as several species of pinnipeds, do not present unusual difficulties in observation. Seals and sea lions offer several advantages for study in their natural habitats. In most species, the breeding season is short and takes place at the same time each year. Mating occurs on land or on ice in many species and these locations are traditional. There are I) I thank MICHAELBONNELL, FINN SANDEGRENand several students for field assistance, IAN STIRLINGand RICHARDGANTT for helpful comments on the manuscript, and CECILE SCHREIBERfor preparing the resume. The work was in part supported by Grant GB-I632I from the National Science Foundation. Behaviour XLI I This content downloaded on Tue, 19 Feb 2013 19:16:23 PM All use subject to JSTOR Terms and Conditions 2 BURNEY J. LEBOEUF few visual obstructionson the rookeriesand since the animals don't move around much, observationscan be made from blinds thereby minimizing disturbance.Individuals can be identified by scars and in a few species, individualscan be marked.Several different species may breed in the same locationthus facilitatingcomparative studies. Males are particularlyinter- esting subjects for sexual researchbecause of the great demandsimposed on them by their social systems. The "haremmaster" is perhaps the best known example of the polygynousmale. The specieswe know most aboutare those whichare of greatestcommercial importanceto man; these include the Alaska fur seal, Callorhinusursinus (BARTHOLOMEW,I953; BARTHOLOMEW& HOEL, I953; PETERSON, I968), the Cape fur seal Arctocephalus pusillus (RAND, 1955) and the Southern elephant seal, Mirounga leonina (LAWS,I956a, I956b,; CARRICK,CSORDAS & INGHAM,I962). Despite intensive study of related phenomena, copulation has been observed rarely, if ever, in the Weddell seal, Leptonychotes wed- delli Lesson, (MANSFIELD, I958; RAY & DE CAMP, I969), the Hawaiian Monk seal, Monachus schauinslandi (KENYON & RICE, I959; WIRTZ,I968), the Grey seal, Halichoerus grypus (HEWER, 1957; CAMERON, 1969), the Harbor seal, Phoca vitulina (SCHEFFER & SLIPP, I944; VENABLES & VENABLES, I957; BISHOP, 1967), and the walrus, Odobenus rosmarus (BROIOKS,I954; LOUGHREY,I959). Investigations of the sea lion family have been limitedby difficulty in distinguishinga mount from a completecopula- tion due to the posture the pair assumes during copulation (PETERSON & BARTHOLOMEW, I967; PETERSON, I968). The purpose of this study was to describe and analyse the sexual behavior pattern in the Northern elephant seal, Mirounga angustirostris. BARTHOLO- MEW(1952) provides a particularly lucid description of the copulatory pattern in this species and LAWS(I956a; i956b) and CARRICKet al. (I962) give a good account of this behavior in the Southern elephant seal M. leonina. The aim of this study was to extend these studies by emphasizing quantitative aspects of the sexual pattern of marked males and females from day to day for periods covering three breeding seasons, relating individual performance to the social context in which it occurred, and comparing the copulatory pattern in elephant seals to other species that have been studied. Particular attention was devoted to differentiating complete copulations from incomplete attempts to mate since few statements about the frequency and time course of matingcan be made withoutthis distinction.Because the social system of elephantseals is quite different from that of sea lions, the former exhibit a social hierarchy and the latter are territorial, differences in their respective copulatory patterns might be expected. This content downloaded on Tue, 19 Feb 2013 19:16:23 PM All use subject to JSTOR Terms and Conditions SEXUAL BEHAVIOR IN NORTHERN ELEPHANT SEAL 3 METHODS Observations were conducted at Afio Nuevo Island during three conse- cutive breeding seasons: I968, I969, and I970. Afio Nuevo Island, 19 miles north of Santa Cruz, California, is the northern-most colony in the breeding range. The reproductive period begins in early December when breeding males arrive and ends around 15 March when the last female departs. The first females arrive in late December and mating occurs between mid-January and mid-March. Elephant seal's breed in two locations on Afio Nuevo Island, a large sandy beach on the northeast side of the island called Area 17 and a smaller sandy cove on the southwest or seaward side of the island called Area 3 (see Figure 2 in ORR & POULTER, I967). Four blinds formed a semi-circle around the breeding beach on Area 17 where the majority of observations were made; one blind overlooked Area 3. The population of breeding males numbered 75-I 15 during the three seasons observed: approximately 5o% of these males were fully developed adults and the rest were sub-adults. The latter ranged in age and size from males just going through puberty, and about the size of females, to males that were just reaching full growth. Even the youngest and smallest sub-adults on the breeding beaches in February and March were sufficiently mature to mate. The number of females in the population ranged from 90oin I968 to 328 in I970. Several observers assisted in the study making it possible to observe the animals an average of 6 hours a day from I December to 15 March each year. Observations usually began at dawn around 0700 hours and ended at sunset around 1700 hours. Observations were made at night when there was suf- ficient moonlight to see the animals. With the aid of binoculars, spotting scopes, cameras and timers, a serial record was kept describing selected behavior patterns and the time at which they occurred. As each male arrived at the start of the season, he was given a name or number which was printed in 6 to 12-inch letters on each side of the animal's back anterior to the hindflippers with a bleaching agent (LE BOEUF & PETERSON, I969a). These marks were readily visible from the blinds and lasted throughout the breeding season until the annual moult in June and July. Numbered metal and plastic tags attached to the webbing of the hindflippers facilitated recognition and remarking in each subsequent season. Approxi- mately 20% of the females on Area 17 were marked with bleach or paint each year. Thirty females were tagged in I969 and I970. During the 3-year period, additional observations were conducted at all This content downloaded on Tue, 19 Feb 2013 19:16:23 PM All use subject to JSTOR Terms and Conditions 4 BURNEY J. LEBOEUF other Northern elephant seal breeding colonies: the large rookeries on San Miguel Island, Isla de Guadalupe, and Islas San Benito, and the smaller rookeries on San Nicolas Island, Los Coronados, and Isla Cedros. The following are various terms used to describe components of sexual behavior in elephant seals: Flipper over back (FOB): foreflipper over back, signalling an attempt to copulate (Fig. iB). No genital contact. Mount: postural adjustment following FOB in which the genitals are apposed and the male exhibits pelvic thrusts without penetration (Fig. ic). FOB is maintained throughout. Lumbar flexure (LF): curvature of the mounter's pelvis toward the mountee which accompanies an especially deep thrust and insertion of the penis into the female's vaginal orifice (Fig. Id, Ie). FOB maintained throughout. Disrupted mount (DM): FOB and mount prevented from proceeding to LF because the male is threatened and moved by another male. Disrupted copulation (DC): withdrawal of the male after LF has occurred due to threat or attack by another male (Fig. if). RESULTS Description of copulation. The salient features of copulation as it occurs on land can be described briefly. Copulation is always initiated by the male. He goes directly to the side of a female lying on her belly, puts a foreflipper over her back, pulls her strongly toward him and attempts to establish genital contact (Fig.