..

Sat upon but not silenced, a tiny pup wails his complaint at being flattened by a two-ton bull rearing up in a vocal threat.

THE

AGGRESSION

OF

THE

BREEDING

BULLS When northern elephant seals haul out

on land to mate, the massive hulls begin a fierce contest for females. Island rookeries resound with their challenges, and combat-often bloody-finally establishes a social hierarchy

by Burney J. Le Boeuf

Few animals fight as fiercely and violently as bull elephant seals. The speed and power of their down­ward·slashing blows are so great that the blubbery exterior of the recipient undulates with the force of impact. Their bloody battles color the water for several yards around them. During the breeding season males bear an assortment of wounds and scars; some have punc­tured eyeballs, split proboscises, or chunks of skin and blubber torn from their backs. What is all this fighting about? Is it advantageous to the species? What are the social

and genetic consequences of fight­ing in this animal?

Elephant seals are seen in the wild by relatively few people, since the northern species, which inhabits the coastal waters off California and Baj a California, Mexico, is rare and its southern relative is cir­cumpolar. The two species look alike except for their size and their most outstanding feature, the pro­boscis. The snout is larger and more pendulous in the northern seal; in its relaxed state it may hang almost a foot below the chin, giving the animal an elephantine

appearance. When the seal vocal­izes, its nose falls into its open mouth. Females and young males lack this elongate appendage.

The southern elephant seal, Mi­rounga leonina, is the largest of the pinnipeds, reaching 20 feet in length and weighing up to three tons. The northern species, M. angustirostris, is a bit smaller, aver­aging up to 16 feet in length and weighing about two tons. Females of both species are petite compared to the males, about 10 to 12 feet long and weighing a little less than a ton. A six-inch layer of blubber makes up about 40 percent of the animal's weight and insulates it against the cold waters it inhabits.

Large, viscid eyes and a thick shield of rugose tissue on the neck and chest, important in absorbing blows during fights, add to the ele­phant seal's reputation as a curious and peculiar animal. It elicits bi­zarre expressions and superlatives such as "grotesque sea cucumber," "the ugliest of animals," and "the world's most improbable animal."

Like most pinnipeds, elephant seals use the sea primarily as a

source of food, but other important biological functions, giving birth, nursing the young, and mating, oc­cur on land. Land areas used by seals are traditional. The animals return to the same location year af­ter year, which makes them easy animals to study in their natural habitat. It has also made them easy prey for sealers.

During the last century, hun­dreds of thousands of elephant seals were killed for the oil that could be rendered from their ample layer of blubber. Gigged and prodded to the water's edge, the seals were shot and their fat flensed in the space of three to four minutes. The slaugh· ter, indiscriminate of age group, was on such a grand scale that both species were nearly exterminated, and the animals soon ceased to be an important source of oil. It was not until 1910 that the southern ele­phant seal had recovered suf­ficiently to elicit further com­mercial exploitation, but this time

The author drips bleach on the pelage of a sleeping seal,

which will keep its new identity until the next molt.

licensing was introduced. Sealing is still permitted a t the largest rook­eries, but the number and type of animal that can be caught is strictly controlled.

The northern elephant seal was virtually extinct by 1869 and no

longer a feasible business enter­prise. In 1890, the known popu­lation consisted of a single herd of fewer than 100 animals on the re­mote island of Guadalupe, 150 miles off the coast of Mexico. The small size of this herd, and its in­accessible hauling grounds, made it

unattractive to sealers. Even so the remaining animals were sought by

collectors for museum specimens. For example, in 1907 Charles Miller Harris reported what a won­derful sight it was to discover what he thought was the last remaining herd of elephant seals:

"After viewing the herd to our satisfaction, we took a number of photographs which are probably the only photographs from life of the elephant seal and which will give the reader a good idea of these rare mammals. Two large bulls were then shot . ... "

Somehow, the number of animals gradually increased. In 1922 when the seals again attracted com-

.Massed harems, with pups and hulls, congest a rookery on Guadalupe Island at the height of the breeding season.

mercial attention, the Mexican gov­ernment gave them complete protec­tion. As the population increased, the breeding range gradually ex­tended' northward. reaching San Miguel Island during the late 1930's. In the 1940's four other rookeries were established: San Benito. Los Coronados. Santa Bar­hara. and San Nicolas. The most recently established rookery is Ano Nuevo Island. 19 miles north of Santa Cruz. California.

The United States government has protected elephant seals since their re·establishment along the California coast. There are approxi­mately 30,000 northern elephant seals in existence today, and their number is still growing-a remark­able comeback for an animal that was once called "one of the bygone wonders of the animal kingdom."

NQrthern elephant seals, which I began studying with the late Rich­ard S. Peterson three years ago, "haul out" on land twice a year. One haul out is for reproductive ac­tivities and lasts from one to three

months depending 01'1 sex; the other is for molting. an annual process in which the entire skin and fur are sloughed off and replaced anew. Molting takes about one month.

Bulls are extremely belligerent upon arrival at the rookeries in early December. the start of the breeding season. Most of their time is spent challenging. fighting, and chasing each other. The male that displaces another becomes domi­nant to him. The sum of these indi­vidual displacements results in a ge­ographical spacing out of males on the beach. so that viewed from a distance the animals resemble mag­nets having a like charge: one re­pels the other and a safe distance between two individuals is always maintained. Aggressive encounters occur on the beach or in the water and continue until the end of the breeding season in mid-March. Breeding bulls do not eat during this period, even though some re­main on land as long as 90 days.

By the time females begin to arrive in late December, the males

have established a peck order, or social hierarchy. Unlike males, fe­males seek out each other's com­pany, and form pods, or harems, which increase in numbers and reach a peak of as many as 300 fe­males during the last week in J anu­ary. After this, harem size gradu­ally declines until all females have left the rookery, usually by the sec­ond week in March.

A female gives birth to a single pup about seven days after coming ashore, and nurses it for the next twenty-seven days. Then, she weans her pup by simply leaving it and re­entering the water. This is the end of the mother-pup relationship. However, the high fat content of the mother's milk has already caused the pup to triple its body weight, going from about 70 to 100 pounds at birth to 200 to 300 pounds four weeks later! The "wean­er" lives on his blubbery fat store while making the transition from suckling milk to eating solid food.

Females come into heat about 24 days after parturition, and for up

86

to a week copulation may take place several times a day and with more than one male. The receptive female is passive and does not in­itiate courtship; she demonstrates no preferences for certain males. In the space of 34 days or less, females give birth, nurse their young, and are reimpregnated. The fertilized ovum, however, does not imme­diately attach to the uterine wall and develop. There is a delay of four months before implantation occurs, and this period, plus an eight-month gestation period, insures that the female will give birth at the same time one year later.

The organization of elephant seal males with respect to females dif­fers from that of fur seals and sea lions, which establish terri tories early in the season and fight to de­fend them. The aggressive encount­ers of fur seals and sea lions are spe­cific to place, not to the individuals involved and females breed on terri­tories with the territory holders.

Fighting in elephant seals is more widespread than in sea lions

and may occur anywhere on or near the rookery. Instead of fight­ing for a place, fights are individ­ual contests over rank in the peck order. Status in this hierarchy directly determines a male's rela­tionship with females.

In all aggressive encounters one male tries to displace another either by threat or by overt attack. A bull threatens his opponent by simply staring at him, by facing him and lifting the head and neck, or by moving in his direction. The most common threat behavior is a vocal challenge issued from a stereotyped posture. With forequarters elevated,

A bull in repose: its long nose, hanging almost a foot below

the chin when relaxed, earned the seal the name "elephant."

--

Newly molted "weaner" has replaced the black fur of its hirth with a silver coat and a thick layer of blubber.

its mouth open and head thrown back, a bull emits three to fifteen loud, low-pitched pulsed sounds. If the threat is effective, the opponent simply moves a few yards away, thus conceding his sub ordinance. If he fails to move or does not move fast enough, he is attacked and bit­ten. If the threatened male is domi­nant to the threatener, the former gives his own vocal reply and the initial threatener retreats. If the re­lationship is not established, both animals continue to vocalize as they come together and fight.

Despite their unwieldy bulk and terrestrial sluggishness, these ani-

mals are remarkably quick and agile once poised and ready to fight. The stance is always the same. In a chest-to-chest con­frontation, the fighters lift their heads as high as possible so that fully one-half the torso, about eight feet, is vertical. With their great heads cocked to one side, they rock back and forth, feinting and butting with the undersurface of the jaw and neck, jockeying for an open shot at each other's neck. The strike is powerful and fast, involving a downward-slashing blow with the wide-open mouth and ending in a rippi ng bite as the animal pulls away. Several blows may be ex­changed before combat is termi­nated. The victor is not always the more aggressive animal, but rather the one who holds his ground; he may even receive all the punish­ment and not land a single blow.

Although the thick shield of cornified epithelial tissue on the un­dersurface and sides of the neck of mature bulls receives most of the blows, both fighters invariably suf-

fer deep cuts and lacerations that bleed profusely. When a seal gets a

bite on his opponent's nose, he holds on and jerks his head violently from side to side, worry­ing it in bulldog fashion. He may not release his grip until the nose is torn and shredded. The fight is over for this unfortunate male, and he beats a quick retreat as soon as he can. The nose can be a nuisance in another way. Usually the strike is delivered in such a way that the flaccid appendage swings out with centrifugal force and actually fol­lows the teeth to the point of im­pact. Sometimes the timing is wrong and the end of the snout is in front of the bared upper canines as the blow lands. The animal bites his own nose!

Despite all the bloodshed, in­juries heal quickly, even those that are remarkably severe. I know of no animal that died from wounds sustained in a fight.

Nine out of ten fights take place on land and last less than a minute. The great fights for high positions

last longer, particularly if one ani­mal is pushed back and the fight continues in the water. Fights in the water last as long as 45 minutes.

Appeasement gestures adopted by the loser to signal defeat and turn off further aggression are common in most animals. But this behavior is either absent or ineffective in ele· phant seals, and the losing fighter is usually given a savage bite on the hack or hind flippers as, giving up, he turns to flee. Even incipient attack is not always signaled in advance. Males that have just lost a

fight, or that have retreated from a confrontation with a near·equal, often sneak up from the rear and bite an unsuspecting subordinate.

Fighting determines the ensuing relationship between two animals. In subsequent encoun ters the win· ner need only threaten the loser to displace him, thereby making his point with less energy expended. Threats outnumber fights by about sixty to one.

For a study area, Peterson and I selected Aiio Nuevo Island, a

unique refuge for four different species of pinnipeds, 19 miles north of Santa Cruz, California. The study conditions were ideal. The colony was small, containing ap· proximately 300 females and 100

males. Blinds overlooking key beaches were built before the am· mals arrived. Proximity to civ· ilization enabled us to work in shifts and thus observe the animals continuously during each day of the breeding season.

The first major problem we faced was one that has plagued many field investigators of animal behav· ior. To fully understand the social behavior of an animal, you must recognize individuals from day to day, and if possible, from year to year. If your subjects all look alike you have to mark them. This task appears deceptively simple but is difficult at best. Usually it is ex· pensive, dangerous, time con· suming, disruptive, and with some animals, impossible. The elephant seal was a notable exception, but we didn't know this when we started.

There were conflicting reports about the approachability of bulls. While the old sealing books said that males were indifferent to man, they indicated in no uncertain terms that bulls were dangerous and would attack: "Always watch you got a clear getaway when they comes for you like that.. .. They'd kill you easy if they wasn't so damn clumsy." It was a pub· lished fact that George Bartholo· mew, a zoologist at UCLA, had ob· tained rectal temperatures from sleeping bulls, and there was a ru· mor that he had even sat on their backs. But we rejected this last story as apocryphal when we saw our first bull haul out at the begin. ning of the breeding season.

We waited until one of them was between fights and in a deep sleep before attempting our first mark. The idea was to get an aniline dye mark on the animal-any kind of mark, at this point we weren't par· ticular. We emptied a fire ex· tinguisher, filled it with the black liquid, pumped up the pressure,

and Peterson, having lost the toss, stalked out to meet "Macho," while I watched from the security of the blind. The bull woke up as soon as the first drops of dye squirted on his back. In an instant, the massive head jerked up and the huge hulk swiveled to face the man. Peterson's response was equally fast; he got the hell out of there. It was the fluid squirting out with too much force that woke the bull, but with· out the pressure we would have to get even closer to the animal, so we abandoned the fire extinguisher.

Mark No.2 was simple and effec­tive. Take a plastic sandwich bag, fill it with marine paint (bright col­ors are best), seal the top with a

rubber band, sneak up to the sleep­ing bull, and let him have it. The identity of the animal is then de­scribed by the location and color of the splotch, for example, CLS =

crimson left side, YLN = yellow left neck. The marks were easy to see and lasted almost the entire sea­son, but with 100 animals to iden­tify you run out of combinations,

and it begins to get confusing. Be­sides, the technique was sloppy and esthetically offensive. By this time, we had learned it was possible to approach within four yards of a bull if he was lying down, leaving us running room in case he made a quick move. A paint roller on a long pole proved useful for putting temporary marks on animals even when they were awake and unco­operative.

The current technique is prob­ably the final solution. In a plastic squeeze bottle, we mix 35 percent hydrogen peroxide with "Lady Clairol Ultra Blue," a commercial emulsifier, shake the bottle, sneak up to the sleeping seal, and write a name on its back in one-foot-high block letters. The pelage is bleached in a few minutes and the name, readable more than 100 feet away, lasts until the animal molts six months later. Long-lasting metal or plastic tags are attached to the hind flippers to facilitate recognition and re-marking from one breeding sea­son to the next. With each male

wearing the equivalent of a football jersey we were in a position to un­derstand the game.

The form of the social hierarchy became clear soon after we identi­fied the bulls and started recording all aggressive encounters, noting in particular who was displaced, where, and by whom. The hier­archy among males is remarkably similar to the peck order one finds among barnyard fowl. Within a single harem, the direction of domi-

Poised and ready to fight, the bull seal in background, left, rocks back and forth on

his belly, looking for an opening. But foreground bull strikes first, center. He follows through with a tearing hite, as the loser hegins his retreat, helow.

nance is essentially linear. The top bull, alias the "beachmaster" or "alpha" male, displaces all other bulls in the vicinity of the females. If there is only one group of fe· males, he is the lord of the entire beach. The second·ranking bull displaces all males except the alpha bull, and so it goes, except for certain deviations from linearity that some· times complicate this simple struc· ture.

A!11ong seals a definite relation· ship exists between all males, cer· tainly all high·ranking adults; one male in a pair dominates the other or is dominated by him. This is un­like the situation in the hierarchies of chickens and a few other animals where "no contest" relationships may occur between individuals.

Whereas high-ranking roosters have first access to food, females, and roosting and bathing areas, the only immediate advantage to high rank in seals is access to females. Females are the focus of male activ­ity once they arrive at the rook­eries. The higher a male's rank, the easier it is for him to get close to females. A male's place at any given time is a function of being pulled by his attraction to females and pushed away by his fear of other males.

The alpha bull locates in or near the group of females. Males with social ranks immediately below him (ranks 2 to 6, for example) are found along the periphery of the fe­male group. Since each male attempts to keep those below him away from females, infiltration be­comes increasingly difficult with decreasing rank. Each male is most occupied with displacing males im­mediately below him in rank, so that resulting fights are usually be­tween individuals of nearly equal size, ability, and rank.

When the harem contains ap­proximately 40 females or less, the alpha bull can successfully keep all other males out. As the number of females increases, the second- and third-ranking males may occupy a peripheral position in the harem. Although the top bull can displace them at will, the distance is too great and the task too much for

him. As soon as he chases No. 2 away from the south section, No.3 enters from the north. If action is taken against No.3, No.2 re-enters. With a harem size of 300 females, six to seven males can enter the ha­rem periodically, but the situation is very fluid.

Te fi"t to 'ni" on the mok­ery in December are mature bulls, usually those that dominated the hierarchy in the previous year. They quickly set up a new social order. Males arriving later are at a dis­advantage since they must fight for a place in the pre-existing order. The frequency and intensity of fighting increases during the second week of January, when arriving fe­males begin to form in definite pods, and continues at a high level through February when the major­ity of females are in estrus. In early January, the alpha bull faces his more serious challenges, and he may have several bloody fights in just a few days. He is often chal­lenged immediately after winning a prolonged, bloody fight, a time when he is tired and vulnerable. If he arrived early in December, he has already lost several hundred pounds and is showing signs of ex­haustion. A defeat sends him crash­ing down several ranks, not just to the second position. If the alpha bull successfully defends his posi­tion during this period he usually retains the alpha position for the entire breeding season.

Good fighting is rewarded. Since females come into heat in the ha· rems, only the few highest.ranking males have access to females and do most of the breeding. There were ll5 males and approximately 225 females in two harems at Aiio Nuevo Island during the 1968 breeding season. Five bulls, or 4

percent of the males, engaged in 85 percent of the copulations observed throughout the entire season, and probably sired most of the off­spring of the following year.

Social rank was highly correlated

with breeding success. In the large harem at Ano Nuevo, the higher a male's rank the more frequently he copulated. The alpha bull always accounted for the greatest propor­tion of matings, about 30 to 40 per­cent of the total in the three years observed. In the small harem, the alpha bull alone did virtually all of the breeding: 73 percent in 1968 and 100 percent in 1969 and 1970! This discrepancy in performance between the alpha bulls on the two beaches was due principally to dif­ferences in harem location. The large harem was located in the cen­ter of a sandy beach on a point and males could approach from all sides. The small harem, situated on a narrow beach in a small cove on the opposite side of the island, was surrounded by steep banks that re­stricted intruding males to entering from the sea.

As shown in several ways, the as­sociation between sex and violence is close in elephant seals. Bulls have a propensity for mating shortly af­ter winning a fight. They do not court the female; they subdue her. If a female is unreceptive to a bull's direct approach, he overpowers her by biting the back of her neck or by dropping the full weight of his head and neck on her body and pinning her down. Most aggressive activity, however, centers around the majority of males that do not mate. Their failure is not due to lack of sexual libido. Even the young pubescent males on the rookery, approximately five years of age, dart in and mount females on the edge of the harem, but they rarely get further than that. Pre­vention of copulation before it oc­curs is the rule. Freedom to mate without interference is the sole pre­rogative of the beachmaster.

For other males, interruptions re-

Even deep wounds from powerful blows heal quickly.

In three years of observation, no animals died from a fight.

suIt from threats or attack by higher-ranking males; the lower their rank, the higher the probabil­ity that they will be disturbed. The desire to prevent others from copu­lating is so great in some males that they will terminate their own copu­lations to chase a lower-ranking male from a female. Those caught flagrante delicto are bitten on the back. This matter of interrupted matings is one of the most obvious differences bel ween the social sys­tems of elephant seals and territo­rial pinnipeds. Steller sea lion and northern fur seal matings are never interrupted. No doubt, this is asso­ciated with the fact that females of those species copulate but once. The female elephant seal copulates sev­eral times a day for several days, and sometimes with several differ­ent males. Since many of these cop­ulations are incomplete, female promiscuity is probably a safety measure insuring pregnancy.

A female is still in estrus when she leaves the harem and goes to sea. To reach open waters she must swim a gauntlet of peripheral males in the shallow water offshore or on the beach near the water's edge. These males wait expressly for de­parting females. As soon as one male mounts, he is threatened by another. In the melee, most females escape while their suitors fight. But about one-third of them copulate before reaching the open sea_ Of course, it is the highest-ranking pe­ripheral male that is most successful.

Selection occurs when mating is nonrandom, and in time, the result is evolutionary change. We have seen that mating is restricted to a few males during one season. But to estimate the degree of selection it is important to determine how long the same males continue to domi­nate breeding. Do the same males monopolize the females for more than one season, or is there a com­plete changeover from one year to the next? Do some males spend their whole lives without ever mat­ing, or is it just a matter of reach­ing a certain level of maturation be­fore a male gets his chance? Tentative answers are beginning to emerge from comparisons of indi­vidual performances in successive breeding seasons.

Seven males accounted for 97 percent of the breeding in 1968.

Five of these continued to do 80 percent of the mating in 1969 and four males were still responsible for 40 percent of the mating in 1970. The top two males in 1968 dropped out of the picture almost completely in the last two years. GLS, ranked third the first year, rose to the al· pha position in 1969. Although he continued to hold this position for the first six weeks of the 1970 sea· son, he was deposed and plummeted down to ninth position when the fe· males started to come into heat. PIN, who ranked fourth in 1968, improved his position the second year by competing on the other side of the island where he became the alpha bull of the small harem. He returned to the large harem in 1970 with about the same rank he had held in 1968, but he did not breed. BO's development is most inter­esting since he progressed from sev­enth to second and finally to first.

Evidently, males do contribute to the population gene pool for more than one season, but the exact length of time still remains to be determined. Are former beachmas· tel'S like GL and GLS "all through," or will they rise again in the hier­archy? They are both still rela­tively young compared to male CLS who ranked second in 1968 and sixth in 1969. Will BO be among the top bulls in 1971 ?

Fighting behavior plays an im­portant and pervasive role in the lives of individuals as well as in the success of the entire species. In a dual selection process, the social system screens the most fit males to sire the next year's offspring, thus enhancing their viability an.d that of the species. First of all, only adult males, 10 to 12 years or older, participate in reproductive activities. Even though males attain puberty at about five years of age, these young males cannot compete effectively with their elders for fe­males. Many males die before reaching breeding age. Those that survive must have warded off dis­ease and parasites, obtained enough to eat, and avoided being eaten by predators. Having passed this fit­ness test, a male must still be healthy and strong enough to fight and beat most of, his fellow survi­vors in order to breed. His success, like survival in general, is undoubt­edly based on a wide assortment of

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Social rank and breeding success among the seven highest-ranking males in 1968 and their performance in two subsequent years at Ano Nuevo Island's large harem.

1968 1969 1970 PERCENTAGE

MALES SOCIAL OF

RANK MATINGS

GL I 37 CLS II 31 GLS III 14 PIN IV 4 YLN V 6 TWO VI 4 BO VII 1

TOTAL: Percentage of mating 97

,x-Absent from harem

genetic traits. Heavy tusks, a thick integumentary shield, and great size are obviously important. The great sexual dimorphism of the species today probably developed over a long period of time as a result of the edge larger males enjoy in fighting. Having stored enough fat to provide for a two- to three-month fast, the breeding bull must time his arrival on the rookery just right; there are disadvantages in arriving too early as well as too late. There are even intellectual requirements; a bull must remember which bulls he has fought and beaten and which have beaten him. Lastly, for about one and a half months, he must be potent, fertile, and willing, again and again. A better system for se­lecting the fittest males to perpetu­ate the species would be difficult to imagine_

Aggressive behavior may In­fluence species development in other indirect and less obvious ways. Limits to population growth and the speed with which new col­onies are established could both derive from the thwarting of males that attempt to break into the social hierarchy and participate in breed­ing, causing them to move to other uninhabited islands and mainland beaches. Subadults are most apt to adopt this solution.

The loud, stereotyped vocaliza­tions of bulls may have important functions other than that of threat. Since, under ideal conditions, the sounds can be heard for several miles, it has been suggested, although not confirmed, that the calls may be important in attracting breeding females to the rookeries, particularly to newly established ones. One aspect of the call seems

PERCENTAGE PERCENTAGE

SOCIAL OF SOCIAL OF

RANK MATINGS RANK MATINGS

XII VI

I .X-

IV VII

II

0 XII 1 1 IV 9

49 IX 2 V 0

4 ·x-

4 XV 0 22 I 28

80 40

to serve, in part, as the basis for recognition between individuals_ At Ano Nuevo each male consistently emits a certain number of pulses in his vocal bursts. One male may settle on three pulses while another signals threat with five. The in­variance ot pulse number in some males can be used to distinguish them from others_ In addition to this characteristic, further cues are provided by differences in pitch, in­tensity, and timbre.

Finally, there is suggestive evi­dence that individuals from one population may be able to recog­nize males from another population by certain temporal characteristics of the pulsed call, particularly the rate at which pulses are emitted. The pulse rate of males within a single population is remarkably constant, but average pulse rate varies considerably between popu­lations. Males at Ano Nuevo Island, for instance, have a pulse rate half that of males at San Nicolas Island, which is about 330 miles to the south. Such geographical differ­ences resemble the local dialects that occur in birds and man. Pre­liminary evidence indicates that certain aspects of. the calls are cop­ied, which would account for the lack ot variation in the calls of a single population both within a single year and from one year to the next_ Dialects may function as isolating mechanisms acting in combination with geographical sep­aration to restrict gene flow be­tween neighboring populations. For this reason, the phenomenon is con­sidered significant for speciation.

Why doe.s an elephant seal fight? Because the consequences are great for him and the species. •