Bruce Bagemihl - Biological Exuberance

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IDENTIFICATION: Males reach 8–10 feet in length and have a massive neck, shoulders, and mane; females are smaller. DISTRIBUTION: Southern coast of Australia; South Island of New Zealand and other subantarctic islands to the south; New Zealand species is vulnerable. HABITAT: Coastal waters and adjacent shores. STUDY AREAS: Dangerous Reef Island, South Australia; Enderby Island, Auckland Islands, New Zealand.

IDENTIFICATION: A dark brown or gray seal with extremely dense fur, large flippers and a relatively small head; females reach 4½ feet in length, males nearly 7 feet. DISTRIBUTION: North Pacific waters; vulnerable. HABITAT: Oceangoing; breeds onshore. STUDY AREAS: St. Paul and St. George Islands, Pribilof Islands, Alaska.

During the breeding season, females of each of these species aggregate into groups among which a smaller number of males are distributed. This organization has been mistakenly interpreted as a “harem” structure, when in fact males have little control over the movements of the females, whose grouping is often the result of seeking each other out while simultaneously avoiding males. In the Northern Fur Seal, nonbreeding animals and juveniles gather on islands separate from the breeding areas; nonbreeding groups also occur in the other two species. Outside of the mating season, Australian and New Zealand Sea Lions form smaller mixed-sex groups, while Northern Fur Seals are oceangoing, relatively solitary, and sex-segregated during the fall, winter, and spring.

Behavioral Expression: In Australian and New Zealand Sea Lions, homosexual mounting is common: one male mounts the other from behind (as in heterosexual copulation) and makes pelvic thrusts against the other male. Homosexual copulation can take place either on the beach or in the surf (the latter especially among older males). All age groups participate, although there is often an age difference between the two males, with the younger male typically mounting the older one (especially in New Zealand Sea Lions). Among younger males, homosexual behavior is often a component of play-fighting, in which the two males stand chest to chest and push against one another, with each trying to grab the other’s neck in his mouth. Female Australian Sea Lions also occasionally mount one another, but lesbian mounting is more common in Northern Fur Seals. During the mating season, one female sometimes copulates with another by mounting her and performing pelvic thrusts; the mounted female often facilitates the homosexual mount by arching her back and extending her flippers, thereby making her genital region more accessible to the other female.

Frequency :Homosexual behavior occurs fairly frequently in Australian and New Zealand Sea Lions and occasionally in Northern Fur Seals.

Orientation: In Australian and New Zealand Sea Lions, younger males that do not associate with female groups may engage exclusively in homosexual activity, since many such individuals (which make up 81 percent of the New Zealand, and 33 percent of the Australian, male population) do not mate heterosexually. In New Zealand Sea Lions, adult breeding males also sometimes participate in homosexual mounting, making them bisexual, whereas in Australian Sea Lions, adult breeding males are exclusively heterosexual. In Northern Fur Seals, all females that participate in lesbian mounting are also active heterosexually, since they also mate with males. In fact, nearly all females involved in homosexual activity are mothers, although not all mothers engage in homosexual mounting. However, the amount of homosexual activity that an individual female participates in may be equal to or greater than her heterosexual activity, since females usually mate with a male only once during the entire breeding season.

In all three of these eared seals, significant proportions of the population do not breed. As noted above, more than 80 percent of New Zealand Sea Lion adult males, and a third of Australian Sea Lion males, do not participate in heterosexual mating. In Northern Fur Seals most males younger than nine years old do not mate because they cannot compete with older males for access to females, while most breeding males actually participate in reproduction for only a single season out of their entire lives. The average male copulates with females only 3–4 times during his life, and many males never do so. In addition, 8–17 percent of females on the breeding grounds do not get pregnant each year, and females generally reproduce only once every five years or so. In fact, nearly 60 percent of the total population consists of nonbreeders that do not even attempt to reproduce. Australian Sea Lions are unusual among mammals in having an exceptionally long or “supra-annual” breeding cycle, 17–18 months from mating to birth (most mammals complete the cycle in less than a year, allowing them to breed annually). Part of the reason for this extended cycle is because of the phenomenon known as DELAYED IMPLANTATION (also found in other seals), in which the fertilized egg fails to develop and instead remains in “suspended animation”—in this species, for as long as eight or nine months. In addition, late-term abortions are relatively common in Australian Sea Lions. Implantation in Northern Fur Seals is delayed for four to five months, but about 11 percent of embryos fail to implant or are aborted or reabsorbed.

In addition to this separation between insemination and fetal development, there is notable spatial and temporal segregation of the sexes in these species. In Northern Fur Seals, males and females go separate ways once the mating season is over: females range widely over the north Pacific Ocean while males remain in the Bering Sea. Since males and females interact for only two months out of the year, this means that the majority of their lives are spent apart from each other. Furthermore, the two sexes are often antagonistic when they are together. Male Northern Fur Seals sometimes try to prevent females from leaving their territory by throwing them bodily and flipping them into the air. Two males may also try to claim the same female by grabbing her with their jaws—sometimes while she is actually giving birth—causing severe lacerations or even death in the resulting tug-of-war. In Australian Sea Lions, “gangs” of younger males roam through the colony, sexually harassing females and attacking those that try to get away. A male New Zealand Sea Lion was once observed trying to copulate with a dead female New Zealand fur seal ( Arctocephalus forsteri ), which he may have killed during a previous mating attempt. Sexual interactions between Northern Fur Seals and California sea lions ( Zalophus californianus ) also occur, and male Northern Fur Seals have also been known to attempt forcible copulation with pups of their own species. In addition, male (and occasionally female) Australian Sea Lions often savagely attack pups, shaking, tossing, and biting them. Death from the resulting injuries is the primary cause of mortality for pups on land, accounting for nearly a fifth of all pup deaths in this species. About 17 percent of all Northern Fur Seal pup fatalities are due to attacks from adults (usually females).