Nonreproductive and Alternative Heterosexualities
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 (
In spite of these severe obstacles facing adult females and young seals, a number of innovative shared parenting or “day-care” arrangements have developed in these species. In Australian Sea Lions, females take turns watching over and defending a group of pups. In Northern Fur Seals, pups gather in nursery groups or PODS for protection while their mothers are away at sea—which is most of the time, since mothers usually spend only one day ashore each week and may be gone for up to 16 days at a time. Female Australian Sea Lions that have lost their own pup also sometimes try to abduct another female’s youngster.
*Bartholomew, G. A. (1959) “Mother-Young Relations and the Maturation of Pup Behavior in the Alaska Fur Seal.”
Bartholomew, G. A., and P. G. Hoel (1953) “Reproductive Behavior of the Alaska Fur Seal,
Gales, N. J., P. D. Shaughnessy, and T. E. Dennis (1994) “Distribution, Abundance, and Breeding Cycle of the Australian Sea Lion
*Gentry, R. L. (1998)
———(1981) “Northern Fur Seal,
Higgins, L. V. (1993) “The Nonannual, Nonseasonal Breeding Cycle of the Australian Sea Lion,
Higgins, L. V., and R. A. Tedman (1990) “Attacks on Pups by Male Australian Sea Lions,
Kenyon, K. W., and F. Wilke (1953) “Migration of the Northern Fur Seal,
*Marlow, B. J. (1975) “The Comparative Behavior of the Australasian Sea Lions
———(1972) “Pup Abduction in the Australian Sea-lion,
Miller, E. H., A. Ponce de Leon, and R. L. DeLong (1996) “Violent Interspecific Sexual Behavior by Male Sea Lions (Otariidae): Evolutionary and Phylogenetic Implications:”
Peterson, R. S. (1968) “Social Behavior in Pinnipeds with Particular Reference to the Northern Fur Seal.” In R. J. Harrison, R. C. Hubbard, R. S. Peterson, C. E. Rice, and R. J. Schusterman, eds.,
Walker, G. E., and J. K. Ling (1981) “New Zealand Sea Lion,