Courtship behavior is defined as “the act of wooing a member of the opposite sex” and is thus a limited part of overall mating or reproductive behavior. Courtship is particularly well developed in monogamous animals or those where direct partner choice is important. Marine birds represent especially good examples. Many marine mammals do not so much as woo members of the opposite sex, but instead males appear to force themselves onto females in estrus, often after having worked out dominance/subservience relationships among themselves. Our discussion here will therefore be a blend of pure courtship behavior and other social interactions that must be a prelude for successful mating. The mere recognition of the opposite sex of the same species, e.g., by sound and sight, is considered a part of courtship in this broader definition (Krebs and Davies, 1993).
I. Pinnipeds
Pinnipeds tend to have polygynous mating systems, with one male attempting to inseminate numerous females. Extreme polygyny is especially well developed on solid land or ice and less so on moving pack or loose ice (Stirling, 1983). Males work out dominance relationships among themselves, usually by aggressive interactions and behavioral bluffing. In elephant seals (Mirounga spp.), only a few of the very largest and most aggressive males attain a status of dominance and father by far the most offspring on a section of beach. Nevertheless, the female has a choice in who mates with her. When a male mounts her, she protests by squawking loudly. This action attracts other males, and the mounting male may be challenged by one or more males who consider themselves as or more dominant (LeBoeuf and Laws, 1994).
While male displays of dominance are believed to function overwhelmingly in male-male advertisements, a part of intra-sexual selection, it is nevertheless possible that male cues may predispose females toward particular males and away from others. This is perhaps most likely in species that use underwater sound for displays, such as the long trills of bearded seals (Erig-nathus barbatus) or the knocking and whistling sounds of walruses (Odobentis rosmarus). Such a potential choice by females of males aggregated on a breeding ground may be an example of lekking behavior, but there is considerable debate among pinniped researchers on this topic (Wells et al, 1999).
Those species where single males occur with single females for some time probably consist of males mating with that female and staying with her during her period of estrus. This is termed “female defense,” but does not imply tnie monogamy, as it is likely diat the male will leave and search for another female in estrus after some time (also termed serial monogamy). Ringed seals (Pusa hispida) on loose ice appeal’ to be serially monogamous. Nevertheless, casual observations indicate that there is much social interaction and sniffing by these males and females when they first meet, and one wonders whether future more detailed studies might find a much more developed courtship than is presendy known. After all, males and females in this species are of similar size and strength; the male is therefore unlikely to be able to force himself on the female, and it need not be automatic that a female accepts any male who happens to come by and show an interest in her (Riedman, 1990).
II. Sea Otters
Sea otter (Enhydra lutris) males actively defend a near-shore area from other males, but females are free to come into or leave this apparent underwater territory, also called a maritcmj. When a female comes into estrus, she tends to associate with only one male for several days. The male mates with her repeatedly and grips her nose, which becomes heavily bloodied and scarred during mating, with his teeth and claws. This behavior may help to stimulate ovulation, as neck biting does in some other carnivores. It is unclear whether it is simply the goodness of the space that attracts a female to a particular male or whether there is courtship behavior beyond grabbing and biting involved.
The marine otter (Lutra felina) of the Chilean Pacific coast probably has a similar maritorial system.
III. Sirenians
The West Indian manatee (Trichechus manatus) is the best known of the three extant manatees and one dugong that form the tropical, small, taxonomic order Sirenia (one cold water dugong, Steller’s sea cow, Hydrodamalis gigas, was extirpated in the 1700s). These manatees aggregate in herds of one female and from 2 to 22 pushing, shoving males. It is believed that the female will therefore mate with more than one male, and it is possible that a form of sperm competition as well as the obvious physical competition for access to the female has evolved. Males also aggregate in herds without females present and with much apparent homosexual mating. Such interactions may be important in practicing the gaining of access to females, what has been termed “scramble competition polygyny.” It is also possible, and not mutually exclusive with the idea of practicing for competition, that males are working out dominance hierarchies in the all-male groups. Females move into shallow water to avoid amorous males, and it is possible that females exercise considerable choice of who gets to mate with them bv making it impossible for some males to gain access. Manatees also use objects in their environment as traditional “rubbing posts” and rub especially their anal area, which has glandular secretions, on these objects. It is not known whether females in estrus might advertise themselves by chemical smell or taste or whether other communication may take place at rubbing areas (Reynolds and Odell, 1991).
Mating in dugongs (Dugong dugon) has not been well described. It appears that at times a single male stays with a single female, whereas at other times, mating aggregations of at least one female and several males occur. Adult male dugongs have small but sharp and hard tusks and can do considerable damage with them to each other and to females. However, it is unknown whether this secondary sexual characteristic functions only as an intrasexual display or as a male to female, or intersexual, display as well. As in manatees, it is likely that females have the capability of at least some choice of mating partner(s), and we therefore assume that some element of “impressing a female,” or courtship behavior, may have evolved (Reynolds and Odell, 1991; Wells et al, 1999)/
IV. Polar Bears
Polar bears (Ursus maritimus) tend to be solitary animals, but males will stay with a female, “guarding” her from other males during a period of estrus. We can assume that these bears, as others, have greeting ceremonies and other interactions during a period of courtship, but details are lacking. Polar bear males have been seen sniffing the tracks of another bear, and it is likely that they—as other bears and many carnivores—find a female in estrus bv her smell. It is also likely that multiple copulations are needed to induce ovulation in the female (Stirling and Guravich, 1988).
V. Cetaceans
Whales, dolphins, and porpoises have a diversity of precop-ulatory behaviors, but how much of these can be described as courtship is unclear. Cetaceans use sound during almost all social interactions, but vision and touch are well developed and appear of great importance in precopulatory displays. Nevertheless, to date, almost all observations have been from above the surface, and to properly describe courtship behaviors, dedicated focal individual and focal group studies underwater will have to proceed.
A. Baleen Whales
Humpback whales (Megaptera novaeangliae) are arguably the best-studied large whale, yet no researcher has reported seeing humpbacks mate. Humpback males on the mating/ calving grounds produce series of sounds (“moans, screams, rumbles, etc.”) that are repeated in exact fashion after some time. These series are therefore properly called song and may last from about 10 to 30 min per song. Interestingly, every male of an extended area (such as around the Hawaiian Islands, in the Caribbean, or off Japan) sings pretty much the same song. The song evolves during the singing season and is therefore different from the beginning to the end of season. It is presently unknown whedier males space themselves underwater by song, whether they attract females by some subtle yet undescribed individual variations in each song, or both. If the latter, the males might be “courting” females by song, although evidence of only males joining each other after singing hints at a male-male aggression function, not courtship. If males space each other by song, perhaps the loudest individual has males farthest from him and may therefore be more eagerly selected by females. However, this is conjecture; it is rather interesting (and somewhat exciting) that there are huge whales out there for which we really still know very little. Humpbacks also aggregate in boisterous surface-active groups of several males and generally only one female. While the males appear to battle for access to the female, it is unknown whedier the female mates with a male by his choice or whether she has an active say in who gets to mate with her. A third, potentially alternative, mating strategy appears to be a male who “shadows” a female for hours to several days in the possible hope that she conies into estrus or is in estrus. This association is called a cow-escort group (Wells et al., 1999).
Even less is known about other whales of the taxonomic family Balaenopteridae, such as blue (Balaenoptera musculus) and fin (B. physalus) whales. These two species produce low-frequency many-second-long moans that travel for tens to hundreds of kilometers. The whales likely communicate with these infrasounds, but whether some aspect of infrasound advertises sexual readiness is not known.
The right whales (Eubalaena spp), bowhead whale (Balaena mysticetus), and gray whale (Eschrichtius robustus) all aggregate into surface active groups of several males and one or a few females. However, these groups are much less aggressive-seeming than those of humpbacks, and one has the impression that males are vying for position near females in a more fluid nonbattling manner. It may be that females incite such aggregations by sound or other displays and that females then have the ability to “choose” the male or males that are most successful in interactions with others. There is some evidence that females at times appear to make it easier for one male than another to gain access to her, but more studies need to be done. At any rate, actual copulations have often been witnessed at the water’s surface for the three species mentioned here, and it is therefore known that both males and females have multiple mating partners over the course of hours or days. The social system is therefore a multimate or promiscuous one, but again the cues used to gauge successful courtship behavior are unknown. Bowhead whales during spring migration, when most mating occurs, also sing, but not as long and complicated songs as humpbacks have. Also, it is unknown whether only males sing. Right, bowhead, and gray whale males have larger testes than predicted by body size, which may allow them to “compete” at the sperm level simply by the axiom that the most sperm in the most females is most likely to lead to most successful pregnancies (Brownell and Ralls, 1986).
B. Toothed Whales
The taxonomic group of odontocete cetaceans encompasses a large variety of animals, from the relatively closed societies of killer (Orcinus orca) and pilot (Globicephala spp.) whales to the large and fluid associations of spinner (Stenella longirostris) and pan-tropical spotted dolphins (S. attenuata). Still, all toothed whales are social creatures, and all have long-term mother-calf bonds of association. In general, we can guess that those animals where males are morphologically different from females (sexually dimorphic) tend toward polvgyny, with the male somehow advertising to males or females to gain greater access than others to females in estrus. Examples would be killer whale males’ larger body size and relatively huge erect dorsal fin; sperm whale (Physeter macrocephalus) males’ huge head and larger size, erupted lower jaw teeth or “tusks” of male beaked whales: and the enormous narwhal (Monodon mo-noceros) male tusk, not usually present in females.
Sperm whale females stay together in their own matriarchal pods, probably for life, whereas maturing males leave. Therefore, mothers and their female offspring are long-term companions. Mature, large, usually single or “lone” males reap-proach these matriarchal pods during the mating season. At that time, some different sounds (from the usual staccato-like clicks that make a pod of sperm whales sound like fat sizzling in a frying pan) are heard, and it is possible that males find the matriarchal group by the calls of females in estrus. It is also possible that the male calls themselves initiate estrus in sexually ready females and/or that the calls are used for inter-male displays.
Species that tend to be generally sexually monomorphic, such as almost all of the smaller dolphins, appear to be multimate or promiscuous. Nevertheless, as one observes these dolphins underwater—and here there is a bit more known as several species have been kept in captivity or have been studied in clear tropical waters—one recognizes that some animals appear to be more preferred partners than others, and that a “pecking” order of who gets to mate with whom may exist. There is much flipper to flipper, tail to belly, rostrum to genital slit, and so on caressing by both males and females, and it is clear that copulation can be initiated by either sex. In these animals, true courtship behavior can be seen, mainly in the form of such caressing but also in interactions by sound. Several dolphin species have larger-than-predicted testes, and it is likely that while both males and females have multiple mating partners, sperm competition exists for these animals as for several species of baleen whales.
A particularly aggressive mating strategy by males has been clearly documented for Indian-ocean bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia. There, several males band together to form a coalition that kidnaps a female from her group, and males repeatedly copulate with her, at times for days. Coalitions attempt to steal females from each other as well. Possible similar situations have been seen elsewhere, but it is unknown whether this behavior, on the margin of “courtship,” is a generalized alternative mating strategy (perhaps by subadult males with less chance to mate with females on their own?) or represents cases of an aberrant behavior (Connor and Peterson, 1994).
