Whale Social Organization
Cetacean societies, the social organization of groups in which whales live, vary tremendously between species and seems to be dependent upon the ecological conditions in which a species lives. Body size, group size, predator avoidance, feeding and mating strategies all interact to determine the social organization of a species.
Some cetaceans are rather solitary, living alone or in small groups, while others, such as the spinner dolphin, appear to be entirely dependent upon large, socially cohesive groups for survival. Still, others live in extended family groups with relationships that last a lifetime.
Our knowledge of baleen whale societies is still rudimentary. Most humpback whale social groups are believed to be short-lived, with the longest known bond occurring between a mother and calf. However, there are some hints of a deeper complexity that await further study. For example, males may cooperate, as well as compete, on the breeding grounds for access to a receptive female; and, some observations of associations between individual whales on the feeding and/or breeding grounds suggest that longer associations may exist than we currently know.
In toothed whales, the picture that often emerges is a society largely determined by longer lasting social bonds, and in some cases, maternal lineages, where offspring spend their lifetime in the same group as their mothers. In killer whales and pilot whales, for example, offspring may spend their entire lives with their mother. Male bottlenose dolphins form long lasting pair bonds that may last in excess of 20 years, while younger male sperm whales form bachelor herds before becoming more solitary by the age of social maturity, around 25 years of age.
In general, our understanding of whale societies is still in its early years. Our understanding of the social lives of these animals is still emerging. Below you will find descriptions of some of the most common groups of humpback whales on their breeding and feeding grounds.
The calf often rests beneath its mother's chin, helping the calf from floating up to the surface.
Females with newborn calves are commonly sighted throughout the winter, often in shallower or more inshore waters than the adult population. After a 10-12 month gestation period, female humpbacks give birth to a single calf. Although a live birth of a humpback whale has never been recorded, there is strong circumstantial evidence that at least some humpbacks give birth on the winter breeding and calving grounds. Typically, the calf stays close to its mom, often maintaining physical contact with her. On the breeding grounds, the calf typically stays close to its mom, often maintaining physical contact by positioning itself near the head or under the chin. As a newborn, the calf's ability to hold its breath is limited. As a result, calves often surface more frequently than the adults in the group, about every 3-5 minutes, compared to about every 10-15 minutes for the adults.
This curious yearling rolls to take a closer look at researchers, while the mom and an escort stay submerged below.
Calves typically nurse for the first 6-12 months of life, usually separating by the end of the first year. These year-old calves are called yearlings, and by the end of the first year they have usually nearly doubled in length, typically approaching 28-30-feet, and increased their weight by about 8 times.
Juveniles, ranging from yearlings to 4-5 year old sub-adults are common on the breeding grounds, but little is known about their behavior patterns. They are typically alone, in juvenile pairs or trios, or in association with adults, where they are often found on the periphery of adult competition groups.
Often a male escort accompanies or "escorts" a cow and calf on the breeding grounds. Genetic tests have shown that these male escorts are not the fathers of the calves. Instead, researchers believe that these males are there to try to mate with the mother when she comes into estrous. Although relatively uncommon, mothers with newborn calves do come into a postpartum estrous and may give birth in successive years. Typically, however, female humpbacks give birth once every 2-3 years once they reach sexual maturity between 4-6 years of age.
Pairs of adult humpback whales are a common social group on both the breeding and feeding grounds. On the breeding grounds, DNA tests have shown that these adult pairs are usually either male-male or male-female pairs. Females rarely associate with one another on the breeding grounds, and may actively avoid each other. Female-male pairs are relatively stable, lasting from several hours to a day or longer. Sometimes these whales are referred to as "breathholders" because they often stay submerged for periods of 20-30 minutes or more! Male-female pairs may lead to the formation of surface-active or competitive groups where other males challenge the primary male escort for his position next to the female.
Lone whales can either be adults, sub-adults (not yet physically mature), or yearlings (year-old calves that have recently been weaned). Since females have rarely been observed alone on the breeding grounds, lone whales are often presumed to be males. However, how a female attracts a male is still unknown.
Song (3.84 MB .mpg)
Singers are most often lone, adult males. Although songs are heard along the migration and in late summer and fall on the feeding grounds, singers are most common on the breeding and calving grounds. Singers are often nearly stationary, although they can travel and sing at the same time. A common posture for a singer is to lie head down, with the tail 7- 15 meters below the surface. At times, male singers have also been found to accompany cows and calves, and single adults, both males and females. Singing whales often sing until either another male called a joiner joins the singer, or the singer stops and swims off to join a group that often includes a female. Learn more about the humpback whale song.
Audio: Listen to a
recording of social sounds from these competitive groups. (209KB .mp3)
Competitive or surface-active groups are common on the breeding and calving grounds and are usually comprised of several males (ranging from 2- 20) competing for access to a single female (with or without a calf). Usually these groups travel fast (10+ knots) and erratically, exhibiting high-energy surface activity. It is not known whether mating occurs in these groups. In these competitive groups, secondary escorts are challenging the close position of the primary escort to the female, sometimes successfully. One feature of larger, surface-active groups includes a wide range of loud underwater vocalizations referred to as social sounds. Often these sounds are heard when a new whale enters the group. It is believed that males produce these sounds.
Humpback whales sometimes feed alone, but when large amounts of fish are available, whales may join together to feed in large groups. On the feeding grounds, humpback whales occasionally work together to herd balls of herring toward the surface. In these groups, whales will use a net of bubbles, often about 10-25 feet wide, to encircle the herring so the whales can simply emerge through the center of the bubblenet to feed on masses of herring in the center of the circle. In Southeast Alaska, these groups often make mysterious and eerie sounds associated with this unique feeding strategy. Groups of over 20 humpback whales have been seen feeding together!
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