Whale Trust Maui Blog

Our knowledge of humpback 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. The easiest way to look at whale “societies” is to break down the different types of whales and groups observed on the water.

Cow and Calf

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.

Yearlings and Sub-Adults

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.

Cow, Calf and Escort 

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.

Adult Pairs

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

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.

Singing Males

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.

Surface-Active or Competitive Groups 
(Male competition for females)

The favorite of whale watchers everywhere, 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.

Feeding Groups (in Summer Feeding Grounds)

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!

Each year, tens of thousands of whales travel thousands of miles from their summer feeding grounds to winter breeding grounds. Hawaii, and most abundantly the shallow waters between Molokai, Lanai, Kahoolawe and Maui, is the largest breeding ground for North Pacific whales, most of whom are coming from the northwest coast of North America.

Although researchers still don’t understand why whales migrate to these winter grounds, it appears to be more for physical than biological characteristics. Most breeding grounds are warmer, shallower, and more protected than summer feeding areas, which may offer increased protection for mothers and their newborn calves. The dense congregation of whales that assemble in these winter grounds also brings together males and females, who may feed in different areas during the summer.

The sea conditions in Hawaii, including calm lees protected from trade winds, clear, warm water, and easy access to humpback whales make the Hawaiian Islands one of the best natural laboratories in the world to study whales.

What is a Breeding Ground?

Humpback whales have a specific reproductive cycle with the same components as all mammals: mating, gestation, birth and nurturing young. The typical reproductive cycle of a mature female humpback is: mating in winter, a year’s gestation, birth of one baby during the following (second) winter, a year’s care of the baby prior to weaning, then separation in the third winter followed by mating again. As most of the mating, birthing and nursing takes place during the winter months, the area they spend the winter becomes the “breeding ground”.

It is important to note, however, the “breeding ground” does not necessarily imply a rigid boundary for these behaviors. Reproductive activities begin, and some births occur, before whales reach Hawaii. In fact, some behaviors such as singing (a behavior not necessarily related to breeding per se but which is prevalent in breeding grounds and generally absent from feeding grounds) begin as early as late fall before the whales leave their summer feeding grounds. Reproductive activities also continue to some extent on the northern migration back to feeding grounds.