Kid's Korner

Week 4: Hawaii Breeding and Calving Grounds

photo: Humpback whale breaching During the winter, humpback whales assemble in lower latitude sub-tropical or tropical waters to mate and to calve. 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. Although in the North Pacific humpback whales are known to assemble in five different areas during the winter (Hawaii, Mexico, Costa Rica, Japan, and the Philippines), individual whales may move between different breeding grounds. For instance, humpback whales seen in Mexico one year have been seen in Hawaii the next year. On one occasion, a humpback whale was seen in Mexico and Hawaii during the same winter.

Hawaii: Home to Nearly 10,000 Humpback Whales in Winter

The Hawaiian Islands comprise the largest known reproductive assembly of humpback whales in the North Pacific Ocean, with an estimated ten thousand humpbacks (or 50% of the population) visiting each year. However, we wouldn’t expect to find 10,000 humpbacks here at one time. Instead, individual whales rrive and depart throughout the season. Humpback whales are distributed throughout the waters around Hawaii, but the highest concentration of whales occur in the four-island region of Maui, Molokai, Lanai, and Kahoolawe, and an area known as Penguin Banks, a shallow bank between Molokai and Lanai.The warm, clear, relatively protected waters, and easy access to humpback whales make the Hawaiian Islands one of the best natural laboratories in the world to study whales.

Why DoThey Come to Hawaii?

Whales travel to Hawaii in the winter for two primary reasons: to mate and to calve. Most, if not all of the behavior, that is observed in Hawaii during the winter months is related to reproduction.While male humpbacks spend their time courting, defending, and competing to win the right to mate with females, females spend their time either trying to become pregnant or giving birth and raising their newborn calves.

When is the Best Time to See Whales?

A few humpback whales begin arriving in Hawaii as early as October (even earlier on a couple of occasions) and some have been sighted here as late as July (Meagan Jones, personal observation). But those are the exceptions.The peak of the humpback whale season in Hawaii (i.e., the time of year when the highest number of whales are present) is generally around February and March.Throughout the winter months, new whales are continually arriving and leaving throughout the winter season.

What DoThey Do in Hawaii?

On the breeding grounds, males engage in three primary behavior patterns: a) singing; b) aggressive and non-aggressive interactions with other males; c) and escorting, guarding or defending females. Much less is known about female behavior patterns on the breeding grounds, but females are generally involved in courtship and mating and/or activities associated with the care and protection of newborn calves.

Social Lives of Humpbacks in Hawaii

There is still much we don’t know or understand about the social lives of these great mammals. Most humpback whale social groups are believed to be short-lived, with the longest known bond occurring between a mother and calf, which lasts approximately a year. In Hawaii, groups of humpback whales are often fluid, and rarely last much longer than a day or two. Some of the most common social groups observed in Hawaii are described in more detail below.

Mothers and Calves

Calves (a baby whale is called a calf) begin their lives during the winter months and as such mothers and newborn calves are commonly sighted throughout the winter in Hawaii, often in relatively shallow waters.A newborn calf typically stays close to its mom, often maintaining physical contact by positioning itself just under her chin or under her belly for nursing while the two are stationary, and alongside her head when traveling. Usually, the mother positions herself where she can keep a close eye on her newborn calf at all times. A male ‘escort’ often accompanies mothers and calves. In fact, up to 75% of mothers and calves are escorted by at least one male. However, research indicates that this male is not likely to be the father of the baby. Instead, he is probably a roving male hoping to mate with the mother. Although relatively uncommon, mothers with newborn calves can come into a postpartum estrous and may give birth in successive years. Recent results of paternity tests suggest that males escorting mother’s can be a successful reproductive strategy for males.

Male-Female Pairs

Adult male and female pairs are one of the most common social groups on the Hawaiian breeding grounds. In these situations, the male is most likely courting and defending his place with the female, hoping to be in the right place at the right time - when she comes into estrous. Alternatively, the pair could have already mated and he could be trying to defend his position ensuring that no other male’s mate with her during this critical time of her cycle. At this point, the exact relationship of male-female pairs is largely unknown.When no other males are around, these groups are generally relatively stable and stationary, with the whales often diving for periods of 20 or 30 minutes and only traveling when at the surface to breathe. As such, they are not a favorite of whale watchers and some researchers refer to them simply as ‘breath-holders’.

Humpback Males Will Fight for a Female

This quiet stability between a male-female pair described above changes dramatically when another male (or males) join(s) the group, challenging the male for his position with the female. During these interactions, males will often fight for the right to mate with the female or at least escort her, sometimes leading to bloody encounters between the males.Whether or not the results of these challenges allow the female to choose her mate or not is not yet known. During these skirmishes, large groups of males may form around one female and are called surface-active groups (or competitive groups). These larger groups are a favorite for whale watchers as the whales often travel in fast, erratic patterns and spend more time at the surface thrashing around.We have seen groups as large as 30 humpbacks form around one female!

Singing Male Humpbacks

During the mating season and along the migration, male humpback whales also sing songs.The sounds that comprise a humpback song are varied and range from high-pitched squeaks to lower frequency roars, ratchets and moans.A striking feature of the song is that it gradually changes or evolves over time. Each year, different sounds and arrangements of sounds form to create new phrases or themes, so that the song gradually changes over time. Despite the constantly changing nature of the song, all singers in a population sing essentially the same version at any one time. In fact, all singers in the North Pacific Ocean (that is, whales in Japan, Hawaii, Mexico and the Philippines) separated by thousands of miles sing essentially the same version of a song at any one time.The songs of humpbacks may be similar across entire ocean basins like the North Pacific Ocean, yet different in separate oceans. Humpback whales in the South Pacific, for instance, have a completely different song from humpback whales in the North Pacific Ocean. Singers are usually, but not always, alone. Often the singer is relatively stationary, staying in one geographical location for extended periods of time. During these stationary periods, singing humpback whales often hang in an upside down, headdown, tail-up position, approximately 15-30 meters below the surface.The singer will maintain this position until it surfaces to breathe and then immediately resumes this position after diving.

To hear humpback whale song, please visit the Whale Trust Sound Gallery here

Why Do Males Sing?

Why they sing such elaborate and ever changing songs is not yet fully understood, butWhaleTrust researchers have spent the last 30 years trying to understand why male humpbacks sing songs.Our research has shown that male singers consistently attract other males (not females).We are now trying to understand why males would approach and join other male singers, and what the role of the female is within the context of the song.We think it might be a way for males to sort out relationships amongst themselves before consorting with a female. In other words, could the song be a way for males to see if they are going to help each other find a female or fight each other for a female?We don’t know if this is right or not, but our research is currently trying to determine if this is one possible explanation as to why males sing during the winter breeding season. At the least, we can say that the song is a communication from male humpbacks during the breeding season. It almost certainly provides the location of the singer, and by association the entire herd, and signals that reproductive activity is underway. The song also likely broadcasts information about the individual singer, but what information is communicated and who the recipient is remains unknown.

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