Humpback whales are viviparous, meaning they give birth to live young that developed in the body of the mother. They engage in seasonal breeding. Females typically produce offspring every two years, and can produce young twice in three years. The number of offspring is generally one. The gestation period ranges from 11 to 11.5 months. The average weaning age is five months. Females and males reach sexual maturity at four to 10 years. [Source: Mindy B. Kurlansky, Animal Diversity Web (ADW)]
Humpback whales migrate to lower latitudes in the winter for breeding. During this time, males exhibit competitive behavior around females and often strike or surface on top of one another, sometimes causing bloody injuries. While breeding hasn’t been directly observed, it is believed that males are competing for access to females. Males also sing complex songs for hours that can be heard 20 miles away — the low-frequency portions of the song are audible much farther in deep water. [Source: NOAA]
Humpbacks hang out in their breeding waters for several months, mating, calving and singing. Females begin breeding at age five and have calves every two or three years. Some have calves every year. Humpbacks don’t seem to eat anything during the breeding season. Males sing particular songs in low, guttural moans and high-pitched whoops and screeches that appear to directed to other males not the females. Sometimes a humpback cow and calf are accompanied by males. These males escort females with calves in hopes that they will be the next ones to mate with the mothers.
Websites and Resources: Humpback organizations and experts: the Maui-based Whale Trust; Lou Herman of the Honolulu-based Dolphin Institute has published more than hundred papers on humpbacks, their songs, their migration patterns, and interaction between mothers and calves. Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Humpback Whale Mating
Humpback whales are polygynous (males have more than one female as a mate at one time, with males competing aggressively for access to oestrous females. No one has seen humpbacks mate but scientists have seen them engage in affectionate and “seductive” behaviors . Describing humpback whale “foreplay,” James Darling wrote in National Geographic, a male blows "bubbles that will rise beneath the genital of the female." As a rule it seems though that no matter what the males do the females seem indifferent.
Females rarely interact with one another in the breeding area in Hawaii. Most have at least one male suitor at their side. When other males are not present the courting male usually follows the female, sometimes angling ahead to alter her court or leaving briefly to scout around and see if any other males are present. All the activity is relatively slow. Having young whales present doesn’t seem to deter the males. Mothers and calves are often accompanied by males, who are not interested in rasing the young — they want to mate with the females.
According to Animal Diversity Web: In males, the length of the penis can be an indication of sexual maturity. However, in some cases, puberty may proceed sexual maturity by one year. In sexually mature males, the weight of the testes and the rate of spermatogenesis increase during the breeding season, coinciding with the ovulation of the females. In the females, after sexual maturity is reached, ovary weight remains fairly constant. As ovulation approaches, "resting" Graafian follicles on the surface of the ovaries enlarge. There generally is only one ovulation per breeding season. [Source: Mindy B. Kurlansky, Animal Diversity Web (ADW) /=]
During humpback mating engagements Males and females first swim in a line; they then engage in rolling, flipping, and tail fluking. Next, both dive and then surface vertically, with ventral surfaces "in close contact." They emerge from the water to a point below their flippers. They then fall back onto the surface of the water together.
Longtime humpback observer Lou Herman told Smithsonian magazine, “We think females choose a particular male but we don’t known that for certain, and we didn’t know what male attributes females prefer. It is suspected they prefer the largest, strongest — and therefore, oldest males.” Some scientists believe that dominant males hang out at the breeding area for a long as possible and mate with a succession of females who come and go.
Humpback Whale Mating Behavior
Most of the mating activity takes place in “competitive pod” comprised of males, sometimes numbering 15 or more, that swarm around the female. A male known to scientists as a “principal escort” stays close to a female and fends off other males, sometimes with long trails of bubbles. They are often the biggest whale around. Secondary escorts are males that are bettered by the primary escort but are big and strong to keep other whales at bay. Primary escorts can gain or lose their status.
The female, referred to as the “nuclear animal,” glides along, setting a slow pace for the mayhem around her. Males veer back and forth, push and shove, whack each other with their flukes and pectoral fins, blow streams, of bubbles and lift each other out of the water during their struggles for dominance, Sometimes there are fierce battles between males, jockeying for position to challenge the principal escort, in which they thump their bodies against one another. Sometimes they draw blood. Sometimes the normally white undersides of their flukes and fins turn pink, likely from the blood from exertion.
Challenging males gulp water to swell their throats, launch themselves backward so they look bigger, smack the surface of the sea with their flippers and breach. Sometimes the males use their massive foreheads to batter one another during battles over a female. Charging males often lunge forward with open jaws to gouge or scrape a rival. Occasionally the fights are deadly. In 1996 a battered dead body of one male was found near a competitive pod in Hawaii.
Douglas Chadwick wrote in National Geographic, “When you have anywhere from four or five to two dozen whales crisscrossing, circling and diving past each other, it is extremely difficult to keep track of who’s doing what. New contestants keep arriving, drawn to the hubbub from surrounding areas, while others peel off or simply lag father and farther behind as they tire...Fresh nicks, scrapes and gouges testify to the serious level of competition. Yet there may be cooperation too, as when two or three males gang up on what looks like an effort to block a female’s progress or to push one of the main escorts off course.” One researcher told Chadwick, “I’ve seen two males pancake a third. One came up under him while the other lunged on his back.”
Account of Humpback Whale Competitive Pod
Virginia Morell wrote in Smithsonian magazine, “Ten males are now swarming around this female. We watch the whales surface and spout, their black backs arching above the waves almost in unison as they breath and dive, They’re packed tightly together, like a team of motorcycle toughs, and they churn the water white and foamy. Sometimes a male surges ahead, braking high above the waves to reveal its long winglike pectoral fins...Whitehook [the principal escort] heaves himself half out of the water to charge headfirst at another male. He then launches himself skyward, then falls backwards...then slaps his long jaw in the water, breaches again.”
A researcher who watching the activity from in the water reported: “the N.A. [female nuclear animal] is about 80 feet down, and Whitehook is right below her, chasing off intruders. It’s classic mate-guarding behavior. He’s making big sweeps with his pectoral fins if any guy comes near her and a if challenger approaches from the front, he leaves her and makes a head-on attack. He sculled backwards once to take a tail swipe at secondary escort, and then sidled up next to her and blew out a linear bubble trail. Right after that, she began surfacing, and everybody followed.”
Picking up the action Morrell wrote, “When the pod resurfaced in the channel, two competitors are oozing blood from their bumpy jaws. Their injuries don’t slow them down; they plunge back into the fray. Whitehook smashes a whale on his left with his lower jaw, whacks another with his pectoral fun, and then rockets skyward while others crash and heave to get out of his way.”
Humpback Whale Calves
Calves are born in the warm tropical waters and subtropical waters of each hemisphere. Newborns are born 4.5 to five meters (13 to 16 feet) in length and weigh around 3 US tons (2,721 kilograms, 2.7 tonnes). They are born 11 months after they are conceived and are nursed by their mother’s rich milk for about a year. They reach 4.8 meters (15 feet) within a couple of weeks and about six meters (25 feet) after the first year.
David Attenborough wrote: “As an infant emerges from its mother she nudges it to the surface to take its first breath. Then it drinks. A slot in her side opens and a nipple protrudes. The baby grabs it with its mouth and the mother squirts out milk by contracting a muscle that encloses her milk store. “
Calves are born without blubber, which keeps them warm in the frigid polar waters. This is one reason presumably the calving areas are in warm water. When a mother and calf are in the breeding area they are often pursued by males. A lot if time and energy is spent trying to keep a safe distance from them or making a run for if too many males appear.
Calves emit soft, whisper-like squeaks, perhaps to avoid being overheard by predators. They suckle underwater. A mother can produce up to 600 liters of milk a day. A calf can grow 45 to 65 kilograms a day, as much as some humans do in their entire lives. The milk is very rich, 46 percent fat, compared to 5 percent for the richest cow’s milk.
Humpback Whale Parenting
Females produce a single calf, on average every 2 to 3 years, although annual calving has been documented in some individuals. During the pre-fertilization, pre-birth and pre-weaning stages provisioning and protecting is done by females. There is no parental involvement other than fertilization by males. During gestation period the embryo grows approximately 17 to 35 centimeters per month. Calves nursed by their mothers for about five months. The females' milk is highly nutritive, containing high amounts of fat, protein, lactose and water. When breeding takes place twice every three years lactation may last longer than the usual five months. If a female is impregnated shortly after parturition, pregnancy and lactation may proceed simultaneously. [Source: Mindy B. Kurlansky, Animal Diversity Web (ADW) /=]
Calves stay near to their mothers for up to one year before weaning. Mothers are protective of and affectionate toward their calves, swimming close and often touching them with their flippers. While calves are not believed to maintain long-term associations with their mothers, they are more likely to be found in the same regions of the feeding and breeding grounds as their mothers. [Source: NOAA]
For calves their mothers can be big play things. They climb up their mother’s back and zip down as if they were slides. Sometimes a calf climbs in to her mother’s rostrum, the broad bench formed by the upper jaws, and are tossed in the air and caught like an Eskimo on a blanket. Favorite places for calves to muzzle are under their mother’ fin and under the throat.
Image Source: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated May 2023