Hawaii's Humpback Whales

Every winter, from November to April, Hawaii is visited by an imposing procession of the world's largest snowbirds: The Hawaiian Humpback whales.

Traveling night and day, at a steady three miles per hour, stopping neither to eat or sleep, the humpback migration leaves its summer feeding grounds off Alaska, to rendezvous in Hawaii's warm waters.

They arrive in pods of two or three, with last year's mothers and their calves arriving first. Sub-adult whales of both sexes come next, with the sexually mature adults following. Pregnant females arrive last.

The pregnant females stay in the northern feeding grounds longer to store the energy necessary for the long voyage south and the trauma of birthing and nursing their young. Only nursing calves feed during their Hawaiian travels - everyone else fasts until their return to the food-rich Alaskan waters.

What impulse causes these mighty leviathans to leave their remote arctic refuges and travel for thousands of miles, fasting all the while, to wind up in the warm, tropical waters of Hawaii? It seems that the humpbacks, like humans, find the balmy Hawaiian surroundings romantic, and come to Hawaii to mate, and give birth.

Birthing and Breeding

Since the gestation period of the humpback whale is roughly twelve months, the yearly vacation provides both an opportunity to meet other whales in a fun, care-free environment, and a safe, nurturing haven to give birth and raise the calves in.

When the time for birthing comes, the mother whale seeks out a relatively shallow, usually inshore area, where she and her calf can be safe from harassment from sharks, boats, and sexually inclined males.

The calf begins to nurse soon after birth. The mother has two nipples, located on either side of the vaginal slit. After finding the nipple, the calf curls its tongue around it. The stimulation of the nipple by the calf results in a reflective squirting of the milk by the mother.

Whale's milk is much thicker and richer than that of land mammals. It has less water than the milk of most terrestrial mammals (40-50% for the humpback whale as opposed to 80-90% for many domestic animals, and much more fat (40-50% versus 2-17%). The calf will consume about 100 -130 gallons of this rich substance per day, which helps it grow at a rate of a foot a month. The new-born humpback, 12 feet long at birth, will double its length within a year.

A few days after birth, the calf is ready to venture out into deeper water, where the mother and calf are often joined by one or more males. Apparently a certain percentage of females are able to be impregnated even though still nursing. These males vie for the female's attention, and fight each other, tail-standing out of the water, belly to belly, to knock each other down and out of contention.

All this male rivalry results in some of the spectacular surface displays that make humpback whale watching so satisfying. Head slaps, head butting, tail slaps, all are meant to discourage fellow suitors, and keep them away from the female. Sometimes the female herself takes the lead, and sets off swiftly, with the competing males in close pursuit, followed by curious non-combatants. These high speed chases are punctuated by shoving and butting matches, as the pursuing males attempt to keep each other away from the female.

After a period of such running warfare, the dominant contestant is determined, and the competition comes to an end, with many of the pursuing males dispersing. Now, it's up to the female to indicate her willingness to mate with the winner, and she does so by engaging in a lot of body contact, including mutual pectoral fin caresses, belly-to-belly rubbing, diving under each other, and nuzzling.

Interestingly, the courting couple is generally attended by other whales. The purpose of their attendance is unclear: Maybe they are hopeful understudies, hoping the female will tire of her choice and pick again.

Surface Displays

Not all humpback acrobatics are related to courting activities: Whales of all ages will slap the water with their tails, producing a huge sound and splash, and even more spectacularly, breach. A breach is an unbelievable display of extraordinary strength and good spirits: Thirty or more tons of whale catapulting vertically out of the ocean with only their tails in the water, rolling over on their backs in the air, and landing on the water in a back flop, creating an unbelievably huge splash, out of which grows an inner, denser fountain as the whale penetrates the water and displaces its enormous bulk.

Humpback Songs

Another fascinating activity that the humpbacks engage in is singing. The humpback's songs are of a complexity and flexibility unknown outside of humans. Unlike bird songs, the humpback songs progressively change from year to year.

A humpback song is composed of a series of discrete notes or units. A unit is the shortest discrete sound noticeable to the human ear. A series of units is a phrase. Phrases are uniform in duration, and may contain repeated sounds. A consecutive group of phrases make up a theme. Although a given theme may vary in the number of phrases it contains, the sequence of the phrases is always the same. Likewise, the sequence in which themes occur is always the same, although some themes may be left out. A predictable series of themes makes up a song.

The whale's song is in a constant state of evolution. As the season progresses, new themes are introduced, and old ones are discarded. Each singer changes his song to keep up with other singers, so that all the singing whales sing the same evolving song.

Only male humpbacks sing, primarily in their Hawaii travels (mating season) so it is supposed that the singing has a reproductive function. Perhaps the singing serves to attract females, or drive away competitors, or maintain a territorial distance between the singers.

Feeding Habits

Although humpbacks don't feed while in Hawaii, their feeding behavior is quite interesting. Baleen whales, like the humpback, basically feed by filling their mouths with food-filled water, and expressing the water out through their baleen plates, which serve as a filter to keep the plankton and small fish in.

Baleen whales are generally divided into three groups, based on their feeding structures and habits: The Balaenidae, the Balaenopteridae, and the Eschrichtiidae.

The Balaenidae, a typical example of which is the Right whale, have a round figure, with a large, deep mouth. These "bucket mouth" whales move slowly, are found relatively close to shore, and float when dead, which made them the "right" whale to hunt for early whalers. They feed by "skimming", slowly swimming back and forth through the swarms of plankton and krill with their huge mouths open, filtering the tiny organisms out of the water that fills their mouths.

The Balaenopteridae includes the humpback whale, the blue whale (the world's biggest animal ever), and the fin whale. This group is characterized by a sleek, streamlined body, a dorsal fin, and a series of pleats that run from the mouth down to the belly button. These pleats allow the whale to remain streamlined for swimming long distances. When feeding time comes, the whale is able to, by allowing the pleats to expand, increase its mouth size more than three times, greatly increasing the amount of water it can take in and filter. Because of their style of feeding, these whales are called "gulpers".

Two techniques are employed by humpbacks to catch their food: Lunge feeding, and bubble net feeding. When lunge feeding, the whale swims through a school of its prey, opens its mouth near the surface of the water, and gulps the prey. A more technical approach, bubble net feeding, involves the whale diving below its prey, and discharging a constant stream of bubbles while circling under the school. As the bubbles rise, they form a noisy, visible "net" which appears to disorient the prey. As the fish coalesce into a tight ball within the closing net, the whale charges from below, bursting through the surface with its mouth open, and engulfs the school.

The only member of the Eschrichtiidae group is the California gray whale. These whales are known as"suckers" because of their feeding techniques: rather than trapping plankton through either skimming or gulping, they feed on crustaceans they stir up out of the ocean floor, through generating enough suction with their tongue to forcefully suck them out of the mud, through the baleen, and into their mouths.

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