Humpback whales that can be seen in the Ogasawara Islands from December to May, include males and females which come to the islands for mating, calving, raising their young, and other breeding-related purposes. As a result, they form breeding groups and various behaviors can be observed. The size of the flock can range from a single individual to a dozen or more, but it is not permanent, and the members and number of flock members change frequently. In the latter half of the season, father and son whales are often seen, and they stay together for almost a year.
【Mating group also known as “mating pods”】
This is a scene of multiple male whales fighting over a single female whale. They are breathing hard, hitting each other with their pectoral fins and tail fins, attacking with the barnacles on their bodies, and performing various other violent behaviors. The formation of the group is temporary, and it seems that the dominance of the males is determined by their violent behavior, and eventually the group breaks up and the winner gets the female whale.
【Baby whales (calves)】
Compared to adult humpback whales, which are 13 to 14 meters long, calves are smaller at about 4 meters, and their milk gray body color makes them easy to spot. Newly born whales have many wrinkle-like lines on their bodies. They also have short breathing intervals of only two to three minutes, compared to the 10 to 15 minutes of adults. These whale calves are like waddling human babies, and many of their behaviors are still a bit fidgety. For example, they may not be able to raise their tail fins properly (they may just be playing with them), they may roll over or may slip into the water without lifting them completely. Then, suddenly, they are jumping around in the water. The way they roll around on top of the mother whale, slapping the surface of the water with both pectoral fins, floating and sinking, is very funny and reminds us that spring has come.
Foraging and Feeding
Humpback whales feed mainly on krill and other zooplankton, as well as schooling fish such as herring and shishamo smelt fish. They swell their pleated ridges from their chin to their belly, swallow the food with the seawater, and push the seawater out between their whiskers with their tongues to scrape up the food.
The North Pacific humpback whale’s “method of eating” is particularly unique, as several humpback whales are known to cooperate with each other. Each whale dives in turn, and one of them emits air bubbles in a spiral turn from the depths. The ascending bubbles form a cylindrical curtain that swallows the fish trapped in it from the bottom.
Singing Humpback Whales (Reproductive Strategy of Male Whales)
It is well known that male birds chirp and sing to attract females and to mark their territories. Similarly, male whales make sounds that echo in the water to show their presence. It is also thought that this sound is made to determine the order of dominance among males and to maintain that order. These sounds consist of short phrases made up of several syllables, and similar phrases are grouped together to form a theme that is repeated.
This complex sound is called a “song,” and the males who sing the song are called “singers”.