| It is generally believed that humpbacks mate and calve in Hawaiian waters, but neither of these activities has been observed. Young calves are frequently seen and are probably born in or near Hawaiian waters. HWRF researchers were involved in the discovery and study of a humpback whale placenta near Maui, possibly the first direct evidence of calving in Hawaiian waters. (See A Large Placenta encountered in the Hawaiian winter grounds of the humpback whale, Megaptera novaeangliae. Linda Silvers, Dan R. Salden, S. Atkinson, M. Iwasa, C. Cambellas. 1997, Marine Mammal Science, 13:711-716.) The gestation period of the humpback is estimated to be 11 to 12 months. The norm is for mothers to calve on a 2-3 year cycle. Recent findings, however, suggest that some females give birth and are impregnated in a single season. The significance of this event has not been determined. |
| Scientists estimate that calves nurse for up to a year, when they are approximately 26-30 feet in length (8-9 meters). The mother's milk is exceptionally high in its fat content (50%) and allows the calves to gain weight quickly. It is imperative for them to develop a thick layer of blubber prior to their 3,000-mile migration back to the cold Alaskan waters. Mothers with calves are often accompanied by a third whale on their breeding grounds. This escort whale appears to be a sexually mature male who is waiting to breed with the female should she become receptive. Other males challenge this primary escort for his position. These challenges result in intense battles, and the sequence of challenges may last for hours. The battles are characterized by head lunges, underwater exhalations, and a general increase in surface activity. These large, combative groups are called "competitive groups." |
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