Each year, tens of thousands of whales travel thousands of miles from their summer feeding grounds to winter breeding grounds. Hawaii, and most abundantly the shallow waters between Molokai, Lanai, Kahoolawe and Maui, is the largest breeding ground for North Pacific whales, most of whom are coming from the northwest coast of North America.
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.
The sea conditions in Hawaii, including calm lees protected from trade winds, clear, warm water, and easy access to humpback whales make the Hawaiian Islands one of the best natural laboratories in the world to study whales.
What is a Breeding Ground?
Humpback whales have a specific reproductive cycle with the same components as all mammals: mating, gestation, birth and nurturing young. The typical reproductive cycle of a mature female humpback is: mating in winter, a year’s gestation, birth of one baby during the following (second) winter, a year’s care of the baby prior to weaning, then separation in the third winter followed by mating again. As most of the mating, birthing and nursing takes place during the winter months, the area they spend the winter becomes the “breeding ground”.
It is important to note, however, the “breeding ground” does not necessarily imply a rigid boundary for these behaviors. Reproductive activities begin, and some births occur, before whales reach Hawaii. In fact, some behaviors such as singing (a behavior not necessarily related to breeding per se but which is prevalent in breeding grounds and generally absent from feeding grounds) begin as early as late fall before the whales leave their summer feeding grounds. Reproductive activities also continue to some extent on the northern migration back to feeding grounds.