Each year, humpback whales start 4400 miles (7000 km) trip from Antarctica toward the Polynesian waters. Between June and September, divers can hear the song of the males, a sort of courtship ritual made for attracting the females. One year later, whales return to the area in order to give birth. Then, mothers brood their calves and feed them at an impressive rhythm of 400 liters a day. Such regime allows young calves to double their weight (which reaches 2 tons) and allows them to undertake the return trip.