Humpback whales are far better known for their bellowing "songs" that can travel up to six miles, but the animals also have quiet voices. Biologists have observed humpback calves “whispering” to their mothers in tones that can be heard only within 330 feet—a strategy to prevent predators, such as orcas, from eavesdropping. Calves also want to avoid adult male humpbacks, which may try to separate the calf from its mother to mate. This shortened time with its mom could ultimately weaken the calf, which needs to drink 50 gallons of milk a day to fuel up for its long migration.