The sperm whale mothers take turns diving for food and babysitting. Even whales cooperate with each other! What a great way to keep the whale calves safe while the adults look for food. Every whale wins!
Source: Kaplan, Matt. (2009, 31 May). Babysitting whales give mums time for a snack. New Scientist. From http://newscientist.com/article/dn17217-babysitting-whales-gi