Whales and Dolphins

Fifty million years ago a wolf-sized mammal with hooves waded into rivers to hunt fish. Over the next ten million years its descendants spent more and more time in the water, until their legs became flippers, their nostrils moved to the top of the head, their fur disappeared and they never came ashore again. They are the cetaceans, the whales, dolphins and porpoises, about 90 species of them, and they include the largest animals ever to have lived and some of the most intelligent.

Mammals in the sea

Whales look like fish but are not. They breathe air, through blowholes on the top of the head, and must surface to do so; a whale that cannot reach the surface drowns. They are warm-blooded, insulated by a thick layer of fat called blubber rather than fur. They give birth to live young, tail first so the calf does not drown during delivery, and nurse them on milk so rich it is like cream, letting a blue whale calf gain 90 kilograms a day. Inside a whale's flipper are the same bones as in a human arm and hand, and many whales still have tiny useless hip bones buried in their flesh, the last trace of legs.

Two ways to eat

Cetaceans divide into two groups. The baleen whales, including the blue, humpback, grey and right whales, have no teeth. Instead the upper jaw carries hundreds of plates of baleen, a bristly material like fingernail, hanging down like a comb. The whale gulps an enormous mouthful of water and prey, then forces the water out through the baleen, trapping the food. A blue whale can take in 80 tonnes of water in one gulp and eats up to four tonnes of tiny shrimp-like krill a day, making the largest animal in history a feeder on some of the smallest.

The toothed whales, including dolphins, porpoises, orcas, beaked whales and the sperm whale, hunt fish and squid with teeth, and find them with sound.

Seeing with sound

Light fades quickly in water, but sound travels far and fast, and toothed whales have made it their main sense. They produce rapid clicks and listen to the echoes, building a picture of their surroundings precise enough to tell a fish's species and to find prey buried in sand. A dolphin can detect a ping-pong ball 70 metres away. The sperm whale's huge square head is largely a sound-focusing organ, and its clicks, the loudest sounds made by any animal, let it hunt giant squid two kilometres down in total darkness, holding its breath for over an hour.

Baleen whales do not echolocate but sing. Humpback males produce long, structured songs, with repeated themes and phrases, lasting up to half an hour and repeated for hours. Every male in an ocean population sings the same song, and the song slowly changes from year to year, with new versions spreading across the Pacific from west to east like a hit record. Blue and fin whales produce deep moans below the range of human hearing that may travel across entire ocean basins.

Minds and cultures

Dolphins recognise themselves in mirrors, a test of self-awareness passed by only a handful of species. Each has a signature whistle that functions like a name and that others use to call it. Orcas live in family pods led by elderly females, and different pods hunt in different ways, some beaching themselves to grab seals, some stunning fish with their tails, some working together to make waves that wash seals off ice, techniques taught to young and passed down for generations. Pods have distinct dialects of calls. This is culture, in the sense that anthropologists use the word, and whales appear to have had it for millions of years.

Hunted and recovering

In the twentieth century industrial whaling killed nearly three million whales. Blue whales fell from perhaps 300,000 to a few thousand, and several species came within a few hundred animals of extinction. A global moratorium on commercial whaling took effect in 1986, and most populations have been slowly recovering since; humpbacks in particular have rebounded strongly. Today the main threats are collisions with ships, entanglement in fishing gear, and the growing noise of shipping, which drowns out the sounds whales depend on.

Why it matters

Whales fertilise the oceans, bringing nutrients from the depths to the surface in their waste and feeding the plankton that produce much of the planet's oxygen. A single great whale carries about 30 tonnes of carbon to the seabed when it dies. And in their songs, their names, their learned hunting traditions and their care for one another, whales are the clearest evidence we have that complex minds have evolved more than once on this planet, and that they can look very different from ours.