The size and colour of the baleen of various whales depends very much on their species. In order to allow the whale to close its mouth comfortably, the baleen plates fold so that they lie on either side of the tongue. When the mouth is opened, they spring back into form and extend from the top jaw to the bottom, held in place by the bottom lip, which prevents them from springing out of the mouth completely. The top of the mouth is arched to accommodate the baleen.

Baleen whales feed by swimming, open-mouthed, through large swarms of plankton. Sizeable gulps of water are pulled through the hairy baleen; trapping the tiny krill in the bristles and then forcing the water back out. For this to occur, the whale uses its tongue to either increase the capacity of the mouth or to force the food down the animal’s throat. Of course, the swarms of plankton may occasionally have other fauna and flora within them, which the whale would then swallow with the rest of its mouthful of krill. However, plankton generally travels with others of its species, limiting the other plants and animals from infiltrating their swarms.

Baleen whales move slower than toothed whales, since they do not need to pursue fast-moving prey that is trying to escape. They are also, generally, larger than toothed species. This is remarkable, since its prey is so much smaller than the squid, fish and small marine mammals on which other toothed cetaceans dine. Because they are larger and slower moving, they require thicker blubber to provide warmth and energy.