They may be some of the largest animals on the planet, but baleen whales dine on some of the smallest animals. Baleen whales, characterized by the long plates of baleen that hang in rows from their upper jaws, come in 12 species, divided into four families. The baleen plates are more like human fingernails than like teeth; they're made of protein. This makes them strong but flexible so that baleen whales can strain water between the comb-like rows and pick out riches from the sea such as plankton and small fish. Once they trap their food using the baleens, the whales filter out any remaining water.
Right whales eat this way, opening their large mouths to graze for small crustaceans as they swim along the water's surface. Right whales are easily recognizable as mostly black whales with white trim. Pigmy right whales follow similar eating patterns, straining crustaceans or small zooplankton for meals [source: Sea World]. Each baleen whale species filters its food in a different way, however. Humpback and blue whales, also known as rorqual whales, expand their throat grooves and gulp huge amounts of water (up to 18,000 gallons, or 68,000 liters). They may feed at the surface or at some depth and catch prey with all that water, usually small fish in schools, and a variety of small crustaceans or squids. Different rorquals have different tastes: Blue whales prefer krill, fin whales like krill, squids and small schooling fishes. Humpback whales prefer mostly krill and small schooling fishes.
Gray whales are the most likely of all baleen families to be seen near coasts. They migrate every year between summer and winter feeding grounds to ensure there is enough food -- making their trek one of the longest migrations of any animal species [source: National Marine Mammal Laboratory]. Gray whales swim on their sides along the ocean floor and suck up mud and dirt, filter-feeding on various crustaceans in the process.
Baleens also have huge tongues, which they probably use to help move food that is trapped inside their baleens and to help with swallowing and pushing water from their mouths. Most of the baleen whale species do the bulk of their eating in the warmer summer months, then use the cooler months for migrating and breeding. A baleen whale might eat up to 4 percent of its body weight each day during feeding season [source: Sea World]. The famous whale blubber -- which can constitute about a quarter of a baleen whale's total weight -- serves an important purpose: The fat it stores saves energy for the winter months, when whales eat less than 1 percent of body weight a day because so little food is available.
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