We take a look at the baleen whale's remarkable feeding technique
What are baleen whales?
Baleen whales are a type of whale famed for their filter feeding technique.
Why are they called baleen whales?
Baleen whales are named after their baleen plates that hang from their upper jaw.
Do baleen whales have teeth?
No, baleen whales don't have teeth. Instead each baleen plate is covered in fine bristles (A in illustration below) that sieve the prey from the water. Baleen whales lost their true teeth millions of years ago.
How do baleen whales hunt their prey?
There are 14 species of baleen whales (or rorquals as they are often known), including blue whales, and all are lunge-feeders. Their strategy is to work up a good head of steam, aim for a particularly dense patch of prey, open wide and gulp in enough water to nearly double their weight. They then squeeze the water out though the baleen plates that grow from their upper jaw, whereupon the prey are sieved out and swallowed.
How do baleen whales manage to gulp down so much food?
Their huge gulp is down to a few factors. Some baleen whales have grooves (E) in the skin and blubber that run from a roqual's chin to its navel allows the mouth to expand spectacularly. A whale can quaff almost its own body weight in food and water in one swig. The remarkable jaw (D) also helps. Most mammals' lower jaws come in one piece, but in baleen whales the left and right halves are separate and only loosely hinged to the skull. This provides the flexibility required for those massive mouthfuls.
But how does a baleen whale put all this together for the ultimate lunge? In 2012 Scientists found an organ (C) that choreographs the precise throat expansion and jaw movement required for the perfect gulp.
Scientists have described a blue whale lunge as "the largest biomechanical event on Earth". Just three lunges burn as much energy as an average human uses in 24 hours. The payoff is that each gulp nets the whale go times the calories it expends - enough to power a person for a month.
What do baleen whales eat?
Although all baleen whales hunt in a similar fashion their diet slightly differs. Blue whales favour krill (during the summer months, they can consume as much as 40 million krill per day), sei whales target even smaller crustaceans called copepods, while humpback whales and Bryde's whales prefer fish. Famously humpbacks prepare for their lunges by herding their prey within nets of bubble But baleen is not confined to rorqual!
Another three families of whales are similarly equipped, though their lack of throat pleats betrays the fact that they do not feed by lunging.
How big are baleen whales?
Baleen whales are usually bigger than toothed whales (apart from the sperm whale) and vary in size from the mighty blue whale, which can grow up to 33m long, to the small pygmy right whale, which is 6.5m long.
Do any other whales feed like baleen whales?
Right whales and their close relative, bowhead, are surface skim-feeders. As they swim water enters their open mouths at the front and exits via the baleen at the sides.
Gray whales, in contrast, suck up sediment from the seabed and filter out creatures buried within it.
And then there's the pygmy right whale, which is not a true right whale but the sole representative of a completely different family about which very little is known. There may be more variations on the baleen theme out there yet.
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