Blue whale calves grow 200 pounds per day for the first year they are alive.
As far as we know, the blue whale is the biggest animal ever to live on Earth. Baby blue whales, or calves, are born big, but it takes a hefty diet to grow to the unparalleled full size of an adult blue whale. After a steady diet of mother's milk and plenty of weight gain, these beasts are well on their way to the massive size for which they are known.
A blue whale calf is a lot bigger than a human baby. In fact, a calf's birth weight is more than 20 times a typical adult human's weight. Every two or three years, a mother blue whale gives birth to a big baby, which weighs as much as three tons and measures as long as 23 feet. A whale's pregnancy lasts about 12 months plenty of time for that unborn baby to balloon in size to his impressive birth weight.
The calf doesn't waste any time gobbling up his mother's milk. Mama produces more than 50 gallons a day, with a fat content as high as 50 percent. Her baby drinks it all up every single day, gaining 200 to 250 pounds every single day. He keeps up that weight gain for 6 to 12 months, packing on about 10 pounds an hour by consuming nothing but milk.
After 6 to 12 months, the blue whale calf is weaned and stops subsisting on his mother's milk. He graduates to eating krill, a small crustacean that is virtually the only thing adult blue whales consume. A blue whale swallows up to 50 gallons of water at once, then forces water back out through a special filter that traps the krill inside his mouth. This filter, called baleen, makes him an efficient eater that can eat as much as six tons of krill in a single day.
The blue whale's massive appetite from infancy through adulthood allows him to reach his infamous size. The adult blue whale weighs as much as 200 tons, more than 50 times his birth weight. As a matter of perspective, the largest land mammal on Earth is the African elephant, which weighs about as much as the blue whale's tongue. Measuring about 100 feet long, these animals owe much of their large size to the rapid weight gain they undergo as calves.