Whales

Transcription

1 1 of 5 02/11/2006 4:36 PM Whales 1 Have you ever been on a whale watching tour? After hours on a boat, you may grow bored and tired. Yet, as soon as you see a group of whales swimming nearby the boat, your spirit was uplifted and became excited. You watch these ocean giants closely. You don't want to shift your focus away for even a second, afraid that you may miss them breaching (leaping out of the water), spyhopping (poking their heads out of the water), or lobtailing (sticking their tails out of the water). In short, whale watching is an extremely rewarding and unforgettable experience! So, let's learn about whales! 2 Whales have streamlined bodies that resemble fish. Although inhabiting underwater, whales are actually mammals, not fish. Like all mammals, whales have lungs and breathe through nostrils. Whales' nostrils, called blowholes, are located on the top of their heads. When whales come to the surface, they first expel used air from their lungs and then take a deep breath of fresh air. As whales exhale, they shoot out a cloud of water vapor and stale air from their blowholes high into the sky. 3 Aside from breathing through lungs, being warm-blooded and feeding young with milk are two other traits shared by every mammal species. Whales are no exception. Besides a couple of whale species that reside in rivers, most whales live in oceans and many of them prefer icy-cold waters near the Arctic and Antarctica. Even though whales are nearly hairless, they have a thick layer of fat under their skin (called blubber) to help them fight off frigid temperatures. 4 After a gestation period ranging from about 10 to 16 months, varied by species, a mother whale gives birth to a single young. The newborn (called a calf) can swim right away, but it stays with its mother for at least a year for protection and nourishment. The mother whale feeds her calf with milk. Whale milk is very rich and fatty. In fact, whale milk can contain up to 50% of fat. By comparison, whole cow milk has a fat content of about 3.25% and human milk roughly 4%. 5 Okay, we know that whales are not fish. But, do you know how to tell if you are looking at a whale or a fish? Of course, the blowhole is a very useful clue. Fish use gills to breathe. Hence, they don't have blowholes. In addition to searching for blowholes, you can distinguish between a whale and a fish by checking the animal's tail. Fish have vertical tail fins and they swim by moving their tails from side to side. Whales, on the contrary, have horizontal tail fins. They propel forward by moving their tails up and down. 6 There are 83 different species of whales in the world. Scientists divide them into two groups -- baleen whales and toothed whales. Baleen whales do not have teeth. Instead, they have comb-like structures (called baleens) that hang from each side of their upper jaws. The inner edge of each baleen has hairy plates that filter krill, plankton, and other small organisms from the water. Of the 12 baleen whale species, blue whales, gray whales, bowhead whales, and humpback whales are the most

2 2 of 5 02/11/2006 4:36 PM famous. 7 Just as the name suggests, toothed whales have teeth. While fish and squids make up their main diet, some toothed whales (such as killer whales or orcas) are known to attack seals. Toothed whales include many familiar faces. Aside from killer whales, dolphins, porpoises, sperm whales, and belugas (or white whales) are all examples of toothed whales. The presence of teeth is not the only way to tell the difference between a toothed whale and a baleen whale. The alternative is to look at the animal's head. Toothed whales have one blowhole, but baleen whales own two. 8 With so many different species of whales, we can only pick a few whose distinctive feature or behavior makes them stand out from the rest of their family members. Let's call the list below the Whale's Hall of Fame -- Blue whales are not only the largest of all whales, but also the largest of all living animals on Earth! Amazingly, blue whales can measure about 80 feet in length and weigh over 250,000 pounds! Sperm whales are the best divers in the whale family. They can dive to a depth of over 9,000 feet and stay underwater for more than 2 hours! If we were to host a swimming contest among all whale species, the killer whale would be the champion. Killer whales swim at an average speed of 40 miles per hour, making them the fastest swimming marine mammal in the world! Gray whales love traveling. Every year, they make an extraordinary roundtrip journey between the Arctic Ocean and the coast off the Baja peninsula, Mexico. Their annual migration route is about 12,500 miles long! Although 71 out of 83 whale species have teeth, narwhals win the title of the whale with the longest tooth. Narwhals have two teeth in their upper jaws. When a male narwhal turns one year old, his left tooth starts growing outward and spiraling clockwise. This tooth just keeps on getting longer until it becomes a tusk that can measure up to 10 feet! Occasionally, we may come across a male narwhal with two tusks or a female narwhal with one tusk. Because of the tusk, the narwhal is nicknamed the "unicorn of the sea." Copyright 2006 edhelper

3 3 of 5 02/11/2006 4:36 PM Name Date Whales 1. What kind of animals are whales? Crustaceans Mammals Amphibians Fish 3. Baleen whales have one blowhole, whereas toothed whales have two. False True 5. What is a baleen? It is a comb-like structure that hangs from each side of a toothed whale's upper jaw. The inner edge of a baleen has hairy plates. Its function is to filter krill, plankton, and other organisms from the water. It is a whale's nostril. 7. Which of the following statements about whales is true? Gray whales travel the longest distance a year of all whales. Blue whales are the best divers of all whales. Killer whales are the largest of all whales. Belugas have the longest teeth of all whales. 9. What is whales' secret to keeping warm? They have a thick layer of fat under their skin. They have waterproof skin. They have a thick layer of fur. They don't have to keep warm, because they all live in tropical waters. 2. Which of the following about whales is true? Blue whales are the largest fish on Earth. "Spyhopping" is an act when whales stick their tails out of the water. Whale milk has very high content of fat. Baleen whales include killer whales, sperm whales, and dolphins. 4. Which of the following is a baleen whale? The narwhal The gray whale The bottlenose dolphin The beluga 6. Which of the following is not a difference between baleen whales and toothed whales? Toothed whales have vertical tail fins, whereas baleen whales have horizontal tail fins. Baleen whales have two blowholes, whereas toothed whales have just one. Baleen whales do not have teeth, whereas toothed whales do. Baleen whales feed on krill, plankton, and other organisms, whereas toothed whales eat fish, squids, and other animals. 8. Which of the following is the world's largest animal? The bowhead whale The whale shark The blue whale The African elephant 10. Which of the following about whales is not true? Baby whales, called calves, usually stay with their mothers for at least a year. Sperm whales are the record holders for the fastest swimming marine mammals. Whales exhale and shoot out a cloud of vapor and used air from their blowholes. Whales have horizontal tail fins. Their swimming style is to move their tails up and

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5 5 of 5 02/11/2006 4:36 PM Whales - Answer Key 1 Mammals 2 Whale milk has very high content of fat. 3 False 4 The gray whale 5 Please choose two of the best answers. 6 Toothed whales have vertical tail fins, whereas baleen whales have horizontal tail fins. 7 Gray whales travel the longest distance a year of all whales. 8 The blue whale 9 They have a thick layer of fat under their skin. 10 Sperm whales are the record holders for the fastest swimming marine mammals.