Lesson 6:Whales of the world


Lesson 6:Whales of the world

Whale-watching trips can be a mix of boredom andexcitement. Watchers are much more likely to see waves thanwhales. However, the moment a whale pokes its head above awave or a tail comes crashing down into the water, the actiongets more intensive.Sometimes whales spy-hop, resting vertically while poppingtheir heads up above the water. At other times, they lob-tail,raising their massive tails into the air and bringing them downwith a splat. They may also breach, or jump right out of theocean.Although whales might remind people of fish, they arereally gigantic mammals. As mammals, they must breathe airinto their lungs and therefore come to the surface from time totime. Instead of a nose with nostrils, a whale has a blowholelocated on the top of its head. When a whale’s blowhole appearsabove the water, a fountain of water may shoot high into the sky.3

Like other mammals, whales give birth to live young.Different species have different gestation periods, ranging fromten to sixteen months. Only one baby whale, called a calf, isborn at a time. Unlike human babies, the infant whale can moveon its own immediately, so it is able to swim from the momentit is born. However, the calf depends on its mother fornourishment. The mother whale feeds her baby very rich milk.The milk’s high fat content helps the baby stay warm in thecold waters that most whale species prefer.Whales are mammals, so they are warm-blooded. A fewspecies live in rivers, but most of the world’s whales inhabit theoceans. Many of these oceanic species thrive in the frigidwaters that flow over the coldest parts of the earth. Unlikemammals on land, whales have no fur or hair to help keep themwarm. Instead, they rely on blubber, which is a thick layer of fatright under their skin to keep them from being stunned bythe cold.4

Almost 90% of whales fall into the toothed category. Asyou probably guessed, toothed whales have teeth. Most toothedwhales are relatively small compared with baleen whales, buttwo kinds—killer whales andsperm whales—can grow quitelarge. Besides having teeth,toothed whales differ frombaleen whales in another easilynoticeable way. Baleen whaleshave two blowholes; toothedwhales only have one.Toothed whale (at right) andbaleen whale (below)baleen6

Here are some specific whale records:• LargestThe largest animalthat has ever lived onBlue WhaleEarth is the blue whale. It cangrow to around 90 to 100 feet (27–30 m) long and can weighover 150 tons (136,078 kg)! Blue whales are baleen whales.• Farthest-travelingGray whales, anotherspecies of baleen whale,migrate as far as 12,500 miles Gray Whale(20,117 km) each year. In thesummer, they feed in the cold Arctic waters, but they givebirth to their young each winter in the much warmer lagoonsoff Baja California. Gray whales swim fairly close to thecoast, and thousands of people flock to America’s Pacificshores to watch them travel in the spring and fall.7

DolphinsDolphins are toothed whales. A dolphin’s sleek body allowsit to swim at hunting speeds of up to 25 miles (40 km) per hour.When the dolphin is moving at a more relaxed pace—notexactly basking in the sun but peacefully swimming along—itstill covers three to seven miles (4.8-11 km) in an hour.There are thirty-seven species of dolphin in the world.Five of these species dwell in rivers in either Asia or SouthAmerica. The rest are marine mammals, making the oceantheir home, and dolphins inhabit the seas of almost every regionof Earth.9

Most dolphin species have longsnouts that look similar to a bird’sbeak. One dolphin species that doesnot have the beaklike feature butdoes have a huge mouth full of sharpteeth is the killer whale. Killerwhales can be found all over theglobe. They, like other dolphins, have become popular inaquariums, theme parks, and even in the movies. Dolphins incaptivity can be treated if they get sick.A good reason for the dolphin’s popularity is itsintelligence. These smart creatures can solve problemsrequiring a great deal of thought. In the wild, theycommunicate with one another to cooperate in hunting andother day-to-day tasks. Scientists rank dolphins, along withprimates, as the most intelligent animals on Earth.10

Since a dolphin is a mammal, it is vital for it to breathe air.Therefore, like other members of the whale family, a dolphincomes equipped with a blowhole on the top of its head. It isbreathtaking to watch dolphins as they leap out of the water,arcing beautifully above the surface. They exhale with a shortburst from their blowhole and then take a long breath.Be careful not to confuse whales’ blowholes with the nosesof other mammals. Blowholes are employed only in breathing,not as organs to pick up smells. In fact, dolphins do not have asense of smell that they can use to hunt, but they compensate byhaving excellent eyesight and amazing hearing in most cases.11

Dolphins travel in groups and are extremely social. Theymaintain contact with one another by making whistling andclicking sounds. They communicate often and for a variety ofreasons. Sometimes they just want to exchange greetings, butdolphin communications are usually about more importantmatters. They warn one another of possibly fatal underwaterdangers and also share information about the location of food.Dolphins work together to capture their prey and to fend offany potentially damaging creatures.12

Dolphin clicks, which are emitted from a mechanism justbelow their blowholes, may not sound like much to human ears.Amazingly, though, these clicks are actually a natural form ofsonar, which is like underwater radar. The clicks bounce offnearby objects, sending echoes back through the water. Theseechoes are picked up by dolphins through their teeth andnerves in their bottom jaws, and the information gets processedin their brains. The dolphins can then “see” an image basedon sound, not sight. Dolphins’ ability to use “echolocation”to pinpoint food helps them survive in even the murkiestof waters.13

Dolphins14People often make the mistake of referring to dolphins as“porpoises.” Actually, dolphins and porpoises are two entirelydifferent groups of toothed whales. Although most dolphinshave beaks, none of the six species of porpoises does. If youwere analyzing the differences between these two creatures,you would see that a dolphin’s teeth are pointed, while aporpoise’s are shaped like shovels. Their behaviors are differentas well. Porpoises travel in very small groups, from two to four.They are also not as sociable with each other as many dolphinspecies are.Staying alive can be an ordeal for whales. In fact, whalesare creatures that may be facing the threat of extinction. Manywhale species are already endangered, and others are likely tobecome threatened if humans do not make it their calling to dosomething to protect them and their environment. The worldwould be far different without these magnificent giants of thedeep.

RespondingTARGET SKILL Cause and Effect What thingshelp dolphins to find food? Copy and complete thechart below.CauseDolphinsare highlyintelligent.Cause?Cause?EffectDolphins are excellent hunters.Write About ItText to Self Have you ever seen a whale on awhale watch or a dolphin at an aquarium? Write aparagraph describing how the animal behaved andhow you felt watching it.15

TARGET VOCABULARYanalyzingbaskingcallingfatalintensivejuvenilemarineordealstunnedtreatingEXPAND YOUR VOCABULARYarcingcompensategestationlagoonsmechanismspiralingTARGET SKILL Cause and Effect Tell how events arerelated and how one event causes another.TARGET STRATEGY Question Ask questions abouta selection before you read, as you read, and afteryou read.GENRE Informational Text gives facts and examplesabout a topic.16

Level: UDRA: 44Genre:Informational TextStrategy:QuestionSkill:Cause and EffectWord Count: 1,4985.2.6HOUGHTON MIFFLINOnline Leveled Books1388009

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