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Mexican axolotl (pronounced ACK-suh-LAH-tuhl) salamanders are amphibians that spend their whole lives underwater. They exist in the wild in only one place—the lake complex of Xochimilco (pronounced SO-chee-MILL-koh), a network of artificial channels, small lakes, and temporary wetlands that help supply water to nearby Mexico City’s 18 million residents. Axolotls have long fascinated scientists for their ability to regenerate lost body parts and for their rare trait of neoteny, which means they retain larval features throughout life. Rather than undergoing typical metamorphosis, axolotls keep their youthful appearance, including their tadpolelike dorsal fin and feathery external gills that fan out from the head. As they age, axolotls simply get bigger and bigger, like amphibious Peter Pans. In rare cases, axolotls have matured past the larval stage and emerged onto land as adult salamanders. Neoteny doesn’t affect the axolotl’s ability to breed. Females mate with males and lay eggs underwater. As Mexico City has grown, the lake complex has shrunk and parts have become contaminated, distressing the axolotl population. The introduction of large numbers of carp and tilapia fish, which compete with axolotls for food and also eat axolotl eggs, has further lowered their population. A 2009 survey suggests there are fewer than 1,200 axolotls in the Xochimilco Lake complex. Axolotls feast on a menu of mollusks, worms, insect larvae, crustaceans, and some fish.
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Bull sharks are among the most dangerous sharks in the world, according to many experts. This is because they’re an aggressive species of shark, and they tend to hunt in waters where people often swim: along tropical shorelines. Bull sharks live throughout the world, in shallow, warm ocean waters. They’ve been known to swim up into freshwater rivers. Humans are not part of a bull shark’s normal prey. Bull sharks will eat almost anything, but their diet consists mainly of fish. They also sometimes eat dolphins and sea turtles. Bull sharks even eat other sharks. They hunt during the day and at night. Sharks must keep salt in their bodies to survive, and most can live only in salt water. But bull sharks have developed special adaptations—the way their kidneys function and special glands near their tails—that help them keep salt in their bodies even when they’re in freshwater. Scientists are still studying these sharks to figure out why they developed this unusual ability.
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Reaching up to 13 feet (4 meters) long and weighing as many as 1,300 pounds (600 kilograms), West Indian manatees look more like small cars than people. Despite their large size, manatees are graceful swimmers. Although they usually move along in slow motion, they can also cruise, or swim at a steady pace, at five miles (eight kilometers) an hour. In short bursts they can even top 15 miles (24 kilometers) an hour! While cruising, manatees push themselves forward by moving their strong tails up and down. They steer with the help of their flexible flippers. When in shallow water, manatees use their flippers to walk, slowly placing one in front of the other. Like whales and dolphins, manatees are mammals. Although they live in water, they have to surface frequently to breathe air. While swimming, manatees take in air every three or four minutes. When they are resting, they can stay underwater for up to 15 minutes. Manatees are gentle animals. They rarely fight, and they have no natural enemies. Subsisting on water plants and plants that grow at the water’s edge, a manatee takes in up to 1 pound (0.5 kilogram) of food for every 10 pounds (5 kilograms) it weighs.
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Caribou are mammals that live in the northern regions of Europe, North America, Asia, and Greenland. When snow begins to fall, caribou move south and travel to more sheltered climes where they can feed on moss or lichens. These members of the deer family dig for food using their large hooves. The underside of each hoof is hollowed out like a big scoop and allows the caribou to dig through snow in search of food. Caribou trek north in the summer in one of the largest animal migrations on Earth. They travel more than 600 miles (965 kilometers) along well-traveled routes. They spend the summer feeding on grasses, mushrooms, and plants in the tundra. They begin to move south in the winter and over one year they will have migrated over 1,600 miles (2,574 kilometers). One adult caribou eats about 12 pounds (5 kilograms) of food each day. Caribou are hunted by indigenous northern people throughout much of their range. Woodland caribou are listed as endangered, but other caribou populations are stable.
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In this issue of National Geographic Kids, photographer Joel Sartore gives you a behind-the-scenes look at his quest to save animals. The National Geographic Explorer travels to zoos, aquariums, and rescue centers around the world to snap pics for his project, the National Geographic Photo Ark. He hopes the photos will inspire people to help endangered animals. You’ll also learn about the threats facing the critters and how you can help.
Then find out how you help save the Earth!

Chipmunks are part of the squirrel family, and while they look similar to their bushy-tailed cousins, chipmunks are actually smaller, with alternating light and dark stripes along their cheeks and backs. There are 25 species of chipmunk, 24 of which live in North America. Chipmunks are excellent tree climbers and swimmers who live in a variety of habitats, including plains, mountains, forests, and deserts. Chipmunks like to live alone in holes or burrows called dens. Chipmunks hibernate in cold weather, which means they spend most of the winter sleeping in their dens. One chipmunk can gather up to 165 acorns in a day. In just two days, a chipmunk can collect enough food to last an entire winter, although chipmunks typically hoard much more food than necessary. Chipmunk young are born in late spring, and stay in the nest for up to six weeks. Female chipmunks have one or two litters per year, each with four or five babies. Chipmunks are 7.2 to 8.5 inches (18.5 to 21.6 centimeters) long including their tails, which can account for nearly half of their length.
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