Wildebeest
The ungainly gnu earned the Afrikaans name wildebeest, or "wild beast," for the menacing appearance presented by its large head, shaggy mane, pointed beard, and sharp, curved horns. In fact, the wildebeest is better described as a reliable source of food for the truly menacing predators of the African savanna: lions, cheetahs, wild dogs, and hyenas.
The gnu (pronounced "g-new" or simply "new") is a member of the antelope family, although its heavy build and disproportionately large forequarters make it look more bovine. Gnus can reach 8 feet (2.4 meters) in length, stand 4.5 feet (1.4 meters) tall at the shoulders and weigh up to 600 pounds (272 kilograms). Both males and females grow horns.
Their habitat comprises the grassy plains and open woodlands of central, southern, and eastern Africa, particularly the Serengeti in Tanzania and Kenya. They travel in large herds and are active day and night, grazing constantly.
Their spectacular northward migration in search of greener pastures is dictated by weather patterns, but usually takes place in May or June. It is considered one of the greatest wildlife spectacles on Earth, involving up to 1.5 million wildebeests as well as hundreds of thousands of other animals, including zebra and gazelle.
Up to 500,000 calves are born in February and March each year, at the beginning of the rainy season. Calves learn to walk within minutes of birth and within days are able to keep up with the herd. Gnus can live to be 20 years old.
Type:
Mammal
Diet:
Herbivore
Average life span in the wild:
20 years
Size:
Up to 4.5 ft (1.4 m)
Weight:
330 to 550 lbs (150 to 250 kg )
Group name:
Herd
Size relative to a 6-ft (2-m) man:
Monarch Butterfly
Monarch butterflies are known for the incredible mass migration that brings millions of them to California and Mexico each winter. North American monarchs are the only butterflies that make such a massive journey—up to 3,000 miles (4,828 kilometers). The insects must begin this journey each fall ahead of cold weather, which will kill them if they tarry too long.
Monarch butterflies begin life as eggs and hatch as larvae that eat their eggshells and, subsequently, the milkweed plants on which they were placed. (Monarchs are dependent on milkweed plants, which larvae eat nearly exclusively.)
Fattening larvae become juicy, colorful caterpillars, then create a hard protective case around themselves as they enter the pupa stage. They emerge as beautifully colored, black-orange-and-white adults. The colorful pattern makes monarchs easy to identify—and that's the idea. The distinctive pattern warns predators that the insects are foul tasting and poisonous.
Butterflies that emerge from chrysalides (pupa state) in late summer and early fall are different from those that do so during the longer days and warmer weather of summer. These monarchs are born to fly, and know because of the changing weather that they must prepare for their lengthy journey.
Only monarchs born in late summer or early fall make the migration, and they make only one round trip. By the time next year's winter migration begins, several summer generations will have lived and died and it will be last year's migrators' great grandchildren that make the trip. Yet somehow these new generations know the way, and follow the same routes their ancestors took—sometimes even returning to the same tree.
Many scientists are concerned about the eastern population of monarchs, which summer east of the Rocky Mountains. This group is occurring in ever smaller numbers, and its survival may be threatened by a series of natural disasters in the Mexican wintering grounds, as well as by reduced acreage of milkweed plants in their summer home.
Type:
Bug
Diet:
Herbivore
Average life span in the wild:
Up to 6 to 8 months
Size:
Wingspan 3.7 to 4.1 in (9.4 to 10.5 cm)
Weight:
.0095 to .026 oz (.27 to .75 g)
Group name:
Flutter
Size relative to a tea cup:
Red Crab
The red crab is a Christmas Island, Australia, original found nowhere else in the world. But on its home turf it is a very significant species—some 120 million individuals cover the rain forest floor and play a major role in determining the structure of the ecosystem.
These large crabs are active during the day but prefer to stay in the shade and can die in the moisture-robbing heat of direct sunlight. They scavenge on fallen leaves, seedlings, fruits, and flowers, recycling nutrients and helping to determine the spread and composition of native flora.
Most of the year red crabs are solitary dwellers of the burrows they dig throughout the forest. During the dry season they retreat into these shelters to retain body humidity and essentially remain there for two to three months.
But when wet season returns in October or November they begin a legendary mass migration to their seaside breeding grounds, moving in colorful waves that wash over all obstacles including roads (necessitating crab tunnels and road closings) and even seaside cliffs.
The annual trek is also intimately tied to the lunar schedule. The crabs arrive at the coast and mate at such a time that the females can produce eggs and develop them in burrows for a dozen or so days before releasing them into the sea precisely when high tide turns between the last quarter and new moon. During this period sea level on the beaches varies the least and offers an easier approach, a factor so important that if weather delays the migration crabs will put off spawning until the next lunar month.
Red crab eggs hatch right away, and young live as larvae in the sea for a month before returning to the shoreline, molting into air breathers, and slowly returning inland to begin the cycle anew.
Type:
Invertebrate
Diet:
Omnivore
Size:
5 in (12.7 cm)
Group name:
Streams
Protection status:
None
Did you know?
Red crabs can stop traffic, puncture tires, and wander through any open doors during their migration to the sea.
Size relative to a tea cup:
Sperm Whale
Sperm whales are easily recognized by their massive heads and prominent rounded foreheads. They have the largest brain of any creature known to have lived on Earth. Their heads also hold large quantities of a substance called spermaceti. Whalers once believed that the oily fluid was sperm, but scientists still do not understand the function of spermaceti. One common theory is that the fluid—which hardens to wax when cold—helps the whale alter its buoyancy so it can dive deep and rise again. Sperm whales are known to dive as deep as 3,280 feet (1,000 meters) in search of squid to eat. These giant mammals must hold their breath for up to 90 minutes on such dives.
These toothed whales eat thousands of pounds of fish and squid—about one ton (907 kg) per day.
Sperm whales are often spotted in groups (called pods) of some 15 to 20 animals. Pods include females and their young, while males may roam solo or move from group to group. Females and calves remain in tropical or subtropical waters all year long, and apparently practice communal childcare. Males migrate to higher latitudes, alone or in groups, and head back towards the equator to breed. Driven by their tale fluke, approximately 16 feet (5 meters) from tip to tip, they can cruise the oceans at around 23 miles (37 kilometers) per hour.
These popular leviathans are vocal and emit a series of "clangs" that may be used for communication or for echolocation. Animals that use echolocation emit sounds that travel underwater until they encounter objects, then bounce back to their senders—revealing the location, size, and shape of their target.
Sperm whales were mainstays of whaling's 18th and 19th century heyday. The animals were targeted for oil and ambergris, a substance that forms around squid beaks in a whale's stomach. Ambergris was (and remains) a very valuable substance once used in perfumes.
Despite large population drops due to whaling, sperm whales are still fairly numerous.
Type:
Mammal
Diet:
Carnivore
Size:
49 to 59 ft (15 to 18 m)
Weight:
35 to 45 tons (31.8 to 40.8 metric tons)
Group name:
Pod
Protection status:
Endangered
Size relative to a bus