Whenever and wherever huge numbers of animals gather together, it is sure to be spectacular. They congregate to meet, court, and mate; to feed when supplies are plentiful; to rest safely in a group, and to prepare for migration…
1. Walruses throw a bachelor party
Walruses love a crowded beach. Each summer more than 12,000 males congregate along the shore and rocky shelves of Round Island, on Alaska’s south-west coast.
They lie in rows, eyes closed, their brown and pink bodies packed so tightly together that the pairs of 20-inch long ivory tusks are the only indication of which end is which. During the preceding winter mating season, they will have fought fiercely with the other males with whom they now share the beach, battling for the right to mate with the females.
The bulls arrive at Round Island in shifts during June, usually about 3,000 at a time. They spend a couple of days ashore, then go to sea to feed for a week before returning to the island for a two-day rest. Meanwhile, the females are feeding and raising their young hundreds of miles north among the ice floes of the Bering and Chukchi seas.
The lifestyle of the walrus is under grave danger due to the effects of climate change. Learn more about how you can help here.
2. Red crabs' long trek to the coast
Photo by Raphael Bick
A 100-million-strong army of red land crabs embarks on a hazardous journey every November. The onset of the rains signals the start of the exodus from their native rain forest on Christmas Island in the Indian Ocean to the sea.
Marching in the cooler parts of the day, the crabs clamber across anything in their path. A million perish on the roads during the two-week journey. Mature males arrive at the coast first and fight for the best mating burrows before the females join them.
After mating, the males head home while the females wait for their eggs to develop. Two weeks later, at the water’s edge, they shake out thousands of eggs from their brood pouches and set off home themselves, followed after 25 days by an army of miniature crabs, each no more than 1/4 inch wide.
3. Bison find hot spots in the snow
North American bison know just how to keep warm. Each winter in Yellowstone National Park, US, hundreds of them gather around the geyser fields and hot springs to survive the worst of the icy weather.
The snow cover here is not as deep as in the rest of the park, so the grasses and sedges are more accessible for the animals to feed on, and it is more comfortable for them to stay close to the warmth of the hot springs.
As the bison stand next to the geysers, steam and spray freeze on their fur and faces, covering them with a thin layer of hoarfrost. Should they leave the immediate area, the snow can be so deep that they have to shovel through 6 ft drifts with their broad noses to reach the plants below.
In blizzards, they stand facing the wind, protected by their thick, shaggy coats.
4. Relaxing with the Beluga whales
Photo by Yuan Yue
July is holiday time for the thousands of belugas (white whales) that gather in the shallow inlets of Canada’s Arctic. They come into the relatively warm fresh water—where they are safe from their main enemy, the killer whale—to give birth, moult, and play.
The congregations are noisy, for the whales constantly chatter with chirps, clangs, screams, grunts, and whistles—behaviour that has earned them the nickname "sea canaries".
In the estuaries, they play with stones and fronds of seaweed. Large stones are held in the mouth or balanced on the top of the head, and seaweed is draped over the body. As soon as the carrier is spotted, other whales bump and jostle it until the stone is dislodged.
One game has tragic undertones. Females have been seen swimming with planks of wood on their backs. They are thought to be whales that have lost a calf and have adopted the wood as surrogate babies.
5. Tiger moths seek an Aegean retreat
In the searing heat of July and August clouds of Jersey tiger moths descend on the Greek island of Rhodes. For a month or more, among the rocks and trees of the "Valley of the Butterflies", they remain immobile by day to conserve energy. At night they go in search of a mate.
The moths are attracted to the valley by the aromatic resin that exudes from the bark of oriental sweet gum trees. Water evaporating from the River Pelekanos below keeps them cool and hydrated. When the worst of the heat has passed, the moths fly off to settle in the surrounding countryside.
6. Butterflies gather on tropical sands
Millions of dazzling yellow male heliconia butterflies are drawn to South America’s tropical rivers, such as the Amazon and Orinoco.
Attracted by the mineral-rich wet sand and puddles, they crowd together on the shore, each one drawing up a solution of minerals and salts through its long, curling proboscis.
During mating, the male butterfly transfers much of his sodium to the female in a sperm package, and he comes to the riverbanks to replenish his supplies. Sodium is essential for the working of their nerves and muscles.
7. Marine Iguanas worship the sun
Like prehistoric monsters from the age of the dinosaurs, rows of 20 or 30 marine iguanas line up on roosting rocks to bask in the sun. These 4 ft long creatures live exclusively on the Galapagos islands off the coast of Ecuador.
They are one of the few sea-going lizards in the world, making brief excursions to feed on the green sea lettuce that grows on submerged rocks 16 ft or more below the water’s surface. The time they spend sunbathing raises their body temperature sufficiently to enable them to swim in the cold waters of the Humboldt Current that sweeps up from the Antarctic to bathe the Galapagos.
The iguanas are attended by rock crabs, which gather round them to pluck ticks and dead skin from their motionless bodies. Occasionally, a basking iguana bursts into life, sneezing a shower of salty vapour to expel excess salt from glands in its nose (see above).
8. Hammerhead sharks find safety in numbers
For protection, hammerhead sharks congregate in vast schools. These are found close to the islands of the eastern Pacific Ocean, such as the Cocos and Galapagos, where the hammerheads are safe from killer whales and other sharks.
The school consists mainly of females. They swim up and down without feeding and every so often the oldest sharks twist and turn, using their body language to keep the younger ones in their place. The school is also a rendezvous for males and females.
Occasionally, a male will grab a female by the pectoral fin. They mate in the depths below. In the evening the school breaks up and the sharks go their separate ways to feed.
9. Monkeys find spring warmth in winter
Photo by Steven Diaz
Japanese macaques, which live the farthest north of any monkey or ape, like to take a hot bath during a winter snowstorm.
Although their thick coats keep out the worst of the cold winter weather of northern Japan, they bathe in steaming spring water to warm up to a comfortable temperature.
One mountain population of macaques on Honshu island even relaxin hot water while a blizzard rages around their heads.
They feed on bark in the depths of winter when most of the vegetation is under snow and so avoid having to move to the lowlands in search of food. In summer they feast on fruits, flowers, and leaves.
10. Jellyfish track the sun
Photo by Nik Ramzi Nik Hassan
Jellyfish in lakes on the islands of Palau in the western Pacific Ocean perform a daily ritual. They pulsate their bells to move them to the sunniest stretches of water.
The jellyfish were trapped here millions of years ago when land levels rose, creating saltwater lakes. Deprived of their natural food, such as small fish, they took to a symbiotic way of life with tiny green algae that now live in their tissues.
The algae synthesize food from sunlight, giving some to their jellyfish hosts. In return, the jellyfish keep the algae in sunlight by following the sun around the lakes
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