Animal Oddities

If you think that science has uncovered all the secrets of the animal kingdom, then think again. The natural world is full of creatures whose appearance, habits or way of life raise all kinds of questions for researchers. Whether it is a blind cave salamander, the elusive freshwater eel or South America's smelly bird, the hoatzin, nature has plenty of curiosities in store.

As the rulers of the planet, humans like to think that it is the large creatures who will emerge victorious from the struggle for survival. However, nature teaches us the oposite: it is often the smallest species which are the toughest and most adaptable.

A perfect example is the water bear (species Echiniscus and Macrobiotus). These invertebrates, which measure less than 1 mm in length, are shaped like cylinders, with a transparent outer skin, known as the cuticle, covering their bodies. Water bears live primarily in fresh water, but can also be found in the coastal regions of the oceans. They are often found in damp mosses or patches of lichen on racks, walls and roofs. In spite of - or perhaps because of - their small body size, these animals can adapt to the most extreme living conditions. If water is scarce, for example, they can expel a large part of their bodily fluids and shrink to egg-shaped cylinders. Water bears can live for a long time in this state of suspended animation, and can withstand vrey difficult conditions. In experiments, water bears have survived unharmed after immersion in sther, in 100% alcohol or in hydrogen sulphide; they seem perfectly happy in a vacuum or in an oven pre-heated to 150C; and recover miraculously after a cold bath in liquid belium at a temperature of -272C. It takes just a little water to bring them back to life. In a short time, the eater bears are flourishing as if nothing had happened.

Small But Active

Another record-breaking animal group is the hummingbirds, which are found mainly in the Americas. One species of hummingbird, the bee hummingbird (Calypte helenae), ranks as the world's smallest and lightest bird. With a length of only 6cm and weighing less than 2g, the bee hummingbird is barely visible when it is in flight.

Hummingbirds are the only birds that can fly bacwards. They feed mainly on the nectar of flowers, a liquid that is rich in energy. Nectar is an ideal food source, for hummingbirds need an incredible amount of evergy to sustain their body metabolism. A hummingbird's wings flap at a rate of about 80 times per second and its tiny heart beats more than 1,000 times per minute. This is why must consume relatively large quantities of food; in the course of a day, a hummingbird consumes about half its body weight in nectar.

Forever Young

We have to go deep under-ground to catch sight of the pink cave olm (Proteus anguinus), a species of slamander. The pink cave olm can only be found in the subterranean waters of the Dinaric Karst, a mountainous area composed of layers of fractured and eroded limestone in southern Slovenia (formerly part of Yugoslavia). The best known site where it can be found is the Adelsberg Cave near the town of Postojna. The caves are a hostile environment for any living creature, but the tiny cave olm has adapted perfectly to this sunless world, because it lacks the pigments that other animals have, its skin is a translucent, plae pink colour, through which the blood vessels can be clearly seen. Because of the lack of sunlight, the creature has no need for vision, its eyes, which are present in the embryos, disappear in later life, and become hidden under the skin. In spite of the difficulty in finding food underground, the cave olm can reach the ripe old age of 30 years.

When scientists first observed the cave olm, they thought it was a larva which was about to change into an adult. However, further studies revealed that this was indeed the adult animal, which had retained its larval features - a phenomenon known to science as neoteny. Although it looks like a larva, the cave olm still has its outer gills, and it is capable of producing young.

Carrying The Brood

There are many ways of reproducing and caring for the young, but one of the strangest belongs to the tongueless Surinam toad (Pipa pipa). These large amphibians are found in the northeastern part of South America - the animal is named for the former Dutch colony of Surinam - where they live in the basins of large rivers such as the Amazon or Orinoco. The Surinam toad has a very flat body and large webbed feet. It lives almost exclusively at water, where it sits motionless for long periods waiting for its prey to come within striking range.

The Surinam toad was first described at the beginning of the 18th century. Since that time, new reports of its peculiar mating habits have appeared time and again. It was not until 1960, though, that a research team succeded in observing captive animals as they mated and laid their eggs.

During the mating ritual, the male toad's front legs clasp the female just in front of her hind legs; the pair then make a longitudinal half-turn aso that their bellies are turned towards the surface of the water. Under the pressure of her partner's gentle massage, the female lays about three to ten eggs, which fall onto the stomach of the male. After another half-turn back into the initial positin, the eggs then reac the bck of the female. At this point, the male bolds the female firmly and fertilisers her. In the hours and days that follow, the skin on the mother's back gradually thickens, forming a kind of pocket or cell around each inividual egg. After a while, the larvae or tadpoles hatch out, but they remain in their cells until they have grown to maturity, a process that takes about three months.

Secret Wedding

Although it took long years of observation and study, researchers finally succeeded in decoding the mating behaviour of the Surinam toad. The situation is different for the European freshwater eel (Anguilla anguilla), whose reproduction is a mystery. To this day, no one has ever observed a sexually active one, and nothing is known about the development of the fertilised egg to the larval stage. However, scientists have discovered a number of facts about the eel's life cycle.

When it is time for mating, the eel leaves European inland waters in autumn and moves towards the salty open ocean, where it disappears into the depths. Scientists have no idea where the animal goes, although they assume that when it is time to mate, in the following spring, the eel will reappear in the eastern part of the Sargaso Sea, south of the island of Bermuda in the western Atlantic Ocean. This means that the animal covers a distance of about 7,000 km on its journey from the other side of the Atlantic. When it arrives in tropical waters, the eel finds the right conditions for reproduction - relatively warm water and a suitable salt content - in water about 5,000 m in depth. It seems that sexual maturation as well as the hatching of eggs requires a minimum temperature of 17C and a pressure 40 times greater than that found in shallower coastal waters.

A critical role is played by the Gulf Stream, the warm-water current that flows along the eastern coast of North America from the Caribbean, and warms the shores of northwestern Europe. The Gulf Stream carries the eel larvae, which are shaped like willow leaves, towards the home of their parents, a journey that takes as muc as three years. In spring, when they reach the European coast, the young larvae change into so-called grass eels. The tide carries them into river mouths and they keep on travelling upstream. As they search for a suitable environment - for example, a lake or pond - the eels become darker in colour. They can get over large obstacles and even travel overland by wriggling through wet grass.

When the eel is between 7 and 20 years old, there will come a day, usually during summer, when it will stop eating. Its secual organs start to developm sinalling that it is time for the great journey. The eel then returns to its spwning grounds in the Sargasso Sea, where it will die after mating has been concluded. To the best of our knowledge, there has not been a single case of a mature eel returning to Europe.

Reversing Roles

The sea horse is one of the loveliest, but also one of the oddest, creatures in the ocean. Sea horses of the genus Hippocampus are, in fact, modified fish; they hold their bodies in a vertical position as they seim, with their head bowed towards the front at right angles. Their skin is make up of bony plates, which from a protective armour. The end of the sea horse's body is drawn into a flexible tail without fins, which they use to cling onto plants. The creature's protruding telescope-lime eyes look a bit like a chameleon's eyes. But the quality that separates sea horses from the majority of fish is the fact that the males look after the offspring, and they do so in a very special way.

A male sea horse has a large pouch on his stomach. During mating, the female inserts her laying tube into the pouch and lays her eggs. The male fertilises the eggs, one after another. The wall of the adbominal pouch begins to thicken and increasingly fills with blood vessels, forming a type of nourishing placenta. After the eggs hatch, the larvae remain in their father's pouch until they have reached a length of about 5mm. At this point, the young sea horses are set free in groups.

A Mammal With A Bill

In the waters of eastern Australia and Tasmania lives what must be the world's oddest mamal; the duck-billed platypus (Ornithorhynchus anatinus). The platypus has a wide shovel-like bill and webbed feet like a duck's; its rump looks like that of a mole; and its flat tail, which serves as fat storege, resembles that of beaver. However, the animal's webbed feet have digging claws similar to a bird's. Strangest of all, this southern-hemisphere mammal also lay eggs!

A male platypus seldom reaches a length of over 50cm and weighs less than 2kg. To defend itself, the platypus has something very rare for mammals - a sting in its heel, which is attached to a poisonous gland. If the animal is handled by humans, it can deliver a painful stng, and the poison is powerful enough to kill a dog. As the female platypus has no teats, she suckles her young with the help of milk glands located under the skin Milk trickles from these glands and runs into a hollow in the middle of her belly.

When the animal dives in search of food, holds of skin cover its eyes and ears. Tiny pores situated around its bill enable the platypus to detect electrical fields created by muscle movements. Thus, the animal can accurately detect its prey, such as insect larvae and small invertebrates, which may be hidden in the mud.

Beyond All Categories

Another mammal that is difficult to classify is the aardvard (Orycteropus afer), which lives in the savannahs of southern Africa and the rain forests of Cameroon and Congo i Central Africa. Its name is derived from the Afrikaans words aarde (earth) and vark (pig), and comes from its pig-like snout and the fact that these nocturnal animals dig holes in which they rest during the day.

The aardvark has a large body, which is covered with a coat of bristly fur. A short neck supports its long, hairless head. Its great ears look like those of a rabbit or donkey, while the thick tail is long and muscular like that of a kangaroo. The aardvard has the ability to close its nostrils completely. This means that no ants or termites - the animal's favourite foods - can climb into its nose while it is eating.

The aardvark's column-like teeth also put it in a class by itself. They continue to grow throughout the animal's life, and slowly wear down on the surface. Each tooth is composed of many hexagonal, parallel prisms, with a tube-like canal in the middle. This is why the order to which the aardvark belongs is called Tubulidentata, meaning 'tube teeth'.

Smelly But Endearing

Scientists are still unsure how to classify the hoatzin (Opisthocomus hoazin), a bird which lives in the rain forests of northern South America. For a long time, it was regarded as a prehistoric relic, and some ornithologists still regard it as a living fossil at the interface between reptiles and birds. The reason for this stems from the claws which the hoatzin chicks have on their wings. These are similar to those of Archaeopterys, a winged and feathered dinosaur that is considered to be the oldest known fossil bird.

Apart from its blue face, round red eyes and spiky crest, the hoatzin has a number of other intriguing features. It is known as a gallinaceous bird because it belongs to the order Gallifomes, which includes domestic fowl and pheasants. Most gallinaceous birds fowl and pheasants. Most gallinaceous birds digest their good in a muscular stomach. The boatzin, however, differs from its fellows in two ways. Firstly, its diet consists almost exclusively of leaves. Secondly, the leave are ground to a mash in the huge muscular pouch in its oesophagus. The gases which it emits have earned it the nickname of 'stink-bird'.

The hoatzin live in flocks and keep in constant contact through their crowing calls. At breeding time, each pair builds a nest on branches close to the water, so the young can drop into the river in case of danger. Using their feet, their claw-like wings and their beaks, the young can then climb back up the tree and into their nest like reptiles.


An Underground State

Communal life is a good way to protect the species. A good example of this is the naked mole rat (Heterocephalus glaber), which lives in underground colonies beneath the savannahs of East Africa. Naked mole rats grow to 10cm in length, and their harless bodies, which lack pigment, look like sausages. Their outsized front teeth mark them as rodents, while their small eyes show that ehey shun the light.

A naked mole rat community functions much like an insect colony; prosiding over a clan of 70 to 80 individuals, a relatively large and aggressive queen reserves the sole right of reproduction, and exercises strict control over her subjects. Younger animals have to look after and rear the young, gather material for nests, provide sufficient food such as roots and tubers, and maintain the colony's tunnel system. The older animals have to dig tunnels and must defend the colony against intruders, especially snakes, the main enemy of the naked mole rat. Living underground in darkness, the naked mole rat has to be able to communicate with other members of the colony. For this reason, the animals make use of chemical, acoustic and tactile signals. Their repertoire of sounds is regarded as the most sophisticated of all the rodents.