More Facts about Animals
 
Types of Togetherness
Biologists divide partnerships between living organisms into four main categories: symbiotic, parasitic, commensal and epizioc.

SYMBIOTIC: A word meaning literally 'living together'. Symbiosis is normally used to mean a close and mutually beneficial relationship between two different organisms. Lichens, for example, are a symbiosis of two organisms - a fungus one and one of the primitive plants known as algea.

PARASITIC: A close and one-sided relationship in which an organism battens onto and lives off its host, harming it in the process. Flat worms, for example, live in the blood vessels of their human hosts.

COMMENSAL: A close and one-sided relationship in which one organism gains benefit, but not at any cost to its partner. The cattle egret, for example, lives off the parasites on the back of cattle and other grazing animals.

EPIZOIC: A close relationship in which one partner lives on the skin of another - or is carried or towed about by it. The remora 'sucker' fish, for example, attaches itself to a larger fish by means of a suction disc on its head.
 

How long they live
Most animals die through violence, disease or accident, not through old age. As a result, the maximum lifespans of animals in the wild are not known with certainty. Most scientists believe that marine animals are generally capable of living longer than land animals because their bodies are cradled and supported by water, are not worn down or worn out so quickly by the effects of gravity. In addition, many cold-blooded animals, such as reptiles, seem to have no fixed adult size, so that they go on growing until they die. Theoretically, some scientist believe, such animals should, if completely protected, live for ever.

In practice, however, few organisms except for bacteria live much longer than man. These are the longest recorded lifespans, in years, for a variety of animals

152 Marion's tortoise 50 Lobster
100 Deep sea clam 40 Cow
90 Killer whale 35 Domestic pigeon
90 Blue whale 34 Domestic cat
90 Fin whale 29 Dog (Labrador)
80 Fresh water oyster 28 Budgerigar
70 Cockatoo 20 Sheep
70 Condor 18 Goat
70 Indian elephant 18 Rabbit
62 Ostrich 10 Golden hamster
62 Horse 6 House mouse
50 Chimpanzee 0.2 House fly
50 Termite

 
Sight Lines
Many creatures see the world very differently from the way humans do, because their eyes have adapted to suit their particular way of life.

BUZZARD : Soaring birds of prey, such as hawks and buzzards, need especially keen eyesight to pick out small animals on the ground. In the fovea, the most sensitive part of the eye's retina, a buzzard has about 1 million light sensitive cells per square millimeter - five times as many as a human. As a result, the images it sees are much sharper.

CAT : Although a cat has poorly developed colour vision, seeing the world largely in black, grey and white, it can see far better in the dark, thanks to a crystaline layer in the retina, which enables it to absorb 50 per cent more light than human eyes. By day, the cat's iris contract into slits to keep out the excessive light.

BEE : Sensitivity to ultraviolet light, invisible to humans, enables bees to spot special honey-guide markings on many flower petals which point the way to nectar and pollen. The same sensitivity allows bees to see the sun, even on a cloudy day, so they can find their way back to the hive. On the other hand, bees cannot see red, perceiving it as blue.

SPIDER : Most spiders have eight simple eyes, known as 'ocelli' arranged around the top of the head so that they can see in all directions at once. In species such as the jumping spider, which stalks its prey rather than waiting for it, two of the eyes at the front are more developed than the rest, allowing the spider to guage distances accurately for its final pounce.

SANDPIPER : Many foraging birds, such as chickens and shore birds, have eyes set on the size of their head, so that each eye sees a different scene. The resulting wide field of vision allows them to spot danger from almost any direction, but limits their ability to judge distances. Shore birds, such as the sandpipers, compensate for this lack of stereoscopic vision by bobbing their heads up and down and sideways to view an oblect from several angles against its background.

BUTTERFLY : Like other adult insects, butterflies have compound eyes, made up of numerous separate eyes - up to 28,000 in a dragonfly, but as few as nine in some ant species. Each mini-eye is equipped with its own tiny lens, so that insects see objects as a mosaic of overlapping points of light, rather like a badly tuned television picture. Compound eyes are unable to focus sharply, but are very good at spotting movements.
 

Song and Dance Routines
Spectacular displays by animals and birds in their springtime courtship rituals are basically identification parades to ensure that each species mates only with its own kind. The songs and dances of the mating season help each to pick the right partner. Most birds and animals go into season as the spring's longer days and the extra sunshine trigger hormones which start their ovulation in the female and sperm in the male. Alerted to one another by mating calls, males and females then go into recognition rituals that can sometimes take days to complete.
    Strong elements of aggression are involved. A male may make instinctive threatening gesturing when a female, summoned by his mating call, enters his territory, and he is only placated by a correct defensive response. Many animals cannot mate until they have been stimulated by the correct sequence of call, colour and movement. A female rock dove, for example, does not ovulatee until she has seen her mate's courtship ritual. By this elaborate, inborn behaviour, nature makes it probable that the female of the species will not waste her brief, often only once a year, period of fertility by mating with the wrong partner
These routines are now thought to also be the male showing off and hoping he is the best of the bunch that may be chasing the female for her favours.
 
Migration
Why Animals Migrate
Food and climate are the great driving forces of migration. Swallows and martins, breeding under the eaves in the European spring, must be back in North Africa before the winter frosts which would kill both them and the insects they feed on. Many whales feed in the rich polar seas and swim to the warmer waters of the tropics to breed. Elk, moose and caribou wander in huge circles seeking sparse forage.
For most migrating animals to stay put would mean to die. But some move without apparent reason; the Arctic tern, for instance. Some scientists have speculated that the migratory patters of some sea creatures may have been established as foraging expeditions when the continents were closer together – and that the enormous distances now travelled by salmon and eels, for example, may have grown imperceptibly from one generation to the next as the oceans widened.

How they do it
It is still not certain how most animals, particularly birds, find their way on long migrations. Experiments have shown that many birds use the sun to navigate, making automatic allowances for its movement across the sky. The pecten, a frond-like projection from the retina of a bird's eye, is believed to be the sextant that guides them through the clear sky… but overcast weather does not stop them reaching their destinations.
     In 1977, Charles Walcott, a biologist at New York University, discovered deposites of magnetic iron oxide in the skulls of pigeons and other migratory birds. It seems that this is used as a built-in compass to give the bird a picture of the Earth's magnetic field, by which it can navigate.
    But how some first year birds find their way unaided to ancestral migratory quarters is still a mystery, probably locked up in the genetic code.
 

Chains of Life
All life on Earth is bound together in complex associations between what is eaten and what eats it – between the hunter and the hunted. Scientists call these associations food chains or food webs. All food webs start with plants, the primary food producers, which use the Sun's energy to convert chemicals into food. Plants are eaten by primary consumers, plant-eating animals such as cattle. They are in turn eaten by secondary consumers: meat eaters such as lions and man. At each level waste material, such as dung and the remains of dead organisms, is droken down by bacteria and fungi, and returned to the soil to be absorbed by plants again. The extermination of a single species in any web can drastically affect all the others. When Myxamatosis was introduced into England in 1954 to kill rabbits, for instance, weeds previously eaten by rabbits spread rapidly and mice and beetle populations dropped sharply because foxes began eating more of them in the absemce of rabbits.

Food, meat and energy
At each level in a food chain, most of the energy contained in the food is used to keep the eater alive and active. Only a small proportion is converted into extra meat for the next predator in the chain. Some animals, such as the pig, convert as much as 20 per cent of their food to meat, but most convert only about 10 per cent. So, for a man to gain 1kg (2.2lb) in body weight, he would need to eat 10kg (22lb) of food such as, say, fish. To gain that much weight, the fish would have to eat 100kg (220lb) of animal plankton, which in turn would need to eat a tonne of plant plankton, the primary probucers.
    The only way to make this more efficient - and thus to make a given area of the Earth support more people – is to shorten the food chain by cutting out some of the intermediate links. If a fish, say, ate plant plankton directly and animal plankton left out of the food chain, a given quantity of plant plankton could support about ten times as many fish – and thus ten times as many people – as present. Man can eat plant foods himself, but most are very low in vital protein. One exception, however, is soya beans, half of whose weight is protein – making them one of the richest protein sources of any food.
 

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