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Natures Secrets
MIGRATION
Millions of birds of many different varieties migrate at the end of summer. With unfailing regularity they leave the regions where they were born to fly to warmer climates for the winter. The following spring they return to their breeding grounds.
Each year these migratory birds travel as much as 20,000 miles, finding their way back on time with extraordinary precision. Some travel as individuals.
Migration is triggered off by the length of daylight, which apparently affects the birds’ nervous systems. When the days get shorter the birds receive the signal to leave for their warmer winter grounds, and, when the daylight increases to a certain level, they receive another signal to return home.
The swallows pictured above are European swallows wintering in Africa.
Each year these migratory birds travel as much as 20,000 miles, finding their way back on time with extraordinary precision. Some travel as individuals.
Migration is triggered off by the length of daylight, which apparently affects the birds’ nervous systems. When the days get shorter the birds receive the signal to leave for their warmer winter grounds, and, when the daylight increases to a certain level, they receive another signal to return home.
The swallows pictured above are European swallows wintering in Africa.
MALE STICKLEBACK
The male stickleback’s belly turns red at the start of the breeding season in spring. Normally the belly of this small fish is silver colored, the rest of it varying from brown to green. But when the time comes for him to mate he becomes very active in attracting females with his bright new color.
In building the home and rearing the family the male stickleback performs many of the functions usually associated with a female fish. He chooses the place for the nest, collects the stems of various aquatic plants and binds them together using a threadlike web secreted from his kidney.
Once the female has been enticed into his nest, she will lay her eggs and depart, leaving him on guard. He watches over the eggs with great care and even looks after the baby fish.
In building the home and rearing the family the male stickleback performs many of the functions usually associated with a female fish. He chooses the place for the nest, collects the stems of various aquatic plants and binds them together using a threadlike web secreted from his kidney.
Once the female has been enticed into his nest, she will lay her eggs and depart, leaving him on guard. He watches over the eggs with great care and even looks after the baby fish.
BIRDS’ EGGS
The roundness of an egg allows pressure to be applied from the outside which would break it if applied from the inside. Thus a helpless chick is protected until the moment it needs to break out from its shell. It can then do this with the gentlest of tapping.
Eggs are hatched by an adult bird sitting on the, and the best container for round objects is a cup-shaped nest which prevents them rolling about. So the best shape for eggs is for one end to be smaller than the other. The normal position for eggs in a nest is to have the smaller ends pointing inwards. This means the eggs take up the minimum of room and make it easier for the sitting bird to cover them.
Birds with scanty nests, as in the case of most sea birds, have more elongated eggs. If such eggs are caught by the wind while lying on some cliff-face or rocky ledge, they will spin round instead of rolling over the edge.
Eggs are hatched by an adult bird sitting on the, and the best container for round objects is a cup-shaped nest which prevents them rolling about. So the best shape for eggs is for one end to be smaller than the other. The normal position for eggs in a nest is to have the smaller ends pointing inwards. This means the eggs take up the minimum of room and make it easier for the sitting bird to cover them.
Birds with scanty nests, as in the case of most sea birds, have more elongated eggs. If such eggs are caught by the wind while lying on some cliff-face or rocky ledge, they will spin round instead of rolling over the edge.
CHAMELEON
A chameleon will change color when it senses danger. This remarkable member of the lizard family can change color to match its background or, at least, to become almost unrecognizable.
The ranges of colors and patterns of the various species differ widely, but most chameleons can become yellow or cream, green or dark brown. They can also adapt spots either dark or light depending on the color of the ground.
Apart from its response to danger, the chameleon will change color according to the light and temperature. This mechanism is controlled from the nervous system and involves the dispersion or concentration of color pigments in the creature’s skin.
The ranges of colors and patterns of the various species differ widely, but most chameleons can become yellow or cream, green or dark brown. They can also adapt spots either dark or light depending on the color of the ground.
Apart from its response to danger, the chameleon will change color according to the light and temperature. This mechanism is controlled from the nervous system and involves the dispersion or concentration of color pigments in the creature’s skin.
SOUND OF BATS
Bats use high-pitched sounds to find their way about. They are nocturnal animals. That is they move about by night. So they have developed their hearing to such an extent that they can find their way by a method known as echolocation.
The blind-flying abilities of bats were first studied by Lazaro Spallanzani (1729-1799). He surgically removed the eyeballs from several bats to prove that they did not need to see to fly.
In the 20th Century, biologists, using electronic instruments, have carried out experiments with bats. They have discovered that bats find out where to go by emitting high-frequency sound and receiving the echoes as they bounce off objects. Most of the sounds have too high a frequency to be heard by the human ear.
Bats commonly fly together in groups, but apparently they are not confused by the sounds and echoes produced by each other. When hunting in woods and in the rain they are able to discriminate between the faint echoes bouncing off insects and those bouncing off the ground, tree-trunks, branches, twigs and raindrops.
These tiny flying mammals have been using the equivalent of our modern sonar device for millions of years.
The blind-flying abilities of bats were first studied by Lazaro Spallanzani (1729-1799). He surgically removed the eyeballs from several bats to prove that they did not need to see to fly.
In the 20th Century, biologists, using electronic instruments, have carried out experiments with bats. They have discovered that bats find out where to go by emitting high-frequency sound and receiving the echoes as they bounce off objects. Most of the sounds have too high a frequency to be heard by the human ear.
Bats commonly fly together in groups, but apparently they are not confused by the sounds and echoes produced by each other. When hunting in woods and in the rain they are able to discriminate between the faint echoes bouncing off insects and those bouncing off the ground, tree-trunks, branches, twigs and raindrops.
These tiny flying mammals have been using the equivalent of our modern sonar device for millions of years.
BEE STING
A bee keeps its sting at the end of its abdomen. At the tip of a bee’s abdomen is a shaft where its stinging thorn is to be found. It can sting several times, but once it leaves the thorn in its victim’s flesh it will not be able to sting again.
It is not true to say that a bee will automatically die once it loses its thorn. Only female bees can sting. Male bees, or drones, lack this means of protecting themselves.
There is a species of which even the female cannot sting. But these bees which live mainly in Africa and South America are not defenseless. If disturbed, they will fly at the intruder in great numbers, crawl into his eyes, ears and hair and smear him with a sticky substance, causing him to retreat in great discomfort.
It is not true to say that a bee will automatically die once it loses its thorn. Only female bees can sting. Male bees, or drones, lack this means of protecting themselves.
There is a species of which even the female cannot sting. But these bees which live mainly in Africa and South America are not defenseless. If disturbed, they will fly at the intruder in great numbers, crawl into his eyes, ears and hair and smear him with a sticky substance, causing him to retreat in great discomfort.