Ride the Wind: Airborne Journeys of Animals and Plants
All the animals and plants in the world live on the earth as well as above its surface For our planet is made up not only of rocks soil and water but also of the gases in its atmosphere Animals and plants and people too live at the bottom of the atmosphere an enormous ocean of air that reaches hundreds of miles above the solid surface of Earth Animals and plants that make air journeys travel through a layer of the atmosphere called the troposphere which can be up to six miles 9 6 km high Air is a real substance even though it is invisible A bird’s wing pushes against the air in its path and the air pushes back against the wing Birds flap their wings to push through the air the way swimmers use their arms to push through water The support of the air allows birds bats and insects to fly and carries seeds and ballooning spiders aloft
Birds and bats are the only vertebrates animals with backbones that can truly fly Some animals such as flying fish can glide for short distances Because a bat’s wing is a thin skinlike substance supported by the long bones of the bat’s fingers and arms bats can vary the outline outline of their wings quickly and easily and thus make sudden turns in the air Bird feathers weigh very little and have a broad surface that catches the wind Bird bones are often hollow and lightweight and form a strong support for the flight feathers of a bird’s wings The breastbone of most birds supports the muscles used in flying the muscles are the heaviest part of a bird’s body Bird wings vary in shape Some like the gull’s are good for soaring as well as for strong and quick flight Others like the wings of the albatross are broader for gliding while still others like those of the swift are narrower for speed
The seasonal journeys of large groups of animals are called migrations migrations Animals migrate when the weather becomes too cold or too hot or when food is unavailable Among migrating birds the Arctic tern is the long distance champion champion of air travelers Each year adult terns fly from the Arctic to the Antarctic and back again The round-trip journey of about twenty-five thousand miles takes eight months of almost nonstop flying flying On its trip the tern passes from a northern summer to a southern southern summer When a tern arrives at its Arctic breeding grounds in spring it returns to the same area it left the previous autumn In the autumn terns from Greenland and Canada ride on westerly winds across the stormy Atlantic Ocean to Europe and then head south along the coast of West Africa While traveling terns plunge into the cold waters along their path to capture fish About February adult terns begin their journey back to the Arctic Most of the young birds remain in the south during their first year By the third spring they fly back to the Arctic to find a mate and breed As adults they will spend the rest of their lives twenty to thirty years following an endless summer around the world
