FACTS AT YOUR FINGERTIPS ENDANGERED ANIMALS BIRDS BROWN BEAR BOOKS
What is a Bird Birds are among the most successful of all groups of animals found everywhere from the bleak icy wastes of the Arctic and Antarctic and the tops of the highest mountains to baking-hot deserts and from the most remote oceanic islands and the interior of vast jungles to farmland and city streets Crucial to this success has been their mastery of flight The whole body of a bird is adapted to this end Its forearms have become modified to form wings the bony tail has been replaced by a fan of feathers many of the bones are hollow and light in weight the jaws are modified into a lightweight horny beak instead of heavy tooth-filled jaws and there is a system of air filled sacs within much of the body Laying large yolk rich eggs enables birds to avoid carrying around a heavy embryo within the body and they have well developed brains and acute senses Birds also have superbly efficient blood-circulatory and respiratory systems enabling many species to fly far fast or high as their needs dictate It is birds that hold the record for long-distance migration many Arctic terns regularly make a round trip of 25,000 miles 40,200 km between the Arctic and the Antarctic each year They also hold records for flight speed the peregrine falcon is the fastest-moving living thing under its own power reaching speeds of 117 miles per hour 188 km h And birds can fly at considerable altitudes a Rüppell’s griffon vulture collided with an aircraft at 37,000 feet 11,300 m The key to their superb powers of flight is the evolution of feathers which distinguish birds from all other animals These structures made of keratin a material similar to that found in your hair and nails form the plumage of the bird which helps it fly and provides insulation colors for camouflage or communication waterproofing and other uses Considering the limitations imposed on them by acquiring the power of flight birds are remarkably 4 The house sparrow is one of the world’s most successful birds yet even this adaptable species has declined in places varied in appearance and lifestyle They have a much greater species diversity than other groups of vertebrates apart from fish with almost 9,800 species over twice as many species as mammals Flightlessness Although the great majority of birds can fly certain groups or individual species have abandoned flight during their evolutionary history Examples include the ratites flightless running birds whose living representatives include the ostrich and kiwis the penguins the kakapo pp 36 37 and extinct birds such as the great auk and dodo Originally this strategy was a neat way of saving energy for birds that lived on islands or other places where there were no land predators and so no need to fly to escape them But flightlessness also meant that many species succumbed to predators such as cats and rats introduced by settlers The History of Birds Birds evolved from reptiles over 160 million years ago These two great groups or classes of animals share
many characteristics including details of their skulls ear bones and lower jaws and similarities between their eggs Although there has been disagreement about which group of reptiles gave rise to birds most researchers think that they evolved directly from small agile lightweight theropod dinosaurs called coelurosaurs that ran on their hind legs Adaptive Radiation The rapid evolution of flowering plants and the insects that depended on them paved the way for an explosion of opportunities for fruit-eating nectar feeding and insect-eating birds especially of the great group known as the passerines perching birds including songbirds Today passerines make up over half of all bird species in the world By 5 to 10 million years ago birds had diversified into a great range of different genera including many that still have representatives today Living birds range in size from the tiny bee hummingbird pp 44 45 smaller than some insects to the mighty ostrich males of which can be 9 feet 3 m tall This impressive natural diversity is being diminished as humans affect the survival of bird species Why Are Birds at Risk Birds are threatened today by a variety of factors over 99 percent of them the result of human activities The effects of habitat destruction and degradation are the major threat to 85 percent of all threatened species The next most important threat comes from direct exploitation affecting 31 percent of the total It is mainly due to hunting for food as with the Baikal teal and the trapping of many millions of birds each Prehistoric birds numbered in order of age include toothed diving seabirds 1 2 giant flightless predators 3 5 ancestors of vultures 4 and flamingos 6 and the largest known flying birds 7 6 1 2 WHAT IS A BIRD year for the cage-bird trade both local and international The latter threat affects some groups of birds particularly seriously notably the parrots such as the salmon-crested cockatoo The third most serious threat is from the introduction by humans of animals especially to islands Almost all extinctions of bird species since 1800 have been of island birds whose lack of natural defenses made them easy targets for introduced predators Today a quarter of all threatened species face this threat the Guam rail became extinct in the wild because of predation by introduced snakes Other species are affected by habitat degradation caused by goats and other grazing animals as well as by alien plants that crowd out the natural vegetation Diseases can have devastating effects on birds Avian malaria spread by introduced mosquitoes was at least partly responsible for the extinction of many species of endemic Hawaiian birds Other threats include pollution acid rain and oil spills In the longer term the impact of climate change due mainly to human-induced global warming will pose an increasing threat to many birds changes in ocean currents are already having a profound effect on some seabirds such as 7 3 5 4 5
