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The whole body of a bird is adapted to this end Its forearms have become modified to form wings the bony tail has been replaced by a fan of feathers many of the bones are hollow and light in weight the jaws are modified into a lightweight horny beak instead of heavy tooth-filled jaws and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
the Galápagos penguin pp 10 11 Seabirds are also threatened by overfishing and huge numbers are killed when they are accidentally caught on the hooks of longlines as with the wandering albatross Poisoning both deliberate and accidental also affects threatened birds such as the Cape griffon vulture as do wars and the disturbance of wary birds especially at their breeding colonies by tourists ramblers climbers watersports enthusiasts and even conservationists The Present Situation Of the 10,027 or so species of birds in the world today 1,240 species almost one in eight are threatened with global extinction unless something is done to save them Of them 190 are Critically Endangered A further 372 species are Endangered another 678 species are Vulnerable and 838 species are Lower Risk near threatened Many subspecies are also in danger The Cape Verde race of red kite p 26 for example is now extinct Already over 120 other species of birds are known biologists mainly in the tropics Many are rare with tiny ranges and in threatened habitats and so were in peril even before they were known to science Few birds are found over all or most of the world the barn owl and cattle egret are the only species to have been recorded on every continent Worst off are the parrots with more species globally threatened than any other family Trapping for the cage-bird trade is a major threat at both local and worldwide levels made even more serious by habitat loss Where the Dangers Lie Of the 12 countries that contain the greatest concentrations of threatened bird species seven are in the Americas The highest densities of threatened birds occur in the Atlantic forests of Brazil and the northern Andes of Colombia and Ecuador Almost half of all the extinctions of birds recorded since 1650 have been from species living in Oceania the islands of the central and south Pacific Ocean and adjacent seas including Australia New Zealand New Guinea New Caledonia the Solomons Fiji and the to have become extinct since the last dodo died in the 1660s almost all of them as a result of human impact Given the natural rate of evolution we would expect one bird species to go extinct every 100 years so 103 in the last 200 years is 50 times the expected rate Each year one or two new bird species are discovered by rest of Melanesia Micronesia and Polynesia Although there are relatively few threatened birds exclusively found in Europe and the Middle East most of the species at risk in these regions make yearly migrations between summer breeding grounds and wintering areas In many cases that pattern of behavior exposes them to a wide range of threats Birds face many threats including introduced predators as with this brown kiwi above and pollution This jackass penguin left is covered in oil from a sunken cargo boat Most-Threatened Habitats Threatened birds are mainly restricted to specific habitats 74 percent depend almost completely on a single type of habitat Of them forest birds form 75 percent of which 93 percent are found only in the tropics and 82 percent are restricted to moist forests 6
WHAT IS A BIRD Percentage of birds threatened 0 2 2 3 3 7 7 42 no data The next most important habitats are grasslands scrublands and savannas with 32 percent of all the world’s threatened species Wetlands too especially freshwater ones are also of great significance holding 12 percent of all threatened birds Conservation There are many reasons for conserving birds They are fascinating creatures that have inspired people over the centuries and people care about them Most importantly birds are good indicators of the state of our environment places that are rich in bird species are also rich in the biodiversity of other classes of animals So where birds are threatened with extinction is often a good indication of general biodiversity loss and damage to ecosystems The task of saving species such as the spoon billed sandpiper whose journeys take them across the globe recognizing no international boundaries requires careful coordination of efforts among nations BirdLife International a global partnership of conservation organizations in over 100 countries is one organization that is dedicated to saving birds and their habitats Threatened birds worldwide Less than 5 percent of the earth’s land surface contains almost 75 percent of threatened bird species Since the greatest threat is habitat destruction and degradation BirdLife International has created a program that will identify about 20,000 Important Bird Areas IBAs throughout the world The most effective way of saving threatened birds is to protect such sites before they suffer threats but sometimes as in Madagascar Hawaii or New Zealand the problems caused by habitat loss introduced animals and other factors mean that the affected species require intensive and costly conservation programs Another problem facing conservationists is that they simply do not have enough information about the range numbers or ecology of many threatened bird species Gaining such knowledge is an important part of their work Knowledge about threatened birds and their habitats is also vital for persuading governments business interests and other decision makers to act in ways that will benefit the birds and for the drawing up and enforcement of agreements at local national or international levels 7
