John James Audubon traveled through untamed wilderness in his quest to observe and paint the birds of America. Even today, birds are the most-watched wildlife around. They are abundant and easy to see, even in cities. Their songs and calls and their bright colors command our attention and capture our imagination.
Birds have certain things in common with other animals. Like mammals (including human beings), all birds are warm-blooded. Birds have well-developed air-breathing lungs and a four-chambered heart. They are vertebrates, with internal skeletons and backbones.
Birds use their hard bills or beaks for defense and nest-building and to get food. Birds lay eggs, a characteristic they share with cold-blooded animals—reptiles, amphibians, fish, and even insects. Most often we think of birds as the animals that fly, but flight is not limited to birds (bats and insects), and not all birds can fly (ostriches, emus, penguins).
So what makes a bird a bird? Feathers. Feathers are unique to birds—all birds have them, and no other animal has a single one.
Feathers are made of keratin, the same substance found in reptile scales, animal fur, and human hair and nails. Feathers streamline a bird’s body, reducing air friction during flight. They are lightweight yet strong, windproof, often waterproof, and superb as insulation.
Scientists have created a system for classifying living things to show their evolutionary relationships by comparing their similarities and differences. The classification categories range from the broadest and most general distinctions, represented by kingdoms, to the most specific, called species. In between are phyla, classes, orders, families, and genera. It is at the class level that bird are set apart from other members of the animal kingdom. Birds and only birds belong to the class Aves—animals with feathers.
Ornithologists (scientists who study birds) then classify birds into about 30 major groups called orders. Ducks, for example, belong to the order Anseriformes, while perching birds like the bluebird belong to Passeriformes. Birds within an order have more in common with each other and are more closely related than they are to birds outside an order.
Within bird orders there are bird families. Some orders have very few families. The ostrich order (Struthioniformes) has only a single family (Struthionidae). At the other end of the spectrum are the perching birds (Passeriformes) with about 74 families and 5,100 or so species. That’s more than half of all the world’s known birds! Families are further divided into genera (the singular form of the word is genus)—groups of closely related species. A species is the smallest group in the classification system. A species is a specific kind of bird (or mammal or reptile, and so on). There are approximately 10,400 different species of birds on Earth.
Birds are commonly grouped and sorted in many other ways besides scientific classification. These more informal groupings—seabirds, waterfowl, raptors, scavengers, etc.—include bird with similar characteristics, habits, or habitats. The informal groupings describe birds that have something in common and often illustrate how different kinds of birds have similarly adapted to different habitats, food sources, and roles in the food web.
Birds live in deserts and forests, on mountaintops and islands, and range from both poles to the tropics. Some birds even live in caves or on the open ocean. The bodies and behaviors of birds are adapted to their particular habitat to ensure their survival. For example, most desert birds eat animals or insects, which are full of moisture, instead of dry seeds, so a meal provides it with both food and water. Wading birds are adapted with long legs and splayed-out toes for searching out food in shallow water. Ducks have webbed feet to serve as paddles for swimming and a special oil gland for waterproofing their feathers. Penguins have more feathers than any other bird plus a layer of blubber under the skin—features that keep them warm in the harshest conditions.
What a bird eats and how it obtains food is another way to sort birds. Birds can be nectar-eaters, insect-eaters, seed-eaters, carrion-eaters, fish-eaters, scavengers, hunters, and grazers. Seed-eaters like finches and cardinals have sturdy crushing beaks, while the beaks of meat-eaters like hawks and eagles (a.k.a. raptors or birds of prey) are hooked for tearing at flesh. Swifts and swallows are insect-eaters that catch prey in flight. Their long, narrow wings allow them to perform amazing aerial maneuvers to chase down bugs and then gulp them into their extra-wide mouths. Many birds fit into more than one of these informal categories.
Birds are part of the balance of nearly every ecosystem on the planet. Birds eat insects and plants, and bird eggs are food for may other animals. Fruit-eating birds help spread seeds, and nectar-eating birds pollinate flowers. Birds have long been considered an important part of human culture. Farmers welcome birds that eat insect pests and weed seeds. Owls and hawks feed on pest rodents. For centuries, people have raised domesticated birds for their eggs, meat, and feathers.
However, the growth of human populations, the clearing of forests for farmland and pastures, and the expansion of cities and suburbs have all had a negative effect on many bird populations. Another very serious threat is climate change, which is already profoundly affecting the lives of birds. According to Audubon’s 2014 “Birds and Climate Change Report,” shrinking and shifting ranges caused by climate change “could imperil nearly half of U.S. birds within this century.” Right now, of the more than 10,400 bird species on Earth, more than 10 percent, or more than a thousand species, are threatened—at risk because of climate change, habitat loss, and other pressures that are reducing their populations. Some of these are familiar backyard birds.
The good news is that all around the world, people are taking steps to protect wild birds. There now seems to be a commitment on national and international levels to address the threat posed by climate change. Local, state, and federal efforts are protecting wild spaces from development and other threats to habitat. But there is still much more to be done. The National Audubon Society and its local chapters, along with other groups, have helped to pass laws that protect birds and regulate hunting. People are helping birds by planting native species and limiting pesticide use in backyards and schoolyards. And everyone can do their own part to reduce emissions that contribute to climate change. Creating wildlife refuges and bird sanctuaries is another way people are helping birds. If you visit one—or even if you take the time to watch the birds in your backyard or neighborhood—you can see for yourself the beauty and diversity of birds.
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