Birds have many common characteristics that categorize them as birds. While they have many attributes that are necessary for their classification, they also have many differences that separate them from other species of birds. Some of the necessary characteristics that birds share are they are warm blooded and have two legs. Their skin is covered with feathers and most of them have hollow bones that aid in flying using their two wings.
Most birds are active during the day but others are active at night, such as owls. They all share a bony or a hard beak and have no teeth. They are also egg layers and they possess a high metabolism. This is nearly a complete list of what birds have in common. They have many more features that separate one species from another.
Many people think of birds as flying animals yet many birds have lost that ability over time. Many birds that reside on islands have no need for flight and are no longer capable of it. The ostrich, penguin, and kiwi are examples of these flightless birds. Most birds feed on nuts, seeds, and insects while others feed on other birds or dead animals.
Some birds are terrified of humans and others have developed such a dependency on them that they are no longer considered ‘wild’. The pigeon, for example, is seen as a nuisance in most cities and towns. Many birds are facing threats from humans and are dangerously nearing extinction. The bald eagle is a prime example of this type an animal until relentless efforts at saving it have increased their population.
Like humans, birds share common characteristics but then vary greatly in their behavior, diet, appearance and habitat. Learning these differences is what makes bird enthusiasts strive to observe and study these animals until they can be understood more fully.