10 Facts About Birds

By Bob Strauss

Animals & Wildlife Expert

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Do You Know These 10 Essential Bird Facts?

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A Swallow. Photo Credit: Getty Images

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There Are About 10,000 Known Bird Species

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A Dove. Photo Credit: Getty Images

Somewhat surprisingly, for those of us proud of our mammalian heritage, there are twice as many species of birds as there are of mammals--about 10,000 and 5,000, respectively. By far the most common types of birds are "passerines," or perching birds, which are characterized by the shape of their feet and their propensity to burst into song. Other notable orders of birds include "gruiformes" (cranes and rails), "cuculiformes" (cuckoos) and "columbiformes" (pigeons and doves), among about 20 other classifications.

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There Are Two Main Bird Groups

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The Tinamou. Photo Credit: Getty Images

Naturalists divide the class of birds, "aves," into two infraclasses: "palaeognathae" and "neognathae." Oddly enough, paleaeognathae, or "old jaws," includes birds that first evolved during the Cenozoic Era--mostly ratites such as ostriches, emus and kiwis. The neognathae, or "new jaws," can trace their roots much farther back into the Mesozoic Era, and includes all other types of birds, including the passerines mentioned in slide #2.

(Most paleognathae are completely flightless, with the odd exception of the Tinamou of Central and South America.)

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Birds Are the Only Feathered Animals

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Puffins. Photo Credit: Getty Images

The major groups of animals can be distinguished by their skin coverings: animals have hair, fish have scales, arthropods have exoskeletons, and birds have feathers. You might think birds evolved feathers in order to fly, but you'd be mistaken on two counts: first, it was the ancestors of birds, the dinosaurs, that first evolved feathers, and second, feathers evolved primarily as a means of conserving body heat, and were only secondarily selected for by evolution to enable birds to take to the air.

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Birds Evolved From Dinosaurs

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The early dino-bird Archaeopteryx. Photo Credit: Getty Images

As mentioned in the previous slide, the evidence is now incontestable that birds evolved from dinosaurs--but there are still a lot of details about this process that have yet to be established. For example, it's likely that birds evolved two or three times, independently, in the course of the Mesozoic Era, but only one of these lineages survived the K/T Extinction and went on to spawn the ducks, doves and penguins we all know and love today.

(And if you're curious why modern birds aren't dinosaur-sized, that all comes down to the mechanics of powered flight and the vagaries of evolution).

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The Closest Living Relatives of Birds Are Crocodiles

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Photo Credit: Getty Images

As vertebrate animals, birds are ultimately related to all the other vertebrate animals that live, or ever have lived, on earth. But you may be surprised to learn that the family of vertebrates to which modern birds are most closely related is the crocodiles, which evolved, like dinosaurs, from a population of archosaur reptiles during the late Triassic period. Dinosaurs, pterosaurs and marine reptiles all went kaput in the K/T Extinction Event, but crocodiles somehow managed to survive (and will gladly eat any birds, close kin or not, that happen to land on their snouts).

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Birds Communicate Using Sound and Color

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A Macaw. Photo Credit: Getty Images

One thing you may have noticed about birds, especially passerines, is that they're fairly small--meaning they need a reliable way to locate one another during mating season. For this reason, perching birds have evolved an intricate variety of songs, trills and whistles, with which they can attract others of their kind in dense forest canopies where they would otherwise be nearly invisible. The bright colors of some birds also serve a signaling function, usually to assert dominance over other males or to broadcast sexual availability.

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Most Bird Species Are Monogamous

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Photo Credit: Getty Images

The word "monogamous" carries different connotations in the animal kingdom than it does in human beings. In the case of birds, it means that the males and females of most species pair up for a single breeding season, mating and then rearing their young--at which point they're free to find other partners for the next breeding season. Some birds, however, remain monogamous until either the male or female dies, and some female birds have a neat trick up their sleeve--they can store the sperm of males, and use it to fertilize their eggs, for up to three months!

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Some Birds Are Better Parents Than Others

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The Sunbird. Photo Credit: Getty Images

There are a wide variety of parenting behaviors across the bird kingdom. In some species, both parents incubate the eggs; in some, only one parents cares for the hatchlings; and in yet others, no parental care is required at all (for example, the Malleefowl of Australia lays its eggs in rotting patches of vegetation, which provide natural heat, and the fledglings are completely on their own after hatching).

And we won't even mention outliers like the Cuckoo Bird, which lays its eggs in other birds' nest and leaves their incubation and feeding to total strangers.

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Birds Have a Very High Metabolic Rate

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A Hummingbird. Photo Credit: Getty Images

As a general rule, the smaller an endothermic (warm-blooded) animal is, the higher its metabolic rate--and one of the best indicators of an animal's metabolic rate is its heartbeat. You may think that chicken is just sitting there, doing nothing in particular, but its heart is actually beating at about 250 beats per minute, while the heart rate of a resting hummingbird measures over 600 beats per minute.

By comparison, a healthy house cat has a resting heart rate of between 150 and 200 bpm, while humans hover around 100 bpm.

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Birds Helped Inspire the Idea of Natural Selection

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A Galapagos Finch. Photo Credit: Getty Images

When Charles Darwin was formulating his theory of natural selection, in the early 19th century, he did extensive research on the finches of the Galapagos Islands. The finches on different islands differed significantly in their sizes and the shapes of their beaks; they were clearly adapted to their individual habitats, yet just as clearly they had all descended from a common ancestor that had landed in Galapagos thousands of years before.

The only way nature could have accomplished this feat was evolution via natural selection, as Darwin proposed in his groundbreaking book On the Origin of Species.