Our planet has a bounty of birds—more than 11,000 species in all. But on a global scale, most have relatively small ranges. And only a few dozen species can be called “cosmopolitan,” with ranges that touch six continents or at least three oceans. These are the birds that tie our human world together—birds that nearly all of us have in common.
The Bird, Barn Swallow is one of the best examples: a bird weighing less than an ounce, whose migratory routes touch Canada, Tierra del Fuego, Norway, Namibia, Russia, Australia, and most places in between. Their gleaming colors and graceful aerobatics delight birdwatchers on every continent save Antarctica.
With their seemingly inexhaustible talent for flight, birds are inherently good at finding new places to live (see the Western Cattle Egret below for a good example). But some species get a helping hand from humans. Some, like Rock Pigeons and House Sparrows, formed a bond with humans centuries ago and have followed us around ever since. Others are brought along for a variety of reasons—parrots and parakeets come with us as pets, for instance—but may escape or be released and gain a toehold on a new continent.
Oceans cover more than two-thirds of the planet, and birds have evolved to exist across most of that endless blue-gray habitat. The Arctic Tern is famous for covering a distance equal to the circumference of the Earth every year. With a lifespan that can exceed 30 years, an Arctic Tern might travel three-quarters of a million miles in its lifetime. Plenty of other seabirds have the ability to spend years on the wing, without touching land—following are a few examples of species that touch at least three of the world’s five oceans in their travels.
The world is a big place, and some widespread bird species don’t quite make it to that sixth continent. Some species fall short through the vagaries of taxonomic changes—for instance the cosmopolitan species previously known as Cattle Egret was recently split into two species (Western and Eastern Cattle Egrets), neither of which make it to six continents. Others, like the Black-crowned Night Heron, come oh-so-close to that sixth continent, but fall just short. We love them anyway: these are our honorable mentions.
