There are approximately 11,000 species of birds extant (now living) in the world, although the exact number is unknown. Some authorities argue that DNA analysis points to perhaps twice that number. In avian taxonomy the largest subdivision of bird types is the order, of which there are 41. Orders include such things as parrots, ostriches, waterfowl, hummingbirds, cuckoos, grebes, loons, flamingoes, herons, owls, hawks, woodpeckers, and the largest one of all with 51% of all bird species, the songbirds, order Passeriformes. (Almost all orders end in -iformes - Owls belong to the order Strigiformes, waterfowl to Anseriformes, etc.) Within each order are one or more families - about 250 of them. Some are quite large like the Tyrannidae, the flycatchers, which contain 447 species. Several, like that of the Kagu, is by itself in the family Rhynochetidae. Like orders, families are distinguished by a particular ending, in this case, -idae. So Paridae includes the chickadees and titmice while Anatidae contains the ducks. There are of course  rules for naming, set out by the International Ornithological Committee. 

Birds are found all over the world except in the center of the ocean and the center of Antarctica. Over their evolutionary time of 200 million years or so they have adapted to a wide variety of habitats with a wide variety of adaptations.

Birds are waterproof; they have a preen (uropygial) gland that produces an oil that the birds rub on their feathers when preening. So not only can they stay dry during a rainy period, but birds like sandpipers, herons, egrets, and plovers can walk through shallow water without soaking their feathers. Ducks, geese, swans, coots, and seabirds of all types can spend days sitting on ponds, lakes, and the ocean, remaining cozy and dry. So watery habitats provide homes for many birds.

On the other end of the spectrum there are many birds that spend their lives in very dry or even desert habitats. They tend to be light colored to reflect the heat, avoid the sun by seeking shade or even using lizard burrows to cool off in as do Hoopoe Larks and Bar-tailed Desert Larks. Black-throated Sparrows have extremely efficient kidneys and excrete almost no liquid. Obtaining moisture from foods like nectar, fruit, and insects. Black-throated Sparrows are able to extract enough water from  food , even seeds, that they may never  take a drink.

Besides being waterproof, feathers provide insulation, allowing birds to inhabit the coldest of environments.The Emperor Penguin breeds in the coldest environment of any bird species with air teperatures of −40 °C (−40 °F), and wind speeds of 144 km/h (89 mph). The Emperor Penguin's average body temperature is 39 °C (102 °F). Feathers provide 90% of the insulation and a layer of fat does the rest.

Forests, especially tropical forests, provide a cornucopia of opportunities for birds to exploit, and they have. There are woodpeckers on the sides of trees, thrushes on the ground, hummingbirds and sunbirds feeding on nectar, and swifts flying above the canopy feeding on insects. 

The natural world is so complex and the vegetation so diverse that birds have had the opportunity to develop different lifestyles, and indeed, different bodies , to adapt to it. We'll examine all those adaptations in detail in future blogs.

Meanwhile, you might want to look at the ever-growing list of bird species' biographies of some interesting birds.