The earth is home to over 10,000 species of birds scattered across a wide range of habitats that include wetlands, woodlands, mountains, deserts, tundra, and the open sea. While experts differ on the fine details about how birds should be classified, there are 30 bird groups that pretty much everyone agrees on, ranging from albatrosses and petrels to toucans and woodpeckers.

01 of 30 Albatrosses and Petrels (Order Procellariiformes) Ben Cranke / Getty Images Birds in the order Procellariiformes, also known as tubenoses, include diving petrels, gadfly petrels, albatrosses, shearwaters, fulmars, and prions, with about 100 living species in all. These birds spend most of their time at sea, gliding over the open water and dipping down to snatch meals of fish, plankton, and other small marine animals. Tubenoses are colonial birds, returning to land only to breed. Breeding sites vary among species, but in general, these birds prefer remote islands and rugged coastal cliffs. They are monogamous, forming long-term bonds between mating pairs. A unifying anatomical characteristic of albatrosses and petrels is their nostrils, which are enclosed in external tubes that run from the base of their bills toward the tip. Amazingly enough, these birds can drink seawater. They remove salt from the water using a special gland located at the base of their bills, after which the excess salt is excreted out through their tubular nostrils. The largest tubenose species is the wandering albatross, which has a wingspan of 12 feet. The smallest is the least storm petrel, which has a wingspan of just over one foot.

02 of 30 Birds of Prey (Order Falconiformes) Josh Miller Photography / Getty Images The Falconiformes, or birds of prey, include eagles, hawks, kites, secretary birds, ospreys, falcons, and old world vultures, approximately 300 species in all. Also known as raptors (but not all that closely related to the raptor dinosaurs of the Mesozoic Era), birds of prey are formidable predators, armed with powerful talons, hooked bills, acute eyesight, and broad wings well-suited for soaring and diving. Raptors hunt by day, feeding on fish, small mammals, reptiles, other birds, and abandoned carrion. Most birds of prey have drab plumage, consisting primarily of brown, grey or white feathers that blend in well with the surrounding landscape. Their eyes are forward-facing, making it easier for them to spot prey. The shape of a Falconiformes' tail is a good clue to its behavior. Broad tails allow greater in-flight maneuverability, short tails are good for speed, and forked tails point to a lifestyle of leisurely cruising. Falcons, hawks, and ospreys are among the more cosmopolitan raptors, inhabiting every continent on Earth except Antarctica. Secretary birds are restricted to sub-Saharan Africa. New World vultures live only in North and South America. The largest bird of prey is the Andean condor, the wingspan of which can approach 10 feet. On the smaller end of the scale are the lesser kestrel and the little sparrowhawk, with wingspans of less than two and a half feet.

03 of 30 Buttonquails (Order Turniciformes) Shantanu Kuveskar / Wikimedia Commons Turniciformes is a small order of birds, consisting of only 15 species. Buttonquails are ground-dwelling birds that inhabit warm grasslands, scrublands, and croplands of Europe, Asia, Africa, and Australia. Buttonquails are capable of flight but spend most of their time on the ground, their dull plumage blending in well with grasses and bushes. These birds have three toes on each foot and no hind toe, which is why they're sometimes referred to as hemipodes, Greek for "half-foot." Buttonquails are unusual among birds in that they're polyandrous. The females initiate courtship and mate with multiple males, and also defend their territory against rival females. After the female buttonquail lays its eggs in a nest in the ground, the male takes over incubation duties and cares for the young after they hatch 12 or 13 days later. There are two subgroups of order Turniciformes. The genus Ortyxelos includes just one species of buttonquail, the quail plover. The genus Turnix comprises 14 species (or more, depending on the classification scheme), including the buff-breasted buttonquail, the small buttonquail, the chestnut-backed buttonquail, and the yellow-legged buttonquail.

04 of 30 Cassowaries and Emus (Order Casuariiformes) Henry Cook / Getty Images Cassowaries and emus, order Casuariiformes, are large, flightless birds equipped with long necks and long legs. They also have shaggy, limp feathers that resemble coarse fur. These birds lack a bony keel on their sternums, or breastbones (the anchors to which a birds' flight muscles attach), and their heads and necks are nearly bald. There are four extant species of Casuariiformes: The Southern Cassowary (Casuarius casuarius), also known as the Australian cassowary, inhabits the lowlands of the Aru islands of southern New Guinea, as well as northeastern Australia.

The Northern cassowary (C. unappendiculatus), also known as the golden-necked cassowary, is a large, flightless bird of northern New Guinea. Northern cassowaries have black plumage, blue-skinned faces, and bright red or orange necks and wattles.

The dwarf cassowary (C. bennetti), also called Bennet's cassowary, inhabits the mountain forests of Yapen Island, New Britain, and New Guinea, and can thrive at elevations as high as 10,500 feet. Dwarf cassowaries are threatened by habitat destruction and degradation. They are also hunted as a source of food.

The emu (Dromaius novaehollandiae) is native to the savannas, sparse forests and scrublands of Australia, where it's the second largest bird after the ostrich. Emus can go for weeks without eating and drinking and are capable of attaining speeds above 30 miles per hour.

05 of 30 Cranes, Coots, and Rails (Order Gruiformes) Nancy Nehring / Getty Images Cranes, coots, rails, crakes, bustards, and trumpeters—about 200 species in all—make up the bird order Gruiformes. The members of this group vary widely in size and appearance but are generally characterized by their short tails, long necks, and rounded wings. Cranes, with their long legs and long necks, are the largest members of the Gruiformes. The sarus crane stands over five feet tall and has a wingspan of up to seven feet. Most cranes are pale grey or white in color, with accents of red and black feathers on their faces. The black-crowned crane is the most ornate member of the breed, with a tuft of golden plumes atop its head. Rails are smaller than cranes and include crakes, coots, and gallinules. Although some rails engage in seasonal migrations, most are weak fliers and prefer to run along the ground. Some of the rails that colonized islands with few or no predators have lost their ability to fly, which makes them vulnerable to invasive predators like snakes, rats, and feral cats. The Gruiformes also include an assortment of birds that don't fit well anywhere else. Seriemas are large, terrestrial, long-legged birds that inhabit the grasslands and savannas of Brazil, Argentina, Paraguay, Bolivia, and Uruguay. Bustards are large terrestrial birds that inhabit dry scrublands throughout the Old World, while the sunbitterns of South and Central America have long, pointed bills and bright orange legs and feet. The kagu is an endangered bird of New Caledonia, with light grey plumage and a red bill and legs.

06 of 30 Cuckoos and Turacos (Order Cuculiformes) Edith Polverini / Getty Images The bird order Cuculiformes includes turacos, cuckoos, coucals, anis and the hoatzin, about 160 species in all. Cuculiformes are found worldwide, although some subgroups are more restricted in range than others. The precise classification of Cuculiformes is a matter of debate. Some experts suggest that the hoatzin is sufficiently distinct from other Cuculiformes that it should be assigned to its own order, and the same idea has been presented for turacos. Cuckoos are medium-sized, slender-bodied birds that live in forests and savannas and feed primarily on insects and insect larvae. Some cuckoo species are notorious for engaging in "brood parasitism." The females lay their eggs in the nests of other birds. The baby cuckoo, when it hatches, will sometimes push the fledglings out of the nest. Anis, also known as New World cuckoos, inhabit the southernmost stretches of Texas, Mexico, Central America, and South America. These black-plumed birds are not brood parasites. The hoatzin is indigenous to the swamps, mangroves, and wetlands of the Amazon and Orinoco River basins of South America. Hoatzins have small heads, spiky crests, and long necks, and are mostly brown, with lighter feathers along their bellies and throats.

07 of 30 Flamingos (Order Phoenicopteriformes) Westend61 / Getty Images Phoenicopteriformes is an ancient order, consisting of five species of flamingos, filter-feeding birds equipped with specialized bills that allow them to extract tiny plants and animals from the waters they frequent. To feed, flamingos open their bills slightly and drag them through the water. Tiny plates called lamellae act as filters, much like the baleen of blue whales. The tiny marine animals on which flamingos feed, such as brine shrimp, are rich in carotenoids. This is a class of proteins that accumulate in these birds' feathers and gives them their characteristic crimson or pink color. Flamingos are highly social birds, forming large colonies consisting of several thousand individuals. They synchronize their mating and egg-laying to coincide with the dry season. When water levels drop, they build their nests in the exposed mud. Parents care for their offspring for a few weeks after hatching. Flamingos inhabit tropical and subtropical regions of South America, the Caribbean, Africa, India, and the Middle East. Their preferred habitats include estuarine lagoons, mangrove swamps, tidal flats, and large alkaline or saline lakes.

08 of 30 Game Birds (Order Galliformes) Robert Trevis-Smith / Getty Images Some of the most familiar birds on earth, at least to people who like to eat, are game birds. The game birds order includes chickens, pheasants, quails, turkeys, grouse, curassows, guans, chachalacas, guineafowl, and megapodes, about 250 species in all. Many of the world's less familiar game birds are subject to intense hunting pressure and on the brink of extinction. Other game birds, such as chickens, quails, and turkeys, have been completely domesticated, often on factory farms, and number in the billions. Despite their rotund bodies, game birds are excellent runners. These birds have short, rounded wings that enable them to fly anywhere from a few feet to almost a hundred yards. This is enough to escape most predators, but not enough to migrate for long distances. The smallest species of game bird is the Asian blue quail, which measures just five inches from head to tail. The largest is the North American wild turkey, which can attain lengths of over four feet and weights of over 30 pounds.

09 of 30 Grebes (Order Podicipediformes) Kathy2408 / Pixabay Grebes are medium-sized diving birds that live in freshwater wetlands around the world, which includes lakes, ponds, and slow-flowing rivers. They are skilled swimmers and excellent divers, equipped with lobed toes, blunt wings, dense plumage, long necks, and pointed bills. However, these birds are fairly clumsy on land, since their feet are positioned far to the rear of their bodies, a configuration that makes them good swimmers but terrible walkers. During breeding season, grebes engage in elaborate courtship displays. Some species swim side-by-side, and as they gain speed they lift their bodies into an elegant, upright display. They're also attentive parents, with both males and females taking care of the hatchlings. There is some controversy about the evolution and classification of grebes. These birds were once pegged as close relatives of loons, another group of skilled diving birds, but this theory has been debunked by recent molecular studies. The evidence shows that grebes are most closely related to flamingos. Further complicating matters, the fossil record for grebes is sparse, with no transitional forms yet discovered. The largest living grebe is the great grebe, which can weigh up to four pounds and measure more than two feet from head to tail. The appropriately-named least grebe is the smallest species, weighing less than five ounces.

10 of 30 Herons and Storks (Order Ciconiiformes) Nature-Pix / Pixabay The bird order Ciconiiformes includes herons, storks, bitterns, egrets, spoonbills, and ibises, a little over 100 species in all. All of these birds are long-legged, sharp-billed carnivores indigenous to freshwater wetlands. Their long, flexible toes lack webbing, enabling them to stand in thick mud without sinking and perch securely on treetops. Most are solitary hunters, stalking their prey slowly before striking quickly with powerful bills. They feed on fish, amphibians, and insects. Ciconiiformes are largely visual hunters, but a few species, including ibises and spoonbills, have specialized bills that help them to locate prey in muddy water. Storks fly with their necks extended straight out in front of their bodies, while most herons and egrets coil their necks into an "S" shape. Another noticeable characteristic of Ciconiiformes is that when they fly, their long legs trail gracefully behind them. The earliest known ancestors of today's herons, storks and their relatives date to the late Eocene epoch, about 40 million years ago. Their closest living relatives are the flamingos (see slide #8).

11 of 30 Hummingbirds and Swifts (Order Apodiformes) Nicman / Pixabay Birds in the order Apodiformes are characterized by their small sizes, short, delicate legs, and tiny feet. The name of this order is derived from the Greek word for "footless." The hummingbirds and swifts included in this group have numerous adaptations for specialized flight. This includes their short humerus bones, long bones in the outer portion of their wings, long primary and short secondary feathers. Swifts are fast-flying birds that dart over grasslands and marshes foraging for insects, which they catch with their short and wide beaks that have rounded, exposed nostrils. There are over 400 species of hummingbirds and swifts alive today. Hummingbirds range across the expanse of North, Central and South America, while swifts can be found on all the world's continents, with the exception of Antarctica. The earliest known members of Apodiformes were swift-like birds that evolved during the early Eocene epoch in northern Europe, about 55 million years ago. Hummingbirds arrived on the scene slightly later, diverging from early swifts sometime during the late Eocene epoch.

12 of 30 Kingfishers (Order Coraciiformes) Nigel Dell / Getty Images Coraciiformes is an order of mostly carnivorous birds that includes kingfishers, toddies, rollers, bee-eaters, motmots, hoopoes, and hornbills. Some members of this group are solitary, while others form large colonies. Hornbills are solitary hunters that vigorously defend their territory, while bee-eaters are gregarious and nest in dense groups. Coraciiformes tend to have large heads in relation to the rest of their bodies, as well as rounded wings. However, the wings of bee-eaters are pointed, so they can maneuver with greater agility. Many species are brightly colored, and all have feet with three forward-pointing toes and one backward-pointing toe. Most kingfishers and other Coraciiformes employ a hunting technique known as "spot-and swoop." The bird sits atop its favorite perch watching out for prey. When a victim comes in range, it swoops down to capture it and return it to the perch for the kill. Once here, the bird begins beating the unfortunate animal against a branch to disable it, or drags it to the nest to feed its young. Bee-eaters, which (as you might have guessed) feed primarily on bees, rub bees against branches to discharge their stingers before swallowing them for a tasty meal. Coraciiformes like to nest in tree holes or dig tunnels into banks of dirt lining the edges of rivers. Hornbills exhibit a unique nest behavior: females, along with their eggs, are isolated in the cavity of a tree, and a small opening in a mud "door" allows the males to pass food to the moms and hatchlings inside.

13 of 30 Kiwis (Order Apterygiformes) Judi Lapsley Miller / Wikimedia Commons Experts disagree about the exact number of species belonging to order Apterygiformes, but there are at least three: the brown kiwi, the great spotted kiwi, and the little spotted kiwi. Endemic to New Zealand, kiwis are flightless birds with tiny, almost vestigial wings. They are strictly nocturnal birds, digging at night with their long, narrow bills for grubs and earthworms. Their nostrils are positioned at the tips of their bills, enabling them to hunt using their acute sense of smell. Perhaps most characteristically, the coarse brown plumage of kiwis resembles long, stringy fur rather than feathers. Kiwis are strictly monogamous birds. The female lays her eggs in a burrow-like nest, and the male incubates the eggs over a period of 70 days. After hatching, the yolk sac remains attached to the newborn bird and helps to nourish it for the first week of its life, at which point the juvenile kiwi sets out from the nest to hunt for its own food. The national bird of New Zealand, the kiwi is vulnerable to mammalian predators, including cats and dogs, that were introduced to these islands hundreds of years ago by European settlers.

14 of 30 Loons (Order Gaviiformes) Jim Cumming / Getty Images The bird order Gaviiformes includes five living species of loons: the great northern loon, the red-throated loon, the white-billed loon, the black-throated loon, and the Pacific diver. Loons, also known as divers, are freshwater diving birds common to lakes throughout the northern parts of North America and Eurasia. Their legs are located towards the rear of their bodies, providing optimum power when moving in the water but making these birds somewhat awkward on land. Gaviiformes have fully webbed feet, elongated bodies that sit low in the water, and dagger-like bills well-suited to capturing fish, mollusks, crustaceans, and other aquatic invertebrates. Loons have four basic calls. The yodel call, used only by male loons, declares territory. The wail call is reminiscent of a wolf cry, and to some human ears it sounds like "where are you?" Loons use a tremolo call when they're threatened or agitated, and a soft hoot call to greet their young, their mates or other nearby loons. Loons only venture onto land in order to nest, and even then, they build their nests close to the water's edge. Both parents care for the hatchlings, which ride on the adults' backs for protection until they're ready to strike out on their own.

15 of 30 Mousebirds (Order Coliiformes) DickDaniels / Wikimedia Commons The bird order Coliiformes includes six species of mousebirds. These are small, rodent-like birds that scurry through trees in search of fruits, berries, and the occasional insect. Mousebirds are restricted to the open woodlands, scrublands, and savannas of sub-Saharan Africa. They usually gather in flocks of up to 30 or so individuals, except during breeding season when males and females pair up. One interesting fact about mousebirds is that they were much more populous during the later Cenozoic Era than they are today. In fact, some naturalists refer to these rare, easily overlooked and virtually unknown birds as "living fossils."

16 of 30 Nightjars and Frogmouths (Order Caprimulgiformes) pen_ash / Pixabay The bird order Caprimulgiformes includes about 100 species of nightjars and frogmouths, nocturnal birds that feed on insects caught either in flight or while foraging on the ground. Nightjars and frogmouths are brown, black, buff, and white. Their feather patterns are often quite mottled, so they blend well into their chosen habitats. These birds tend to nest either on the ground or in the crooks of trees. Nightjars are sometimes called "goatsuckers," from the once-common myth that they suckled goat milk. Frogmouths earned their name because their mouths resemble frog mouths. Nightjars have a near-global distribution, but frogmouths are restricted to India, Southeast Asia, and Australia.

17 of 30 The Ostrich (Order Struthioniformes) Volanthevist / Getty Images The sole member of its order of birds, the ostrich (Struthio camelus) is a true record-breaker. Not only is it the tallest and heaviest living bird, it can sprint at speeds of up to 45 miles per hour and jog for extended distances at a sustained pace of 30 mph. Ostriches have the largest eyes of any living terrestrial vertebrate, and their three-pound eggs are the largest produced by any living bird. In addition to all this, the male ostrich is one of the few birds on Earth to possess a functioning penis. Ostriches live in Africa and thrive in a wide variety of habitats, including deserts, semi-arid plains, savannas, and open woodlands. During their five-month breeding season, these flightless birds form flocks of five to 50 individuals, often intermingling with grazing mammals such as zebras and antelopes. When breeding season is over, this larger flock breaks down into small groups of two to five birds that care for the newborn hatchlings. Ostriches belong to a clan (but not order) of flightless birds known as the ratites. Ratites have smooth breastbones lacking keels, the bone structures to which flight muscles would normally be attached. Other birds classified as ratites include cassowaries, kiwis, moas, and emus.

18 of 30 Owls (Order Strigiformes) TonW / Pixabay The bird order Strigiformes consists of over 200 species of owls, medium to large birds equipped with strong talons, downward-curving bills, acute hearing, and keen eyesight. Because they hunt by night, owls possess especially large eyes (which are good at gathering sparse light in dim conditions) as well as binocular vision, which helps them hone in on prey. In fact, you can blame the shape and orientation of its eyes for an owl's strange behavior. This bird can't rotate its eyes to change its point of focus but instead has to move its entire head. Owls have a head-twisting range of 270 degrees. Owls are opportunistic carnivores, feeding on everything from small mammals, reptiles, insects, and other birds. Lacking teeth, they swallow their prey whole, and about six hours later they regurgitate the indigestible parts of their meal to create a pile of bones, feathers or fur. These owl pellets often accumulate in the debris beneath owl nesting and roosting sites. Owls live on every continent except Antarctica, inhabiting a wide variety of terrestrial habitats ranging from thick forests to wide-open grasslands. Snowy owls haunt the tundras surrounding the Arctic Ocean. The most widespread owl, the common barn owl, can be found in temperate, tropical, and coniferous forests. Owls, unlike most other birds, do not build nests. Instead, they use the discarded nests built by other bird species in previous seasons or make their homes in random crevices, depressions on the ground or the hollows of trees. Female owls lay between two and seven roughly spherical eggs that hatch at two-day intervals. This distribution in age means that if food is scarce, the older, larger chicks commandeer the bulk of the food. This causes their smaller, younger siblings to starve to death.

19 of 30 Parrots and Cockatoos (Order Psittaciformes) Tambako the Jaguar / Getty Images The bird order Psittaciformes includes parrots, lorikeets, cockatiels, cockatoos, parakeets, budgerigars, macaws, and broad-tailed parrots, over 350 species in all. Parrots are colorful, sociable birds that form large, noisy flocks in the wild. They're characterized by large heads, curved bills, short necks, and narrow, pointed wings. Parrots live in tropical and subtropical regions throughout the world and are most diverse in South America, Australia, and Asia. Parrots have zygodactyl feet, which means that two of their toes point forwards and two point backward. This arrangement is common in tree-dwelling birds that climb branches or maneuver through dense foliage. Psittaciformes also tend to be brightly-colored, and many have more than one color. Multiple bright colors help camouflage these birds against the bright green, high-contrast backdrops of tropical forests. Parrots are monogamous, forming strong pair bonds that are often sustained during the non-breeding season. These birds perform simple courtship displays and preen each other to maintain the pair bond. Psittaciformes, including parrots and cockatoos, are also extremely intelligent. This helps to explain why they're such popular house pets, but it also contributes to their dwindling numbers in the wild. Most parrots feed almost exclusively on fruit, seeds, nuts, flowers, and nectar, but some species enjoy the occasional arthropod (such as the larvae of invertebrates) or small animals (such as snails). Lories, lorikeets, swift parrots, and hanging parrots are specialized nectar feeders. Their tongues have brush-like tips that enable them to eat nectar easily. The large bills of most parrots enable them to effectively crack open seeds. Many species use their feet to hold the seeds while eating.

20 of 30 Pelicans, Cormorants, and Frigatebirds (Order Pelecaniformes) St Lowitsch / EyeEm / Getty Images The bird order Pelecaniformes includes various species of pelican, including the blue-footed booby, the red-billed tropicbird, cormorants, gannets, and the great frigatebird. These birds are characterized by their webbed feet and their various anatomical adaptations to catching fish, their primary food source. Many species of Pelecaniformes are accomplished divers and swimmers. Pelicans, the most familiar member of this order, have pouches on their lower bills that enable them to efficiently scoop up and store fish. There are seven major pelican species: the brown pelican, the Peruvian pelican, the great white pelican, the Australian pelican, the pink-backed pelican, the Dalmatian pelican, and the spot-billed pelican. Some Pelecaniformes species, such as cormorants and gannets, ingest stones that weigh them down in the water and help them to hunt more efficiently. These birds are characterized by their streamlined bodies and narrow nostrils, which prevent water from rushing in during deep dives. One intriguing species, the flightless cormorant, has adapted so well to a diving lifestyle that it has lost the ability to fly altogether. This bird lives on the Galapagos Islands, which are completely free from predators.

21 of 30 Penguins (Order Sphenisciformes) PTNorbert / Pixabay Not quite as cute and cuddly as they're portrayed in movies, penguins are flightless birds with stiff wings and unique coloring. They have distinct black or gray feathers along their backs and white feathers on their bellies. The wing bones of these birds have been fused by evolution to form flipper-like limbs, which enable them to dive and swim with great skill. Penguins are also characterized by their long, laterally narrow bills, short legs that are positioned toward the rear of their bodies and four forward-pointing toes. When on land, penguins hop or waddle. Those living in Antarctic climates, where snow persists throughout the year, like to slide quickly on their stomachs and use their wings and feet for steering and propulsion. When swimming, penguins often launch themselves straight up out of the water and then dive back beneath the surface. Some species can remain submerged for over 15 minutes at a time. The order Sphenisciformes includes six subgroups and about 20 species of penguins. The most diverse are the crested penguins, a subfamily that includes the macaroni penguin, the Chatham Islands penguin, the erect-crested penguin, and three species of rockhopper penguin (eastern, western, and northern). Other penguin groups include banded penguins, little penguins, brush-tailed penguins, great penguins, and megadyptes. Penguins also have a rich and diverse evolutionary history, including some genera (like Inkayacu) that lived in near-temperate climates millions of years ago.

22 of 30 Perching Birds (Order Passeriformes) Mark L Stanley / Getty Images Perching birds, also known as passerines, are the most diverse bird group, consisting of over 5,000 species of tits, sparrows, finches, wrens, dippers, thrushes, starlings, warblers, crows, jays, wagtails, swallows, larks, martins, warblers, and many others. True to their name, perching birds have a unique foot structure that allows them to tightly grip thin branches, twigs, slender reeds, and flimsy grass stems. Some species can even hold fast to vertical surfaces, such as rock faces and tree trunks. In addition to the unique structure of their feet, perching birds are notable for their complex songs. The passerine voice box (also called a syrinx) is a vocal organ located in the trachea. Although perching birds aren't the only birds to possess syrinxes, their organs are the most highly developed. Every passerine has a unique song, some of them simple, others long and complex. Some species learn their songs from their parents, while others are born with the innate ability to sing. Most perching birds form monogamous pair bonds during breeding season, establishing territories where they build nests and raise young. Chicks are born blind and without feathers and require a high level of parental care. Perching birds have a wide variety of bill shapes and sizes, which often reflect a given species' diet. For example, passerines that feed on seeds usually have short, conical bills, while insectivores possess thinner, dagger-like bills. Nectar-feeders like sunbirds have long, thin, downward-curving bills that enable them to extract the nectar from flowers. As with their bills, plumage colors and patterns vary widely among perching birds. Some species are dull in color, while others possess bright, ornamental feathers. In many passerine species, males have vivid plumage, while females display a subdued palette.

23 of 30 Pigeons and Doves (Order Columbiformes) Tom Meaker / EyeEm / Getty Images The bird order Columbiformes includes over 300 species of Old World pigeons, American pigeons, bronzewings, quail-doves, American ground doves, Indo-Pacific ground doves, crowned pigeons, and more. You may be surprised to learn that the words "pigeon" and "dove" are mostly interchangeable, although "pigeon" tends to be used when referring to larger species and "dove" when referring to smaller species. Pigeons and doves are small- to medium-sized birds characterized by their short legs, portly bodies, short necks, and small heads. Their plumage usually consists of various tones of grey and tan, although some species have iridescent swatches of feathers adorning their necks, as well as bars and spots on their wings and tails. Pigeons and doves are equipped with short bills, hard at the tip but softer at the base where the bill meets the naked cere (a waxy structure that covers the portion of the bill closest to the face). Pigeons and doves thrive in grasslands, fields, deserts, agricultural lands, and (as any New York City resident knows) urban areas. They also, to a lesser extent, flock in temperate and tropical woodlands, as well as mangrove forests. The Columbiforme bird with the widest range is the rock dove (Columba livia), the city-dwelling species commonly referred to as the classic "pigeon." Pigeons and doves are monogamous. Pairs often remain together for more than one breeding season. Females usually produce multiple broods each year, and both parents share in the incubation and feeding of young. Columbiformes like to build platform nests, which are assembled out of twigs and occasionally lined with pine needles or other soft materials like root fibers. These nests can be found on the ground, in trees, on bushes or cacti, and on building ledges. Some species even build their nests atop the vacant nests of other birds. Columbiformes usually lay one or two eggs per clutch. The incubation period lasts between 12 and 14 days, depending on species. After hatching, adults feed their chicks crop milk, a liquid produced by the lining of the female's crop that provides necessary fats and proteins. After 10 to 15 days, adults nurture their young with regurgitated seeds and fruit, shortly after which the fledglings leave the nest.

24 of 30 Rheas (Order Rheiformes) Jurgen & Christine Sohns / Getty Images There are only two species of rhea, order Rheiformes, both of which inhabit the deserts, grasslands, and steppes of South America. As is the case with ostriches, the breastbones of rheas lack keels, the bone structures to which flight muscles usually attach. These flightless birds have long, shaggy feathers and three toes on each foot. They're also equipped with a claw on each wing, which they use to defend themselves when threatened. As birds go, rheas are relatively uncommunicative. The chicks peep and the males bellow during mating season, but at other times these birds are unnervingly quiet. Rheas are also polygamous. Males court as many as a dozen females during mating season, but they're also responsible for building the nests (which contain the eggs of various females) and caring for hatchlings. As big as they are—a greater rhea male can attain a height of almost six feet—rheas are mostly vegetarian, though they occasionally supplement their diets with small reptiles and mammals.

25 of 30 Sandgrouses (Order Pteroclidiformes) PHOTOSTOCK-ISRAEL/SCIENCE PHOTO LIBRARY / Getty Images Sandgrouses, order Pteroclidiformes, are medium-sized, terrestrial birds indigenous to Africa, Madagascar, the Middle East, central Asia, India, and the Iberian Peninsula. There are 16 sandgrouse species, including the Tibetan sandgrouse, the pin-tailed sandgrouse, the spotted sandgrouse, the chestnut-bellied sandgrouse, the Madagascar sandgrouse, and the four-banded sandgrouse. Sandgrouses are about the size of pigeons and partridges. They're characterized by their small heads, short necks, feather-covered legs, and rotund bodies. Their tails and wings are long and pointed, well-suited for taking to the air quickly to escape predators. The plumage of sandgrouses has colors and patterns that enable these birds to blend in with their surroundings. The feathers of desert sandgrouses are fawn, gray, or brown in color, while steppe sandgrouses often have striped patterns in orange and brown. Sandgrouses feed primarily on seeds. Some species have specialized diets consisting of seeds from a few specific types of plants, while others occasionally supplement their diets with insects or berries. Since seeds are very low in water content, sandgrouses travel frequently to watering holes in large flocks that number in the thousands. The plumage of grown birds is particularly good at absorbing and holding water, which enables adults to transport water to their chicks.

26 of 30 Shorebirds (Order Charadriiformes) Ed Burns / EyeEm / Getty Images As you can guess from the name, shorebirds live along shores and coastlines. They also frequent a wide range of marine and freshwater wetlands, and some members of the group— gulls, for instance—have expanded their range to include dry inland habitats. This order of birds comprises about 350 species, including sandpipers, plovers, avocets, gulls, terns, auks, skuas, oystercatchers, jacanas, and phalaropes. Shorebirds generally have white, gray, brown, or black plumage. Some species have bright red or yellow feet, as well as red, orange, or yellow bills, eyes, wattles or mouth linings. Shorebirds are accomplished flyers. Some species undertake the longest and most spectacular migrations in the avian kingdom. Arctic terns, for example, fly round-trip each year from the southern waters of the Antarctic, where they spend the winter months, to the northern Arctic, where they breed. Young sooty terns leave their natal colonies and head out to sea, flying almost constantly, and remain there for the first several years of their life before returning to land to mate. Shorebirds subsist on a wide variety of prey, including marine worms, crustaceans, and earthworms. Perhaps surprisingly, they almost never eat fish. Their predatory styles also vary. Plovers forage by running across the open ground and pecking at prey. Sandpipers and woodcocks use their long bills to probe the mud for invertebrates. Avocets and stilts swish their bills back and forth in shallow water. There are three major families of shorebirds: Waders, about 220 species, include sandpipers, lapwings, snipes, plovers, stilts, and various other species. These birds inhabit coasts and shorelines, as well as other open habitats.

Gulls, terns, skuas, jaegers, and skimmers form a group of a little over 100 species. These shorebirds are often recognizable by their long wings and webbed feet.

Auks and their relatives—murres, guillemots, and puffins—account for 23 species of swimming shorebirds. They are often likened to diving petrels and penguins.

27 of 30 Tinamous (Order Tinamiformes) Domini Sherony / Wikimedia Commons Tinamous, order Tinamiformes, are ground-dwelling birds indigenous to Central and South America, comprising about 50 species. In general, tinamous are well-camouflaged, with patterned plumage ranging in color from light to dark brown or gray. This helps them to avoid predators like humans, skunks, foxes, and armadillos. These birds are not particularly enthusiastic fliers, which makes sense. Molecular analysis shows that they're closely related to flightless ratites like emus, moas, and ostriches. Tinamiformes is one of the most ancient bird orders, the earliest fossils dating to the late Paleocene epoch. Tinamous are small, plump, vaguely comical-looking birds that rarely exceed a few pounds in weight. Although they're difficult to see in the wild, they do have distinctive calls, which range from cricket-like chirping to flute-like melodies. These birds are also known for their hygiene. Adults will wash in the rain whenever possible, and enjoy taking numerous dust baths during dry spells.

28 of 30 Trogons and Quetzals (Order Trogoniformes) Bob Gibbons / Getty Images The bird order Trogoniformes includes about 40 species of trogons and quetzals, tropical forest birds indigenous to the Americas, southern Asia, and sub-Saharan Africa. These birds are characterized by their short beaks, rounded wings, and long tails. Many of them are brightly-colored. They feed mostly on insects and fruit, and build their nests in tree cavities or the abandoned burrows of insects. As mysterious as their vaguely alien-sounding names, trogons and quetzals have proven difficult to classify. In the past, naturalists have lumped these birds in with everything from owls to parrots to puffbirds. Recent molecular evidence points to trogons being closely related to mousebirds, order Coliiformes, from which they may have diverged as far back as 50 million years ago. Adding to their allure, trogons and quetzals are rarely seen in the wild and are considered an especially desirable find for ornithologists.

29 of 30 Waterfowl (Order Anseriformes) Tyler Brenot / Wikimedia Commons The bird order Anseriformes includes ducks, geese, swans, and the loud birds known, somewhat unnervingly, as screamers. There are about 150 living waterfowl species. Most prefer freshwater habitats like lakes, streams, and ponds, but some live in marine regions during the non-breeding season. The plumage of these medium-to-large birds usually includes subtle variations of gray, brown, black, or white. Some screamers have ornamental feathers on their heads and necks, while others have brightly-colored patches of blue, green, or copper on their secondary feathers. All waterfowl are equipped with webbed feet, an adaptation that allows them to move through the water more easily. However, you may be surprised to learn that most of these birds are strict vegetarians. Only a few species gorge themselves on insects, mollusks, plankton, fish, and crustaceans. Waterfowl often find themselves on the wrong end of the food chain, not only at the hands of humans who enjoy duck dinners, but also are preyed upon by coyotes, foxes, raccoons, and striped skunks. They also become prey for meat-eating birds like crows, magpies, and owls.