Flight, the major avian adaptation, is thought to have contributed to birdsí rapid speciation and successful adaptations to habitats world wide. Class Aves includes more than 8500 species of birds and is divided into two superorders, the Palaeognathae (e.g., ratites and tinamous) and the Neognathae (e.g., all other modern birds). Classification of birds is fluid. Bird life spans vary from the maximal life span of 1.5 years in the Greater Prairie Chicken (ref. Tymphanuchus cupido) to the 58 year life span of the RoyalAlbatross (Diomedea chrysostoma. The vast majority of birds are socially monogamous and a sizable subset maintain pair bonds over many annual reproductive attempts.
STRUTHIONIFORMES (ostriches, emus, cassowaries, kiwis)
Struthioniformes include the ostrich of Africa as well as emus, cassowaries and kiwis. Struthioniformes arose in the Miocene, late in the evolution of most modern birds (Proctor and Lynch 1993). With some weighing in excess of 150 kilograms and standing over two meters, Struthioniformes are the largest living birds (Pettingill 1985, Welty 1982). Unique features include a flat sternum, heavily-muscled legs, and two to four short toes. Birds of this order have sparse feathering on the head, neck, or legs and relatively small brains. They hatch precocial young from eggs which weigh roughly three pounds, measure 7 by 5.5 inches, and comprise 1.7 percent of the adultís body weight (Pettingill 1985: 295). Ostriches are polygynous (e.g., males mate with two or more females), a characteristic which has been positively associated with birds living in open habitats (Verner 1964).
Kiwis are flightless, terrestrial birds with four toes and hair-like feathers. Kiwis (as well as some sea birds and nocturnal birds of prey) have a higher body temperature at night than that during the day (Gill 1995) and experience greater body temperature fluctuations and lower resting temperatures than other birds. Kiwis have a superior sense of smell which may be attributable to their elongated bill with nostrils at the tip, large nasal cavities, and mammal-like olfactory system (Pettingill 1985:104). Kiwi eggs are large relative to total body mass; egg mass is approximately a quarter of the birdís total body weight (Pettingill 1985, 295). The Brown Kiwiís 75-80 day incubation is one of the longest incubation periods among birds (Frith 1962).
The two species of rheas are flightless and distributed through the neotropics. The earliest fossil record for Rheiformes appeared in the Eocene epoch (37 to 53 million years ago, Proctor and Lynch 1993). Like the Struthioniformes, rheas have a flat sternum, heavy legs, and precocial young. However, they are smaller (1.5 meters) and originated in South America.
Tinamous are distributed throughout the Neotropics, and include 47 species in 9 genera. The earliest tinamous appeared in the Pliocene epoch between two and several million years ago (Proctor and Lynch 1993). Tinamiformes are poor fliers though they have functional wings. The young are precocial (Gill 1995:619). Unique to Tinamiformes and ratites (Rheiformes, Struthioniformes, Casuariiformes, and Dinornithiformes) is a configuration of nasal bones known as the paleognathous palate. The Solitary Tinamou has lived for as long as 15 years in captivity.
There are 17 species in one family of penguins found between the Southern Hemisphere and the Galapagos Islands. They are piscivorous marine divers with webbed feet and modified wings for swimming (Welty 1985). Sphenisciformes are characterized by a large keel and small, dense, waterproof feathers. They lack brood patches, and instead monogamous pairs incubate 1 to 2 eggs (and subsequently brood young) on top of their feet (Gill 1995:392, 625). Penguins are thought to have evolved from Procellariform-like birds with whom they share tubular nostril construction (Simpson 1946, Sibley and Ahlquist 1990, Ho et al. 1976), and similar courting and feeding behaviors (Gill 1995:625).
The four species of loons can be found in North America and Eurasia. They breed along lakes and rivers and winter along the coast. Loons are webbed-toed divers with short legs well back near the tail. Loons dive to depths of 75 meters for periods up to 8 minutes at a time to forage for fish, frogs, and aquatic invertebrates (Gill 1995:649). Gaviiformes are perenially monogamous and produce small broods of precocial young after 3 to 4 weeks of incubation (Gill 1995:649).
Twenty-one extant species of grebes inhabit lakes, ponds, and marshes (Udvardy and Farrand 1994). They are an old order (approximately 70 million years). They are pandemic, medium-sized diving birds with short, posterior-positioned legs and lobed toes adapted for swimming but resulting in limited land movement. Feeding on fish, insects and other aquatic animals, grebes digest their own feathers to trap fish bones for later regurgitation or delayed digestion (Gill 1995:623). Grebes build platform nests over water using aquatic weeds. They winter along coastlines. Most grebes are black and white with little sexual dimorphism.
PROCELLARIIFORMES (tube-nosed sea birds)
Procellariiformes (albatrosses, shearwaters and petrels) are distributed worldwide. Some of the oldest fossils date back more than 65 million years (Proctor and Lynch 1993). These birds have tubular nostrils and a keen sense of smell, a hooked beak, oily feathers, long narrow wings, and webbed feet (Gill 1995:627; Udvardy and Farrand 1994). They vary in size from the six inch Least Storm Petrel to the Wandering Albatross with an almost twelve foot wingspan (Gill 1995:627). The typically grey, black, brown, and white-colored Procellariiformes are particularly noteworthy for their near-effortless ability to soar for long periods of time.
Residing in the oceans for most of the non-breeding season, most Procellariiformes are perennially monogamous. Procellariiformes feed on marine animals (e.g., fish, squid, crustaceans) or plankton on the surface of the water. Shearwaters and Petrels live on the oceans during the non-breeding season, breed on islands and coastlines, and often winter in North America (Udvardy and Farrand 1994). Some are sexually dimorphic and breed in burrows along the coast and on islands (Gill 1995:627; Udvardy and Farrand 1994). Most Petrel pair bondings last for one season (65%), with 58% of bonds attributable to loss of a partner (Warham 1990, 204). Divorces appear to be rare among petrels.
Most albatrosses breed on pelagic island beaches or along remote coastal regions. They are perennially monogamous and lay one egg per clutch. Incubation and fledging take 190 to 365 days; species with the longest nestling periods reproduce only every other year or less. Age-dependent reproductive rate of sea birds increases with age (Wooller et al. 1992), while death rates may not rise geometrically over time.
PELECANIFORMES (pelicans, gannets, and cormorants)
Pelecaniformes include pelicans (8 species), tropicbirds (3 species), boobies and gannets (9 species), cormorants (38 species), frigatebirds (5 species), and snakebirds (4 species). Fossil records indicate that pelicans first appeared 26 to 37 million years ago (Proctor and Lynch 1993). The order is primarily distributed through the Tropics and Subtropics world-wide. Most Pelecaniformes are medium to large bodied, fish and squid-eating birds. They have webbed feet with four toes, a long bill, poorly or undeveloped nostrils, and a gular sac (throat pouch). Cormorants, boobies, and gannets lack external nostril openings and breathe through the mouth (Gill 1995:629). Feeding techniques vary from diving and piercing or pursuing fish in the water, to air-borne diving and scooping activities. With the exception of tropicbirds, Pelecaniformes are born without down. Monogamous pairs nest in colonies on the ground, on cliffs, or in trees, laying one to three eggs per clutch.
CICONIIFORMES (wading birds, herons and storks)
Ciconiiformes includes 6 families with 119 species of herons, egrets, bitterns, storks, ibises, spoonbills, and flamingos. Storks first appeared 37 to 53 million years ago, while ibises and herons first 53 to 65 million years ago (Proctor and Lynch 1993). Stork habitats include tropical and temperate marshes of Eurasia (Udvardy and Farrand 1994). Sixty-five species of medium-sized bitterns and herons are found worldwide. Unique to Herons and Shoebills are powderdowns, disintegrating feathers which condition the remainder of their plumage, and unique to Ibises and Shoebills are grooves on the bill which run from the nostril to the bill tip (Gill 1995:635).
Ranging in size from the foot-tall Least Bitterns to the five foot Goliath Herons, Ciconiiformes are waders with long necks, long legs, and (except for Flamingos) un-webbed toes. They feed predominantly on fish, frogs and aquatic or terrestrial invertebrates. Nesting singly or in colonies, Ciconiiformes build stick nests in marshes or along shores (Welty 1984); however, storks, herons, and ibises build their nests in trees and bushes (Udvardy and Farrand 1994) and sometimes rooftops.
ANSERIFORMES (ducks, geese and swans)
Anseriformes includes over 160 species in four families, the Anatidae (swans, geese and typical ducks), Dendrocygnidae (Whistling ducks), Anseranatidae (Magpie goose), and Anhimidae (screamers). Anseriformes are relatively modern, having appeared 26 to 37 million years ago (Gill 1995:Proctor and Lynch 1993). Characteristics common to this order include depressed bills with filtering "teeth" for surface feeders and stronger, broader bills for deeper divers. All have short legs, webbed feet, oily feathers, unspotted eggs and hatch downy, precocial chicks. While most waterfowl are monogamous, male Anseriformes do not assist in chick-rearing (Gill 1995:631). Geese and swans are sexually monomorphic and perennially monogamous while ducks are sexually dichromatic and seasonally monogamous. The young of some geese remain with the parents for two years resulting in overlapping broods.
Although most Anseriformes are aquatic, geese forage primarily in terrestrial habitat (Evardy, 1994) while ducks forage primarily in water. Across the species, diets include plant parts as well as insects, fish, and snails and other aquatic invertebrates. Body lengths range from 12 to 72 inches (Pettingill 1985). Anseriformes may be related to the early sea birds or to Galliformes (Johnsgard 1968, Prager and Wilson 1976).
FALCONIFORMES (birds of prey)
The predatory Falconiformes include the diurnal vultures, eagles, hawks, kites, harriers, osprey, caracaras, and falcons. Wingspans range from 13 centimeters in the Philippine Falconet to 3 meters in the Andean Condor (Gill 1995:637). Eagles and hawks appear to have evolved during the Eocene, while falcons appeared in fossil record more recently during the Miocene (Proctor and Lynch 1993). This order is characterized by strong, sharp, hooked beaks with a fleshy cere at the bill base and sharply-pointed talons. Reversed sexual dimorphism (females larger than males) is common. Most Falconiformes breed in trees; they lay three to five eggs per clutch (fewer in larger species) and hatch downy young whose eyes are already open. After leaving the nest, young continue to receive food from parents for some months (Gill 1995:637).
Accipitridae includes 240 species of hawks and eagles distributed worldwide. These raptors generally take ground or aquatic prey and build nests in trees or on pinnacles. The Falconidae include 63 species of falcons and caracaras that inhabit open country and take prey on the wing. Falcons nest in cliff crevices, hollow trees, and on the ground. Recent analysis confirms the monophyly of Falconiformes (Griffiths 1994) although some researchers speculate that New World vultures are more closely related to the Ciconiiformes (Ligon 1967, Sibley and Ahlquist 1990).
GALLIFORMES (fowl-like birds, gallinaceous birds)
There are 263 species of Galliformes in six families. They are found world-wide (except Antarctica and southern South America). Galliformes include curassows, grouse, ptarmigan, quails, partridge, pheasants, peafowl, and turkeys. Galliformes are strong runners with heavy feet and strong breast muscles. They nest on the ground and are subject to high rates of predation They are herbivorous and insectivorous, often gregarious, and nest on the ground. Their precocial young are commonly hatched in large clutches that band into larger groups. Most species are polygynous (some form mating leks) and exhibit both body size and chromatic sexual dimorphism.
GRUIFORMES (cranes, rails, and coots)
The order Gruiformes includes 14 families with 170 species of prairie and marsh-dwelling birds, of which 80% are rails and coots. They date back 37 to 53 million years (Proctor and Lynch 1993). Gruiformes lack a crop, and possess short, rounded wings. Birds of this order are terrestrial, aquatic, or marsh-dwelling, and most have slightly-webbed or unwebbed toes. With the exception of the cranes and bustards, the young tend to be precocial. Some members of this order are polyandrous (females compete for and mate with many males).
Rails have laterally compressed bodies adept for movement among reeds and cattails, and large feet with long toes. Coots are adept open-water swimmers with lobed feet. Gallinules are more brightly colored than the more cryptic rails and coots (Udvardy and Farrand 1994).
CHARADRIIFORMES (shorebirds and gulls)
Order Charadriiformes is comprised of 18 families (more than 300 species) of shore birds, such as oystercatchers, plovers, snipes, sandpipers, avocets, gulls, terns, and auks. This group is sometimes included as a suborder of the Ciconiiformes (Sibley and Ahlquist 1990) but we consider them separately. Shorebirds are an old group, dating back more than 65 million years (Proctor and Lynch 1993). The toes of these birds are often webbed, their plumage compact, and they tend to be strong fliers. Dietary habits of Charadriiformes range from probing and plucking insects from mud, scavenging on shorelines, skimming the oceans, and stealing food from other birds, to deeper diving activities in search of marine fish. Many species are gregarious, however nesting is established singly and on the ground. Young are precocial.
More gulls than terns may be found in cooler climates (Udvardy and Farrand 1994). Terns which primarily feed on fish are often characterized with black caps and straight bills while gulls may be characterized with slightly hooked bills, semi-precocial young, and white, black, and grey markings.
COLUMBIFORMES (pigeons and doves)
Worldwide, Columbiformes include more than 300 small, medium, and large size pigeon and dove species as well as the extinct dodo. Columbiformes have narrow bills, cere at the base of the bill, short legs with reticular scales, small neck, and a small head. Adults lay clutches of two eggs from which altricial young are hatched. Columbiformes young are fed a rich substance produced from the lining of the crop known as "pigeon milk" (Welty 1985) by both males and females. Pigeons are unique in their ability to drink water by sucking rather than tilting and tossing water back with their heads (Gill 1995:651).
Psittaciformes includes approximately 350 species of tropical parrots, macaws, and lories and comprises the most endangered group with high rates of threatened species (Gill 1995:653). Psittaciformes are characterized by a strong, narrow, hooked beak, an upper mandible which is hinged movably to the skill, and green, colorful, or black plumage. Size varies from 7 to 90 centimeters, their tongues are fleshy, and their toes are positioned two in the front and two in the back. Parrots and macaws are predisposed to nesting in holes, and are gregarious.
Cuculiformes encompasses two families -- Musophagidae (Turacos) and Cuculidae (cuckoos and roadrunners) that are mostly native to the tropics. Members of Family Cuculidae include cuckoos, coucals, roadrunners, and anises. Old World cuckoos are brood parasites Ė laying their eggs in the nests of other birds. American cuckoos lay eggs in their own nests (Udvardy and Farrand 1994). Cuculiformes date from 26 to 37 million years ago (Proctor and Lynch 1993). This order is not closely related to any other extant order.
Strigiformes include over 140 species of effective, silent, nocturnal predators. They have large more forward facing eyes and bony plates of cylindrical construction useful for telescopic vision (Gill 1995:661). In addition to keen hearing, owls have facial feather plates that amplify sound. Soft, dense plumage allows for silent flight. With strong hooked beaks, strong feet, sharp talons, and feathered legs, owls feed mainly on small rodents and shrews as well as on insects, frogs, fish, reptiles, and other birds (Gill 1995:661). Generally, owls use abandoned nests of other birds, burrows, or natural cavities, laying clutch sizes according to resource availability. Strigiformes is one of the older orders with origins between 53 and 65 million years ago (Proctor and Lynch 1993).
CAPRIMULGIFORMES (nightjars and goatsuckers)
There are 98 species of Caprimulgiformes in five families including Nightjars, Oilbirds, and Goatsuckers. They are small to medium sized insectivores. The wide mouths of Caprimulgiformes have insect-netting bristles which improve their ability to successfully hunt for insects at twilight and which protect their eyes from damage related to in-flight insect collisions. They lay one or two eggs directly onto the ground, into tree crevices, or on cave ledges (Gill 1995:663).
APODIFORMES (swifts and hummingbirds)
There are two families of Apodiformes, the Hemiprocnidae (swifts) and the Trochilidae (hummingbirds). Apodiformes have pointed wings, short thick humeri, and unfeathered oilgland, and lack of a crop in adults. The Trochilidae include more than 100 species of hummingbirds that range from 2 to 20 grams and are sexually dichromatic with brilliant, often iridescent, plumage. They are primarily nectivores with some insectivory and are able to torpor. Hummingbirds are polygynous New World birds and females raise their young without paternal assistance. The 74 species of swifts range from 9 to 150 grams and are not sexually dimorphic. They catch insects on the wing and some may echolocate. This order may be paraphyletic (Sibley and Ahlquist 1990).
Coliidae, the one family of Coliiformes includes six species of mousebirds and colies all native to sub-Saharan Africa. Coliiformes originated 7 to 26 million years ago (Proctor and Lynch 1993).
The characteristically gregarious Coliiformes are small birds with crests, long tails, and opposable first and fourth toes which are used for climbing through brush. They build platform-like nests in their savannah, woodland, and brushy habitats, and feed on fruits, berries, buds and flowers (Gill 1995:655). Clutches of 2 to 4 eggs are incubated, at least in some species, by both sexes. Young hatch naked and altricial.
There are 34 species in the two families of Trogoniformes. All trogons are tropical and subtropical. They have short broad bills and wings, weak feet with the first two toes pointed backward and the third and fourth toes pointed forward, long tails, and iridescent, dense and typically green plumage. Trogoniformes feed on insects and fruit. They nest in cavities where they hatch blind and naked chicks (Gill 1995:667). They may be distantly related to Coraciiformes (Maurer and Raikow 1981, Sibley and Ahlquist 1990).
CORACIIFORMES (kingfishers, rollers, bee-eaters, hoopoes)
Nine families of small to medium sized birds comprise the Coraciiformes. There are 94 species of kingfishers (Alcedinidae), twelve rollers (Coraciidae), 26 bee-eaters (Meropidae), and 56 species of hornbills (Bucerotidae) in this order that originated 53 to 65 million years ago (Proctor and Lynch 1993). Coraciiformes have a strong bill, toes with the third and fourth toes joined at the base, and brightly colored plumage. Their omnivorous diet includes fruits, arthropods, fish and invertebrate aquatic life, and worms. They hunt using several strategies (e.g., sit and wait, probing into crevices , and feeding in flight). These birds nest in cavities, raising altricial young. Social organization varies from perenially monogamous (hornbills) to seasonal monogamy (kingfishers) to cooperative-breeding (kookaburras, bee-eaters, southern hornbills). Coraciiformes may not be monophyletic (Cracraft 1981; Maurer and Raikow 1981).
PICIFORMES (woodpeckers, toucans, jacamars and puffbirds)
Piciformes are comprised of the tropical and subtropical toucans, honeguides, and barbets (Ramphastidae, Indicatoridae, and Capitonidae), the tropical, subtropical, and temperate woodpeckers (Picidae), and neotropical, jacamars and puffbirds (Galbulidae, Bucconidae). Piciformes have highly specialized bills for feeding on foods such as worms, caterpillars, and insects found beneath the bark or in seeds of trees; however, Toucans also eat the eggs and young of other birds. Stiffened tail feathers facilitate upright perching on tree trunks and branches (Gill 1995:671). Little sexual dimorphism is apparent in the Piciformes; they nest in cavities or holes and bear altricial young. Monogamy and biparental care is common, however, some species are cooperative breeders (aracaris) and some are nest parasites (honeyguides).
PASSERIFORMES (perching or song birds)
Fifty percent of 9672 known bird species are Passeriformes. Due to convergent evolution, subdivision of the order into smaller groups is difficult. Using DNA comparisons and the same criteria as used with non-passerines, Sibley and Ahlquist (1990) divided Passeriformes into 45 families. Passeriform feet are adapted to perching. These birds have relatively large brains and exhibit high capacity for learning vocalizations (Gill 1995:675). With a few exceptions, Passeriformes feed on seeds, fruit or nectar, or insects. All forms of mating system and social organization are found; however, in all, young are altricial. Crows and jays are evidenced in fossil records as of the Miocene Period while sparrows, swallows, and nuthatches appeared more recently (Proctor and Lynch 1993).
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