The
Diversity of The World of Life
Higher
Reptiles & Their Descendants (Diapsida)
Birds
(Aves)
Biology
Representatives
Archaeopteryx
True
Birds (Euornithes)
Hesperornis
etc. (Hesperornithiformes)
Ichthyornis (Ichthyornithiformes)
Modern
Birds (Neornithes)
Modern
Birds with a Reptilian Palate
(Palaeognathae)
Tinamous (Tinamiformes)
Rheas
(Rheiformes)
Ostrich
(Struthioniformes)
Emus &
Cassowaries
(Casuariformes)
Elephant
Birds (Aepyornithiformes)
Moas
(Dinornithiformes)
Kiwis
(Apterygiformes)
Modern
Birds with a Less Reptilian Palate (Neognathae)
Grebes
(Podicipediformes)
Penguins
(Sphenisciformes)
Albatrosses,
Storm-Petrels,
etc. (Procellariiformes)
Tropicbirds,
Frigatebirds,
Boobies,
Cormorants,
Pelicans,
etc. (Pelecaniformes)
Waterfowl: Ducks, Geese, Swans, etc.
(Anseriformes)
Flamingos
(Phoenicopteriformes)
Herons, Bitterns,
Ibises,
Spoonbills, & Storks
(Ciconiiformes)
New
World Vultures
(including Condors), Osprey,
Hawks,
Eagles,
Secretarybird,
Falcons,
etc. (Falconiformes)
Fowl: Guineafowl, Peafowl,
Pheasants, Turkeys, Chickens,
Grouse, Quail, Partridge, etc. (Galliformes)
Marsh Birds etc.: Crakes, Rails, Coots,
Gallinules,
Cranes,
Limpkin,
Bustards,
etc. (Gruiformes)
Shorebirds
etc.: Painted
Snipes, Sandpipers,
Curlews,
Woodcocks,
Oystercatchers,
Avocets,
Stilts, Coursers,
Plovers,
Lapwings, Gulls,
Terns, Skimmers,
Auks,
Puffins,
etc. (Charadriiformes)
Loons
etc. (Gaviiformes)
Pigeons & Doves
(Columbiformes)
Parrots,
Macaws, Parakeets, Cockatoos,
& Lories
(Psittaciformes)
Mousebirds, or Colies
(Coliiformes)
Cuckoos,
Roadrunners, etc. (Cuculiformes)
Barn
Owls & Typical
Owls (Strigiformes)
Frogmouths,
Potoos,
Nightjars,
Whippoorwills, etc.
(Caprimulgiformes)
Swifts,
Hummingbirds,
etc. (Apodiformes)
Trogons
& Quetzals (Trogoniformes)
Kingfishers,
Kookaburras, Bee-Eaters,
Hoopoe,
Hornbills,
etc. (Coraciiformes)
Jacamars,
Honeyguides,
Woodpeckers,
Flickers, Barbets,
Toucans, etc.
(Piciformes)
Perching Birds & Songbirds: Woodcreepers,
Antbirds,
Antshrikes,
Antwrens, Antvireos, Gnateaters,
Lyrebirds,
Bowerbirds,
Honeyeaters,
Shrikes,
Vireos,
Crows,
Ravens,
Jays,
Magpies, Birds-of-Paradise,
Butcherbirds,
Drongos,
Waxwings,
Thrushes,
Robins, Old
World Flycatchers,
Starlings,
Mynahs, Oxpeckers, Mockingbirds,
Catbirds,
Nuthatches,
Creepers,
Wrens,
Gnatcatchers,
Tits,
Titmice,
Chickadees,
Swallows,
Martins, Bulbuls,
African
Warblers,
Old
World Warblers, Larks,
Old
World Sparrows, House
Sparrow,
Wagtails,
Weavers,
Goldfinches,
House Finch,
New
World Sparrows, Towhees, Old World Buntings,
Tanagers,
Honeycreepers, Cardinals,
Orioles,
Blackbirds,
Grackles,
Cowbirds, etc. (Passeriformes)
Biology
APPROXIMATE NUMBER OF KNOWN SPECIES WORLDWIDE
9,000
ENVIRONMENTS
Marine, freshwater, terrestrial, and aerial! As you
will read, birds have many adaptations for flight (in addition to wings).
DESCRIPTION
Archaeopteryx (extinct) had bird-like feathers but
toothed, reptilian jaws; a long tail; and separate fingers, each with claws.
Ironically, although birds undoubtedly evolved from reptiles, the most likely ancestor of birds was not a
"bird-hipped" dinosaur (such as a stegosaur) but rather a
"lizard-hipped" dinosaur, probably a "theropod" (a
carnivorous lizard-hipped dinosaur that ran on its hindlegs), such as a little cousin of
T. rex.
Other theories hold that birds evolved earlier in prehistory, not
from a dinosaur but rather from a more primitive reptile, perhaps a common
ancestor to crocodilians.
Modern birds exhibit evidence of a reptilian
ancestry. The hind legs of a bird, with claws on the toes, are
typically covered with reptilian scales and the rest of the body is
typically covered with feathers (evolved from reptilian scales).
The fore legs of a bird are typically modified into "airfoil" wings (each
including three fused fingers). There is a stout "keel" on the breastbone (to which the flight
muscles are attached). The
bones are very strong and hollow (and, thus, lightweight), sometimes
internally "trussed" (reinforced with criss-crossed bracing,
like inside an airplane wing).
The
mouth bears a tongue and jaws but no teeth -- instead, there is a horny
beak. The eyes bear lids and
tear glands. There is
typically a well-developed neck (useful in preening feathers) and a short
tail (modified for flight).
Primitive modern birds (such as ostriches) have a reptilian
"palate" (roof of the mouth), usually no powers of flight, and
an often large body; whereas advanced modern birds (typical birds) have a
less reptilian palate, usually good powers of flight, and a usually smaller size.
However, birds are no smaller than the smallest hummingbird:
If these warm-blooded creatures (See below) were any smaller, they
would lose precious body heat more quickly than they could re-generate it (hence,
hummingbirds, like shrews, have a very rapid metabolism -- constantly replenishing lost body heat
-- and a very anti-social nature -- each bird protecting a territory
with vital supplies of nectar etc.).
FEEDING HABITS
Scavenging, filter-feeding (ex. flamingos), herbivorous,
carnivorous, and even parasitic (Cuckoos, for example, are "nest
parasites": They lay their eggs in the nests of other birds;
their hatchlings do away with the other eggs or hatchlings; and the bird(s)
who built the nest then raise the young of the cuckoo, not realizing it is
not their own).
MOTION
The wings of birds evolved from the front legs of their reptilian ancestors.
The wing of a bird is supported by three fused fingers and is covered by numerous
lightweight feathers (whose "barbs" on the central shaft are easily
preened back into shape if
disturbed). The basic shape
of the wing of a bird is that of an "airfoil" (a design copied
by the Wright Brothers): The
wing is basically curved on top (and thick in front and thin in back, to
reduce drag). With its
lightweight, hollow bones and its strong flight muscles attached to the
stout "keel" of its breastbone, a bird typically flaps its wings
forwards through the air (something like a person rowing a boat through
the water); and as
it does so, air that travels over the upper, curved surface of the wing
covers a greater distance than air flowing straight under the lower
surface of the wing: The air
above the wing is in effect "thinned out" relative to the air under the
wing -- the air pressure above the wing is less than the air pressure
under the wing -- so the
wing (and the rest of the bird) is lifted upwards, into the sky.
The tail acts like a balance and a rudder.
Because the shape of the wing and the tail and their "angle of
attack" into the wind can be changed, birds -- from soarers to
flappers -- are more aerobatic than any aircraft ever made by us human
beings.
The wings of penguins have been modified from flying
structures to swimming flippers. The
feet of many waterfowl are webbed, for paddling (In addition, waterfowl
have an especially well-developed oil gland, near
the tail, for waterproofing their feathers).
The feet of various other birds are adapted for perching, for
seizing prey, for scratching, for kicking, etc.
Because a bird typically supports its entire weight on its
rear legs when not flying (and especially when landing), the
"pelvis" (hip region) and the bones in the hind legs of a bird are
typically very strong (like those of its presumably "bipedal"
reptilian ancestors).
DIGESTION
With no teeth, birds typically have beaks that are highly
adapted to their various foods. For
example, seed-eaters have stout beaks; flamingoes have filtering beaks;
hummingbirds have tubular beaks, able to reach deep within flowers to the
nectaries; and birds of prey have very strong and sharp beaks.
The gut of a bird usually includes a "crop",
which stores foods, and a "gizzard", which has strong, horny walls and often contains stones,
consumed by the bird, that grind-up foodstuffs. Because
flight requires much power, the gut of a bird is very efficient; and birds
typically eat high-energy foods, such as insects, fruits, or seeds,
instead of low-calorie grasses or leaves.
RESPIRATION
Many air sacs extend from the lungs of a bird throughout
its body, even into the hollow bones; inhalation and exhalation move air
through this complex respiratory system very efficiently (Some birds can
even fly at very high altitudes, where the air is very "thin") --
flight is a very powerful activity, consuming much oxygen.
Song birds sing by vibrations lower in the throat than the
voice box in humans.
CIRCULATION
Birds have a heart with four chambers -- two "atria"
(one receiving blood from the veins, the other receiving blood from the
lungs) and two "ventricles" (one pumping blood to the lungs, the
other pumping blood out into the arteries) -- there is no inefficient
mixing of "oxygenated" and "deoxygenated" blood, as in
fish, amphibians, and most reptiles.
Birds that fly require the rapid circulation of relatively large volumes
of blood (carrying food and oxygen into
tissues and wastes out of them); they have a very rapid heartbeat and a relatively high
blood pressure.
Birds are "endothermic" (so-called
"warm-blooded") -- biochemical reactions release heat, carried
by the blood throughout the tissues, resulting in a relatively high and
constant temperature within the body (which is insulated with feathers, especially
fuzzy "down"), thus helping to maintain their "high
metabolic rates" (relatively active lifestyles).
Birds sometimes cool down by panting (like dogs)
"Migrating" birds fly to warmer regions, nearer the equator,
before winter arrives, and to more temperate (or polar) regions, with longer daylight hours (and thus longer
food-growing hours), in spring and summer.
EXCRETION
Nitrogen-rich and other wastes (as in our urine) are very
efficiently cleansed from the blood of a bird by a great many tubules within a pair
of kidneys and are excreted (although not through a heavy urinary bladder)
into a "cloaca" chamber, which also receives digestive wastes
and opens as the anus.
Excess
nitrogen in birds is typically excreted as "uric acid", which is
relatively insoluble in water (an advantage within the egg).
Terrestrial vertebrates typically secrete less precious
water from their kidneys than do aquatic species.
Sea birds typically excrete excess salt
through their nostrils.
COORDINATION
The growth, development, and behavior of birds is under
genetic and hormonal control, influenced by the environment. In
particular, seasonal
changes in the environment typically trigger hormonal changes, bringing
about such activities as migration or breeding.
Birds typically have relatively large brain, although their
higher thought processes are usually not well developed: The
"brain power"of birds is typically devoted to the complex
coordination required for flight (and the considerable powers of navigation
for migrating species).
Typically flying high in the air (above the vegetation, etc. on the
ground below), birds typically have a poor sense of smell but great powers of
sight.
Songbirds produce and recognize the calls of potential mates
-- experiments have shown that in at least some species this ability is
learned to a great extent while a young bird listens to older birds sing.
The colorful feathers of birds often serve to visually
identify potential mates. Female birds, however, sit on nests more
often and
thus tend to be more camouflaged and less colorfully feathered than the males
of their species (For example, the peacock is striking; the peahen is
drab).
The sociable flocks of "birds of a feather" help improve
contacts for mating, and
the "courts" of crows often "verbally" scold and at
least temporarily banish members of the group who are "found
guilty" of engaging in anti-social behavior (Crows have relatively
high intelligence).
REPRODUCTION
Birds reproduce sexually, with the sexes separate; and as
at least originally terrestrial vertebrates, they "copulate" (mate with physical
contact). Birds
often have complex mating rituals, often involving elaborate,
species-specific dances, to go with their often species- and sex-specific
plumage.
The fertilized eggs of birds are
typically hard-shelled and laid in terrestrial environments -- the developing
"embryo" within is bathed and cushioned by an "amniotic
sac", fed from a "yolk sac", and "oxygenated" by
an "allantois" membrane. Typically,
birds keep their eggs and hatchlings warm, by sitting upon them in
specially constructed nests.
After the breeding season, adult birds typically "molt" their feathers,
although not all at once (they can usually continue to fly until they grow
a new set).
Representatives
Higher
Reptiles & Their Descendants (Diapsida)
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