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Our Free Newsletter: The Birder Alert!
Bird characteristics: What makes a bird a bird? Birds
were able to become flying machines largely through the evolutionary gifts of
feathers, powerful wings, hollow bones, warm blood, a remarkable respiratory
system, and a large, strong heart.
These adaptations all boil down to the two prime requirements
for any flying machine: high power and low weight. Let's explore some of these
bird characteristics and bird anatomy:
Bird have descended from bipedal, reptilian-like dinosaurs that lived in the
Jurassic period approximately 150 millions years ago and are scientifically classified as
Kingdom: Animalia Phylum: Chordata Class: Aves
Members of the class
Aves are placed into more than 2 dozen orders, such as the Passeriformes
(perching birds). The orders are divided into approximately 160 families which can be
recognized by the ending of "idae" such
as Turdidae, the Thrush family, which includes robins, thrushes, and
The next 2 groups,
genus and species are combined to give the bird's scientific name. No other
creature in the animal world may share that combination of names.
Each genus is made
up of the species considered most closely related; all members of a genus are
descended from a shared ancestral species. The name of the genus is capitalized,
the name of the species is not, and both are italicized.
Thus, the classification of the American Robin is as follows:
In order to meet the rigorous demands for air consumption that
intense living, flight, and song impose on them, birds must have ample and
efficient breathing machinery.
Not only is their respiratory system the most efficient known
among all vertebrates, but it is unique in basic structure.
Humans and other mammals breathe by means of a cul-de-sac
respiratory system in which inhaled fresh air is mixed with residual stale air
remaining in the dead-end alveoli of the lungs, which can never be completely
Birds, on the contrary, have a complex weight-reducing system of
air sacs and interconnecting tubes that make possible a more thorough bathing of
the lung cells with fresh air. This is a very unique bird characteristic.
To help supply heavy oxygen demands, the lungs are supplemented by a series of
air sacs that let the bird inhale more air than the lungs can hold at one time.
These air sacs fill all the available spaces within the body cavity and also
contribute to the bird's lightness.
The size and number
of air sacs depend on how much buoyancy a bird requires for flight.
Soaring species have air sacs extending to their hollow bones, others have a
series of small air sacs paralleling the trachea.
diving birds use the reserve air in the sacs while submerged, but deep divers
have reduced air sacs to eliminate buoyancy.
Vision is the bird's most highly developed sense. Unlike most
animals, they see in color. Birds can distinguish objects much farther away than
can humans, and their vision is in fact the most highly developed of any animal.
Birds have big eyes. Hawks, eagles, and owls often
have eyes actually larger than human's.
A human eye weighs less than 1% of the weight of the head, whereas a
starling's eye accounts for some 15% of its head weight. A unique bird
The value of the large size is, of course, that it provides larger and
sharper images - most valuable qualities for rapidly moving animals.
The position of the eyes in a bird's head show close correlation
with its life habits.
At one extreme, the mud-probing American Woodcock has eyes set
high and back on the head, out of the way of vegetation and splattering mud.
This position is also effective from preventing surprise attacks from behind.
Because of the location of the eyes, the Woodcock has more
effective binocular vision of objects to the rear than of objects in front of
The eyes of hawks and other predators are directed more toward
the front, since they usually pursue prey in front of them.
Owls nearly match
man with their frontal eyes, but unlike human's their eyes are almost immovably
locked in their sockets. In compensation for this rigidity, they have flexible
necks that allow them to twist their heads at least 270
The rear wall of a bird's eye is densely lined
with a sensory receptor layer of rods and cones that form the retina, the
surface on which images are formed.
The rods are sensitive to light, especially at low
intensities; the more rods it has, the better a bird is able to see at dusk or
Birds that are nocturnal (active during the
night), such as owls and goatsuckers, have more rods than cones. Remember, Cones
The cones function in bright light to form sharp
images and distinguish shades of color. So cones are more numerous than rods in
the retinas of diurnal (active during the day) birds.
After all, why would birds have all those pretty-colored plumages if they only
could see black & white Well like a black skimmer, we've just skimmed the
surface of bird characteristics, but hope this has sparked an interest to learn
more about the fascinating world of birds. Enjoy!
Note on above books:
I personally know Stephen Kress (one of the Backyard Birdwatcher authors)
and his books are always full of useful information. This one has become a
favorite among birders of all levels. But any of the books listed above would
make a good resource for learning about birds and attracting them to your