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Species
Almost every structure in a bird's body is changed in some way that enhances flight. The bones are honey-combed - strong but light. Another adaptation reducing the weight of birds is the absence of some organs. Females, for instance, have only one ovary.
Birds are toothless, an adaptation that trims the weight of the
head. Food is not chewed in the mouth but ground in the gizzard,
a digestive organ near the stomach. The bird's beak, made of keratin,
has proven to be easily modified during evolution, taking
on a great variety of shapes suitable for different diets.
Flight and Sight
Flying requires great expenditure of energy from an active metabolism.
Birds are endothermic; they use their own metabolic heat to maintain
a warm, constant body temperature, aided by insulation provided
by feathers and a layer of fat.
An efficient circulatory system with a four-chambered heart that
segregates oxygenated blood from oxygen-poor blood supports the
high metabolic rate of the bird's cells. The efficient lungs have
tiny tubes leading to air sacs that help dissipate heat and contribute
to the trimming of density.
For safe flight, senses, especially vision, must be acute. Birds
have excellent eyes, perhaps the best of all vertebrates. The
visual areas of the brain are well developed, as are the motor
areas; flight also requires fine coordination.
Reproduction
With brains proportionately larger than those of reptiles and
amphibians, birds generally display more complex behaviour. Avian
behaviour is particularly intricate during breeding season when
birds engage in elaborate ritual courtship.
Since eggs are shelled when laid, fertilization must be internal.
The act of copulation is somewhat awkward because the male of
most bird species has no penis. He must climb atop the female's
back and then twist her tail so the mates' vents, the openings
to their cloacas, can come together. After eggs are laid, the
avian embryo must be kept warm through brooding by the mother,
father, or both, depending on their species.
What Makes a Bird: Feathers and Wings
The bird's most obvious adaptation for flight is its wings, Their
shape conforms to the same principles of aerodynamics as the wings
of an airplane, but the avian wings must provide propulsion as
well as lift.
The combination of extreme lightness and strength make feathers
one of the most remarkable vertebrate adaptations. Feathers are
made of keratin, the same protein that forms our hair and fingernails
and the scales of reptiles. In fact, feathers evolved from reptilian
scales. Only birds have feathers. Indeed, the presence of feathers
is enough to classify an animal as a bird.
Endangered Species
The great diversity of habitats found in the southern Okanagan
and Similkameen valleys of British Columbia is reflected in the
rich fauna of breeding birds. Because of low numbers and restricted
distribution, many of these species have been placed on British
Columbia's Red List, a compilation of species considered at great
risk.
The Sage Grouse (Centrocercus urophasianus) is an
example of a species of the Family Phasianidae (Partridges, Grouse
and allies); it lived in the Okanagan Valley in historical times
but is now extirpated.
The threatened Yellow-breasted Chat (Icteria virens)
and the endangered Sagebrush Brewer's Sparrow (Spizella
breweri breweri) belong to the Family Emberizidae (Wood
Warblers, Tanagers, Buntings, Blackbirds and allies).
The White-headed Woodpecker (Picoides albolarvatus)
is a threatened member of the Order Piciformes (Woodpeckers).
The Burrowing Owl (Athene cunicularia) is an endangered
member of the Family Strigidae (Typical Owls).
All of these species of birds are limited in their distribution
by availability of suitable habitat. The grasslands, waterside
vegetation and pine forests in which they live in the Thompson-Okanagan
valleys are being diminished by expanding towns, intensive agriculture,
and a multitude of other industrial uses and developments.
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