 So now they will be officially recognized as separate species.
Past taxonomy has been based on morphology, behavior, habitat, nest characteristics, etc., but most recently DNA hybridization techniques have been used with probably the most accurate results of any method.
What are birds? There are about 10,000 species of birds in about 170 families with 1 to 300 birds per family. When one looks at modern forms of birds only, birds form a homogeneous and distinct group, compared to the other vertebrate classes.
Birds are characterized by:
3. Laying of eggs
4. Lack of teeth; epidermal covered bony beak.
5. Pneumatic bones.
6. Adaptations for flight (about 123 flightless)
c. centralization of weight
d. efficient metabolism
e. visual acuity
f. motor development of brain
Ornithologists are both professional and amateur, but most professionals, about 80%, work on some aspect of the ecology of birds (rather than physiology, anatomy, etc.) This is primarily because birds are so easy to study in the field and harder to keep in the lab than other vertebrates. Much of what we know about the physiology of birds is based on work on chickens, pigeons, and house sparrows.
Although much of the recent ornithological research is ecological, the emphases are in areas such as populations (movement, decline, increase), metabolism in the field, genetics, taxonomy, effects of environmental changes on birds, and the fossil record.
The set of birds in any defined area is called the avifauna. The diversity of the avifauna is dependent both the climate and vegetation structure, primarily. Tropical forests have the highest bird species diversity and the tundra and open ocean the lowest. The only place where there are no breeding birds is the center of Antarctica. In North America, excluding Mexico, there are approximately 775 breeding bird species.
The spatial distribution of birds is due to the adaptations of birds – they are adapted to particular habitats. The temporal distribution of the birds is essentially one of migration. Classically, migration is a north-south oriented movement between a breeding and wintering range. But migrations may be very short such as down the slope of a mountain to a lower elevation (vertical migration).
Birds can be conveniently categorized by their migratory or non-migratory status in an area.
a. Residents: those birds that do not enter or leave the state/country/area during migration. Generally, these birds do not move very far during their lifetime.
b. Transients: migrate through in the spring and/or fall but do not nest in the area. Some are pure transients that merely pass through.
c. Winter visitors: are those birds whose breeding range is somewhere north.
d. Summer visitors: are those birds whose winter range is somewhere to the south.
e. Perennial visitors: are those of which individuals are always around.
f. Casual visitors and accidentals (occur unexpectedly). The remaining 6% defy categorization.