BIRDS
Reptiles
and birds present numerous morphological similarities, which
imposed their ranking into one group, called sauropsidia. Comparative
anatomy and palaeontology agree that birds evolved from reptiles.
Birds
are homoiotherm (warm-blooded) vertebrates, with thin skin,
which is
covered by feathers. Birds have
adopted to flying, with some exceptions, e.g., the ostrich,
who lost this ability. The forelimbs are modified as flight
organs, called wings. Birds living constantly in a certain place
are called resident. Species migrating forming large
flocks to warmer territories to spend the winter and come back
in spring, are called migratory. Other species passing
over a certain place, are called passerines, and finally,
endemics live constantly in a certain geographical
area. The place used by a bird to lay its eggs is its home.
Migrating is a hereditary instinct, evolved from older habits,
when birds were forced to move from one area to another due
to heavy climate or geological changes, in order to find better
feeding and living conditions. Migrations are performed in
large groups, by both genders or by one gender or by several
different species
and 
birds
usually follow the same route.
The
birds' skeleton is thin but very powerful. In order for the
bones to be light, they contain numerous cavities filled with
air; these are called pneumatic bones. They are joined in such
a way that they form a compound and solid pattern, capable of
resisting air's pressure during the flight.
Birds
lack teeth and lips. Their jaws (bills) are covered by keratin
plaques, forming the beak, which is used for capturing food,
taking care of feathers, collecting, transportating and depositing
nesting material, defense, etc. The form of the beak is related
to the type of the bird's diet.
Smell
and taste are senses poorly developed, while hearing and vision
are extremely keen in birds. Their eyesight is much stronger
than the mammals'. Birds have five times better visual capacity
than humans. Furthermore, their pupils dilate significantly,
in order for the images to be lighter. Finally, apart from nocturnal
predators, such as owls etc., which have their eyes located
in the front of their heads, other birds have a very wide vision
range, up to 300 degrees, without moving their head.
Birds
exist on planet Earth for c. 200 million years. They consist
of c. 8,700 species and their population globally is estimated
to be c. 100 billion individuals. In Europe 475 species have
been recorded, and in Greece 436 species, 2/3 of which nest
here. It is assumed that in Parnitha 131 species are present
(Amorgianiotis & Chatzirvasanis,
1997).
Bird
list
