Falconiformes comprises a vast group of species, commonly known
as birds of prey or diurnal raptors. It now seems certain that
they constitute a polyphy-letic group and they must be divided
into two orders, Accipitriformes and Falconiformes, to obtain
monophyletic groupings. Nevertheless, many systematic uncertainties
remain, because fossils able to confirm the existence of a common
ancestor have not been found, even at the level of single families.
Five families have been described: Cathartidae, the American vultures;
Pandionidae, with a single cosmopolitan species; Accipitridae,
with the greatest number of genera and species; Sagittaridae,
with a single species exclusive to Africa; Falconidae, probably
a separate order.
Because of the strong adaptive radiation (even within families),
there are few traits shared by all species. Body size is extremely
variable, even among the Italian species, ranging from 25-30 cm
total length and 150-200 g weight of the Merlin (Falco columbarius)
to 100 cm and 10-12 kg of the Black Vulture (Aegypius monachus).
The shape of the wing is extremely variable, according to the
type of predation and habitat. There are generally 10 long primaries,
used for flight, and one short primary. In the genus Accipiter,
the latter is absent. There are usually 12 retrices in the
small-medium species, 14 in the big vultures of the genus Gyps.
The bill is curved and hooked, adapted for snatching and tearing
flesh. The horny structure of the bill terminates at the base
with a naked area of skin forming a characteristic cere, where
the nostrils open. The structure of the tarsi, legs and talons
varies according to the type of prey: long toes and sharp curved
claws in the ornithophagous species, short toes and strongly curved
talons in those that capture reptiles, slightly curved talons
in the genus Pernis and in vultures. The claw of the posterior
toe is generally the longest. Unlike in other groups of birds,
the right ovary and oviduct are developed and functional. The
senses of hearing and sight are very well developed. The density
of cones in the retina is the highest of all vertebrates. Some
species present sexual dimorphism, with females larger than males.
Small species have complete annual moults, while large species
have continuous moults. Therefore, adults of the large species
present plumage formed by feathers of different generations. The
chicks are semi-altricial and nidicolous.
In Italy, 40 species have been recorded, belonging to 3 families:
Pandionidae, Accipitridae and Falconidae. The following accidental
species in Italy are not considered in this volume: Black-winged
Kite Elanus caeruleus (3 records), Levant Sparrowhawk Accipiter
brevipes (2 records), Tawny Eagle Aquila
rapax (2 records), Steppe Eagle Aquila
nipalensis (8 records), Imperial Eagle
Aquila heliaca (15 records), Amur Falcon Falco
amurensis (1 record), Barbary Falcon
Falco pelegrinoides (9 records).