Falcons are roughly divisible into three or four groups.
The first contains the kestrels (probably excepting the American kestrel); usually small and stocky falcons of mainly brown upperside color and sometimes sexually dimorphic; three African species that are generally gray in color stand apart from the typical members of this group.
Kestrels feed chiefly on terrestrial vertebrates and invertebrates of appropriate size, such as rodents, reptiles, or insects.

The second group contains slightly larger (on average) species, the hobbies and relatives.
These birds are characterized by considerable amounts of dark slate-gray in their plumage; their malar areas are nearly always black.
They feed mainly on smaller birds.

Third are the peregrine falcon and its relatives, variably sized powerful birds that also have a black malar area (except some very light color morphs), and often a black cap, as well.
Otherwise, they are somewhat intermediate between the other groups, being chiefly medium gray with some lighter or brownish colors on their upper sides.
They are, on average, more delicately patterned than the hobbies and, if the hierofalcons are excluded (see below), this group typically contains species with horizontal barring on their undersides.
As opposed to the other groups, where tail color varies much in general but little according to evolutionary relatedness, However, the fox and greater kestrels can be told apart at first glance by their tail colors, but not by much else; they might be very close relatives and are probably much closer to each other than the lesser and common kestrels.
The tails of the large falcons are quite uniformly dark gray with inconspicuous black banding and small, white tips, though this is probably plesiomorphic.
These large Falco species feed on mid-sized birds and terrestrial vertebrates.

Very similar to these, and sometimes included therein, are the four or so species of hierofalcons (literally, "hawk-falcons").
They represent taxa with, usually, more phaeomelanins, which impart reddish or brown colors, and generally more strongly patterned plumage reminiscent of hawks.
Their undersides have a lengthwise pattern of blotches, lines, or arrowhead marks.

While these three or four groups, loosely circumscribed, are an informal arrangement, they probably contain several distinct clades in their entirety.

A study of mtDNA cytochrome b sequence data of some kestrels identified a clade containing the common kestrel and related "malar-striped" species, to the exclusion of such taxa as the greater kestrel (which lacks a malar stripe), the lesser kestrel (which is very similar to the common, but also has no malar stripe), and the American kestrel, which has a malar stripe, but its color pattern–apart from the brownish back–and also the black feathers behind the ear, which never occur in the true kestrels, are more reminiscent of some hobbies.
The malar-striped kestrels apparently split from their relatives in the Gelasian, roughly 2.0–2.5 million years ago (Mya), and are seemingly of tropical East African origin.
The entire "true kestrel" group—excluding the American species—is probably a distinct and quite young clade, as also suggested by their numerous apomorphies.

Other studies have confirmed that the hierofalcons are a monophyletic group–and that hybridization is quite frequent at least in the larger falcon species.
Initial studies of mtDNA cytochrome b sequence data suggested that the hierofalcons are basal among living falcons.
The discovery of a NUMT proved this earlier theory erroneous.
In reality, the hierofalcons are a rather young group, originating at the same time as the start of the main kestrel radiation, about 2 Mya.
Very little fossil history exists for this lineage.
However, the present diversity of very recent origin suggests that this lineage may have nearly gone extinct in the recent past.

The phylogeny and delimitations of the peregrine and hobbies groups are more problematic.
Molecular studies have only been conducted on a few species, and the morphologically ambiguous taxa hav
Falcons are roughly divisible into three or four groups. The first contains the kestrels (probably excepting the American kestrel); usually small and stocky falcons of mainly brown upperside color and sometimes sexually dimorphic; three African species that are generally gray in color stand apart from the typical members of this group. Kestrels feed chiefly on terrestrial vertebrates and invertebrates of appropriate size, such as rodents, reptiles, or insects.
The second group contains slightly larger (on average) species, the hobbies and relatives. These birds are characterized by considerable amounts of dark slate-gray in their plumage; their malar areas are nearly always black. They feed mainly on smaller birds.
Third are the peregrine falcon and its relatives, variably sized powerful birds that also have a black malar area (except some very light color morphs), and often a black cap, as well. Otherwise, they are somewhat intermediate between the other groups, being chiefly medium gray with some lighter or brownish colors on their upper sides. They are, on average, more delicately patterned than the hobbies and, if the hierofalcons are excluded (see below), this group typically contains species with horizontal barring on their undersides. As opposed to the other groups, where tail color varies much in general but little according to evolutionary relatedness, However, the fox and greater kestrels can be told apart at first glance by their tail colors, but not by much else; they might be very close relatives and are probably much closer to each other than the lesser and common kestrels. The tails of the large falcons are quite uniformly dark gray with inconspicuous black banding and small, white tips, though this is probably plesiomorphic. These large Falco species feed on mid-sized birds and terrestrial vertebrates.
Very similar to these, and sometimes included therein, are the four or so species of hierofalcons (literally, "hawk-falcons"). They represent taxa with, usually, more phaeomelanins, which impart reddish or brown colors, and generally more strongly patterned plumage reminiscent of hawks. Their undersides have a lengthwise pattern of blotches, lines, or arrowhead marks.
While these three or four groups, loosely circumscribed, are an informal arrangement, they probably contain several distinct clades in their entirety.
A study of mtDNA cytochrome b sequence data of some kestrels identified a clade containing the common kestrel and related "malar-striped" species, to the exclusion of such taxa as the greater kestrel (which lacks a malar stripe), the lesser kestrel (which is very similar to the common, but also has no malar stripe), and the American kestrel, which has a malar stripe, but its color pattern–apart from the brownish back–and also the black feathers behind the ear, which never occur in the true kestrels, are more reminiscent of some hobbies. The malar-striped kestrels apparently split from their relatives in the Gelasian, roughly 2.0–2.5 million years ago (Mya), and are seemingly of tropical East African origin. The entire "true kestrel" group—excluding the American species—is probably a distinct and quite young clade, as also suggested by their numerous apomorphies.
Other studies have confirmed that the hierofalcons are a monophyletic group–and that hybridization is quite frequent at least in the larger falcon species. Initial studies of mtDNA cytochrome b sequence data suggested that the hierofalcons are basal among living falcons. The discovery of a NUMT proved this earlier theory erroneous. In reality, the hierofalcons are a rather young group, originating at the same time as the start of the main kestrel radiation, about 2 Mya. Very little fossil history exists for this lineage. However, the present diversity of very recent origin suggests that this lineage may have nearly gone extinct in the recent past.
The phylogeny and delimitations of the peregrine and hobbies groups are more problematic. Molecular studies have only been conducted on a few species, and the morphologically ambiguous taxa hav
Falcon