Classification problems 
Traditionally, all the raptors are grouped into four families in this single order. However, in Europe, it has become common to split the order into two: the falcons and caracaras remain in the order Falconiformes (about 60 species in 4 groups), and the remaining 220-odd species (including the Accipitridae – eagles, hawks, and many others) are put in the separate order Accipitriformes. The idea that Falconiformes should be divided into smaller orders comes from the suggestion that the order may not share a single lineage that is exclusive of other birds, but instead are descended independently from different lineages. Their shared characteristics would then be the result of convergent evolution. An additional suggestion is that the Cathartidae (New World Vultures) are not Falconiformes at all, but are more closely related to the storks, and so belong either in the stork's order Ciconiiformes, or in their own separate order, the Cathartiformes. However, morphological evidence supports the common ancestry of the Falconiformes, and the Strigiformes (owls) may be very close to the Falconiformes as well. Furthermore, the family Horusornithidae, a prehistoric family known only from fossils, seems to possess characteristics intermediate between hawks and falcons, suggesting they both evolved from a common ancestor similar to a Horusornithid.
The American Ornithologists' Union provisionally reintegrated the New World vultures (family Cathartidae) into Falconiformes in 2007. This goes against the influential Sibley-Ahlquist taxonomy, in which all the raptors are placed into Ciconiiformes, but the Cathartids are considered to be outside the lineage that includes other raptors. While the latter may be correct, the "Ciconiiformes" sensu Sibley and Ahlquist are a paraphyletic, artificial assemblage and one of the weakest points of their classification scheme.
Karyotype analysis indicates that New World vultures are indeed distinct, and the Accipitridae stand apart from all other falconiform birds in that their microchromosomes show a high degree of merging to medium-sized chromosomes, which is unique in birds. Whether this has any bearing on the validity of the proposed Accipitriformes is still a matter of dispute, but it at least proves that the accipitrids are a monophyletic group.
Comparative gene studies published in 2008 suggested that the falcons are more closely related to the parrots and passerines than to other birds including the Accipitridae, so that Falconiformes are not monophyletic even if the Cathartidae are excluded.. Indeed, a 2011 analysis of transposable element insertions shared between the genomes of falcons, passerines, and parrots, but not present in the genomes of other birds, confirmed that falcons are a sister group of the combined parrot/passerine group (Psittacopasserae) and that Falconiformes are paraphyletic.
Falconiformes are known from the Middle Eocene (the possibly basal genus Masillaraptor from the Messel Pit). They typically have a sharply hooked beak with a cere (soft mass) on the proximodorsal surface, housing the nostrils. Their wings are long and fairly broad, suitable for soaring flight, with the outer 4–6 primaries emarginated.
Falconiformes have strong legs and feet with raptorial claws and an opposable hind claw. Almost all Falconiformes are carnivorous, hunting by sight during the day or at twilight. They are exceptionally long-lived, and most have low reproductive rates.
The young have a long, very fast-growing fledgling stage, followed by 3–8 weeks of nest care after first flight, and 1 to 3 years as sexually immature adults. Females are bigger than males. Sexual dimorphism is generally most extreme in specialized bird-eaters, such as the Accipiter hawks and Falco falcons, in which a female may be more than twice as heavy as her mate; it borders on non-existent among the vultures. Monogamy is the general rule, although an alternative mate is often selected if one dies.
Falconiformes are among the most diverse orders in size. The smallest species is believed to be the Black-thighed Falconet, small males of which can weigh only 28 g (1 oz), measure 14 cm (5.5 inches) and have a wingspan of 26 cm (10.3 inches). The largest species is the Cinereous Vulture, at up to 14 kg (31 lbs), 118 cm (46 inches) and 3 m (10 feet) across the wings.
- Falconidae: caracaras, falcons, falconets, hobbies, kestrels
- Cathartidae: New World vultures, condors
- Pandionidae: Osprey
- Accipitridae: buzzards, eagles, harriers, hawks, kites, Old World vultures
- Sagittaridae: Secretary Bird
See also 
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (April 2009)|
- "Place Cathartidae in their own order". Retrieved 24 June 2011.
- Banks, Richard C.; Chesser, R. Terry; Cicero, Carla; Dunn, Jon L.; Kratter, Andrew W.; Lovette, Irby J.; Rasmussen, Pamela C.; Remsen, J. V. et al. (2007). "Forty-eighth Supplement to the American Ornithologists' Union Check-List of North American Birds". The Auk 124 (3): 1109–1115. doi:10.1642/0004-8038(2007)124[1109:FSTTAO]2.0.CO;2. Retrieved 2009-05-31.
- American Ornithologists' Union. "Check-List of North American Birds". Retrieved 2009-05-31.
- de Boer 1975.
- Amaral & Jorge 2003.
- Federico et al. 2005.
- Hackett et al. 2008.
- Suh A, Paus M, Kiefmann M, et al (2011). "Mesozoic retroposons reveal parrots as the closest living relatives of passerine birds". Nature Communications 2 (8): 443–8. doi:10.1038/ncomms1448. PMC 3265382. PMID 21863010.
- Amaral, Karina Felipe; Jorge, Wilham (2003). "The chromosomes of the Order Falconiformes: a review" (pdf). Ararajuba 11 (1): 65–73. ISSN 0103-5657. OCLC 23686049. Retrieved 2011-05-26.
- de Boer, L. E. M. (1975). "Karyological heterogeneity in the Falconiformes (aves)". Cellular and Molecular Life Sciences 31 (10): 1138–1139. doi:10.1007/BF02326755. PMID 1204722.
- Federico, Concetta; Cantarella, Catia Daniela; Scavo, Cinzia; Saccone, Salvatore; Bed'hom, Bertrand; Bernardi, Giorgio (2005). "Avian genomes: Different karyotypes but a similar distribution of the GC-richest chromosome regions at interphase". Chromosome Research 13 (8): 785–793. doi:10.1007/s10577-005-1012-7. PMID 16331410.
- Hackett, S. J.; Kimball, R. T.; Reddy, S.; Bowie, R. C. K.; Braun, E. L.; Braun, M. J.; Chojnowski, J. L.; Cox, W. A. et al. (2008). "A Phylogenomic Study of Birds Reveals Their Evolutionary History". Edward L. Braun, Michael J. Braun, Jena L. Chojnowski, W. Andrew Cox, Kin-Lan Han, John Harshman, Christopher J. Huddleston, Ben D. Marks, Kathleen J. Miglia, William S. Moore, Frederick H. Sheldon, David W. Steadman, Christopher C. Witt, Tamaki Yuri. Science 320 (5884): 1763–1768. doi:10.1126/science.1157704. PMID 18583609. Retrieved 2011-05-26.
- Eaglewatch: Birds of prey and owls around the world (in Dutch; click on "Language / Taal" at top right for the English version)
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