Community hub
Recent from talks
Knowledge base stats:
Talk channels stats:
Members stats:
Changeable hawk-eagle
The changeable hawk-eagle (Nisaetus cirrhatus) or crested hawk-eagle is a large bird of prey species of the family Accipitridae. More informal or antiquated English common names include the marsh hawk-eagle or Indian crested hawk-eagle. It is a member of the subfamily Aquilinae, with signature feathers, absent in tropical raptors from outside this subfamily, covering the tarsus. It was formerly placed in the genus Spizaetus, but studies pointed to the group being paraphyletic resulting in the Old World members being placed in Nisaetus and separated from the New World species. It is a typical "hawk-eagle" in that it is an agile forest-dwelling predator and like many such eagles readily varies its prey selection between birds, mammals or reptiles as well as other vertebrates. Among the members of its genus, the changeable hawk-eagle stands out as the most widely distributed, adaptable and abundant species. Individuals show a wide range of variation in plumage from pale to dark, varying with moult and age giving rise to the name "changeable".
The changeable hawk-eagle was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it with the eagles, hawks and relatives in the genus Falco and coined the binomial name Falco cirrhatus. Gmelin's description was based on the "crested Indian falcon" or the Falco Indicus cirratus that had been first described in 1676 by the English naturalists Francis Willughby and John Ray from a live bird kept in the Royal Aviary in St James's Park, London. The changeable hawk-eagle was formerly placed in the genus Spizaetus but it and nine other Old World hawk-eagles were moved to the resurrected genus Nisaetus following the publication in 2005 and 2007 of two molecular phylogentic studies. The genus Nisaetus had been introduced in 1836 by the English naturalist Brian Houghton Hodgson. The genus name Nisaetus combines the Medieval Latin nisus for a sparrowhawk with the Ancient Greek aetos meaning "eagle". The specific epithet cirrhatus is from Latin cirratus meaning "curly-headed".
The taxonomy of the wide-ranging changeable hawk-eagle is complex and confusing, with few authorities agreeing on whether the species in fact houses a species complex. Gamauf et al. (2005) analyzed mtDNA cytochrome b and control region sequence data of a considerable number of specimens of the crested hawk-eagle and some relatives. Despite the large sample, even the most conspicuous dichotomy - that between the crested and crestless groups - was not as well resolved as it might have been expected to be. At least one widely accepted genetic study has resulted in a recent revision to the recognition of a new species, as the Flores hawk-eagle has traditionally been treated as a subspecies of the changeable hawk-eagle, but it is now often treated as a separate species, N. floris. The Flores and changeable hawk-eagles are regarded as sister species. The three small-island taxa (N. c. andamanensis, N. c. vanheurni, and N. floris) as a whole each appear as monophyletic lineages. Their placement is even more unresolved, with N. floris being apparently a very ancient lineage. The other two seem quite certainly to derive from N. c. limnaeetus. The latter taxon has a confusing phylogeny. Different lineages exist that are apparently not stable in space and time, are best described as polytomy, from which the similar island taxa derive. Obviously, N. c. limnaeetus does not represent a monophyletic lineage. Neither the biological nor the phylogenetic species concepts, nor phylogenetic systematics can be applied to satisfaction. The crested group apparently is close to becoming a distinct species. The island taxa derived from N. c. limnaeetus appear to have undergone founder effects, which has restricted their genetic diversity. In the continental population, genetic diversity is considerable, and the evolutionary pattern of the two studied genes did not agree, and neither did the origin of specimens show clear structures. N. c. limnaeetus thus is best considered a metapopulation.
Gamauf et al. (2005) therefore suggest the island taxa which are obviously at higher risk of extinction are, for conservation considered evolutionary significant units regardless of their systematic status. This case also demonstrates that a too-rigid interpretation of cladistics and the desire for monophyletic taxa, as well as universal application of single-species concept to all birds will undermine correct understanding of evolutionary relationships. It would even not be inconceivable to find mainland lineages to group closely with the western island taxa, if little genetic drift had occurred in the initial population. nonetheless, the divergence of this species' lineages seems to have taken place too recently to award them species status, as compared to the level of genetic divergence at which clades are usually considered distinct species. N. c. limnaeetus appears for all that can be said with reasonable certainty basal pool of lineages in the crestless group that, despite not being monophyletic, should be considered a valid taxon as long as gene flow is possible through its range. In addition, as ancient DNA from museum specimens was used extensively, the possibility of ghost lineages must be considered. If it is assumed that all or most of the ancient lineages still exist today, considerable recombination must have taken place as the two genes' phylogenies do not agree much, indicating a healthy level of gene flow. Whether this still holds true today remains to be determined.
Two distinct groups exist in the changeable hawk-eagle; one with crests and one without or with hardly visible crests. A 2020 study found that the reproductive isolation between the two groups was weak and recommended treating the two groups as conspecific. Dark morphs exist for some populations.
Changeable hawk-eagle group
Crestless changeable hawk-eagle group
The changeable hawk-eagle is a largish but slender eagle. They fall near the middle of sizes among the currently accepted species in the genus Nisaetus. As in most birds of prey, females are larger than males with an average overall size difference of 7% but this can individually range to an 18-22% difference, with island races apparently thought to be less dimorphic on average. Size is quite variable and total length has been reported in the past to vary from 51 to 82 cm (20 to 32 in) and wingspan from 100 to 160 cm (39 to 63 in), however these figures appear to include the much more massive hawk-eagles from Flores that are currently considered their own separate species by modern authorities. Nonetheless, total lengths of up to 77 cm (30 in) have been listed for N. c. limnaeetus in Nepal. Ali & Ripley (1978) estimated these average total lengths for the following subspecies: N. c. cirrhatus at 72 cm (28 in), N. c. limnaeetus at 70 cm (28 in) and N. c. andamanensis at 61 cm (24 in). Legge (1880) measured the length of Sri Lankan changeable hawk-eagles (N. c. ceylanensis) without including the beak as 55 to 60 cm (22 to 24 in). The average length of birds from the Philippines (N. c. limnaeetus) was measured as 58.4 cm (23.0 in) in males and 64.9 cm (25.6 in) in females. Weights in this species have been reported from 1.2 to 1.9 kg (2.6 to 4.2 lb) but the source of this is unclear and it probably underrepresents the size variation known to occur in the species. The only precise body masses known for the species are derived from the Philippine population, where males average 1.36 kg (3.0 lb) and females average 1.6 kg (3.5 lb) but they could weigh in excess of 1.81 kg (4.0 lb).
Hub AI
Changeable hawk-eagle AI simulator
(@Changeable hawk-eagle_simulator)
Changeable hawk-eagle
The changeable hawk-eagle (Nisaetus cirrhatus) or crested hawk-eagle is a large bird of prey species of the family Accipitridae. More informal or antiquated English common names include the marsh hawk-eagle or Indian crested hawk-eagle. It is a member of the subfamily Aquilinae, with signature feathers, absent in tropical raptors from outside this subfamily, covering the tarsus. It was formerly placed in the genus Spizaetus, but studies pointed to the group being paraphyletic resulting in the Old World members being placed in Nisaetus and separated from the New World species. It is a typical "hawk-eagle" in that it is an agile forest-dwelling predator and like many such eagles readily varies its prey selection between birds, mammals or reptiles as well as other vertebrates. Among the members of its genus, the changeable hawk-eagle stands out as the most widely distributed, adaptable and abundant species. Individuals show a wide range of variation in plumage from pale to dark, varying with moult and age giving rise to the name "changeable".
The changeable hawk-eagle was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it with the eagles, hawks and relatives in the genus Falco and coined the binomial name Falco cirrhatus. Gmelin's description was based on the "crested Indian falcon" or the Falco Indicus cirratus that had been first described in 1676 by the English naturalists Francis Willughby and John Ray from a live bird kept in the Royal Aviary in St James's Park, London. The changeable hawk-eagle was formerly placed in the genus Spizaetus but it and nine other Old World hawk-eagles were moved to the resurrected genus Nisaetus following the publication in 2005 and 2007 of two molecular phylogentic studies. The genus Nisaetus had been introduced in 1836 by the English naturalist Brian Houghton Hodgson. The genus name Nisaetus combines the Medieval Latin nisus for a sparrowhawk with the Ancient Greek aetos meaning "eagle". The specific epithet cirrhatus is from Latin cirratus meaning "curly-headed".
The taxonomy of the wide-ranging changeable hawk-eagle is complex and confusing, with few authorities agreeing on whether the species in fact houses a species complex. Gamauf et al. (2005) analyzed mtDNA cytochrome b and control region sequence data of a considerable number of specimens of the crested hawk-eagle and some relatives. Despite the large sample, even the most conspicuous dichotomy - that between the crested and crestless groups - was not as well resolved as it might have been expected to be. At least one widely accepted genetic study has resulted in a recent revision to the recognition of a new species, as the Flores hawk-eagle has traditionally been treated as a subspecies of the changeable hawk-eagle, but it is now often treated as a separate species, N. floris. The Flores and changeable hawk-eagles are regarded as sister species. The three small-island taxa (N. c. andamanensis, N. c. vanheurni, and N. floris) as a whole each appear as monophyletic lineages. Their placement is even more unresolved, with N. floris being apparently a very ancient lineage. The other two seem quite certainly to derive from N. c. limnaeetus. The latter taxon has a confusing phylogeny. Different lineages exist that are apparently not stable in space and time, are best described as polytomy, from which the similar island taxa derive. Obviously, N. c. limnaeetus does not represent a monophyletic lineage. Neither the biological nor the phylogenetic species concepts, nor phylogenetic systematics can be applied to satisfaction. The crested group apparently is close to becoming a distinct species. The island taxa derived from N. c. limnaeetus appear to have undergone founder effects, which has restricted their genetic diversity. In the continental population, genetic diversity is considerable, and the evolutionary pattern of the two studied genes did not agree, and neither did the origin of specimens show clear structures. N. c. limnaeetus thus is best considered a metapopulation.
Gamauf et al. (2005) therefore suggest the island taxa which are obviously at higher risk of extinction are, for conservation considered evolutionary significant units regardless of their systematic status. This case also demonstrates that a too-rigid interpretation of cladistics and the desire for monophyletic taxa, as well as universal application of single-species concept to all birds will undermine correct understanding of evolutionary relationships. It would even not be inconceivable to find mainland lineages to group closely with the western island taxa, if little genetic drift had occurred in the initial population. nonetheless, the divergence of this species' lineages seems to have taken place too recently to award them species status, as compared to the level of genetic divergence at which clades are usually considered distinct species. N. c. limnaeetus appears for all that can be said with reasonable certainty basal pool of lineages in the crestless group that, despite not being monophyletic, should be considered a valid taxon as long as gene flow is possible through its range. In addition, as ancient DNA from museum specimens was used extensively, the possibility of ghost lineages must be considered. If it is assumed that all or most of the ancient lineages still exist today, considerable recombination must have taken place as the two genes' phylogenies do not agree much, indicating a healthy level of gene flow. Whether this still holds true today remains to be determined.
Two distinct groups exist in the changeable hawk-eagle; one with crests and one without or with hardly visible crests. A 2020 study found that the reproductive isolation between the two groups was weak and recommended treating the two groups as conspecific. Dark morphs exist for some populations.
Changeable hawk-eagle group
Crestless changeable hawk-eagle group
The changeable hawk-eagle is a largish but slender eagle. They fall near the middle of sizes among the currently accepted species in the genus Nisaetus. As in most birds of prey, females are larger than males with an average overall size difference of 7% but this can individually range to an 18-22% difference, with island races apparently thought to be less dimorphic on average. Size is quite variable and total length has been reported in the past to vary from 51 to 82 cm (20 to 32 in) and wingspan from 100 to 160 cm (39 to 63 in), however these figures appear to include the much more massive hawk-eagles from Flores that are currently considered their own separate species by modern authorities. Nonetheless, total lengths of up to 77 cm (30 in) have been listed for N. c. limnaeetus in Nepal. Ali & Ripley (1978) estimated these average total lengths for the following subspecies: N. c. cirrhatus at 72 cm (28 in), N. c. limnaeetus at 70 cm (28 in) and N. c. andamanensis at 61 cm (24 in). Legge (1880) measured the length of Sri Lankan changeable hawk-eagles (N. c. ceylanensis) without including the beak as 55 to 60 cm (22 to 24 in). The average length of birds from the Philippines (N. c. limnaeetus) was measured as 58.4 cm (23.0 in) in males and 64.9 cm (25.6 in) in females. Weights in this species have been reported from 1.2 to 1.9 kg (2.6 to 4.2 lb) but the source of this is unclear and it probably underrepresents the size variation known to occur in the species. The only precise body masses known for the species are derived from the Philippine population, where males average 1.36 kg (3.0 lb) and females average 1.6 kg (3.5 lb) but they could weigh in excess of 1.81 kg (4.0 lb).