Changeable Hawk Eagle
Encyclopedia
The Crested Hawk-Eagle or Changeable Hawk-eagle (Nisaetus cirrhatus) is a bird of prey
species of the family
Accipitridae
. 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 (Hodgson, 1836) and separated from the New World
species.
Crested Hawk-Eagles breed in southern Asia in India
and Sri Lanka
, and from the southeast rim of the Himalaya across Southeast Asia
to Indonesia
and the Philippines
. This is a bird occurring singly (outside mating season) in open woodland, although island forms prefer a higher tree density. It builds a stick nest in a tree and lays a single egg
.
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The Crested Hawk-Eagle is a medium-large raptor at about 60–72 cm (23.6–28.3 in) in length. It is a relatively slender forest eagle with some subspecies
(especially limnaetus) being dimorphic
giving the name of "Changeable". This, and also a complicated phylogeny further complicates precise identification.
Normally brown above; white below with barring on the undersides of the flight feathers and tail; black longitudinal streaks on
throat and chocolate streaks on breast. Some subspecies have a crest of four feather
s, but this is all but absent in others. The sexes are quite similar in their plumage, but males are about 15% smaller than females. The underparts and head of juveniles are whitish or buff
with few dark streaks.
The wings are long and parallel-sided, and are held flat in flight, which helps to distinguish this species from the similar Mountain Hawk-Eagle. In overhead flight, comparatively rounded wings (upturned at tip), longish tail, white body (spotted with brown) and grey underside of wings (streaked and spotted) are leading pointers.
Call is a loud, high-pitched ki-ki-ki-ki-ki-ki-ki-ki-kee, beginning short, rising in crescendo and ending in a scream.
s, birds and reptile
s. They like to keep a sharp lookout perched bolt upright on a bough amongst the canopy foliage of some high tree standing near a forest clearing (see photos). There they wait for junglefowl, pheasants, hares and other small animals coming out into the open. The bird then swoops down forcefully, strikes, and bears the prey away in its talons (Ali & Daniel1983).
has traditionally been treated as a subspecies of the Crested Hawk-Eagle, but it is now often treated as a separate species, N. floris.
Two distinct groups exist in the Crested hawk-eagle; one with crests and one without or with hardly visible crests. Dark morphs exist for some populations.
Crested Hawk-Eagle
Crestless Changeable Hawk-Eagle
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.
The three small-island taxa (N. c. andamanensis, N. c. vanheurni, and N. floris
) also 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. It appears as if the crested group is close to becoming a distinct species. The island taxa derived from N. c. limnaeetus appear to have undergone founder effect
s, which has restricted their genetic diversity. In the continental population, genetic diversity is considerable, and the evolutionary pattern of the 2 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 that the island taxa which are obviously at higher risk of extinction are, for conservation
considered evolutionary significant unit
s 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 evolution
ary 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 clade
s 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 lineage
s 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.
Bird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....
species of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Accipitridae
Accipitridae
The Accipitridae, one of the two major families within the order Accipitriformes , are a family of small to large birds with strongly hooked bills and variable morphology based on diet. They feed on a range of prey items from insects to medium-sized mammals, with a number feeding on carrion and a...
. It was formerly placed in the genus Spizaetus
Spizaetus
Spizaetus is the typical hawk-eagle birds of prey genus found in the tropics of the Americas. It was however used to indicate a group of tropical eagles that included species occurring in southern and southeastern Asia and one representative of this genus in the rainforests of West Africa. The Old...
, but studies pointed to the group being paraphyletic resulting in the Old World
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
members being placed in Nisaetus (Hodgson, 1836) and separated from the New World
New World
The New World is one of the names used for the Western Hemisphere, specifically America and sometimes Oceania . The term originated in the late 15th century, when America had been recently discovered by European explorers, expanding the geographical horizon of the people of the European middle...
species.
Crested Hawk-Eagles breed in southern Asia in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, and from the southeast rim of the Himalaya across Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
to Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
and the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
. This is a bird occurring singly (outside mating season) in open woodland, although island forms prefer a higher tree density. It builds a stick nest in a tree and lays a single egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
.
Description
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
(especially limnaetus) being dimorphic
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
giving the name of "Changeable". This, and also a complicated phylogeny further complicates precise identification.
Normally brown above; white below with barring on the undersides of the flight feathers and tail; black longitudinal streaks on
throat and chocolate streaks on breast. Some subspecies have a crest of four feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s, but this is all but absent in others. The sexes are quite similar in their plumage, but males are about 15% smaller than females. The underparts and head of juveniles are whitish or buff
Buff (colour)
Buff is a pale yellow-brown colour that got its name from the colour of buff leather.Displayed on the right is the colour buff.EtymologyAccording to the Oxford English Dictionary, buff as a descriptor of a colour was first used in the London Gazette of 1686, describing a uniform to be "A Red Coat...
with few dark streaks.
The wings are long and parallel-sided, and are held flat in flight, which helps to distinguish this species from the similar Mountain Hawk-Eagle. In overhead flight, comparatively rounded wings (upturned at tip), longish tail, white body (spotted with brown) and grey underside of wings (streaked and spotted) are leading pointers.
Call is a loud, high-pitched ki-ki-ki-ki-ki-ki-ki-ki-kee, beginning short, rising in crescendo and ending in a scream.
Ecology
Crested Hawk-Eagles eat mammalMammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, birds and reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s. They like to keep a sharp lookout perched bolt upright on a bough amongst the canopy foliage of some high tree standing near a forest clearing (see photos). There they wait for junglefowl, pheasants, hares and other small animals coming out into the open. The bird then swoops down forcefully, strikes, and bears the prey away in its talons (Ali & Daniel1983).
Nesting
- Season: December to April.
- Nest: a large stick platform lined with green leaves, high up in a forest tree.
- Eggs: a single one, greyish white, unmarked or with faint specks and blotches of light reddish at the broad end.
Systematics
The Flores Hawk-EagleFlores Hawk-eagle
The Flores Hawk-eagle, Nisaetus floris , is a fairly large, up to long, raptor in the family Accipitridae. Adults have dark brown upperparts, a brown tail with six bars, a white patch in the wings that is visible in flight, white underparts, and a white head with fine brownish streaks on the crown...
has traditionally been treated as a subspecies of the Crested Hawk-Eagle, but it is now often treated as a separate species, N. floris.
Two distinct groups exist in the Crested hawk-eagle; one with crests and one without or with hardly visible crests. Dark morphs exist for some populations.
Crested Hawk-Eagle
- Nisaetus cirrhatus cirrhatus
- Gangetic plain southwards throughout India
- Crested, no dark morph.
- Nisaetus cirrhatus ceylanensis
- Sri Lanka (possibly also Travancore)
- Smaller than nominate, crest proportionally longer on average. Apparently no dark morph.
Crestless Changeable Hawk-Eagle
- Nisaetus cirrhatus limnaeetus
- NepalNepalNepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...
, NE India, via Burma and Malay PeninsulaMalay PeninsulaThe Malay Peninsula or Thai-Malay Peninsula is a peninsula in Southeast Asia. The land mass runs approximately north-south and, at its terminus, is the southern-most point of the Asian mainland...
along Wallace LineWallace LineThe Wallace Line separates the ecozones of Asia and Wallacea, a transitional zone between Asia and Australia. West of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origin is present...
to PhilippinesPhilippinesThe Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam... - Much like nominate except crest. Dimorphic, with the dark morph chocolate-brown all over, tail base might appear lighter in flight.
- Nisaetus cirrhatus andamanensis
- Andaman IslandsAndaman IslandsThe Andaman Islands are a group of Indian Ocean archipelagic islands in the Bay of Bengal between India to the west, and Burma , to the north and east...
- Similar to N. c. limnaeetus. Apparently no dark morph.
- Nisaetus cirrhatus vanheurni
- Simeulue Island
- Similar to N. c. limnaeetus. Apparently no dark morph.
Gamauf et al. (2005) analyzed mtDNA cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
and control region sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
data of a considerable number of specimens of the Crested Hawk-Eagle and some relatives. Despite the large sample, even the most conspicuous dichotomy
Dichotomy
A dichotomy is any splitting of a whole into exactly two non-overlapping parts, meaning it is a procedure in which a whole is divided into two parts...
- that between the crested and crestless groups - was not as well resolved as it might have been expected to be.
Flores Hawk-eagle
The Flores Hawk-eagle, Nisaetus floris , is a fairly large, up to long, raptor in the family Accipitridae. Adults have dark brown upperparts, a brown tail with six bars, a white patch in the wings that is visible in flight, white underparts, and a white head with fine brownish streaks on the crown...
) also 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
Polytomy
A polytomy , meaning many temporal based branches, is a section of a phylogeny in which the evolutionary relationships can not be fully resolved to dichotomies. In a phylogenetic tree, a polytomy is represented as a node which has more than two immediate descending branches...
, 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. It appears as if the crested group is close to becoming a distinct species. The island taxa derived from N. c. limnaeetus appear to have undergone founder effect
Founder effect
In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, using existing theoretical work by those such as Sewall...
s, which has restricted their genetic diversity. In the continental population, genetic diversity is considerable, and the evolutionary pattern of the 2 studied genes did not agree, and neither did the origin of specimens show clear structures. N. c. limnaeetus thus is best considered a metapopulation
Metapopulation
A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1970 to describe a model of population dynamics of insect pests in agricultural fields, but the idea has been most...
.
Gamauf et al. (2005) therefore suggest that the island taxa which are obviously at higher risk of extinction are, for conservation
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
considered evolutionary significant unit
Evolutionary Significant Unit
An Evolutionarily Significant Unit is a population of organisms that is considered distinct for purposes of conservation. Delineating ESUs is important when considering conservation action.This term can apply to any species, subspecies, geographic race, or population...
s regardless of their systematic
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
status. This case also demonstrates that a too rigid interpretation of cladistics
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
and the desire for monophyletic taxa, as well as universal application of single species concept to all birds will undermine correct understanding of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary relationships. It would even not be inconceivable to find mainland lineages to group closely with the western island taxa, if little genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
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 clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s are usually considered distinct species.
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
pool of lineages in the crestless group that, despite not being monophyletic, should be considered a valid taxon as long as gene flow
Gene flow
In population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...
is possible through its range. In addition, as ancient DNA
Ancient DNA
Ancient DNA is DNA isolated from ancient specimens. It can be also loosely described as any DNA recovered from biological samples that have not been preserved specifically for later DNA analyses...
from museum specimens was used extensively, the possibility of ghost lineage
Ghost lineage
A ghost lineage is a phylogenetic lineage that is inferred to exist but has no fossil record....
s must be considered. If it is assumed that all or most of the ancient lineages still exist today, considerable recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
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.