crested serpent-eagle
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The crested serpent eagle (''Spilornis cheela'') is a medium-sized bird of prey that is found in forested habitats across
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
. Within its widespread range across the
Indian Subcontinent The Indian subcontinent is a physiographical region in Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian Ocean from the Himalayas. Geopolitically, it includes the countries of Bangladesh, Bhutan, In ...
,
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
and
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea ...
, there are considerable variations and some authorities prefer to treat several of its
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. Not all specie ...
as completely separate species.Ferguson-Lees, James & Christie, David A. (2001). ''Raptors of the World.'' Christopher Helm, London. In the past, several species including the
Philippine serpent eagle The Philippine serpent eagle (''Spilornis holospilus'') is an eagle found in the major islands of the Philippines. It is sometimes treated as a race of the crested serpent eagle ('' Spilornis cheela''). This species is usually found in forest cle ...
(''S. holospila''), Andaman serpent eagle (''S. elgini'') and South Nicobar serpent eagle (''S. klossi'') were treated as subspecies of the Crested serpent eagle. All members within the species complex have a large looking head with long feathers on the back of the head giving them a maned and crested appearance. The face is bare and yellow joining up with the ceres while the powerful feet are unfeathered and heavily scaled. They fly over the forest canopy on broad wings and tail have wide white and black bars. They call often with a loud, piercing and familiar three or two-note call. They often feed on snakes, giving them their name and are placed along with the '' Circaetus'' snake-eagles in the subfamily Circaetinae.


Description

This medium-large, dark brown eagle is stocky, with rounded wings and a short tail. Its short black and white fan-shaped nuchal crest gives it a thick-necked appearance. The bare facial skin and feet are yellow. The underside is spotted with white and yellowish-brown. When perched the wing tips do not reach until the tail tip. In soaring flight, the broad and paddle-shaped wings are held in a shallow V. The tail and underside of the flight
feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premie ...
s are black with broad white bars. Young birds show a lot of white on the head. The tarsus is unfeathered and covered by hexagonal scales. The upper mandible does not have an overhanging festoon to the tip.


Size

This species of serpent eagle manifests an unusual amount of size variation across its assorted subspecies. Total length of fully-grown crested serpent eagles can vary from and wingspan can vary from .Clark, W.S., J. S. Marks, and G. M. Kirwan (2020). ''Crested Serpent-Eagle (Spilornis cheela)'', version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. The largest proportioned race appears to be the nominate, ''S. c. cheela'', with a wing chord of in males and in females, tail lengths of and tarsus length of . In comparison, ''S. c. minimus'', probably the smallest race, has a wing chord of in males and in females, tail lengths of around and tarsal length of around . Weights are more fitfully reported but are estimated to vary perhaps threefold between assorted races. In very small subspecies such as ''S. c. asturinus'' body masses were found to be in a male and in a female. In ''S. c. palawanesis'', body mass was reported at in males and in females. Serpent eagles from Borneo, ''S. c. pallidus'', may between . Mainland forms are typically larger but a weight of was cited for the fairly small mainland race, ''S. c. burmanicus''. In the race ''S. c. hoya'', weights were much higher, averaging ; meanwhile, in the same race, 8 males averaged and 6 females averaged . In some cases, serpent eagles may attain estimated weights of approximately .


Taxonomy

The crested serpent eagle is placed along with the snake eagles of the genus ''Circaetus'' in the subfamily Circaetinae. The nominate subspecies has a black throat while the peninsular Indian form has a brownish throat. There are clinal latitudinal variations, with size decreasing southward. The small islands taxa are generally smaller in size than the taxa from the Asian mainland/larger islands in a phenomenon termed as insular dwarfism. Within its widespread range across tropical Asia, 21 subspecies have been proposed: * ''S. c. batu'' from southern Sumatra and Batu, * ''S. c. bido'' from
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
and Bali, * ''S. c. burmanicus'' in most of
Indochina Mainland Southeast Asia, also known as the Indochinese Peninsula or Indochina, is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to the west an ...
, * ''S. c. hoya'' from
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
, * ''S. c. malayensis'' of the Thai-Malay Peninsula and northern
Sumatra Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent i ...
, * ''S. c. melanotis'' in Peninsular India, * ''S. c. palawanensis'' from
Palawan Palawan (), officially the Province of Palawan ( cyo, Probinsya i'ang Palawan; tl, Lalawigan ng Palawan), is an archipelagic province of the Philippines that is located in the region of Mimaropa. It is the largest province in the country in t ...
, * ''S. c. pallidus'' from northern
Borneo Borneo (; id, Kalimantan) is the third-largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java, west of Sulawesi, and e ...
, * ''S. c. richmondi'' from southern Borneo, * ''S. c. ricketti'' in northern
Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making ...
and southern
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
, * ''S. c. rutherfordi'' from
Hainan Hainan (, ; ) is the smallest and southernmost province of the People's Republic of China (PRC), consisting of various islands in the South China Sea. , the largest and most populous island in China,The island of Taiwan, which is slightly l ...
, and * ''S. c. spilogaster'' of Sri Lanka. The remaining sub-species are all restricted to smaller islands: * ''S. c. abbotti'' (Simeulue serpent eagle) from Simeulue, * ''S. c. asturinus'' (Nias serpent eagle) from
Nias Nias ( id, Pulau Nias, Nias language: ''Tanö Niha'') (sometimes called Little Sumatra in English) is an island located off the western coast of Sumatra, Indonesia. Nias is also the name of the archipelago () of which the island is the centre ...
, * ''S. c. baweanus'' (Bawean serpent eagle) of the Bawean, * ''S. c. davisoni'' in the Andamans, * ''S. c. minimus'' (Central Nicobar serpent eagle) from the central Nicobars, * ''S. c. natunensis'' (Natuna serpent eagle) from
Natuna ''(Sacred Ocean, Fortune Land) , image_map = , pushpin_map = Indonesia Riau Islands#Indonesia Sumatra#Indonesia#South China Sea , pushpin_map_caption = Location in Riau Islands##Location in Sumatra##Location in I ...
, * ''S. c. perplexus'' (Ryukyu serpent eagle) from
Ryukyu The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yonagu ...
, and * ''S. c. sipora'' (Mentawai serpent eagle) from Mentawai. The last seven (with English names in brackets) are sometimes treated as separate species. Although the crested serpent eagle remains widespread and fairly common overall, some of the taxa that are restricted to small islands are believed to have relatively small populations that likely are in the hundreds. The rarest is probably the Bawean serpent eagle with a declining population of about 26–37 pairs, which makes it critically endangered.


Behaviour and ecology

The crested serpent eagle is a
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchocephalia ...
eater which hunts over forests, often close to wet grassland, for
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more ...
s and lizards. It has also been observed to prey on birds, amphibians, mammals and fishes. It is found mainly over areas with thick vegetation both on the low hills and the plains. This species is a resident species, but in some parts of their range they are found only in summer. The call is a distinctive ''Kluee-wip-wip'' with the first note being high and rising. They call a lot in the late mornings from their perches where they spend a lot of time and they rise on thermals in the mornings. In southern Taiwan, males have a larger home range than females. Males on average had a home range of 16.7 km2 while females used about 7 km2. When alarmed, they erect the crest and the head appears large and framed by the ruff. They will sometimes follow snakes on the ground. They roost in the interiors of trees with dense foliage. A radio-telemetric study of the species in Taiwan found that the birds spend 98% of the day perched and usually finding food in the morning hours. They appear to use a sit and wait foraging strategy. The breeding season begins in late winter when they start courting and establishing territories. The eggs are laid in early summer. Old nests are often refurbished and reused in India but a study in Penang found them to build fresh nests each year. A study in India found that most nests were built along riverine trees. The nest is a large platform built high on a tree. Both birds in a pair build the nest but the female alone incubates. The male guards when the female forages. In central India, the ''
Terminalia tomentosa ''Terminalia elliptica'' is a species of '' Terminalia'' native to southern and southeast Asia in India, Nepal, Bangladesh, Myanmar, Thailand, Laos, Cambodia, and Vietnam.Sal and Saaj Deforestation in West Nepal"Terminalia Tomentosa"/ref> It is a ...
'' is often used while '' Terminalia bellirica'' and '' Dalbergia latifolia'' was often used in southern India. In Penang, the nest trees were typically large and isolated from other trees with lot of room for the birds to fly in and out. The nests are lined with green leaves collected from nearby and are placed facing down on the nest floor. The usual clutch is one egg but two are sometimes laid and only a single chick is successfully raised in a season. When eggs are lost, a replacement is laid two to seven weeks later. The eggs hatch after about 41 days and the young fledge after about two months. Nests are defended by the parents. Several species of endoparasitic nematodes have been recovered from the intestines of crested serpent eagles, including ''Madelinema angelae''. Avian pox virus infections which cause warts on the face have been observed in a wild bird living in Taiwan. A number of ectoparasitic bird lice have been described from the species including ''Kurodaia cheelae''. In Penang, it was found that cinereous tits (''Parus cinereus ambiguus'') tended to nest close to nesting crested serpent eagles, presumably due to safety from predators like crows that may be driven off by the eagles. They have also been found to visit the nests of the eagles to collect fur from the remains of dead mammal prey.


References


External links


Photographs and videos

Call recordings
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