Crested Serpent-eagle
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The crested serpent eagle (''Spilornis cheela'') is a medium-sized
bird of prey Birds of prey or predatory birds, also known as (although not the same as) raptors, are hypercarnivorous bird species that actively predation, hunt and feed on other vertebrates (mainly mammals, reptiles and smaller birds). In addition to speed ...
that is found in forested habitats across
tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
. Within its widespread range across the
Indian Subcontinent The Indian subcontinent is a physiographic region of Asia below the Himalayas which projects into the Indian Ocean between the Bay of Bengal to the east and the Arabian Sea to the west. It is now divided between Bangladesh, India, and Pakista ...
,
Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...
and
East Asia East Asia is a geocultural region of Asia. It includes China, Japan, Mongolia, North Korea, South Korea, and Taiwan, plus two special administrative regions of China, Hong Kong and Macau. The economies of Economy of China, China, Economy of Ja ...
, there are considerable variations and some authorities prefer to treat several of its
subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
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 The Andaman serpent eagle (''Spilornis elgini''), also known as the Andaman dark-serpent eagle or the dark serpent eagle, is a medium-sized bird in the family Accipitridae, the raptor family, that is only found in India on the Andaman Islands. It ...
(''S. elgini'') and
South Nicobar serpent eagle The Great Nicobar serpent eagle (''Spilornis klossi''), also known as the South Nicobar serpent eagle, is a species of bird of prey in the family Accipitridae. It is probably the smallest known eagle, with a weight of about , a wingspan of and a ...
(''S. klossi'') were treated as subspecies of the Crested serpent eagle. All members within the
species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
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
cere The beak, bill, or Rostrum (anatomy), rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, wikt:grasp#Verb, grasping, and holding (in wikt:probe ...
s 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 ''Circaetus'', the snake eagles, is a genus of medium-sized eagles in the bird of prey family Accipitridae. They are mainly resident African species, but the migratory short-toed snake eagle breeds from the Mediterranean basin into Russia, the ...
'' snake-eagles in the subfamily
Circaetinae Circaetinae is a subfamily of the family Accipitridae which contains a group of medium to large broad-winged birds of prey. The group is sometimes treated as tribe Circaetini. These birds mainly specialise in feeding on snakes and other reptiles ...
.


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 an exa ...
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 Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...
. Within its widespread range across tropical Asia, 21 subspecies have been proposed: * ''S. c. batu'' from southern Sumatra and
Batu Batu may refer to: Geography *Batu City, a city in East Java, Indonesia *Batu Islands, an archipelago of Indonesia * Batu, Iran, a village in Razavi Khorasan Province, Iran * Batu, Kuala Lumpur, an area in Malaysia *Batu (town), Ethiopia * Batu ...
, * ''S. c. bido'' from
Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
and
Bali Bali (English:; Balinese language, Balinese: ) is a Provinces of Indonesia, province of Indonesia and the westernmost of the Lesser Sunda Islands. East of Java and west of Lombok, the province includes the island of Bali and a few smaller o ...
, * ''S. c. burmanicus'' in most of
Indochina Mainland Southeast Asia (historically known as Indochina and the Indochinese Peninsula) 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 th ...
, * ''S. c. hoya'' from
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...
, * ''S. c. malayensis'' of the
Thai-Malay Peninsula The Malay Peninsula is located in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The area contains Peninsular Malaysia, Southern Tha ...
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 list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
, * ''S. c. melanotis'' in
Peninsular India South India, also known as Southern India or Peninsular India, is the southern part of the Deccan Peninsula in India encompassing the states of Andhra Pradesh, Karnataka, Kerala, Tamil Nadu and Telangana as well as the Union territories of In ...
, * ''S. c. palawanensis'' from
Palawan Palawan (, ), officially the Province of 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 terms of total area of . The capital and largest c ...
, * ''S. c. pallidus'' from northern
Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
, * ''S. c. richmondi'' from southern Borneo, * ''S. c. ricketti'' in northern
Vietnam Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about and a population of over 100 million, making it the world's List of countries and depende ...
and southern
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
, * ''S. c. rutherfordi'' from
Hainan Hainan is an island provinces of China, province and the southernmost province of China. It consists of the eponymous Hainan Island and various smaller islands in the South China Sea under the province's administration. The name literally mean ...
, 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 Simeulue is an island of Indonesia, off the west coast of Sumatra. It covers an area of 1,754 square kilometre (677 square miles), including minor offshore islands. It had a population of 80,674 at the 2010 census and 92,865 at the 2020 census ...
, * ''S. c. asturinus'' (Nias serpent eagle) from
Nias Nias (, Nias: ''Tanö Niha'') 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, but also includes the Batu Islands to the southeast and the small ...
, * ''S. c. baweanus'' (Bawean serpent eagle) of the
Bawean Bawean () is an List of islands of Indonesia, island of Indonesia located approximately north of Surabaya in the Java Sea, off the coast of Java. It is administered by Gresik Regency of East Java province. It is approximately in diameter and ...
, * ''S. c. davisoni'' in the
Andamans The Andaman Islands () are an archipelago, made up of 200 islands, in the northeastern Indian Ocean about southwest off the coasts of Myanmar's Ayeyarwady Region. Together with the Nicobar Islands to their south, the Andamans serve as a mari ...
, * ''S. c. minimus'' (Central Nicobar serpent eagle) from the central
Nicobars The Nicobar Islands are an archipelagic island chain in the eastern Indian Ocean. They are located in Southeast Asia, northwest of Aceh on Sumatra, and separated from Thailand to the east by the Andaman Sea. Located southeast of the Indian sub ...
, * ''S. c. natunensis'' (Natuna serpent eagle) from
Natuna Natuna Regency is an islands regency located in the northernmost part of the Province of Riau Islands, Indonesia. It contains at least 154 islands, of which 127 of them are reported as uninhabited. This archipelago, with a land area of 1,978.49& ...
, * ''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 Geography of Taiwan, Taiwan: the Ryukyu Islands are divided into the Satsunan Islands (Ōsumi Islands, Ōsumi, Tokara Islands, Tokara and A ...
, 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 In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
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 An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...
.


Behaviour and ecology

The crested serpent eagle is a
reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...
eater which hunts over forests, often close to wet grassland, for
snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
s and
lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
s. It has also been observed to prey on birds, amphibians, mammals, fishes, termites and large earthworms. 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
thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
s 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'' (sin. ''Terminalia tormentosa'') 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"Te ...
'' is often used while ''
Terminalia bellirica ''Terminalia bellirica'', known as baheda, bahera, behada, beleric or bastard myrobalan (Arabic: beliledj بليلج, borrowed from Middle Persian Balilag), Persian بلیله (Balileh), Sanskrit: Vibhītaka बिभीतक, Aksha is a large ...
'' and ''
Dalbergia latifolia ''Dalbergia latifolia'' (synonym ''Dalbergia emarginata'') is a premier timber species, also known as the Indian rosewood ( Tamil / தமிழ்: Eetti / ஈட்டி) ( Telugu / తెలుగు: Irugudu/ ఇరుగుడు). It is n ...
'' 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 tit The cinereous tit (''Parus cinereus'') is a species of bird in the tit family Paridae. This species is made up of several populations that were earlier treated as subspecies of the great tit (''Parus major''). These birds are grey backed with whi ...
s (''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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crested serpent eagle The crested serpent eagle (''Spilornis cheela'') is a medium-sized bird of prey that is found in forested habitats across tropical Asia. Within its widespread range across the Indian Subcontinent, Southeast Asia and East Asia, there are considera ...
Articles containing video clips
crested serpent eagle The crested serpent eagle (''Spilornis cheela'') is a medium-sized bird of prey that is found in forested habitats across tropical Asia. Within its widespread range across the Indian Subcontinent, Southeast Asia and East Asia, there are considera ...
Birds of Indomalaya
crested serpent eagle The crested serpent eagle (''Spilornis cheela'') is a medium-sized bird of prey that is found in forested habitats across tropical Asia. Within its widespread range across the Indian Subcontinent, Southeast Asia and East Asia, there are considera ...