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 considerable variations and some authorities prefer to treat several of its subspecies as completely separate species.[2] In the past, several species including the Philippine serpent eagle (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.

Crested serpent eagle
Adult (ssp. melanotis, Bandipur National Park, India)
Call of ssp. melanotis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Accipitriformes
Family: Accipitridae
Genus: Spilornis
Species:
S. cheela
Binomial name
Spilornis cheela
Latham, 1790

Description
Subspecies S. c. pallidus from the lowlands of northern Borneo

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 feathers are black with broad white bars. Young birds show a lot of white on the head.[3][4] The tarsus is unfeathered and covered by hexagonal scales. The upper mandible does not have an overhanging festoon to the tip.[5]

Distribution, taxonomy and status
Immature ssp. perplexus (Iriomote Okinawa)

Within its widespread range across tropical Asia, 21 populations have been named as subspecies.[2] The most widespread sub-species are the nominate from along the sub-Himalayan range in India and Nepal,

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,
  • 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,
  • S. c. perplexus (Ryukyu serpent eagle) from Ryukyu, and
  • S. c. sipora (Mentawai serpent eagle) from Mentawai.

The last seven (with English names in brackets) are sometimes treated as separate species.[2] 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.[2] The rarest is probably the Bawean serpent eagle with a declining population of about 26–37 pairs, which makes it critically endangered.[6][7][8][9]

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.[3] 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.[2][7]

The specific name cheela is derived from the Hindi name for kites.

One syntype specimen of Spilornis rutherfordi Swinhoe (Ibis, 1870, p.85.), the Hainan subspecies, is held in the collections of National Museums Liverpool at World Museum, with accession number T2819 (male adult). The specimen was collected in Hainan, China in February 1868 by Robert Swinhoe and came to the Liverpool national collection via Canon Henry Baker Tristram’s collection which was purchased in 1896.

Behaviour and ecology
Crested serpent eagle - (Spilornis cheela) 1

The crested serpent eagle, as its English name suggests, is a reptile eater which hunts over forests, often close to wet grassland,[10] for snakes and lizards. It has also been observed to prey on birds, amphibians, mammals and fishes.[11] It is placed along with the snake eagles of the genus Circaetus in the subfamily Circaetinae.[12] 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.[3][13]

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.[3] 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.[14] When alarmed, they erect the crest and the head appears large and framed by the ruff.[5] They will sometimes follow snakes on the ground.[15] They roost in the interiors of trees with dense foliage.[16] 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.[17]

In flight the wide white band is distinctive

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.[18] 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 is often used while Terminalia bellirica and Dalbergia latifolia was often used in southern India.[11] 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.[15][18] 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.[5][19][20][21]

Several species of endoparasitic nematodes have been recovered from the intestines of crested serpent eagles, including Madelinema angelae.[22][23] Avian pox virus infections which cause warts on the face have been observed in a wild bird living in Taiwan.[24] A number of ectoparasitic bird lice have been described from the species including Kurodaia cheelae.[25] 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.[18]

References
  1. BirdLife International (2012). "Spilornis cheela". IUCN Red List of Threatened Species. 2012. Retrieved 26 November 2013.CS1 maint: ref=harv (link)
  2. Ferguson-Lees, James & Christie, David A. (2001). Raptors of the World. Christopher Helm, London. ISBN 0-7136-8026-1
  3. Rasmussen PC; JC Anderton (2005). Birds of South Asia: The Ripley Guide. Volume 2. Smithsonian Institution & Lynx Edicions. pp. 92–93.
  4. Blanford, WT (1895). The Fauna of British India, including Ceylon and Burma. Birds. Volume 3. London: Taylor and Francis. pp. 357–360.
  5. Ali, S; SD Ripley (1978). Handbook of the Birds of India and Pakistan. Volume 1 (2nd ed.). New Delhi: Oxford University Press. pp. 329–334.
  6. Nijman, V. (2006). "The endemic Bawean Serpent-eagle Spilornis baweanus: habitat use, abundance and conservation". Bird Conservation International. 16 (2): 131–143. doi:10.1017/S0959270906000219.
  7. Mayr, E; Cottrell, G W, eds. (1979). Check-List of Birds of the World. Volume 1 (2nd ed.). Cambridge, Massachusetts: Museum of Comparative Zoology. pp. 311–315.
  8. Oberholser, HC (1923). "The birds of the Natuna Islands". Bulletin of the United States National Museum. 159: 18–21.
  9. Sclater, WL (1918). "Descriptions of new hawks". Bulletin of the British Ornithologists' Club. 38 (245): 37–41.
  10. Ueta, M; Minton, JS (1996). "Habitat preference of Crested Serpent Eagles in Southern Japan" (PDF). J. Raptor Res. 30 (2): 99–100.
  11. Gokula, Varadarajan (2012). "Breeding ecology of the crested serpent eagle Spilornis cheela (Latham, 1790) (Aves: Accipitriformes: Accipitridae) in Kolli Hills, Tamil Nadu, India". Taprobanica. 4 (2): 77–82. doi:10.4038/tapro.v4i2.5059.
  12. Lerner, Heather R.L.; Mindell, David P. (2005). "Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA". Molecular Phylogenetics and Evolution. 37 (2): 327–46. doi:10.1016/j.ympev.2005.04.010. PMID 15925523.
  13. Purandare, K. (2002). "Attempt by the crested Serpent Eagle Spilornis cheela to seize the Indian cobra Naja naja". J. Bombay Nat. Hist. Soc. 99 (2): 299.
  14. Chou, Ta-Ching; Bruno A. Walther; Pei-Fen Lee (2012). "Spacing Pattern of the Crested Serpent Eagle (Spilornis cheela hoya) in Southern Taiwan" (PDF). Taiwania. 57 (1): 1–13. Archived from the original (PDF) on 2013-12-03. Retrieved 2013-02-05.
  15. Naoroji, Rishad K; Monga, SG (1983). "Observations on the Crested Serpent Eagle (Spilornis cheela) in Rajpipla forests – South Gujarat". J. Bombay Nat. Hist. Soc. 80 (2): 273–285.
  16. Baker, ECS (1914). "Some notes on tame Serpent Eagles". The Avicultural Magazine. 5 (5): 154–159.
  17. Chia-hong Liu (2010). Diurnal activity pattern of Crested Serpent Eagles Spilornis cheela hoya in Kenting, southern Taiwan (in Chinese). Unpublished Masters Thesis. Archived from the original on 2012-04-02. Retrieved 2011-09-13.
  18. Cairns, J (1968). "The serpent eagles Spilornis cheela of Penang Island, Malaya". Ibis. 110 (4): 569–571. doi:10.1111/j.1474-919X.1968.tb00064.x.
  19. Daly, W. Mahon (1895). "The southern Indian harrier eagle". J. Bombay Nat. Hist. Soc. 9 (4): 487.
  20. Osman, SM (1972). "The Crested Serpent Eagle". J. Bombay Nat. Hist. Soc. 69 (3): 461–468.
  21. Hume, AO (1890). The nests and eggs of Indian birds. Volume 3. R H Porter, London. pp. 152–154.
  22. Schmidt GD; Kuntz, Robert E. (1971). "Nematode Parasites of Oceanica. XI. Madelinema angelae gen. et sp. n., and Inglisonema mawsonae sp. n. (Heterakoidea: Inglisonematidae) from Birds". Journal of Parasitology. 57 (3): 479–484. doi:10.2307/3277897. JSTOR 3277897. PMID 5104559.
  23. Yoshino, T.; Shingake, T.; Onuma, M.; Kinjo, T.; Yanai, T.; Fukushi, H.; Kuwana, T.; Asakawa, M. (2010). "Parasitic helminths and arthropods of the Crested Serpent Eagle Spilornis cheela perplexus Swann, 1922 from the Yaeyama". Journal of the Yamashina Institute for Ornithology. 41 (1): 55–61. doi:10.3312/jyio.41.55.
  24. Chen CC, Pei KJ, Lee FR, Tzeng MP, Chang TC (2011). "Avian pox infection in a free-living crested serpent eagle (Spilornis cheela) in southern Taiwan". Avian Dis. 55 (1): 143–146. doi:10.1637/9510-082610-Case.1. PMID 21500652.
  25. Price RD; Beer, JR (1963). "The Genus Kurodaia (Mallophaga: Menoponidae) from the Falconiformes, with Elevation of the Subgenus Falcomenopon to Generic Rank". Annals of the Entomological Society of America. 56 (3): 379–385. doi:10.1093/aesa/56.3.379.
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