Indian Peafowl

Indian Peafowl
Male (peacock) displaying
Female (peahen)
Conservation status

Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Galliformes
Family: Phasianidae
Genus: Pavo
Species: P. cristatus
Binomial name
Pavo cristatus
Linnaeus, 1758

The Indian Peafowl or Blue Peafowl (Pavo cristatus) is a large and brightly coloured pheasant native to South Asia, but introduced and semi-feral in many other parts of the world. The male, peacock, is predominantly blue with a fan-like crest of spatula-tipped wire-like feathers and is best known for the long train made up of elongated upper-tail covert feathers which bear colourful eyespots. These stiff and elongated feathers are raised into a fan and quivered in a display during courtship. The female lacks the train, has a greenish lower neck and has a duller brown plumage. They are found mainly on the ground in open forest or cultivation where they forage for berries, grains but will also prey on snakes, lizards, and small rodents. Their loud calls make them easy to detect, and in forest areas, often indicate the presence of a predator such as a tiger. They forage on the ground, moving in small groups and will usually try to escape on foot through undergrowth and avoid flying. They will fly up into tall trees to roost, however.

Contents

Description

Head of a peacock

The male, peacock, is a large bird with a length from bill to tail of 100 to 115 cm (40 to 46 inches) and to the end of a fully grown train as much as 195 to 225 cm (78 to 90 inches) and weigh 4–6 kg (8.8-13.2 lbs). The females, or peahens, are smaller at around 95 cm (38 inches) in length and weigh 2.75–4 kg (6-8.8 lbs). Their size, colour and shape of crest make them unmistakable within their native distribution range. The male is metallic blue on the crown, the feathers of the head being short and curled. The fan-shaped crest on the head is made of feathers with bare black shafts and tipped with blush-green webbing. A white stripe above the eye and a crescent shaped white patch below the eye are formed by bare white skin. The sides of the head have iridescent greenish blue feathers. The back has scaly bronze-green feathers with black and copper markings. The scapular and the wings are buff and barred in black, the primaries are chestnut and the secondaries are black. The tail is dark brown and the "train" is made up by elongated upper tail coverts (more than 200 feathers, the actual tail has only 20 feathers) and nearly all of these feathers end with an elaborate eye-spot. A few of the outer feathers lack the spot and end in a crescent shaped black tip. The underside is dark glossy green shading into blackish under the tail. The thighs are buff coloured. The male has a spur on the leg above the hind toe.[2][3]

The adult peahen has a rufous-brown head with a crest as in the male but the tips chestnut edged with green. The upper body is brownish with paler mottling. The primaries, secondaries and tail are dark brown. The lower neck is metallic green and the breast feathers are dark brown glossed with green. The rest of the underparts are whitish.[2] Downy young are pale buff with a dark brown mark on the nape connecting with the eyes.[4] Young males looks like the females but the wings are chestnut coloured.[4][5]

The most common calls of the birds are a loud pia-ow or may-awe. The frequency of calling increases before the Monsoon season but may also be delivered in alarm or when they are disturbed by loud noises. In forests, theirs calls often indicate the presence of a predators such as the tiger.[2][5] They also make many other calls such as a rapid series of ka-aan..ka-aan or a rapid kok-kok.[5][6]

A white mutant that is maintained by breeding in many parks such as this one at the Jardin des Plantes, Paris
The "ocellate" tail coverts of a peacock

A melanistic form with black wings, initially considered as a subspecies P. c. nigripennis, also known as a Japanned Peafowl was a topic of some interest during Darwin's time.[4] It is however only a case of genetic variation within the population. Other variations include the pied and white forms all of which are the result of allelic variation at specific loci.[7][8]

Etymology

The Latin genus name Pavo and the Anglo-Saxon Pawe (from which the word "Peacock" is derived) are believed to be echoic in their origin and based on the usual call of the bird. The species name cristatus refers to the crest.[9]

The earliest usage of the word in written English is from around 1300 and spelling variants include pecok, pekok, pecokk, peacocke, peocock, pyckock, poucock, pocok, pokok, pokokke, and poocok among others. The current spelling was established in the late 17th century. Chaucer (1343–1400) used the word to refer to a proud and ostentatious person in his simile "proud a pekok" in Troilus and Criseyde (Book I, line 210).[10]

The Greek word for peacock was taos and was related to the Persian "tavus" (as in Takht-i-Tâvus for the famed Peacock Throne[11]). The Hebrew word tuk (plural tukkiyim) has been said to have been derived from the Tamil tokei but sometimes traced to the Egyptian tekh.[12][13]

Distribution and habitat

The elongated upper tail coverts make up the "train" of the peacock

The Indian Peafowl is a resident breeder across the Indian subcontinent and is found in the drier lowland areas of Sri Lanka. In South Asia, it is found mainly below an altitude of 1800 m and in rare cases seen at about 2000m.[14] It is found in moist and dry-deciduous forests, but can adapt to live in cultivated regions and around human habitations and is usually found where water is available. In many parts of northern India, they are protected by religious sentiment and will forage around villages and towns for scraps. Some have suggested that the peacock was introduced into Europe by Alexander the Great[15], while others suggest that the bird had reached Athens by 450 BC and may have been introduced even earlier.[16] It has since been introduced in many other parts of the world and has become feral in some areas.[5]

Behaviour and ecology

Peafowl are best known for the male's extravagant display feathers which, despite actually growing from their back, are thought of as a tail. The "train" is in reality made up of the enormously elongated upper tail coverts. The tail itself is brown and short as in the peahen. The colours result from the micro-structure of the feathers and the resulting optical phenomena.[17] The long train feathers develop only after the second year of life. Fully developed trains are found in birds older than four years. In northern India, these begin to develop each February and are moulted at the end of August.[18]

The ornate train is believed to be the result of female sexual selection as males raised the feathers into a fan and quiver it as part of courtship display. Many studies have suggested that the quality of train is an honest signal of the condition of males and that peahens select males on the basis of their plumage. More recent studies however, suggest that other cues may be involved in mate selection by peahens.[19][20]

Indian Peahen with immatures at Hodal in Faridabad District of Haryana, India

Peafowl forage on the ground in small groups, known as musters, that usually have a cock and 3 to 5 hens. After the breeding season, the flocks tend to be made up only of females and young. They are found in the open early in the mornings and tend to stay in cover during the heat of the day. They are fond of dust-bathing and at dusk, groups walk in single file to a favourite waterhole to drink. When disturbed, they usually escape by running and rarely take to flight.[5]

Peafowl produce loud calls especially in the breeding season. They may call at night when alarmed and neighbouring birds may call in a relay like series. Nearly seven different call variants have been identified in the peacocks apart from six alarm calls that are commonly produced by both sexes.[21]

Peafowl roost in groups during on tall trees but may sometimes make use of rocks, buildings or pylons. In the Gir forest, they chose tall trees in steep river banks.[22][23] Birds arrive at dusk and call frequently before taking their position on the roost trees.[24] Due to this habit of congregating at the roost, many population studies are made at these sites. The population structure is not well understood, in a study in northern India (Jodhpur) the number of males was 170-210 for 100 females but a study involving evening counts at the roost site in southern India (Injar) suggested a ratio of 47 males for 100 females.[6]

Breeding

The rear view of a displaying male showing the short tail feathers

Peacocks are polygamous, and the breeding season is spread out but appears to be dependent on the rains. Several males may congregate at a lek site and these males are often closely related.[25] Males at lek appear to maintain small territories next to each other and they allow females to visit them and make no attempt to guard harems. Females do not appear to favour specific males.[26] The males display in courtship by raising the upper-tail coverts into an arched fan. The wings are held half open and drooped and it periodically vibrates the long feathers producing a ruffling sound. The cock faces the hen initially and struts and prances around and sometimes turns around to display the tail.[5] Males may also freeze over food to invite a female in a form of courtship feeding.[27] Males may display even in the absence of females. When a male is displaying, females do not appear to show any interest and usually continue their foraging.[6] The peak season in southern India is April to May, January to March in Sri Lanka and June in northern India. The nest is a shallow scrape in the ground lined with leaves, sticks and other debris. Nests are sometimes placed on buildings[28] and in earlier times have been recorded using the disused nest platforms of the Indian White-rumped Vultures. The clutch consists of 4-8 fawn to buff white eggs which are incubated only by the female. The eggs hatch after about 28 days to hatch. The chicks are nidifugous and follow the mother around after hatching.[2] Downy young may sometimes climb on their mothers back and the female may carry them in flight to a safe tree branch.[29][30] An unusual instance of a male incubating a clutch of eggs has been reported.[5][31]

Feeding

Peafowl are omnivorous and eat seeds, insects, fruits, small mammals and reptiles. They feed on small snakes but keep their distance from larger ones.[32] In the Gir forest of Gujarat, are large percent of their food is made up of the fallen berries of Zizyphus.[33] Around cultivated areas, peafowl feed on a wide range of crops such as groundnut, tomato, paddy, chilly and even bananas.[6] Around human habitations, they feed on a variety of food scraps and even human excreta.[5]

Mortality factors

Thayer in his "Peacock in the Woods" (1907) suggested that the ornate tail was an aid to camouflage

Adult peafowl can usually escape ground predators by flying into trees. Leopards are able to ambush them however, and in some areas such as the Gir forest, peafowl are common prey.[23] Foraging in groups provides some safety as there are more eyes to look out for predators.[34] They are sometimes hunted by large birds of prey such as the Changeable Hawk-eagle and Rock Eagle-owl.[35][36] Chicks are prone to predation. Adults living near human habitations are sometimes hunted by domestic dogs or by humans in some areas (southern Tamil Nadu) for folk-remedies involving the use of "peacock oil".[6]

In captivity, birds have been known to live for 23 years but it is estimated that they live for only about 15 years in the wild.[37]

Conservation and status

The peacock became associated with pomp, pride and vanity as shown in this caricature of "Sir Vane Peacock" based on the work of J J Grandville

Indian Peafowl are widely distributed in the wild across South Asia and protected both culturally in many areas and by law in India. Conservative estimates of the population put them at more than 100,000.[38] Illegal poaching for meat however continues and declines have been noted in parts of India.[39]

Crosses between a male Green Peafowl, Pavo muticus and a peahen produces a stable hybrid called a "spalding", named after Mrs. Keith Spalding, a bird fancier in California.[40] There can be a problem if birds of unknown pedigree are released into the wild.

Poaching of peacocks for their meat, feathers and accidental poisoning by feeding on pesticide treated seeds are known threats to wild birds.[41] Methods to identify if feathers have been plucked or have been shed naturally have been developed as Indian law allows the collection of feathers that have been shed.[42]

In parts of India, the birds can be a nuisance to agriculture as they damage crops.[5] They can also be a problem in gardens and homes where they damage plants, attack their reflections breaking glass and mirrors, perch and scratch cars or leave their droppings. Many cities where they have been introduced and gone feral have peafowl management programmes. These include educating citizens on how to prevent the birds from causing damage while treating the birds humanely.[43][44][45]

In culture

Statue of Murugan or Skanda from the temple at Tiruvottiyur

Prominent in many cultures, the peacock has been used in numerous iconic representations, including being designated the national bird of India in 1963.[5] The peacock, known as Mayura in Sanskrit, has enjoyed a fabled place in India since and is frequently depicted in temple art, mythology, poetry, folk-music and traditions.[46] Many Hindu deities are associated with the bird, Krishna is often depicted with a feather in his headband, while worshippers of Shiva associate the bird as the steed of the God of war, Karthikeya (also known as Skanda or Murugan). In Buddhist philosophy, the peacock represents wisdom.[47] Peacock feathers are used in many rituals and ornamentation. Peacock motifs are widespread in Indian temple architecture, old coinage, textiles and continue to be used in many modern items of art and utility.[16] In Greek mythology the origin of the peacocks plumage is explained in the tale of Juno and Argus.[40] The main figure of the Kurdish religion Yezidism, Melek Taus, is most commonly depicted as a peacock.[48][49] Peacock motifs are widely used even today such as in logo of the US NBC television network and the Sri Lankan Airlines.

Juno and Argus, by Rubens (c 1620)

These birds were often kept in menageries and as ornaments in large gardens and estates. A reference in the Bible mentions a peacock owned by King Solomon (I Kings, chapt X 22 and 23). In medieval times, knights in Europe took a "Vow of the Peacock" and decorated their helmets with its plumes. Feathers were buried with Viking warriors[50] and the flesh of the bird was said to cure snake venom and many other maladies. Numerous uses in Ayurveda have been documented. Peafowl were said to keep an area free of snakes.[51]

The colours of the peacock and the contrast with the much duller peahen were a puzzle to early thinkers. Charles Darwin wrote to Asa Gray that the "sight of a feather in a peacock’s tail , whenever I gaze at it, makes me sick!" as he failed to see an adaptive advantage for the extravagant tail which seemed only to be an encumbrance. Darwin tried to develop a second principle of "sexual selection" to resolve the problem. American artist Abbott Handerson Thayer tried to show, from his own imagination, the value of the eyespots in camouflage in a 1907 painting.[52] It was only in the 1970s that this apparent contradiction was resolved based on the evolution of honest signalling and the handicap principle of Amotz Zahavi.[53]

In Anglo-Indian usage of the 1850s, to peacock meant making visits to ladies and gentlemen in the morning. In the 1890s, the term "peacocking" in Australia referred to the practice of buying up the best pieces of land ("picking the eyes") so as to render the surrounding lands valueless.[54] The English word "peacock" has come to be used to describe a man who is very proud or gives a lot of attention to his clothing.[55]

References

  1. ↑ BirdLife International (2009) Pavo cristatus In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. www.iucnredlist.org Retrieved on 2010-02-15.
  2. ↑ 2.0 2.1 2.2 2.3 Whistler, Hugh (1949). Popular handbook of Indian birds (4 ed.). Gurney and Jackson, London. pp. 401–410. ISBN 1406745766. http://www.archive.org/stream/popularhandbooko033226mbp#page/n458/mode/1up/. 
  3. ↑ Blanford, WT (1898). Fauna of British India. Birds. 4. Taylor and Francis, London. pp. 681–70. http://www.archive.org/stream/birdsindia04oaterich#page/68/mode/1up. 
  4. ↑ 4.0 4.1 4.2 Baker, ECS (1928). Fauna of British India. Birds. Volume 5 (2 ed.). Taylor and Francis, London. pp. 282–284. http://www.archive.org/stream/BakerFbiBirds5/BakerFBI5#page/n304/mode/1up/. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 Ali, S & S D Ripley (1980). Handbook of the birds of India and Pakistan. 2 (2 ed.). Oxford University Press. pp. 123–126. ISBN 0195620631. 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Johnsingh,AJT; Murali,S (1978). "The ecology and behaviour of the Indian Peafowl (Pavo cristatus) Linn. of Injar". J. Bombay Nat. Hist. Soc. 75 (4): 1069–1079. 
  7. ↑ Somes, RG Jr. and R. E. Burger (1991). "Plumage Color Inheritance of the Indian Blue Peafowl (Pavo Cristatus): Blue, Black-Shouldered, Cameo, and Oaten". Journal of Heredity 82: 64–68. doi:10.1093/jhered/82.1.64 (inactive 2010-06-02). 
  8. ↑ Somes, RG Jr. and R. E. Burger. "Inheritance of the White and Pied Plumage Color Patterns in the Indian Peafowl (Pavo cristatus)". J. Hered. 84: 57–62. 
  9. ↑ Johnsgard, P.A. (1999). The Pheasants of the World: Biology and Natural History. Washington, DC: Smithsonian Institution Press. p. 374. ISBN 1-56098-839-8. 
  10. ↑ Weekley, E (1921). An etymological dictionary of modern English. John Murray, London. http://www.archive.org/stream/etymologicaldict00weekuoft#page/528/mode/1up/. 
  11. ↑ Lal, Krishna (2007). Peacock in Indian art, thought and literature. Abhinav Publications. ISBN 8170174295. 
  12. ↑ Burton, R F (1884). The book of the sword. Chatto and Windus, London. p. 155. http://www.archive.org/stream/booksword00unkngoog#page/n197/mode/1up/. 
  13. ↑ Hehn, Victor; James P. Mallory (1976). Cultivated plants and domesticated animals in their migration from Asia to Europe: historico-linguistic studies Volume 7 of Amsterdam studies in the theory and history of linguistic science Amsterdam studies in the theory and history of linguistic science. Series I, Amsterdam classics in linguistics,1800-1925. John Benjamins Publishing Company. p. 263. ISBN 9027208719. 
  14. ↑ Dodsworth, PTL (1912). "Occurrence of the Common Peafowl Pavo cristatus, Linnaeus in the neighbourhood of Simla, N.W. Himalayas". J. Bombay Nat. Hist. Soc. 21 (3): 1082–1083. 
  15. ↑ Whitman, CH (1898). "The birds of Old English literature". The journal of Germanic Philology 2 (2): 40. http://www.archive.org/stream/cu31924031439544#page/n43/mode/1up/. 
  16. ↑ 16.0 16.1 Nair, P. Thankappan (1974). "The Peacock Cult in Asia". Asian Folklore Studies 33 (2): 93–170. http://www.nanzan-u.ac.jp/SHUBUNKEN/publications/afs/pdf/a272.pdf. 
  17. ↑ Blau, S.K. (2004). "Light as a Feather: Structural Elements Give Peacock Plumes Their Color". Physics Today 57 (1): 18–20. doi:10.1063/1.1650059. http://www.aip.org/pt/vol-57/iss-1/p18.html. 
  18. ↑ Sharma, IK (1974). "Ecological Studies of the Plumes of the Peacock (Pavo cristatus')". The Condor 76 (3): 344–346. http://elibrary.unm.edu/sora/Condor/files/issues/v076n03/p0344-p0346.pdf. 
  19. ↑ Loyau, A.; Saint Jalme, M., and Cagniant, C. (2005). "Multiple sexual advertisements honestly reflect health status in peacocks (Pavo cristatus)". Behavioral Ecology and Sociobiology 58 (6): 552–557. doi:10.1007/s00265-005-0958-y. 
  20. ↑ Takahashi, M.; Arita, H., Hiraiwa-Hasegawa, M., Hasegawa, T. (2008). "Peahens do not prefer peacocks with more elaborate trains". Animal Behaviour 75 (4): 1209–1219. doi:10.1016/j.anbehav.2007.10.004. 
  21. ↑ Takahashi M & T Hasegawa (2008). "Seasonal and diurnal use of eight different call types by Indian peafowl ( Pavo cristatus )". Journal of Ethology 26 (3): 375–381. doi:10.1007/s10164-007-0078-4. 
  22. ↑ Trivedi,Pranav; Johnsingh,AJT (1996). "Roost selection by Indian Peafowl (Pavo cristatus) in Gir Forest, India". J. Bombay Nat. Hist. Soc. 93 (1): 25–29. 
  23. ↑ 23.0 23.1 Parasharya,BM; Mukherjee, Aeshita (1999). "Roosting behaviour of Indian Peafowl Pavo cristatus". J. Bombay Nat. Hist. Soc. 96 (3): 471–472. 
  24. ↑ Navaneethakannan,K (1984). "Activity patterns in a colony of Peafowls (Pavo cristatus) in nature". J. Bombay Nat. Hist. Soc. 81 (2): 387–393. 
  25. ↑ Petrie M, Krupa A, Burke T. (1999). "Peacocks lek with relatives even in the absence of social and environmental cues". Nature 401: 155–157. http://www.nbb.cornell.edu/neurobio/BioNB427/READINGS/Sherman1999.pdf. 
  26. ↑ Rands, M.R.M.; M.W. Ridley, A.D. Lelliott (1984-08). "The social organization of feral peafowl". Animal Behaviour 32 (3): 830–835. doi:doi: DOI: 10.1016/S0003-3472(84)80159-1. 
  27. ↑ Stokes, AW & H. Warrington Williams (1971). "Courtship Feeding in Gallinaceous Birds". The Auk 88 (3): 543–559. http://elibrary.unm.edu/sora/Auk/v088n03/p0543-p0559.pdf. 
  28. ↑ Vyas,R (1994). "Unusual breeding site of Indian Peafowl". Newsletter for Birdwatchers 34 (6): 139.. http://www.archive.org/stream/NLBW34_6#page/n21/mode/1up. 
  29. ↑ Singh, H (1964). "Peahens flying up with young". Newsletter for Birdwatchers 4 (1): 14. http://www.archive.org/stream/NLBW4#page/n14/mode/1up. 
  30. ↑ "Photograph showing peahen carrying chick". http://www.ee.tamu.edu/~aravindg/peahen_chick.jpg. 
  31. ↑ Shivrajkumar,YS (1957). "An incubating Peacock (Pavo cristatus Linn.)". J. Bombay Nat. Hist. Soc. 54 (2): 464. 
  32. ↑ Johnsingh,AJT (1976). "Peacocks and cobra". J. Bombay Nat. Hist. Soc. 73 (1): 214. 
  33. ↑ Trivedi,Pranav; Johnsingh,AJT (1995). "Diet of Indian Peafowl Pavo cristatus Linn. in Gir Forest, Gujarat". J. Bombay Nat. Hist. Soc. 92 (2): 262–263. 
  34. ↑ Yasmin,Shahla; Yahya,HSA (2000). "Group size and vigilance in Indian Peafowl Pavo cristatus (Linn.), Family: Phasianidae". J. Bombay Nat. Hist. Soc. 97 (3): 425–428. 
  35. ↑ Dhanwatey, Amrut S (1986). "A Crested Hawk-Eagle Spizaetus cirrhatus (Gmelin) killing a Peafowl Pavo cristatus Linnaeus". J. Bombay Nat. Hist. Soc. 83 (4): 202. 
  36. ↑ Tehsin,Raza; Tehsin,Fatema (1990). "Indian Great Horned Owl Bubo bubo (Linn.) and Peafowl Pavo cristatus Linn". J. Bombay Nat. Hist. Soc. 87 (2): 300. 
  37. ↑ Flower, M.S.S. (1938). "The duration of life in animals - IV. Birds: special notes by orders and families". Proceedings of the Zoological Society of London: 195–235. 
  38. ↑ Madge S & P McGowan (2002). Pheasant, partridges and grouse, including buttonquails, sandgrouse and allies. Christopher Helm, London. 
  39. ↑ Ramesh, K. & P. McGowan (2009). "On the current status of Indian Peafowl Pavo cristatus (Aves: Galliformes: Phasianidae): keeping the common species common". Journal of Threatened Taxa 1 (2): 106–108. http://threatenedtaxa.org/ZooPrintJournal/2009/February/o184526ii09106-108.pdf. 
  40. ↑ 40.0 40.1 Jackson, CE (2006). Peacock. Reaktion Books, London. pp. 10–11. ISBN 9781861892935. 
  41. ↑ Alexander JP (1983). "Probable diazinon poisoning in peafowl: a clinical description". Vet Rec. 113 (20): 470. 
  42. ↑ Sahajpal, V., Goyal, S.P. (2008). "Identification of shed or plucked origin of Indian Peafowl (Pavo cristatus) tail feathers: Preliminary findings". Science and Justice 48 (2): 76–78. 
  43. ↑ "La Canada, California, City Council, Peafowl Management Plan Update". http://www.lacanadaflintridge.com/city/council/agendaitems/2009/120709/item8.pdf. 
  44. ↑ "East Northamptonshire plan". http://www.east-northamptonshire.gov.uk/downloads/Peafowl_Peacocks.pdf. 
  45. ↑ "Living with peafowl. City of Dunedin, Florida". http://www.dunedingov.com/docs/leisureservices/livingwithpeafowl.pdf. 
  46. ↑ Fitzpatrick J (1923). "Folklore of birds and beasts of India". J. Bombay Nat. Hist. Soc. 28 (2): 562–565. 
  47. ↑ Choskyi, Ven. Jampa (1988). "Symbolism of Animals in Buddhism". Buddhist Hiamalaya 1 (1). http://ccbs.ntu.edu.tw/FULLTEXT/JR-BH/bh117490.htm. 
  48. ↑ Empson, RHW (1928). The cult of the peacock angel. HF & G Witherby, London. http://www.archive.org/details/MN40203ucmf_2. 
  49. ↑ Springett, BH (1922). Secret sects of Syria and the Lebanon. George Allen & Unwin Ltd, London. http://www.archive.org/details/secretsectsofsyr032392mbp. 
  50. ↑ Tyrberg T (2002). "The archaeological record of domesticated and tamed birds in Sweden". Acta zoologica cracoviensia 45: 215–231. http://www.isez.pan.krakow.pl/journals/azc_v/pdf/45/16.pdf. 
  51. ↑ "Letter from the Desk of David Challinor, November 2001". Smithsonian Institution. http://si-pddr.si.edu/dspace/bitstream/10088/1193/1/November_2001.pdf. 
  52. ↑ Boynton, Mary Fuertes (1952). "Abbott Thayer and Natural History". Osiris 10: 542–555. 
  53. ↑ Zahavi, Amotz; Avishag Zahavi, Amir Balaban, Melvin Patrick Ely (1999). The handicap principle: a missing piece of Darwin's puzzle. Oxford University Press. ISBN 0195129148. 
  54. ↑ Partridge, E & Paul Beale (2002). A dictionary of slang and unconventional English. Routledge. ISBN 0415291895. 
  55. ↑ "Advanced Learners Dictionary". Cambridge University Press. http://dictionary.cambridge.org/dictionary/british/peacock. 

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