This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Mention ‘peacock’ (or ‘peafowl’) and the vast majority of people will think of Pavo cristatus, the mostly Indian, blue-plumaged Indian peacock. Distinctive features of the males of this species include a face marked with black and white stripes, a crest composed of wire-like shafts tipped with blue, fan-shaped tufts, orange-brown primary feathers, dark-brown-and-white stripes on the scapulars and wing coverts, and of course an iridescent blue neck and breast and a massive ‘train’ formed of uppertail coverts marked with eyespots. Females have white bellies, brown backs and greenish necks, and of course lack the long ‘trains’ of males.
But there’s another peafowl: the Green peacock P. muticus, also sometimes called the Burmese peacock. Historically occurring across the woodlands, forests and montane grasslands of southern Asia from north-eastern India eastwards to Vietnam and south to Malaysia and Java (but with no recorded presence on Sumatra or Borneo), it has undergone a massive and worrying decline since the middle of the 20th century and is now rare and restricted to a shrinking number of isolated populations. A reliance on regular sources of water and use of forest edges and cultivated areas may bring it regularly within range of humans and its decline is predominantly due to hunting and habitat loss.
Something we have to sort out up front here is the apparent interchangeability of the terms ‘peacock’ and ‘peafowl’. No, the latter term is not used specifically for females, nor is the former exclusively used for males. It seems that both can be used in the singular, but that only the latter can be used in the plural. My just-arrived-at convention is that we speak of ‘peacocks’ when addressing members of a single taxon (e.g., this article is about the Green peacock) but use ‘peafowl’ when referring to peacocks of more than one taxon (e.g., there are two living species of peafowl).
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Green peacocks typically have a more erect-necked look than Indian peacocks and are larger and taller overall. They’re also far less sexually dimorphic: the female is about the same in appearance as the male but for her absence of the train. That reduced amount of sexual dimorphism may tell us something about sociosexual behaviour – read on. As you can see from the photos used here, the Green peacock really is a spectacular, striking and large bird. Indeed, with a total length of up to 3 m for a train-bearing male, this is the world’s longest gamebird. Large individuals can weight 5 kg.
The many kinds of Green peacock
Not all populations are alike within this species; three subspecies have typically been considered valid (Madge & McGowan 2002) but there are suggestions that this classification is too simplistic and that several additional forms need to be recognised. P. m. muticus is endemic to Java and is the greenest and most brightly coloured of the three. P. m. imperator is actually the best known one: it’s the one that used to occur throughout southeast Asia and adjacent Burma and China. The head crest is formed from narrow, tufted feathers and the neck, breast and flanks are mostly green but with black centres; metallic blue or blue-green feathers are present on the head and parts of the neck and breast too. Finally, P. m. spicifer is the dullest of the three, with near-black secondaries and wing coverts, and slightly blue neck and breast feathers. This more pronounced bluish-ness makes or made it the subspecies most similar to the Indian peacock. Reported only from north-east India and north-west Burma, it may perhaps be extinct (Madge & McGowan 2002).
Additional subspecies recognised by some authors include P. m. yunnanensis from Yunnan, China, P. m. annamensis from south-east Asia and Yunnan and P. m. javanensis from Java. If the species really does include this many distinct taxa, it is (or was) evidently diverse genetically.
A long history of peafowl
Genetic data suggests that Indian and Green peafowl diverged about 3 million years ago (Ouyang et al. 2009). If correct, this means that both are old and substantially distinct; it also raises the question as to how old those Green peacock subspecies are, and already there are suggestions from some in the pheasant world that the Green peacock is actually a species complex and that taxonomic revision is appropriate.
Intriguingly, fossil peafowl from Europe have been said to be more similar to Green peacocks than to Indian peacocks (Mourer-Chauviré 1989). However, this is almost certainly more to do with the fact that both the fossil specimens and the Green peacock share large size and hence are similarly proportioned when it comes to those parts of anatomy most frequently preserved as fossils, like tarsometatarsi and spur bones.
As we saw in a recent article, fossil peafowl are known from the Miocene and Pliocene of Europe; they were also present in Europe in the Early Pleistocene too (Mourer-Chauviré 1989). Pavo bravardi (originally described in 1849 as a junglefowl) from France, Greece, Bulgaria, Moldavia and Ukraine seems to have been a cool-adapted animal, and indeed its fossils are, in Bulgaria, found in association with those of ptarmigan (Boev 1998). P. moldavicus from the Pliocene of Moldavia (Bocheński & Kurochkin 1987) is probably synonymous with P. bravardi (Mourer-Chauviré 1989).
Another European member of Pavo – P. aesculapi – is known from the Late Miocene of Greece and elsewhere in Europe. There’s also a Kenyan fossil Pavo (as yet unnamed to species level) from the Pliocene.
We don’t yet know how these fossil peafowl were related to the modern ones, but they do show that peafowl of the modern sort – that is, members of the clade Pavo – have been around since the Late Miocene at least. Even better, some entirely extinct phasianids might also be members of the peafowl lineage, in which case the group has a record stretching back to the Middle Miocene. The best known of these is Miophasianus altus, known from widespread localities across Europe (Sánchez Marco 2006) and often said to be one of the largest of fossil gamebirds. Cheneval (2000) was first to suggest that it might be a peacock. Linquornis gigantis, also from the Middle Miocene but this time from China, is also large (similar to living Pavo) and sometimes said or implied to be peacock-like (Zelenkov & Kurochkin 2010) while Lophogallus narabulakensis from the Middle Miocene of Mongolia was also large and peacock-like (Zelenkov & Kurochkin 2010).
The great problem with so many Cenozoic fossil birds is that there has – so far – been little effort to investigate their relationships empirically: conclusions are generally done by reference to overall similarity (indeed, quite a few Cenozoic bird specialists are avowed anti-cladists). Furthermore, the fossil taxa themselves are frequently represented by scrappy remains (the fossil peafowl and peafowl-like phasianids mentioned here, for example, are named for isolated or partial limb bones, not whole or semi-whole skeletons), and hence are not ideal subjects for phylogenetic investigation anyway. More fossils are always needed.
However, what material we have indicates that peafowl have a record going back well into the Miocene – an observation consistent with phylogenetic trees that show pavonines (the members of the pheasant group that includes peacock-pheasants, argus pheasants and peafowl) diverging from an ancestor that later gave rise to northern pheasants, grouse, turkeys and other lineages (e.g., Kriegs et al. 2007, Kimball et al. 2011): in other words, diverging early on in the history of the group.
Incidentally, the molecular clocks and divergence dates suggested for various gamebird lineages have been controversial and sometimes faulty due to the misinterpretation of fossils used as calibration points (see Ksepka 2009). I was surprised to see one recent suggestion positing the divergence time for pavonines and their presumed closest relatives (junglefowl and kin in the phylogeny concerned) to date to the Eocene-Oligocene boundary (Kan et al. 2010). That’s much older than the fossils suggest, and indeed inconsistent with the gamebird fossil record as a whole: crown-galliforms aren’t present until the end of the Oligocene. I think that results such as this are inaccurate and presumably caused by incorrect assumptions about molecular clock rates.
Which social system for you, Green peacock?
Like the better-known Indian peacock, the Green peacock is mostly assumed to be polygamous or polygynous, with males holding harems of several females and advertising their presence with loud calls that are apparently less piercing than those of the Indian peacock.
However, the species apparently does not form leks like the Indian peacock and there are suggestions, stemming from observations made in captivity, that these birds might actually be monogamous and with males performing an extensive role in parental care. This would explain the strong similarity present between males and females and wouldn’t be entirely discordant with what we already know about pavonines, since the Congo peacock Afropavo congensis is apparently monogamous.
It used to be thought that the presence of well-developed spurs in gamebirds was tidily correlated with the mating system: the Green peacock has large spurs, suggestive of polygyny or polygamy. However, at least one study has found that the correlation supposed to exist here is actually ambiguous (Sullivan & Hillgarth 1993). Clearly, better data on wild Green peacocks is needed before we can state anything with confidence about the mating and breeding behaviour of this species.
All in all, a remarkable bird: one that we really need to understand better, and one that we really need to see conserved before it becomes too late. Many thanks for Markus Bühler for providing the great photos used here.
For previous Tet Zoo articles on gamebirds, see…
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Bocheński, Z. & Kurochkin, E. N. 1987. New data on Pliocene phasianids (Aves, Phasianidae) of Moldavia and s. Ukraine. Acta zoologica Cracoviensia 30, 81-96.
Boev, Z. 1998. Peafowls (g. Pavo Linnaeus, 1758) and ptarmigans (g. Lagopus Brisson, 1760): an unique coexistence in North Bulgaria over 3 m.y. ago. Biogeographica 19, 220-222.
Cheneval, J. 2000. L’avifaune de Sansan. Mémoires du Muséum national d’Histoire naturelle 183, 321-388.
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Madge, S. & McGowan, P. 2002. Pheasants, Partidges & Grouse, Including Buttonquails, Sandgrouse and Allies. Christopher Helm, London.
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Sánchez Marco, A. 2006. Miophasianus and Palaeoperdix (Galliformes, Aves) from three Miocene localities of Spain. Estudios Geológicos 62, 249-256.
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Zelenkov, N. V. & Kurochkin, E. N. 2010. Neogene phasianids (Aves: Phasianidae) of Central Asia: 3. Genera Lophogallus gen. nov. and Syrmaticus. Paleontological Journal 44, 328-336.