The Grey-headed Swamphen(Earlier known as purple swamphen) is a "swamp hen" in the rail family Rallidae. Also known locally as the pūkeko, African purple swamphen, purple moorhen, purple gallinule or purple coot. From its French name talève sultane, it is also known as the sultana bird.
There are 13 or more subspecies of the purple swamphen (depending on the authority) which differ mainly in plumage colour. The subspecies groups are: P. p. porphyrio in the Mediterranean, P. p. madagascariensis in Africa, P. p. poliocephalus in tropical Asia, P. p. melanotus in much of Australasia, P. p. indicus in Indonesia and P. p. pulverulentis in the Philippines. European birds are overall purple-blue, African and south Asian birds have a green back, and Australasian and Indonesian birds have black backs and heads.
The nominate subspecies, P. p. porphyrio (Linnaeus, 1758), is found in Iberia, France, Sardinia and North Africa to Tunisia. P. p. madagascariensis (Latham, 1801) occurs in Egypt, sub-Saharan Africa and Madagascar, and resembles the nominate but with bronze green or green-blue back and scapulars. P. p. caspius (Hartert, 1917) from the Caspian Sea area, is like poliocephalus, but larger.
P. p. seistanicus (Zarudny & Harms, 1911) occurs from Iraq to Pakistan, as poliocephalus, but larger; smaller than caspius. P. p. poliocephalus (Latham, 1801) is found from India and Sri Lanka to south China and north Thailand, and has been introduced to Florida. It has cerulean blue scapulars, face throat and breast. P. p. indicus (Horsfield, 1821) occurs from Sumatra to Sulawesi and Bali, and has a large shield, black upperparts, and the side of the head is blackish. P. p. virdis (Begbie, 1834) occurs in South East Asia, and resembles indicus but the side of the head is cerulean blue. P. p. pulverulentus (Temminck, 1826) from the Philippines has olive-chestnut mantle and scapulars, and the whole plumage is tinged with ash-grey.P.
p. melanotus (Temminck, 1820) occurs in north and east Australia, New Zealand and the surrounding islands. It has a small shield, shorter toes, black upperparts, and a purple throat and breast. P. p. pelewensis (Hartlaub & Finsch, 1872) from Palau, resembles melanotus but has greener upperparts and is smaller. P. p. melanopterus (Bonaparte, 1856) is found from the Lesser Sundas and Moluccas to New Guinea. It is as melanotus but smaller, more variable and less blue in the upperparts. P. p. bellus (Gould, 1820) from West Australia is as melanotus but has a cerulean blue throat and breast. P. p. samoensis (Peale, 1848) occurs from New Guinea to New Caledonia and Samoa, and is as melanotus but smaller, with a brown tinge on the back. (Wikipedia)
(This picture was taken at purbasthli near Nabadwip of West Bengal)