Photospot: Blue Pigeons
by Roger Safford, from Bulletin of the African Bird Club volume 5.2, September 1998
The tropical islands of the south-west Indian Ocean are rich in endemic genera, but most of these are restricted to Madagascar. Many of the birds that have reached the remoter archipelagoes - the Comoros, Seychelles and Mascarenes - are from widespread groups like the white-eyes, Zosterops, and paradise-flycatchers, Terpsiphone. Only two regional endemic genera are known to have reached every archipelago: the fodies, Foudia, and the blue pigeons, Alectroenas. By virtue of their distinctiveness and restricted range, these could be considered the most characteristic birds of the region. Whilst the fodies have attracted much conservation and research effort, the blue pigeons have not.
Three species survive today: Seychelles Blue Pigeon, A. pulcherrima, ('very beautiful') on most of the granitic Seychelles, Comoro Blue Pigeon, A. sganzini, on the Comoros (nominate race) and Aldabra (A. s. minor), and Madagascar Blue Pigeon, A. madagascariensis, on Madagascar. At least two species are extinct. The Mauritius Blue Pigeon, A. nitidissima, ('very bright') survived well into the 19th century (1), its extinction probably caused by a combination of hunting, habitat destruction and predation. Unidentified species once occurred on St Pierre and Providence, in the coralline Seychelles (3), probably Réunion and possibly Rodrigues (1). Pleasingly, the surviving species are still fairly common over much of their ranges, and none is considered threatened or even near-threatened.
These are very beautiful birds. The blue is, in all cases, a rich and rather unusual hue, and the long, pointed neck feathers are as impressive in silvery-white on the Comoro and Seychelles species as in silvery-blue on Madagascar. Red caruncles on the face are another characteristic feature. It is tantalizing to see the three museum skins of the extinct Mauritius Blue Pigeon, which seemed to combine the best features of the three survivors: a head and neck like the Comoro bird, and a red tail, as on Madagascar.
Blue pigeons are arboreal and sometimes gregarious: flocks of 15 occur on the Comoros (pers. obs) and up to 100 in fruiting Ficus trees in the Seychelles (R. Lucking pers. comm.). One reason for the success of the surviving island species seems to be their willingness to take fruits from introduced trees as well as those from native species. On Grande Comore (Ngazidja), they take Psidium cattleianum (Strawberry Guava) and Solanum auriculatum fruit (pers. obs), and the Seychelles Blue Pigeon eats Chrysobalanus icaco (Coco-plum) (pers. obs.), wild guavas and cinnamon berries (3). These are among the most abundant weeds on their respective islands, ensuring a plentiful food supply. Only the basics of the breeding ecology are known. Nests are very simple constructions of a few, apparently casually placed, twigs situated in trees. Just one egg is the usual clutch (2,4). The frail nests are seemingly prone to failure, nesting success being low in the Seychelles (R. Lucking pers. comm.). Swooping advertising flights and a bowing display are typical of these as well as other large pigeons; the bowing display is made particularly impressive as the birds vibrate their lanceolate neck feathers (5).
References
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