The White-throated Rail Dryolimnas cuvieri on Aldabra

Abstract
The White-throated Rail of Aldabra, Dryolimnas cuvieri aldabranus , is the last surviving flightless bird in the western Indian Ocean. Their numbers are estimated very approximately as at least 1000 birds, mostly found on Middle Island but also on Polymnie, He aux Cedres, Michel, and many of the small islets off the lagoon shore of Middle Island. The adults have no serious predators in their present range, but were probably exterminated from South and West Islands by cats. Rails apparently thrive in areas with quite high populations of rats. They are omnivorous, though preferentially insectivorous and occasionally scavenging. They often feed by following tortoises, taking invertebrates from the disturbed litter. The range of calls is wide, and those recognized are listed with their suggested functions. Pair formation was not seen, and evidently takes place well before September. The pairs remain intact at least until February, when the chicks are nearly full grown. Monogamy is the rule although one exception to this is described. Display is described, particularly the aggressive defence of the nest. Two clutches were found, of three and four eggs. The development of the chicks is described; they are nidifugous, and are fed by their parents at least while still in down. It is suggested that some young at least may stay with their parents until the start of the next breeding season. The mortality of young birds is probably very high. Masses, measurements, and moult of trapped birds are given, and criteria given for separating the sexes. Sightings of marked birds indicated that while most birds are sedentary and territorial during the breeding season, some are transient and may move as far as 1 1/2 km. Conservation is discussed, with particular reference to the postponed military development. Although the species apparently thrives in its present range, it is so restricted as to give rise to grave concern for its future.

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