An Aldabra rail population on Picard Island reached an estimated 2,765 adults in a 2011 survey, with territorial pairs about 10% above an earlier forecast for the island.
A 2013 study by Seychelles Islands Foundation (SIF) researchers covered Oct. 31 to Nov. 28, at the start of the breeding season. Survey teams estimated 1,106 territories. They estimated two adults per territory and added 553 nonbreeding adults, using an assumed rate of one nonbreeder for every two territories. That method produced an estimated total of 2,765 adults, with a range of 2,100 to 3,220; it was not a direct count of every bird. SIF later described Picard's population as nearly 3,000 in 2012.
The population followed a 1999 transfer of 18 rails from Malabar, another island in the Aldabra atoll. A separate 2002 study says 20 birds were initially captured, but two died in captivity; the other 18 were released and made it through their first breeding period. Within two months, eight pairs had produced at least 13 chicks, the study reports. It estimated Picard's population at no fewer than 51 by the close of the 2001 breeding season.
The rail had disappeared from Picard soon after 1910. The 2013 paper identifies introduced feral cats as a main factor in the local loss. The 2002 study says cats had not been documented killing rails and that their role was inferred from the pattern of local extinctions. It also says cats were not specifically targeted for removal on Picard and had not been seen since pet cats were removed in the 1970s; the 2013 paper describes the cats as eradicated from the island.
The 2013 researchers compared their estimate of 1,106 territories with an earlier forecast of roughly 1,000 breeding pairs on Picard by 2010, putting the estimate about 10% higher. They called for rail population checks at five-year intervals and an investigation into removing cats from Grande Terre. SIF says that option remains under consideration.
