Background information and definitions
Thirty-three species of rails and crakes (Rallidae) are globally threatened, of which 13 are flightless (Taylor 1996). These species are unlikely to rapidly colonise new areas or recolonise former ranges, especially as several live on islands. Therefore translocating birds to new suitable habitats is likely to be an important conservation tool.
Taylor, P.B. (1996) Family Rallidae (rails, gallinules and coots) pp 108–209 in: (eds J. del Hoyo, A. Elliott & J. Sargatal) Handbook of the birds of the world: Volume 3. Hoatzin to auks. Lynx Edicions, Barcelona.
Supporting evidence from individual studies
A review (Bunin et al. 1997) of adult survival and reproductive success of takahe Porphyrio hochstetteri populations established on four offshore islands in New Zealand (by translocating birds from the species’ remaining natural range in Fiordland, South Island) found that adult survival was at least as high as in Fiordland (annual survival on islands of 83-100% vs. 73-97% for Fiordland). However, island pairs produced significantly fewer juveniles each year (average of 0.56-0.65 juveniles/pair/year for 43 island breeding attempts vs. 0.85-0.86 juveniles/pair/year for 171 Fiordland breeding attempts), despite laying more eggs (average of 3.4-3.5 eggs/pair/year for 43 island breeding attempts vs. 1.9-2.0 eggs/pair/year for 122 Fiordland breeding attempts), probably due to the milder climate (and hence longer breeding season) and the removal of non-viable eggs on islands. Breeding success was lowest for island pairs in their first year of reproduction (four juveniles from 43 clutches), compared to second or third attempts (11 from 36 and six from 13 clutches, respectively). Island birds were moved during 1984-91 to avoid introduced mammalian predators in Fiordland, whilst the Fiordland population was also intensively managed: single eggs were often removed from two-egg broods and artificially incubated with chicks reared in captivity until around 1 year old, when they were released back into the wild (see ‘Artificially incubate and hand-rear birds in captivity’ for details).Study and other actions tested
A review of a translocation programme for white-throated (Aldabra) rails Dryolimnas cuvieri (formerly D. aldabranus) on Aldabra atoll, Seychelles, in 1999-2001 (Wanless et al. 2002) found that all 18 birds successfully released survived from November 1999 until at least April 2000, with 17 being seen again between December 2000 and April 2001 (the remaining bird was recorded in an inaccessible part of the island). An estimated 15-16 chicks fledged in 1999-2000, with all known mortality (30%) occurring within three weeks of hatching. In 2000-1 at least 20 chicks were fledged, leading to a minimum population of 51 birds, an increase of 183% in 18 months. Birds were transported from Île Malabar during pair formation and transferred to Île Picard within three days. There, birds were held in 30 m2 enclosures near good quality habitat and provided with shelter, fresh water and food for six or 14 days before release. Food was provided to birds that stayed in or around the cages after release.Study and other actions tested
An analysis of takahe Porphyrio hochstetteri breeding records from four offshore predator-free islands in New Zealand during 1991–2000 (Jamieson & Wilson 2003) found that all eleven translocated birds survived the journey and attempted to breed. There were no differences in age of first breeding attempt between translocated birds of either sex compared with birds born on the islands (2.3-2.6 years old for six male and five female translocated birds vs. 2.1-2.9 for ten male and 11 female resident birds). In addition there were no differences in hatching or fledging rates between pairs containing two, one or no translocated birds (approximately 40% hatching success and 70% fledging success for three pairs of translocated birds vs. 25% and 30% for eight resident pairs and 25% and 30% for five pairs with one resident and one translocated bird). Birds were transferred between Tiritiri Matangi Island, Kapiti Island, Mana Island and Maud Island, and were supplied with supplementary food and kept in pens at the release site for two or three days before release. ‘Resident’ birds were descended from birds that had been translocated from the New Zealand mainland in the past.Study and other actions tested