Demography of takahe (Porphyrio hochstetteri) in Fiordland: environmental factors and management affect survival and breeding success

The last remaining natural population of the critically endangered takahe (Porphyrio hochstetteri) is confined to the Murchison Mountains in Fiordland, New Zealand. This mainland population contains about half of the c. 300 remaining takahe and benefits from one of the costliest recovery programmes in the country. Management activities include deer culling, stoat trapping, nest manipulation (e.g. removal of infertile eggs) and captive rearing of chicks. To determine what effect this intensive management has had on the recovery of the Fiordland takahe population, we modelled 25 years of survival and breeding success data as a function of environmental factors (e.g. precipitation, temperature, beech seedfall, tussock flowering) and specific management activities (egg manipulation, captive rearing, stoat control). Annual adult survival, estimated at 78% (credibility interval (CI) = 75–81%), is significantly increased to 85% (76–92% CI) in presence of stoat trapping, but is still low relative to introduced takahe populations on offshore islands and other large New Zealand bird species in predator-free environments. This suggests that the harsh environment of Fiordland may be suboptimal habitat in terms of survival for takahe. On the other hand, reproductive output in Fiordland is similar to that for introduced island populations, and is improved even further by management. Number of chicks per pair fledged with nest manipulation and captive rearing is estimated at 0.66 compared with 0.43 in the absence of nest management. The difference is explained mainly by low fledging success in the wild, especially for double clutches, which justifies the practice of removing one of two viable eggs and transferring it to a captive-rearing facility. The results of this study indicate that current management activities such as stoat trapping and captive rearing have a strong positive effect on population growth of the Murchison Mountains takahe population.