Action: Release captive-bred individuals into the wild to restore or augment wild populations of waders
A review of black stilt Himantopus novaezelandiae releases in New Zealand found that birds had low survival (13–20%) and many moved away from their release sites so, in consequence, that they could not be managed and were unlikely to interact with stilt populations in the wild.
Captive breeding is normally used to provide individuals which can then be released into the wild to either restore a population in part of the species’ former range, or to augment an existing population.
Release techniques vary considerably, from ‘hard releases’ involving the simple release of individuals into the wild to ‘soft releases’ which involve a variety of adaptation and acclimatisation techniques before release or post-release feeding and care. The following section includes studies describing the overall effects of release projects. Studies that compare specific release techniques are described elsewhere (‘Use holding pens at release sites’, ‘Use ‘anti-predator training’ to improve survival after release’ etc).
Supporting evidence from individual studies
A review of critically endangered black stilt (kaki) Himantopus novaezelandiae releases in riverine habitats in South Island, New Zealand, between 1993 and 2005 (van Heezik et al. 2009) found that 13-20% of 464 birds released were alive two years after release. However, 32% of birds that reached breeding age did not remain at their release site and 15% moved to an area where they could no longer be managed and were unlikely to reproduce successfully. The authors argue that this second category of birds is “effectively dead” as they no longer contribute to the wild population. Birds were released into populations that needed supplementation; therefore movements away from the release site could also be detrimental. Eggs were taken from wild and captive-bred birds and artificially incubated. Birds were not held at the release site before release, but food was provided at release site for between six weeks and two months. This study is also discussed in ‘Release birds as adults or sub-adults, not juveniles’ and ‘Release birds in groups’.