Release captive-bred individuals into the wild to restore or augment wild populations of waders
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
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 speciesâ former range, or to augment an existing population.
Release techniques vary considerably, from âhard releasesâ involving the simple release of individuals into the wild to âsoft releasesâ 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 (âUse holding pens at release sitesâ, âUse âanti-predator trainingâ to improve survival after releaseâ 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 âeffectively deadâ 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 âRelease birds as adults or sub-adults, not juvenilesâ and âRelease birds in groupsâ.Study and other actions tested