Release captive-bred individuals into the wild to restore or augment wild populations of vultures
Overall effectiveness category Likely to be beneficial
Number of studies: 5
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 â€˜hard releasesâ€™ involving the simple release of individuals into the wild to â€˜soft 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 (â€˜Use holding pens at release sitesâ€™, â€˜Use â€˜anti-predator trainingâ€™ to improve survival after releaseâ€™ etc).
Supporting evidence from individual studies
A small study using Andean condors Vultur gryphus to develop release techniques for Californian condors Gymnogyps californianus (Wallace & Temple 1987) found that 7 of 11 (64%) Andean condors released in arid mountains in northern Peru in 1980-1 survived for at least 18 months after release. All mortalities occurred in the first six months after release. This study is discussed in more detail in â€˜Artificially incubate and hand-rear birds in captivityâ€™ and â€˜Provide supplementary food after releaseâ€™.Study and other actions tested
A replicated study over 12 years (Bose & Sarrazin 2007) of the same programme as in Sarrazin et al. 1996 showed that the number of nesting pairs of griffon vultures Gyps fulvus in the release site in southern France increased steadily from three to 33 (fledging a total of 95 young) over 11 breeding seasons following the release of 59 captive-bred birds during 1981â€“1986. The majority of wild-born and young-released birds nested first at four years old. The effect of the age birds were released at is discussed in â€˜Release birds as adults or sub-adults, not juvenilesâ€™.Study and other actions tested
A replicated study of a reintroduction programme for Andean condors Vultur gryphus found that 19 of the 22 birds released at PÃ¡ramo sites in the Colombian Andes between 1989 and 1992 were alive in 1993 (Lieberman et al. 1993). This represents an increase of almost 100% on the previous Colombian population, estimated at ten pairs. The three birds that died did not appear to be affected by human activity. Releases were at three sites, using birds bred in zoos in the USA, with acclimatisation periods of between 17 and 103 days. After releases, food was provided irregularly at multiple sites (to encourage birds to search for carrion). Birds ranged over nearly 200 km2 over two years, which is less than ranges for reintroduced condors in arid habitats in Peru.Study and other actions tested
A replicated study over ten years of a griffon vulture Gyps fulvus reintroduction programme in river gorges in Aveyron, southern France (Sarrazin et al. 1996) found that 39 adult and 20 immature (less than four years old) birds released between 1980 and 1986 had high survival rates. Survival rates of the wild-bred offspring of the released birds were also high: 86% for the first three years of life and 99% from then on. Of the 18 marked vultures recovered dead between 1981 and 1991, 12 (67%) had died as a result of electrocution. Reproduction of the released birds is discussed in Bose & Sarrazin 2007, the effect of age at release is discussed in â€˜Release birds as adult or sub-adults, not juvenilesâ€™ and the education programme that accompanied the releases is discussed in â€˜Use education programmes and local engagement to help reduce pressures on speciesâ€™.Study and other actions tested
Further analysis of the reintroduction programme discussed in Sarrazin et al. 1994 and Sarrazin et al. 1996 found that the breeding population of griffon vultures Gyps fulvus in the release area in southern France increased from approximately 13 pairs in 1987 to 130 breeding pairs in 2005, following the release of 61 captive-bred birds (Bose & Sarrazin 2007). Eleven young adult (between five and nine years old) releases fed their chicks at a lower rate than eight wild-bred birds, but in all age classes there was no difference in feeding rates or dominance of released, compared with wild-bred birds.Study and other actions tested