Release captive-bred individuals into the wild to restore or augment wild populations of storks and ibises

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
Share Tweet Email

View assessment score

How is the evidence assessed?

Effectiveness

20%
Certainty

20%
Harms

2%

Calculating overall effectiveness category

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 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).

Study locations

Key messages

A replicated study and a review of northern bald ibis Geronticus eremita release programmes in Europe and the Middle East found that only one of four had resulted in a wild population being established or supported, with many birds dying or dispersing, rather than forming stable colonies.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated study in southeast Turkey in 1977-88 (Akçakaya 1990) found that northern bald ibis Geronticus eremita bred or kept in captivity did not increase the Turkish population. From 1981-88, 67 individuals were released and 12 (18%) migrated with the wild population (note: this excludes 1984, 1986 and 1987, for which data were not available). There was high winter mortality among birds that did not migrate and also high mortality on migration. The wild population in the study area declined over the study period, with five pairs in 1986, seven in 1987 and only four birds returning in 1988. This study is also described in ‘Use captive breeding to increase or maintain populations’ and ‘Provide artificial nesting sites’.
Study and other actions tested
Referenced paper
Akçakaya H.R. (1990) Bald ibis Geronticus eremita population in Turkey: an evaluation of the captive breeding project for reintroduction. Biological Conservation, 51, 225-237.
A 2007 review of northern bald ibis (waldrapp) Geronticus eremita conservation (Bowden et al. 2007) found varying success in release programmes, dependent on the techniques used. Trials in Israel using a variety of techniques (described in ‘Release birds as adults or sub-adults, not juveniles’ and ‘Clip birds’ wings on release’) found that all 56 birds released became emaciated and disorientated and formed poor social bonds. Similarly, the release of 73 birds in Spain between 2004 and 2006 has not resulted in the formation of a stable colony. However, the release of 43 birds in Austria has led to the establishment of a colony in the wild. This study is also discussed in ‘Use captive breeding to increase or maintain populations’, ‘Artificially incubate and hand-rear birds in captivity’, ‘Use holding pens at release sites’, ‘Release birds as adults or sub-adults, not juveniles’, ‘Clip birds’ wings on release’, ‘Use microlites to help birds migrate’ and ‘Foster birds with non-conspecifics’.
Study and other actions tested
Referenced paper
Bowden C.G.R., Boehm C., Jordan M.J.R. & Smith K.W. (2007) Why is reintroduction of northern bald ibis Geronticus eremita so complicated? An overview of recent progress and potential. Pages 27-35 in: Toronto, Onatario, Canada.

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Bird Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Release captive-bred individuals into the wild to restore or augment wild populations of rails Action Link	Unknown effectiveness (limited evidence)	3	Synopsis Link
Release birds in ‘coveys’ Action Link	Unknown effectiveness (limited evidence)	3	Synopsis Link
Release captive-bred individuals into the wild to restore or augment wild populations of songbirds Action Link	Likely to be beneficial	6	Synopsis Link