Use appropriate populations to source released populations

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

View assessment score

How is the evidence assessed?

Effectiveness

53%
Certainty

31%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Some bird species follow instinctive migration patterns, which vary between populations (Berthold et al. 1984), and populations are likely to be adapted for local environmental conditions. If individuals from one population are released into another area, this could result in maladaptive behaviours, with birds migrating in the wrong direction, or breeding at the wrong time. Sourcing individuals for release from the area that they will be released into may, therefore, improve success rates.

Berthold, P. (1984) The endogenous control of bird migration: a survey of experimental evidence. Bird Study, 31, 19–27.

Study locations

Key messages

A replicated study from Sweden and a small study from France found that birds sourced from populations distant from where they were released were less successful than birds from the area.
In Sweden, released white storks Ciconia ciconia from North Africa produced fewer than half the chicks as those that naturally re-colonised, whilst both studies found that storks and little bustards Tetrax tetrax were less likely to migrate than birds originating in the release area.

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 southern Sweden in 1989-2005 (Olsson 2007) found white storks Ciconia ciconia that naturally re-colonised the region in 1989 from the nearest remaining population (in northeast Europe) and their direct descendants fledged over twice as many chicks as birds descended from a reintroduced population which originated in north Africa (average of 1.9 fledglings/pair for birds descended from wild birds vs. 0.9 fledglings/pair for birds descended just from reintroduced birds). In addition, birds with wild ancestry were significantly more likely to migrate than birds only descended from captive individuals (11 of 18 storks confirmed as migrating had some wild ancestry, as did eight of ten storks that probably migrated. A total of 101 storks in the population had some wild ancestry, compared to 189 descended solely from captive storks). The original reintroduction was of 15 birds from a breeding centre in Switzerland, of which eight bred, leading to 470 descendants between 1980 and 2005. Approximately 82% of the current Swedish population is descended from four captive birds. A total of 12 native birds re-colonised, with 14% of the total population being descended from four of these.
Study and other actions tested
Referenced paper
Olsson O. (2007) Genetic origin and success of reintroduced white storks. Conservation Biology, 21, 1196-1206.
A small study in southern France and Spain in 1997-2007 (Villers et al. 2010) found that six little bustards Tetrax tetrax originating in Spain but hand-reared and released in France did not migrate to Spain (with the possible exception of one bird that could not be tracked). By contrast, 13 out of 21 wild adults from France (62%) and six of eight hand-reared French chicks (75%) migrated. The authors conclude that hand-rearing does not affect migration probability, but that genetic origin appears to.
Study and other actions tested
Referenced paper
Villers A., Millon A., Jiguet F., Lett J.-M., Attie C., Morales M.B. & Bretagnolle V. (2010) Migration of wild and captive-bred little bustards Tetrax tetrax: releasing birds from Spain threatens attempts to conserve declining French populations. Ibis, 152, 254-261.

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
Provide supplementary food after release Action Link	Likely to be beneficial	3	Synopsis Link
Release captive-bred individuals into the wild to restore or augment wild populations of cranes Action Link	Likely to be beneficial	6	Synopsis Link
Release captive-bred individuals into the wild to restore or augment wild populations of bustards Action Link	Unknown effectiveness (limited evidence)	4	Synopsis Link