Release captive-bred individuals into the wild to restore or augment wild populations of owls

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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How is the evidence assessed?

Effectiveness

24%
Certainty

15%
Harms

0%

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 study in the USA found that a barn owl Tyto alba population was established following the release of 157 birds in the area over three years.
A replicated, controlled study in Canada found that released burrowing owls Athene cunicularia had similar reproductive output, but higher mortality than wild birds, and no released birds returned after migration, although return rates for released birds’ offspring were no different from wild birds.

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 study in 1985 and 1986 (Henke & Crawford 1987) found three barn owl Tyto alba nests each year in a riverine marsh site in Missouri, USA, with at least 11 eggs being laid and a minimum of seven chicks fledging (complete data are not included). The site was the location of a reintroduction programme in 1983-5 which released 157 owls, and at least two and probably more of the parents at the nests found were captive-bred.
Study and other actions tested
Referenced paper
Henke R. & Crawford W. (1987) Common barn-owls from captive propagation found nesting in the wild. Journal of Raptor Research, 21, 74.
A replicated, controlled study in mixed grasslands in Saskatchewan, Canada, in the springs of 1997-2000 and 2002 (Poulin et al. 2006), found that 12 of 26 pairs of burrowing owls Athene cunicularia released together stayed together for the first breeding season, with eight pairs fledging a total of 43 young. Six birds paired with wild owls, raising 31 young in their first years. Reproductive output did not differ between wild and captive pairs, but mortality of released owls was significantly higher than wild birds (19% of 52 released birds dying vs. 4% of 780 wild birds). Five birds (10%) failed to migrate and no released birds returned after migration. Only one offspring from released birds returned to the area the following year, but this was not significantly different from return rates for the offspring of wild birds. This study also describes fostering and release techniques (see ‘Foster chicks with wild conspecifics’ and ‘Use holding pens at release sites’).
Study and other actions tested
Referenced paper
Poulin R.G., Todd D., Wellicome T.I. & Brigham R. (2006) Assessing the feasibility of release techniques for captive-bred burrowing owls. Journal of Raptor Research, 40, 142-150.

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 birds as adults or sub-adults, not juveniles Action Link	Unknown effectiveness (limited evidence)	8	Synopsis Link
Release captive-bred individuals into the wild to restore or augment wild populations of owls Action Link	Unknown effectiveness (limited evidence)	2	Synopsis Link
Clip birds’ wings on release Action Link	Unknown effectiveness (limited evidence)	4	Synopsis Link