Foster eggs or chicks of owls with wild conspecifics

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

Effectiveness

35%
Certainty

21%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Natural variations in reproductive output can be detrimental when populations are very small, for example if pairs fail to produce fertile eggs or some pairs repeatedly fail to raise offspring successfully. One way to minimise this problem is to foster eggs and chicks between nests. Eggs and chicks from nests with more offspring than they are likely to be able to raise can be moved to those with infertile eggs. Alternatively, if a pair produces fertile eggs or healthy chicks but consistently fails to raise chicks then it may be possible to transfer offspring to a more successful pair.

In other circumstances it may be possible to foster chicks with other species (‘cross-fostering’). Studies describing this intervention are discussed in the following section ‘Foster eggs or chicks with wild non-conspecifics (cross-fostering).’

Study locations

Key messages

A replicated study in the USA found high fledging rates for barn owl Tyto alba chicks fostered to wild pairs.
A replicated controlled study from Canada found that captive-reared burrowing owl Athene cunicularia chicks fostered to wild nests did not have significantly lower survival or growth rates than wild chicks.

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 Utah, USA (Marti & Wagner 1980), found that eight of ten barn owl Tyto alba chicks fostered to wild owl pairs in 1978 fledged successfully, with one male being confirmed as breeding in 1979, 60 km from the fledging site. Six young (all of which fledged) were placed in existing broods, with either one or two chicks in each, and four chicks were used to replace a clutch of four infertile eggs (two of these later died after falling from the nest).
Study and other actions tested
Referenced paper
Marti C.D. & Wagner P.W. (1980) Successful releases of captive barn owls. Raptor Research, 14, 61-62.
A replicated, controlled trial in mixed grasslands in Saskatchewan, Canada, in 2001-3 (Poulin et al. 2006), found that captive-reared burrowing owl Athene cunicularia chicks fostered to wild nests appeared to have lower survival rates than their wild foster siblings, but that this difference was not significant (six of nine foster owls died before migration vs. two of nine wild chicks). There were no differences in growth rates between wild chicks and captive chicks fostered at two to four days after hatching, three weeks after hatching or six weeks after hatching. In total, 54 birds were fostered, but not all could be monitored. Foster parents were supplied with one dead mouse a day for each fostered chick in their brood. This study is also discussed in ‘Release captive bred individuals’ 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
Foster eggs or chicks of woodpeckers with wild conspecifics Action Link	Unknown effectiveness (limited evidence)	3	Synopsis Link
Provide supplementary food for gulls, terns and skuas to increase reproductive success Action Link	Likely to be beneficial	6	Synopsis Link
Foster eggs or chicks of cranes with wild non-conspecifics (cross-fostering) Action Link	Unknown effectiveness (limited evidence)	2	Synopsis Link