Foster eggs or chicks of owls with wild conspecifics
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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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).’
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
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
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This Action forms part of the Action Synopsis:Bird Conservation
Bird Conservation - Published 2013