Action: Foster eggs or chicks of waders with wild non-conspecifics (cross-fostering)
Key messagesRead our guidance on Key messages before continuing
- A replicated and controlled study from the USA found that killdeer Charadrius vociferus eggs incubated and raised by spotted sandpipers Actitis macularia had similar fledging rates to parent-reared birds.
- A replicated and controlled study from New Zealand found that cross-fostering black stilt Himantopus novasezelandiae chicks to black-winged stilt H. himantopus nests significantly increased nest success, but that cross-fostered chicks had lower success than chicks fostered to conspecifics’ nests.
If the wild populations of a species are very small then it may not be possible to foster offspring to conspecifics. However, it may be possible to foster chicks and eggs to a similar, but more abundant species, if one is present. This can increase the reproductive output of the wild population of the endangered species, or even allow for the reintroduction of a population into parts of its former range.
Supporting evidence from individual studies
A replicated and controlled experiment on two islands in Lake Michigan, USA, in 1987-9 (Powell & Cuthbert 1993) found that killdeer Charadrius vociferus eggs incubated and raised by spotted sandpipers Actitis macularia did not have significantly different hatching or fledging rates, compared to parent-reared eggs and chicks (47% hatching success, 0.8 fledglings/pair and 48% fledging success for cross-fostered chicks, n = 16 broods vs. 54%, 0.6 fledglings/pair and 27% for parent-reared chicks, n = 24 broods). There were no significant behavioural differences between parent-reared and cross-fostered chicks and one cross-fostered chick was seen two years after fledging, when it courted and mated with wild killdeer. No parent-reared chicks were seen again but the authors note that killdeer have low site-fidelity and so may not be seen again.
A replicated and controlled study in mountain streams and rivers in South Island, New Zealand, in the austral springs of 1981-7 (Reed et al. 1993) found that fledging success of managed black stilt Himantopus novasezelandiae nests was at least ten times that reported from unmanaged nests (13-27 chicks fledging in the population each year, a 20-42% fledging rate vs. 2% reported in another study for unmanaged nests). Eggs were removed from black stilt nests and artificially incubated (see ‘Artificially incubate and hand-rear birds in captivity’), before being returned as they were hatching. If replacement in the original nest was not possible then eggs were placed in a foster nest, either another black stilt nest or a black-winged stilt H. himantopus nest. Fledging rates and recruitment to the local population were higher for chicks fostered by black stilts than cross-fostered chicks (66% of 50 chicks fostered by black stilts were resighted and five recruited locally vs. 19% of 21 cross-fostered chicks, with a single recruit). The authors note that cross-fostered chicks followed their foster parents on migration, probably leading to low recruitment.