Action: Foster eggs or chicks of vultures with wild conspecifics
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Two small studies, one a New World vulture and one of an Old World species found that single chicks were successfully adopted by foster conspecifics, although in one case this led to the death of one of the foster parents’ chicks.
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 small study on a farm in North Carolina, USA, in June 1975 (Stewart 1983) found that transferring a 35-40 day-old (American) black vulture Coragyps atratus chick from a nest that was about to be destroyed to a nest containing two 30-35 day-old chicks led to the successful rearing of the fostered chick. However, the smaller of the two chicks originally in the nest was neglected by its parents and died soon after the foster chick was introduced. No data on the fledging success or subsequent survival of the surviving chicks is provided.
A small study on Sicily, Italy (Di Vittorio et al. 2006), found that a captive-bred Egyptian vulture Neophron percopterus chick fostered into a wild nest in July 2003 was accepted by the foster parents and their two chicks and fledged successfully when approximately 90 days old. The chick was placed in the nest when 60 days old and competed successfully for food. The parents were supplied with supplementary food to ensure that the burden of feeding three chicks was not excessive (vultures tend to raise one or two chicks).
- Stewart P.A. (1983) Adoption of introduced young and neglect of own by nesting black vultures. Wilson Bulletin, 95, 310-311
- Di Vittorio M., Falcone S., Diliberto N., Cortone G., Massa B. & SarÃ M. (2006) Successful fostering of a captive-born egyptian vulture (Neophron percnopterus) in Sicily. Journal of Raptor Research, 40, 247-248