Action: Artificially incubate and hand-rear cranes in captivity
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A replicated and controlled study and a small study, both from the USA, found that hand-reared birds showed normal reproductive behaviour and higher survival than parent-reared birds.
Artificial incubation involves removing eggs from incubating parents and using an incubator to hatch them. Techniques can be extremely complex, with precision humidity and temperature control and turning of the eggs to ensure correct development Hand-rearing can be used with chicks from artificially-incubated eggs or with chicks removed from parents after hatching and involves manually feeding chicks until independence. Both techniques can be used to encourage parents to produce more offspring, or when naturally-raised chicks and eggs have low survival.
Supporting evidence from individual studies
In order to test hand-rearing techniques for use with whooping cranes Grus americana, a small study in the USA in 1992-3 (Duan & Bookhout 1997) investigated the behaviour of hand-reared male greater sandhill cranes G. canadensis tabida after release and found that they exhibited normal reproductive behaviour. All six paired with females in 1992 (none nested); four pairs nested in 1993, with one nest flooding but the others producing one or two eggs each. The hand-reared males incubated the eggs and three hatched (the remaining nest with two eggs was abandoned following the researchers’ visit), although none of the chicks survived more than a week. The authors conclude that reproductive behaviour is not affected by hand-rearing, which consisted of ‘isolation rearing’ – with the birds not given any access to humans, but instead reared by puppets heads (to avoid imprinting on human carers, see ‘Use puppets to increase the survival or growth of hand-reared chicks’ for studies on this intervention).
A replicated, controlled study in a breeding centre in Mississippi, USA, between 1989 and 1996 (Ellis et al. 2000) found that first-year survival of captive-bred, hand-reared Mississippi sandhill cranes Grus canadensis pulla was higher than for captive-bred, parent-reared birds (approximately 85% survival for 56 hand-reared birds vs. 77% for 76 parent-reared birds). Hand-reared birds were reared with mounts of brooding adults and heat lamps, and were taught to feed by costumed humans with mounts of crane (see ‘Use puppets to increase the survival or growth of hand-reared chicks’ for more information). Details of the releases are discussed in ‘Release captive-bred individuals’.
- Duan W. & Bookhout T.A. (1997) Breeding behavior of isolation-reared sandhill cranes. Journal of Field Ornithology, 68, 200-207
- Ellis D.H., Gee G.F., Hereford S.G., Olsen G.H., Chisolm T.D., Nicolich J.M., Sullivan K.A., Thomas N.J., Nagendran M. & Hatfield J.S. (2000) Post-release survival of hand-reared and parent-reared Mississippi sandhill cranes. The Condor, 102