Action: Artificially incubate and hand-rear rails in captivity
A controlled before-and-after study from New Zealand found that post-release survival of hand-reared takahe Porphyrio hochstetteri (formerly P. mantelli) was as high as wild-reared birds and that six of ten released females raised chicks.
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
A controlled before-and-after study between 1991 and 1994 in Fiordland National Park, South Island, New Zealand (Maxwell & Jamieson 1997), found that post-release survival of hand-reared takahe Porphyrio hochstetteri (formerly P. mantelli) was at least as high as that of wild-reared birds, despite differences between movements and habitat selection (50-100% survival between one and two years for 31 hand-reared birds vs. 0-100% of 12 wild birds; ranges come from different release years). In addition, survival of wild birds between six months and one year old (before hand-reared birds were released) was lower than for captive birds (100% survival for 62 captive-reared birds vs. 25-100% survival for 24 wild birds), especially in years with particularly low temperatures. Causes of death were varied and often unknown. Survival rates did not differ between male and female hand-reared birds, but females were significantly more likely to form pairs than males (89% of nine females forming pairs vs. 25% of eight males). Six of ten captive-reared females nested in the summer after release and two raised a chick to at least six months old. The authors note that low reproductive success in first-time breeders is common. Eggs were taken from the wild and hand-reared using a glove puppet, whilst being played calls of brooding adults (see ‘Use puppets to increase the survival or growth of hand-reared chicks’ for more studies of this intervention). They were moved to outdoor pens at three months old, to larger pens at six months and finally released at approximately one year old.