Low reproductive success of the endangered takahe Porphyrio mantelli on offshore island refuges in New Zealand

Published source details Bunin J.S., Jamieson I.G. & Eason D. (1997) Low reproductive success of the endangered takahe Porphyrio mantelli on offshore island refuges in New Zealand. Ibis, 139, 144-151.
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This study is summarised as evidence for the following.

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A review (Bunin et al. 1997) of adult survival and reproductive success of takahe Porphyrio hochstetteri populations established on four offshore islands in New Zealand (by translocating birds from the species’ remaining natural range in Fiordland, South Island) found that adult survival was at least as high as in Fiordland (annual survival on islands of 83-100% vs. 73-97% for Fiordland). However, island pairs produced significantly fewer juveniles each year (average of 0.56-0.65 juveniles/pair/year for 43 island breeding attempts vs. 0.85-0.86 juveniles/pair/year for 171 Fiordland breeding attempts), despite laying more eggs (average of 3.4-3.5 eggs/pair/year for 43 island breeding attempts vs. 1.9-2.0 eggs/pair/year for 122 Fiordland breeding attempts), probably due to the milder climate (and hence longer breeding season) and the removal of non-viable eggs on islands. Breeding success was lowest for island pairs in their first year of reproduction (four juveniles from 43 clutches), compared to second or third attempts (11 from 36 and six from 13 clutches, respectively). Island birds were moved during 1984-91 to avoid introduced mammalian predators in Fiordland, whilst the Fiordland population was also intensively managed: single eggs were often removed from two-egg broods and artificially incubated with chicks reared in captivity until around 1 year old, when they were released back into the wild (see ‘Artificially incubate and hand-rear birds in captivity’ for details).