Mohua and stoats: A population viability analysis

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Abstract
Population viability analysis was used to assess the survival prospects of mohua (Mohoua ochrocephala) populations of varying sizes, with different breeding strategies and suffering predation episodes at varying frequencies, from the South Island of New Zealand. Mohua populations in which most pairs attempted to raise two broods of chicks each year were more vulnerable to episodic stoat (Mustela erminea) predation than were populations in which pairs attempted to raise only one brood. However, those populations in which most pairs raised two broods had a much better ability to recover following predation. High stoat numbers every year would lead to the extinction of mohua populations regardless of their size and breeding strategy, but one‐brood populations would decline more slowly. If stoat populations were high only once every 5 years (the likely natural rate in South Island beech forests), small populations, and populations in which most pairs raised only one brood a year, would have very low survival prospects, but two‐brood populations of more than about 40 pairs would have good survival prospects. Reduction in stoat densities, particularly in years when their numbers are high, is likely to have a substantial positive effect on mohua populations.