Threshold harvesting as a conservation or exploitation strategy in population management

Was extinction of New Zealand's avian megafauna an unavoidable consequence of human arrival?

Human overexploitation contributed strongly to the loss of hundreds of bird species across Oceania, including nine giant, flightless birds called moa. The inevitability of anthropogenic moa extinctions in New Zealand has been fiercely debated. However, we can now rigorously evaluate their extinction drivers using spatially explicit demographic models capturing species-specific interactions between moa, natural climates and landscapes, and human colonists. By modelling the spatial abundance and extinction dynamics of six species of moa, validated against demographic and distributional inferences from the fossil record, we test whether their extinctions could have been avoided if human colonists moderated their hunting behaviours. We show that harvest rates of both moa birds (adults and subadults) and eggs are likely to have been low, varying between 4.0-6.0 % for birds and 2.5-12.0 % for eggs, annually. Our modelling, however, indicates that extinctions of moa could only have been avoided if Polynesian colonists maintained unrealistically expansive no-take zones (covering at least half of New Zealand's land area) and held their annual harvest rates to implausible levels (just 1 % of bird populations per annum). Although too late for moa, these insights provide valuable lessons and new computational approaches for conserving today's endangered megafauna.