Using population viability analysis and fossil records to inform the conservation of pāteke (Anas chlorotis)

Population decline and extinction are often driven by multiple stressors. Since AD 1500, the predicted global extinction rates for birds is estimated to be at least 80-times higher than the long-term background average. Pāteke/brown teal (Anas chlorotis) is a threatened waterfowl endemic to Aotearoa New Zealand, with a current population of c. 2500, spread across two remnant populations and a handful of reintroduction sites. The decline of pāteke since the arrival of humans results from habitat loss and fragmentation, predation, and other anthropogenic interactions. One of the two remnant populations is located on Aotea Great Barrier Island and has been declining since the 1980s. We used a combination of population viability analyses and species distribution modelling to better understand (1) the drivers of the decline on Aotea, (2) the management interventions that are most likely to reduce extinction risk and, (3) the pre-historic distribution of pāteke across Aotearoa. Our models were informed by a combination of seven years of intensive monitoring data from Aotea, and nationally distributed fossil records. Population viability analysis results suggest that over the next 100 years the pāteke population on Aotea has a 46% chance of extinction and a 99% chance of falling below an abundance of 50 individuals. Management should focus primarily on the adult life-stage, as protecting this stage resulted in the most significant increases in population growth rates. Species distribution modelling results suggest that historically, pāteke were present across much of coastal Aotearoa. Just as population declines are frequently the result of multiple stressors, multiple interventions are often required to halt extinctions. For pāteke, this will mean controlling multiple mammalian predator species, improving habitat quality, and re-establishing populations across their former range.