Using ecological niche models to infer the distribution and population size of parakeets in New Caledonia

- We use maximum entropy niche models to infer the distribution of parakeets in New Caledonia.
- We develop a new method for estimating population size by correlating abundance with habitat suitability.
- Projections indicate that parakeet populations are likely to recede in response to climate change.
- Our research suggests that the current reserve system is inadequate, and should be extended.

Knowing the distribution and abundance of species is critical for conservation, yet field surveys are often limited in their spatial extent. In this study, we use ecological niche models to infer the current and future distribution of New Caledonian Parakeets (Cyanoramphus saisseti), Horned Parakeets (Eunymphicus cornutus), and Ouvéa Parakeets (Eunymphicus uvaeensis) in New Caledonia. In addition, we present a new method of assessing the population size of each species based on the relationship between local abundance and modelled habitat suitability. According to our estimates, there are 5708 (5048-6174) New Caledonian Parakeets on the main island of New Caledonia, distributed over an area of 2783 km2, of which 1939 km2 is forested. We estimate there to be 8690 (7934-9445) Horned Parakeets, and their distribution extends over 3482 km2, including 2162 km2 of forest. In comparison, the Ouvéa Parakeet has a very restricted range of 34 km2 (most of which is forested), and a population estimated at 1730 (963-3203) individuals. Projections involving simulated climate change suggest that populations of New Caledonian Parakeets and Horned Parakeets may recede into areas at higher altitudes in the future, primarily along the central mountain chain of the mainland. It is difficult to predict how the Ouvéa Parakeet will respond to the climatic changes forecast for Ouvéa, as the species is expected to face climatic conditions in the future that are different from any of those currently experienced on the island. Our research demonstrates that the current reserve system in New Caledonia is unlikely to provide sufficient protection for parakeets. Hence, we believe that existing Important Bird Areas (IBAs) should be evaluated for their current and future potential as reserves.