Free-roaming dogs but not invasive mammals established in the wild endanger the flightless kagu of New Caledonia

Abstract

Species on islands that evolved without mammalian predators are commonly considered naïve to these introduced animals and therefore potentially vulnerable to predation. The endemic kagu Rhynochetos jubatus, a flightless bird, is the most emblematic species of New Caledonia. As the natural top predator of the ground fauna in rainforest, it is an excellent umbrella species for conservation on mainland New Caledonia (Grande-Terre) where it lives. Here, we assess the impact of invasive mammalian species on kagu and propose specific conservation actions. We conducted intensive research over 20 years and directly measured effects of each introduced species at each stage of the kagu life span. At the population level, we assessed kagu and predator abundance at sample sites in 2001–2016 throughout Grande-Terre. At the individual level, we studied reproduction and mortality in three kagu populations in 1991–1993 and 2002–2022. We found no evidence that any of the invasive mammalian species established in the wild pose a threat to kagu. Instead, only domestic dogs, which are not established in the wild, cause significant predation and associated extreme population fluctuations. Free-roaming domestic dogs limit suitable kagu habitat to less than half of the current rainforest. Island-wide, community-based management of dogs could lead to a significant increase in kagu numbers and, as the kagu is the top predator of ground fauna, produce benefits at the ecosystem level.