Controlling invasive predators enhances the long-term survival of endangered New Zealand long-tailed bats (Chalinolobus tuberculatus): Implications for conservation of bats on oceanic islands

Abstract

Invasive mammalian predators pose one of the greatest threats to biodiversity globally, particularly on oceanic islands. However, little is known about the impacts of these invasive predators on bats (Chiroptera), one of the most specious mammal groups, and one of the most widespread groups of mammals threatened on oceanic islands (>200 spp.). Nearly 50% of the world's threatened bats are island endemics and because they are often the only native mammals on islands, they fulfil important ecological roles such as pollination and seed dispersal. Long-tailed bats (Chalinolobus tuberculatus) are critically endangered because of predation by exotic mammals, particularly ship rats (Rattus rattus), introduced by humans to the island archipelago of New Zealand. We monitored the survival of bats in three colonies in temperate rainforest in Fiordland over 22years. Since 2009, we controlled predators during irruption phases and compared survival of bats in previously untreated areas with survival in forest blocks treated using rodenticides deployed in bait stations. Survival was estimated using multi-state mark-recapture models in Program Mark 7.0 with >15,000 bats tagged. Survival was primarily dependent on year and age of bats, although seedfall intensity of the dominant canopy tree and predator management was also influential. Survival in long-tailed bats was as high as, or higher, than figures for bats generally in years with low predator numbers or predator control. Survival was markedly higher in treatment years when predators were managed (0.82 compared to 0.55). Population modelling indicated managed colonies will increase (λ>1.05) whereas unmanaged colonies will decline (λ=0.89−0.98) under scenarios that reflect increased frequency of beech mast and predator irruptions. Thus, effective predator control is essential for recovering long-tailed bat populations. Warming temperatures indicate that predator irruptions are becoming more frequent, which would require more predator control in the future than at present if declines in bat populations are to be reversed. These results are relevant to the conservation of threatened bats on oceanic islands, given the abundance of exotic mammalian predators, particularly ship rats, on them.