Declining endemicity and expanding ubiquity: detecting and monitoring population responses to Climate Change in Australia’s tropical montane avifauna.

Alexander Anderson (1), Collin Storlie (1), Yvette Williams (1), Luke Shoo (3), Stephen Williams (1)

1 Centre for Tropical Biodiversity and Climate Change, James Cook University, Queensland, Australia

2 The University of Queensland, Brisbane, Queensland, Australia

Worldwide, species distributions are shifting in response to climate change, resulting in increased extinction risk for many species. Montane tropical rainforests are important reservoirs of endemic bird diversity, but narrow thermal tolerances and restricted distributions make these faunas particularly vulnerable. In the Australian Wet Tropics (AWT), climate niche modelling predicts range contractions of cool-adapted upland endemic species, and expansion of lowland generalists. However, validating such predictions through the detection of range changes is often challenging, as patterns of distribution and abundance are often difficult to quantify. Efforts focused at range margins face the challenge of recording rare colonisation events or confirming local extinctions, both tasks complicated by low detectability. Estimating density and elevational abundance responses using hierarchical models, we have overcome some of these challenges for a diverse assemblage of rainforest specialist species in the AWT. We have recently refined our analysis of long-term monitoring data to show predictions are rapidly materialising, with significant changes in the distributions of 23 of 48 species. Integrating models of abundance response with available habitat area in elevational bands, we highlight synergistic effects of up-slope shift and declining habitat area in driving rapid population declines in 14 species, 5 of which are endemic to the region. In contrast, a further 10 species show population increases, all of which are widespread lowland species adapted to warmer climates. Challenges remain in accurately characterising the influence of detectability for rarer species and those that occur in groups. Measuring shifts is also a challenge at the upper extremes of these gradients, where species are most at risk. Much future work remains in understanding the repercussions of these assemblage changes in terms of ecosystem function.