Canopy dieback is exacerbating bird population decline in South Australian woodlands

Dieback is an emerging threat to forests globally, but its long-term impact on biodiversity remains sparsely investigated. In this study, we integrate multiple datasets to assess whether canopy dieback in stringybark eucalypt ( Eucalyptus obliqua, L'Hérit. and Eucalyptus baxteri (Benth.) Maiden & Blakely ex J.M. Black) woodlands of the Mount Lofty Ranges in South Australia contributes to declines in bird populations. Using 20 years of monitoring data on bird populations and tree canopy condition, we investigate which woodland species are impacted by canopy dieback. Overall, results suggest that many woodland birds have been gradually declining over time and that canopy dieback may be accentuating declines. While only the Striated Thornbill ( Acanthiza lineata ) significantly declined over time with the amount of dieback in generalised mixed-effect models, estimated marginal means suggested aggravated abundance declines for species foraging in the canopy or on invertebrates when severe dieback occurs. These findings support previous work suggesting that canopy dieback can negatively affect habitat specialists and canopy-dependent species. Future increases in canopy dieback, driven by increases in drought and heat stress severity under climate change, are therefore likely to add pressure on already declining bird populations that are vulnerable to canopy loss. Consequently, management of biodiversity dependent on tree canopies will need to account for future habitat loss from dieback.