The impact of a mega‐fire on tree hollow loss and nest box occupancy by secondary cavity‐nesting cockatoos

Abstract

Tree hollows are important structural habitat features for secondary cavity‐nesting birds, however, there has been limited research on how fire severity and frequency affect hollow abundance. Following a mega‐fire on Kangaroo Island during the 2019–2020 Australian bushfire season, we conducted an opportunistic post‐fire assessment of the fate of 144 monitored hollows in Eucalyptus cladocalyx and Eucalyptus leucoxylon trees used by endangered glossy black‐cockatoos (Calyptorhynchus lathami halmaturinus) and yellow‐tailed black‐cockatoos (Zanda funerea). We investigated the relationship between burn severity, inter‐fire interval, tree species and landscape position on the likelihood of tree hollow loss. We also compared the occupancy of nest boxes by both cockatoo species in fire‐affected catchments pre‐fire (2015–2017; 59 nest boxes) and post‐fire (2020–2022; 52 nest boxes). Surveys revealed that 64.4% of monitored tree hollows within the burnt area were destroyed, as were the trees that contained them. Most monitored tree hollows (76.9%) were in areas that had not experienced fire in >50 years prior to the 2019–2020 fires. Tree hollow loss in 2020 was 29 times greater than the mean annual loss of 1.6% recorded in the 22 years prior. Burn severity, inter‐fire interval, landscape matrix and tree species were poor predictors of hollow loss. However, increasing distance from forest edge slightly increased the probability of hollow loss. Post‐fire, the proportion of nest boxes used for nesting by glossy black‐cockatoos per annum increased to 0.70 ± 0.09, compared to 0.50 ± 0.03 pre‐fire. However, the proportion of nest boxes used for nesting by yellow‐tailed black‐cockatoos per annum remained similar (post‐fire 0.32 ± 0.12; pre‐fire 0.28 ± 0.05). The mega‐fires on Kangaroo Island in 2019–2020 resulted in tree hollow loss on a much larger scale than recorded in the 22 years prior, and subsequently, nest boxes have become an important resource for the endangered glossy black‐cockatoo.