Habitat requirements of an arboreal Australian snake (Hoplocephalus bitorquatus) are influenced by hollow abundance in living trees

Abstract

The value of tree hollows (cavities) to wildlife is well documented among birds and mammals, however few studies focus on their importance for snakes. Given increasing concern about the global net loss of hollow-bearing trees, it is imperative that studies extend to other vertebrate classes that may be dependent on this structural habitat component. We tested the hypothesis that habitat selection of an arboreal elapid, the pale-headed snake (Hoplocephalus bitorquatus), is primarily influenced by shelter requirements at multiple spatial scales. Consistent with our hypothesis, snake detection was biased towards a riparian ecosystem where hollow-bearing tree density was on average nine times greater than adjoining vegetation communities. In contrast, we found that the relative abundance of potential prey was equivalent among vegetation communities (frogs: P = 0.882; geckos: P = 0.306). At the microhabitat scale, snakes selected live hollow-bearing trees that were significantly larger (mean diameter: 74.5 cm ± 3.4, s.e.) than those otherwise available (42.4 ± 1.2 cm, s.e.) and estimated to be on average 111 years old. We recorded temperatures inside tree cavities to investigate whether the preference for live trees might be influenced by temperature buffering. Temperatures inside live trees were up to 16.4 °C below ambient in summer and 13.0 °C above ambient in winter. Temperature buffering was more pronounced in living trees (regression of cavity temperature against ambient, winter: r = −0.621; summer: r = −0.630) compared to dead trees (winter: r = −0.219; summer: r = −0.328), suggesting microhabitat selection may be driven by thermal requirements. Our study demonstrates the important role that mature, live hollow-bearing trees play in habitat selection by the pale-headed snake. It also suggests that the conservation of this species will be difficult in environments where such trees have been depleted due to land management practices. Managing forests for the persistence and recruitment of live hollow-bearing trees must be the primary conservation objective for threatened hollow-dependent fauna globally.