Out on a limb: conservation implications of tree-hollow use by a threatened snake species (Hoplocephalus bungaroides: Serpentes, Elapidae)

Habitat requirements of arboreal reptiles may determine their vulnerability to anthropogenic disturbance, but have attracted little research. We studied habitat use by the broad-headed snake Hoplocephalus bungaroides, a threatened species from southeastern Australia. Intensive radio-tracking of 22 broad-headed snakes (from 1992 to 1995 in Morton National Park, 160 km south of Sydney) provided detailed information on the habitat requirements of these animals. During spring, broad-headed snakes were sedentary and used rocks and crevices on exposed cliff edges as diurnal retreat sites. These results are consistent with the widespread view that this species is restricted to rocky, outcrops. However, >80% of our telemetered snakes moved away from the rock outcrops to open woodland during the summer. Radio-tracked snakes used one to nine trees each summer and spent long periods (up to 48 days) sequestered inside tree-hollows. Tree use was highly non-random; the snakes actively selected dead rather than live trees, large rather than small trees and trees with many branches and hollows. The selection of trees with hollow branches may reflect the thermo-regulatory opportunities provided by this microhabitat, and/or the abundance of potential prey (arboreal mammals) in tree-hollows. Our radio-tracked snakes actively selected grey gums Eucalyptus punctata and Sydney peppermints E. piperita, but avoided the most common tree species on our study sites (turpentine Syncarpia glomulifera). Our study shows that persistence of broad-headed snakes in an area may depend crucially not only on suitable rocky habitat, but on adjacent forests. Hence, forestry practices should be designed to ensure that suitable 'habitat trees' are retained in forested areas near rocky cliffs.