Arboreality in Snakes: Ecology of the Australian Elapid Genus Hoplocephalus

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Abstract
Broad-headed snakes (Hoplocephalus spp.) are unusual among Australian elapids in being arboreal. Dissection of 332 specimens provided data on body sizes, sexual size dimorphism, food habits, reproductive cycles, fecundities and probable growth rates. Females grow larger than males in all 3 Hoplocephalus spp. H. bitorquatus feeds mainly on arboreal pelodryadid frogs, H. bungaroides on lizards, and H. stephensi on lizards, mice and frogs. All species are viviparous, with ovulation occurring in late spring and birth in late summer. Young at birth are large (SVL 20 cm) relative to maternal size (SVL 50 to 70 cm), and litters are small (usually 4 to 6 young). Size-frequency distributions suggest sexual maturation at 3 to 4 yr of age in H. bitorquatus. Most adult female Hoplocephalus reproduce only once every 2 yr, or less often. Compilation of published data on snake faunas of several continents reveals that: food habits of arboreal and terrestrial snakes usually are similar; arboreality is more common in some taxonomic groups (e.g., colubrids) than in others (e.g., elapids); and the proportion of arboreal species in a snake fauna is highly correlated with annual precipitation. These findings may explain why arboreality is rare in Australian snakes.