When, where and why do people encounter Australian brownsnakes (Pseudonaja textilis : Elapidae)?

Abstract

Encounters between humans and dangerously venomous snakes put both participants at serious risk, so the determinants of such encounters warrant attention. Pseudonaja textilis is a large fast-moving elapid snake responsible for most snakebite fatalities in Australia. As part of a broad ecological study of this species in agricultural land near Leeton, New South Wales, we set out to identify factors influencing the probability that a human walking in farmland would come into close proximity to a brownsnake. Over a three-year period, we walked regular transects to quantify the number and rate of snake encounters, and the proportion of snakes above ground that could be seen. The rate of encounters depended upon a series of factors, including season, time of day, habitat type, weather conditions (wind and air temperature) and shade (light v. dark) of the observers’ clothing. Interactions between factors were also important: for example, the effect of air temperature on encounter probability differed with season and snake gender, and the effect of the observers’ shade of clothing differed with cloud cover. Remarkably, even a highly-experienced observer actually saw <25% of the telemetrically monitored snakes that were known to be active (i.e. above ground) nearby. This result reflects the snakes’ ability to evade people and to escape detection, even in the flat and sparsely vegetated study area. The proportion of snakes that were visible was influenced by the same kinds of factors as described above. Most of the factors biasing encounter rates are readily interpretable from information on other facets of the species’ ecology, and knowledge of these factors may facilitate safer coexistence between snakes and people.