Environmental factors affecting the capture of southern hairy-nosed wombats (Lasiorhinus latifrons) by stunning

Abstract

A 'stunning' technique, combining a rifle shot with spotlighting and hand netting was used for the live-capture of southern hairy-nosed wombats. A successful stun was defined as a rifle shot that resulted in the temporary deafening and disorientation of a wombat. When combined with spotlighting, this technique enabled catchers with nets to approach the wombat undetected to secure an easy capture. Environmental factors (temperature, humidity, dew point, light and wind) were examined in order to determine the optimal conditions for the use of this capture procedure. In all, 558 shots were fired, resulting in ~25% of successful stuns. Stunning was primarily affected by temperature and humidity in a normally distributed manner. Stunning was greatest between 12°C and 18°C with a success rate of 40–51%. At temperatures either side of this significantly fewer stuns were achieved, and below 6°C or above 24°C no successful stuns were recorded. Likewise, stunning worked best at humiditys of 70–90%, declined when humidity was >90% and did not work at all at a humidity of 40% or less. Together, temperature and humidity data suggest that air density, for which these parameters are correlates, may be the key component in the success of this capture technique. Variation in stunning success resulting from changes in temperature and humidity may affect either the frequency spectrum of the sound created by the shot or perhaps the manner in which the eardrum receives the sound. Other factors, including dew point and light, also varied significantly with stunning, but were considered of less importance. Whatever the controlling factors, it was clear that stunning, in combination with spotlighting and netting is a rapid, highly effective, and potentially much less stressful method of capturing southern hairy-nosed wombats than the methods that have been used previously.