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Abstract
Bats are most vulnerable whilst in their roost, and activities that result in roost destruction or disturbance have the potential to cause declines in species of conservation significance. However, conservation efforts for bat colonies can be limited by a lack of understanding of the effect of certain disturbances. An evaluation drilling programme conducted in close proximity to historical underground gold workings near Marble Bar provided an opportunity to examine the short-term effect of this type of activity on colonies of the bats Macroderma gigas and Rhinonicteris aurantia. A non-invasive approach to assessing the impact of the associated activity was developed, which simultaneously realised the best economy of moving a drill rig. Bats were subject to several types of potential disturbance (from noise and vibration) from earthmoving equipment, the drill rig and the booster compressor. Monitoring involved continuous acoustic and visual observations of mine entrances during drilling, direct counts of emerging bats each evening after drilling, and surveys of other mines in the local area throughout the study. R. aurantia was present throughout the drilling programme, but actual numbers could not be determined accurately. A marked increase in the number of M. gigas was observed, thought to be independent of the activities associated with the drilling programme and possibly due to concurrent human activities in other local mines or natural factors. It was concluded that short-term activities associated with drilling that are not within 25 m of a mine entrance or 85 m of the roost site within the structure, and that do not intersect workings, might not constitute a significant disturbance to these bats. However, the long term cumulative effects of this and other disturbances, and in the context of contemporaneous activities at other roosts in the district, are unknown.
Keywords: bats; conservation significance; Marble Bar; minerals exploration, drilling; roost destruction
Introduction
The diurnal refuge, or roost, of bats is a major influence in their ecology, offering protection from exposure to daytime ambient conditions and predators, promoting energy conservation, and facilitating social interactions (Kunz & Lumsden 2003). Bats are vulnerable to the destruction of their roosts, as well as disturbances while in them, which are issues for many species worldwide (Hutson et al. 2001; Mickleburgh et al. 2002). Cave roosting bats will...