Zoology - Theses
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ItemActivity of insectivorous bats at gold mining water bodies: risks associated with consumption of cyanide-bearing waste solutions( 2013)Insectivorous bats (microbats) are commonly recorded in large numbers in the airspace above water bodies from dusk to early evening when they emerge from daytime roosts to forage and drink by swooping down to lap at the water’s surface while in flight (i.e. drinking on the wing). Microbats are known to visit and interact with wastewater impoundments at gold mines, which contain cyanide. When cyanide concentrations exceed a critical toxicity threshold significant mortality events can occur in microbats. Despite this evident risk, monitoring of microbats at the majority of gold mines in Australia is either inadequate or non-existent. In this thesis I address the lack of prescriptive methods for monitoring microbat interactions with water bodies at gold mines by firstly investigating the level to which microbats produce echolocation calls associated with drinking. Through the development of a novel monitoring technique, I recorded the first empirical evidence that microbats produce terminal buzz calls while drinking on the wing. These findings indicate that the occurrence of both foraging and drinking buzzes should be considered in the design of future ecological research comparing microbat foraging rates in the airspace above different water bodies. I investigated activity of bats in the airspace above two water bodies at Cowal Gold Mine, western New South Wales, Australia. Microbat activity was highly variable across nights and months, however overall activity was similar at both the cyanidebearing tailings dam and a rainwater-derived farm dam. The regular presence and highly variable activity of microbats in the airspace above water bodies at this gold mine are consistent with the findings of previous studies investigating wildlife cyanide toxicosis risks at gold mines. During this study, tailings slurry and supernatant pooling within the tailings dam were consistently well below the industry protective concentration limit of 50 mg/L weak acid dissociable (WAD) cyanide. Therefore, wastewater solutions stored within this open impoundment posed an extremely low risk of wildlife cyanide toxicosis, including to microbats. Several studies have shown that elevated levels of salinity in mine waste solutions stored in open impoundments prevent wildlife cyanide toxicosis by eliminating drinking and reducing foraging. This appears to be consistent for diurnal wildlife interacting with open impoundments, however the risks to nocturnal wildlife of cyanide exposure are unclear. I investigated the activity of microbats in the airspace above hypersaline cyanide-bearing tailings dams, other saline water bodies and fresh (potable to wildlife) water bodies at two gold mines in the Goldfields of Western Australian: Sunrise Dam Gold Mine (SDGM) and Kanowna Belle Gold Mine (KBGM). Microbats were recorded in the airspace above each water body, but were more active at fresh than saline water bodies. While considerably more terminal echolocation buzz calls were recorded in the airspace above fresh than saline water bodies at both mine sites, it was not possible to determine whether these buzz calls corresponded to foraging or drinking bouts. However, at SDGM no drinking bouts were observed in 33 h of thermal video footage recorded at one hypersaline tailings dam, suggesting that this water is not used for drinking, and is only used in a very limited way for foraging. As there is no information on salinity tolerances of microbats, it is not possible to quantify the concentration range (likely between brackish and saline) where salinity becomes a physiological stressor to microbats, thereby precluding drinking. It could be assumed that microbats would not be able to tolerate salinity in drinking water at concentrations greater than those documented as toxic for saline-adapted Australian terrestrial wildlife. Therefore when managing sites to avoid wildlife mortalities, adopting the precautionary principle, microbats are unlikely to drink hypersaline solutions (≥50,000 mg/L total dissolved solids). At mining operations that produce potable wastewater solutions, the most effective mechanism for preventing cyanide toxicosis to wildlife, including microbats, is reducing the concentration of cyanide in tailings discharged to open impoundments to below 50 mg/L WAD. Capping spigot discharge concentration at this level will result in habitats downstream of the spigot (i.e. fast-flowing tailings streams and ponding supernatant) being consistently well below 50 mg/L WAD cyanide.