Measuring mortality in short-tailed bats (Mystacina tuberculata) as they return from foraging after an aerial 1080 possum control operation

Lesser short-tailed bats (Mystacina tuberculata) feed on arthropod taxa known to consume 1080 baits. Thus, they may be vulnerable to secondary poisoning after control operations for brushtail possum (Trichosurus vulpecula) using aerially broadcast 1080 baits. Short-tailed bat mortality was monitored during 11 days after 1080 baits were broadcast over their winter foraging area. Monitoring involved catching a sample of 269 bats as they arrived at a roost after foraging, then holding them in captivity for 48 hours. None of the captured bats displayed any symptoms of 1080 poisoning. Power analysis indicates that there was a ³ 0.95 probability of detecting mortality when the actual mortality rate was above 11.1 deaths per thousand foraging flights. Uncertainties in assumptions about the bats’ behaviour mean that the overall population mortality corresponding to this minimum detectable mortality rate may range from 5.4 to 28.4%, with a best estimate of 14.4%. Although it can be concluded that this 1080 operation probably did not cause major mortality of short-tailed bats, several replicate trials are required before a generalised conclusion can be drawn about the fate of short-tailed bats following aerial 1080 operations. More information about short-tailed bat population demography is required to assess the impact of 1080 operations on population viability.