A report to the Commonwealth Department of the Environment
David A. Westcott, Daniel K. Heersink, Adam McKeown, Peter Caley
This report reviews past and current monitoring of Australia’s two threatened flying-fox species, the spectacled flying-fox (Pteropus conspicillatus) and the grey-headed flying-fox (P. poliocephalus). On the basis of this review we then consider their current conservation status.
Both the spectacled and grey-headed flying-foxes were listed as Vulnerable under the EPBC Act on the basis of Criterion 1 of the Act (decline in numbers). The spectacled flying-fox also met Criterion 5 (probability of extinction in the wild is at least 10% in the medium-term). Listing against these criteria means that in any re-assessment of the status of these species a key consideration must be the issue of their current and predicted population trends.
In this report we draw together data on the species population dynamics from past and current monitoring programs. We consider the results of the programs and describe the errors associated with them. In light of this we then provide an assessment of the species current status and trend.
The spectacled flying-fox has shown a decline from a population of 214,750 in November of 2005 to 92,880 in November of 2014. This decline appears to be associated with three periods of perturbation: two large perturbations, Cyclones Larry (2006) and Yasi (2011), and then a series of smaller perturbations occurring in the cooler months of each year starting in 2011 and occurring each year thereafter. The cause of the smaller perturbations is unknown.
Overall we suggest that the decline exhibited by the spectacled flying-fox (as much as 62%) over a 10 year period, when extrapolated out to three generations, is sufficient warrant its listing as Endangered under the EPBC against Criteria 1 and 5.
The grey-headed flying-fox has been monitored in a number of programs, most recently the National Flying-Fox Monitoring Program. The NFFMP surveys the species across its range every quarter and has done so since November 2012. Based on these surveys we estimate the current population to be 680,000 (±164,500).
Monitoring of grey-headed flying-foxes was also conducted in the period 1998-2005. Comparison of results between the two phases of monitoring is too risky, because the differences in the methods used and uncertainty about the survey coverage of the extent of the population. However, we recognise that, irrespective of these concerns, these comparisons will be made. If this is to happen, then it is important to ensure that appropriate qualifications and corrections are incorporated and so we attempt to do this. Once such considerations are incorporated we estimate that the population has remained relatively stable, but potentially has declined slightly, across the two periods.
Given that the identified threats to the species continue to be threats and that new threats are emerging, e.g. extreme heat events, we suggest that the grey-headed flying-fox’s status should at the very least remain as Vulnerable.