Roadkill is the biggest threat to the survival of Tasmanian devils after facial tumours and now a study by an international collaboration of experts has found a correlation between death by car strikes and time in captivity.
Devils that spent several generations in captivity became naïve to wild conditions.
A University of Sydney collaborative research study assessing the viability of captive-bred Tasmanian devils released into the wild in Tasmania has found devils that spent one or less generations in captivity fared better post-release than those that had been in human care over several generations.
Tasmanian devil populations have been decimated by the transmissible Devil Facial Tumour Disease, (DFTD) in the past 20 years. There has been an 80 percent decline in devil sightings in Tasmania and some subpopulations have been reduced by 90 percent.
The Save the Tasmanian Devil Program was formed by the Tasmanian government to determine strategies to address this decline, including the establishment of a captive breeding program of healthy devils.
To protect against extinction, an ‘insurance’ population was created in 2006, aimed at establishing a DFTD-free captive population to maintain 95 percent wild-sourced gene diversity for 50 years.
Previous releases of captive devils into the wild, ito Maria Island, resulted in an unexpectedly high survival rate of founder devils. However, Maria Island is a national park with very few man-made threats.
Researchers studied devil survival after subsequent releases at two locations on mainland Tasmania, which showed a much higher mortality of the captive-bred devils, particularly in the first six weeks after release.
The results are published today in Nature's Scientific Reports.
Lead author from the University of Sydney Dr Catherine Grueber said: “We found that those devils that had spent several generations in captivity had become naïve to wild conditions, which included human infrastructure including roads, cars and people.
“Devils from a variety of facilities were released, and all appeared to be vulnerable to vehicle strike; there was also no clear effect of the age or sex of the devils.
"We found that the most important factor was generation time: after just a few generations in captivity, released devils were more likely to be hit by car.”
Program Manager of the Save the Tasmanian Devil Program Dr David Pemberton said the integration of the research with management in real-time had allowed adaptive management decisions regarding the wild release of devils.
“Wild devils are vulnerable to vehicles due to their propensity to travel long distances, use roads for dispersal, travel at night and scavenge on roadkill,” Dr Pemberton said.
“Part of the roadkill mitigation is adapting the metapopulation strategy.
"This is a transformational result and a fantastic opportunity for all of us as conservation managers to fine-tune the Tasmanian devil captive breeding program to minimise the generational period that devils remain in captivity.
University of Sydney co-author Dr Carolyn Hogg said understanding the factors that influence survival upon release, allowed the team to redesign their selection methods and criteria for those individuals to be released.
Further mitigation of roadkill issues is the subject of ongoing work, including soft release tactics (using feed stations to keep devils away from roads), cuing avoidance behaviours of cars, employment of virtual fence technology, signage on major roads, and public outreach.
This study was undertaken by the Save the Tasmanian Devil Program, University of Sydney, the Zoo and Aquarium Association Australasia and San Diego Zoo Global.
Photo at top of page: A wild Tasmanian devil killed by a vehicle. Credit: Oli Gales.