The Save the Tasmanian Devil Program’s (STDP) Annual Monitoring Project was developed to investigate the status of wild Tasmanian devil populations and any change over time to inform decisions on conservation strategies.
Through this project long-term population data is collected including abundance, age and sex structure, and disease prevalence from eight different sites across the State. This project is currently funded by Toldeo Zoo in the US with Dr Samantha Fox from the STDP managing it as the Adjunct Biologist to the zoo.
Tasmanian devil pouch with four tiny imps.
In order to determine how much help Tasmanian devils need to survive into the future, it is vital the STDP measures what is happening to devils in the wild. While early research indicated that devil facial tumour disease (DFTD) caused such a high mortality rate in devils that they could become extinct, today, monitoring results are interpreted in the context of whether Tasmanian devils are persisting in the wild, declining further towards extinction or recovering.
Several methods are used by the STDP to gather data as part of the annual monitoring program; these include spotlight surveys, trap-release surveys, and camera surveys.
Trap-release surveys commenced in 2003 and confirmed the trend seen in Statewide spotlight surveys that devil numbers had decreased by 80% in areas affected by DFTD. These surveys involve trapping wild devils in specially designed traps that provide shelter to the devils and minimize the chances of them injuring themselves. STDP staff then place a microchip under the skin between their shoulders, measure their disease status and other attributes such as sex, weight and reproduction and release the devil back into the wild. Each microchip number is unique, therefore individual devils can be easily identified.
One of the benefits of trap-release in comparison to spotlight and camera surveys is that they involve handling and close examination of devils, which allows for individual-specific records of disease and reproductive status.
STDP trap-release sites are now monitored at least once per year in order to estimate the number of devils residing in each area, their population structure including age, sex ratio, and prevalence of disease, and to obtain important biological samples before releasing devils back into the wild.
STDP wildlife biologist Clare Lawrence sets a devil trap at the annual monitoring site known as Woolnorth. Traps are placed in sheltered locations, and are baited with fresh meat.
Spotlight surveys involve counting all animals observed along 185 transects around the State that are 10 km in length. These transects are driven once per year. Spotlight surveys have been conducted systematically across Tasmania for over 30 years. They were designed to monitor population trends in browsing animals such as Bennett’s wallabies and Tasmanian pademelons, however all non-domestic species have been recorded. As a result they are an invaluable source of information on the long-term trends in devil counts.
The technology for camera surveys was not widely accessible when the recovery program for Tasmanian devils commenced, however there have been rapid advancements in the cost, accessibility and functionality of remote cameras over the last 10 years. As a result, 32 cameras are now deployed by the STDP annually in the north-eastern region of Tasmania. They are used to determine if there have been any changes in the distribution of devils in the area believed to be affected by DFTD for the longest, and they may yield information in the future as to how the reduced densities of devils wrought by DFTD might affect other co-occurring species.
Photo of an adult Tasmanian devil (note the large ears with tattered edges which are typical of adult devils) taken using a remote camera which is triggered by heat and motion. The camera uses an infra-red flash so it is less likely to disturb animals when they are photographed (and hence the pink colouration of the photo). Devils and other animals are photographed when they come to investigate the scent lure placed in front of the camera.
It was the results from spotlight and trap-release surveys that resulted in the recognition of the Tasmanian devil as a threatened species and gave rise to the recovery program.
The combination of the different data collection methods provides for a monitoring approach that gains coarse trend spotlight count information across most of the devil’s range which is complemented by more detailed information from individual trapping and camera survey sites.
Recent findings by The STDP and its collaborators* have found that devils have persisted in the wild to-date. There is evidence of ongoing small decline in devil numbers across the area impacted by the disease. Moreover there has been a large shift in age structure towards young devils in diseased areas. Devils have managed to partially compensate for the large impact that DFTD has on their populations by breeding younger and having more pouch young in diseased sites. This compensation has not been enough to offset the impact of the disease with devil densities reduced by 80% in areas impacted by the disease, which means these small and potentially isolated populations are susceptible to being impacted by other threats such as roadkill, dog attack, loss of genetic diversity, bushfire, and drought.
Fieldwork and analysis of monitoring data has been conducted in collaboration with private land holders and supporting institutions. Tasmanian devils have been monitored for up to 10 years which has resulted in the compilation of valuable long-term data sets. Collaboration with management and research institutions has been a very important component of the monitoring program.
For example San Diego Zoo Global have provided analytical support to the STDP to estimate the long-term impacts of disease on devil numbers and potential population mechanisms such as changes in breeding rates or sex ratios that might signal future population change. Data has also been collected in collaboration with the University of Tasmania and in 2014 Toledo Zoo provided financial support for the Annual monitoring program to conduct trap-release monitoring trips for five years. The results of wild devil monitoring, including the methods used, are shared with members of the public, conservation managers, and researchers around the world and may give insight into the conservation and management of other species.
STDP Annual Monitoring Project 2018 Summary Report (3Mb)
Hawkins, C.E., Baars, C., Hesterman, H., Hocking, G.J., Jones, M.E., Lazenby, B., Mann, D., Mooney, N., Pemberton, D., Pyecroft, S. and Restani, M., 2006. Emerging disease and population decline of an island endemic, the Tasmanian devil Sarcophilus harrisii. Biological Conservation, 131(2), pp.307-324.
Lachish, S., McCallum, H. and Jones, M., 2009. Demography, disease and the devil: Life‐history changes in a disease‐affected population of Tasmanian devils (Sarcophilus harrisii). Journal of Animal Ecology, 78(2), pp.427-436.
*Lazenby, B.T., Tobler, M.W., Brown, W.E., Hawkins, C.E., Hocking, G.J., Hume, F., Huxtable, S., Iles, P., Jones, M.E., Lawrence, C. and Thalmann, S., 2018. Density trends and demographic signals uncover the long‐term impact of transmissible cancer in Tasmanian devils. Journal of Applied Ecology 55(3): 1368 - 1379.
McCallum, H., Jones, M., Hawkins, C., Hamede, R., Lachish, S., Sinn, D.L., Beeton, N. and Lazenby, B., 2009. Transmission dynamics of Tasmanian devil facial tumor disease may lead to disease‐induced extinction. Ecology, 90(12), pp.3379-3392.