Sympathy for the devil – part three
By Jack Ashby, on 3 March 2011
From April 2010 I spent about five months undertaking several zoological field projects across Australia. I worked with government agencies, universities and NGOs on conservation and ecology studies ranging from Tasmanian devil facial tumour disease, the effect of fire, rain and introduced predators on desert ecology and how to poison cats. This series of blog posts is a delayed account of my time in the field.
Weeks Six and Seven
Over the past two weeks I’ve described a project involving trapping Tasmanian devils to study Devil Facial Tumour Disease (DFTD). My next fieldwork looked at the effect of the devil population crash on other mammals. I had a some time before then so I decided to walk over the middle third of the island on the amazing Overland Track through the mountainous wilderness of the UNESCO World Heritage Area.
I had done this hut-to-hut walk in the height of the summer before, and now in mid-winter it was completely different – many of the tarns were completely frozen over and the higher paths were under a solid inch of ice. Nevertheless, in larger lakes I managed to find a few platypuses, my favourite animal, and reminded myself of the excitement of searching out wild animals on foot, rather than only seeing them in traps.
The density of mammals in Tasmania is very high. How are these populations reacting to the sudden disappearance of their largest native mammalian carnivore? This question is the remit of a PhD student in the University of Tasmania (UTas) Zoology Department. I joined her for about a week in the forests around the central north of the state to collect some data.
This study doesn’t involve trapping any animals – there are a number of ways to assess animal populations and trapping is just one of them. Sand pads are used in much of the world – allowing identification by footprints, but I suspect that this would’t be too successful in Tassie because of all the rain. We used hair tubes and camera traps. Camera traps work when an animal crosses an infra-red beam, which starts the recording, and to increase our chances we put down bait for both carnivores and herbivores. The herbivore bait was peanut butter mixed with oats, the carnivore bait was dried liver soaked in mutton bird (shearwater) oil. This smells disgusting . The oil is a by product of quota-based hunting, only permitted by aborigines.
Hair tubes are segments of pipe open at both ends,with bait in the middle, or a funnel flat one one side with bait at the narrow end. Strips of double-sided sticking tape are arranged around the inside, and any animals that come and go can be identified by the unique structure of the hairs they leave on the tape.
We would spend the days setting these traps in 2km transects in different kinds of forest and collecting them three days later. The evenings, at a mouse-infested cabin in the wombat-infested Narawntapu National Park, were spent identifying the animals caught on camera, cleaning the traps and sticking the hairy tape onto bits of paper for analysis back at UTas.
One of the sites was a forest near Penguin where five years earlier I saw my first devils, whilst camped out in a crumbling shack with some road-kill wallabies staked down as bait. Since then DFTD has arrived in the area and devils have all but disappeared there. When any species is removed from an ecosystem it can have profound effects on the other species in its food web. What seems to be happening is that as devils decline feral cat numbers rise. Cats have a devastating effect on wildlife and elsewhere in Australia many species have been hunted to extinction by them. Foxes and cats have given Australia the worst count of recent mammal extinctions anywhere in the world.
Surprisingly foxes never made it to Tasmania, until now. One was recorded on CCTV coming out of a shipping container in 1998 and others are believed to have been released since, possibly deliberately. An entire armed government taskforce “Fox Free Tasmania” is dedicated to hunting down reported sightings. The thing is, only a couple of carcasses have ever been seen, and none have been trapped live or on camera. While scientific consensus is that foxes are now at large in Tasmania, there is a fairly large group of people who say it’s a green conspiracy, and that the evidence has been faked. This is just another example of the massively polarised political scene in Tassie, with “greenies” on one side, and “rednecks” on the other, neither of which has a nice word to say about the other.
We didn’t find any foxes this week, but it is widely feared that having kept the fox at bay for so long, the disappearance of the devil has allowed the alien predator to establish itself.
The early evidence of this study seems to suggest that the next largest native predator – the spotted-tail quoll – is experience a population increase, while its smaller relative the eastern quoll’s numbers are dropping. This isn’t too surprising as cats are more likely to have an effect on the smaller species as their own number rise to fill niches vacated by devils. A surprising result also suggests that rodent numbers are increasing (both native and non-native mice and rats) – not what you’d expect with more cats around.
I was sad to leave the green forested wonderland of Tasmania, but excited at the prospect of spending a month with a team from the University of Sydney camping rough in the bright red centre of Australia, trapping small mammals and lizards in the Simpson Desert.
UPDATE: PART SEVEN HERE