Macropod habitat use and response to management interventions in an agricultural–forest mosaic in north-eastern Tasmania as inferred by scat surveys

1. What they did

Tasmanian pademelons and red-necked wallabies are among the most common native herbivores in Tasmania, and they are treated as pests because they graze pasture, crops and young plantation trees. The authors wanted to know where these two species spend their time in a landscape mixing farmland, plantation forest and native forest, how that changes with the seasons, and how it changes after two kinds of management: shooting and fencing. Instead of collaring individual animals, they used droppings (scats) as a whole-landscape measure of how much each habitat was being used.

• Transects. In the Scottsdale region of north-east Tasmania they laid out 127 permanent transects, each 100 m long, spread over four sites and stratified across the three habitats. They also described the vegetation and ground cover along each transect.
• Scat counts. In each of six small circular plots per transect, they identified pademelon and wallaby pellets using a field guide to Australian tracks and scats (Triggs 1996), counted them and removed them. Transects were first cleared in December 2008, then resurveyed at about six-week intervals through summer and autumn 2009, and once more in spring. This gave a scat deposition rate (scats per square metre per day) for each habitat, species and period.
• Management. At two sites, a qualified marksman culled about 400 macropods in late summer (February 2009) and about 100 in mid-winter (July 2009). At one of these sites, a 2 km wallaby mesh fence with electric standoffs was built along the edge of farmland in mid-autumn (April 2009). Two sites were left alone as controls.
• Scat endurance. To check that scats would not vanish between surveys, they placed ten fresh pellets (five from each species) in each of 15 quadrats across the three habitats in January 2009 and checked them about five and ten months later.

2. What they found

How long scats last

• Scats lasted well: 92% were still there after five months (summer to winter) in all three habitats. After about 11 months, 70% of pademelon and 80% of wallaby scats remained identifiable.
• Scats lasted longest in native forest and broke down fastest on agricultural land, for both species. Wallaby scats lasted slightly longer than pademelon scats.

Habitat use at the control sites

• Both species used all three habitats year round, but scat deposition was far higher on agricultural land than in plantation or native forest.
• Pademelon scat deposition on farmland was highest in early autumn and dropped in late autumn and spring. Wallaby scat deposition was lower in late autumn and spring than in summer and early autumn.
• Pademelons favoured farmland all year; wallabies favoured it most in summer.

After shooting and fencing

• On agricultural land, distance from the intervention site best explained scat deposition after each intervention: the closer to the shooting or fencing, the fewer fresh scats.
• This pattern was strong for both species after the summer cull, for pademelons only after the winter cull, and weaker (but present) for both species after fencing.
• In plantation and native forest there were no clear trends after any intervention.
• The authors note that they had few transects between 1.5 and 3 km from the interventions, so these patterns need caution.

3. What they concluded

• Scat counts are a useful, quick and cost-effective way to measure macropod habitat use, and can be used alongside or instead of radio-telemetry.
• Both species select farmland, pademelons more strongly, probably because the smaller pademelons need higher quality food. Wallabies, with larger home ranges, can use a wider range of habitats.
• Seasonal changes in food, temperature, breeding activity and predators probably drive the seasonal patterns.
• Shooting and fencing reduced the use of farmland, but only close to where they happened. Combined with the concurrent GPS study, this suggests shooting reduces animal numbers locally, and fencing pushes animals away from the fenced area.

4. How tracking was or was not used

The study is built on signs: pademelon and wallaby scats were identified to species, counted and cleared on fixed plots, and their rate of deposition was used as an index of how much each habitat was used. A field experiment tested how long scats of each species stay identifiable in each habitat. No footprints or trailing were used. The authors cite earlier work showing that seasonal vegetation growth can change how visible scats are to observers.

5. Tracker or observer certification

Not reported. The paper does not say who identified and counted the scats or how their identifications were checked. This matters because the two species’ scats had to be told apart for every result. The acknowledgements thank a number of people for technical and field support.

6. Other technologies, skills or innovations

• A scat endurance trial with colour-coded paperclips marking each pellet, scored present or absent over about 11 months.
• Habitat description with the Braun-Blanquet cover-abundance scale and a Bitterlich wedge for tree basal area.
• Comparison with a concurrent Global Positioning System (GPS) collar study of the same animals (Wiggins et al. 2010).

7. Implications for conservation (from the paper)

• Managing pest herbivores needs a whole-landscape view: shooting and fencing only had a local effect, and seasonal and habitat factors also drive where animals feed.
• Controlling native herbivores in mixed farm and forest landscapes is a formidable challenge, and the timing of interventions may itself change how animals use the landscape.
• Fencing can protect specific places from browsing, but may shift animals to neighbouring land.