Evaluation of Three Relative Abundance Indices for Assessing Dingo Populations

1. What they did

Counting carnivores directly is hard and expensive, so managers often rely on indexes of relative abundance instead. The authors compared three ways of measuring dingo activity from tracks, to find which is most sensitive, how often stations should be checked, and the strengths and weaknesses of each.

On a cattle property in south-western Queensland they laid out two 50 km transects along vehicle tracks. Every kilometre had one station of each type:

• Fatty Acid Scent (FAS) index. A square metre of raked earth with a small plaster disc soaked in a synthetic scent in the centre, a method long used for coyotes in the western United States. Each station was scored as visited or not visited by a dingo each day.
• Buried Meat (BM) index. A square metre of raked earth with a 50 to 100 g piece of fresh kangaroo meat buried 5 to 10 cm deep, scored the same way.
• Activity index. A 1 m wide strip raked across the whole road (with fine dust or sand sieved on where the ground was hard), with no attractant. Here the team counted the number of dingo tracks crossing the strip each day, then swept it.

Each site had 100 FAS stations, 100 BM stations and 50 activity stations. A discreet mark in the corner of each station showed whether rain, livestock or vehicles had wiped out all tracks; if the mark was gone, the station was left out. Stations were checked daily until the running mean settled (changed by 10% or less from one day to the next).

To create three dingo densities, they then reduced the population twice with 1080-poisoned baits along the transects (first one bait per km for 24 hours, then one per 500 m for 48 hours), and repeated the indexes after each baiting. Finally they treated each 1 km segment as a unit and asked how often each method scored a dingo as present, if stations had been read every 1, 2, 3 or 4 days.

2. What they found

Reading the stations

• All three indexes reached the stopping point within four or five days, except when rain made too many stations unreadable.
• Up to eight dingo tracks crossed a single activity station in a day, but more than 85% of the 491 stations with dingo tracks had fewer than four.
• Some tracks were certainly lost to vehicles and cattle. Birds (mainly corvids) removed 110 scent discs and 205 meat baits over 2700 station-days, and 21 activity stations were destroyed in 1350 station-days.

Agreement between the indexes

• The three indexes followed daily changes in dingo activity closely, with correlation coefficients of 0.847 to 0.910.
• But they did not always show the expected fall after baiting. In the north transect, the BM and activity indexes rose after the second baiting; in the south transect, the FAS and BM indexes rose after the first baiting.
• Dingoes removed 23 poison baits in the first baiting and 45 in the second (68 in all). In the second baiting, 30 baits were visited but left alone, against 1 in the first.

Sensitivity

• The activity index detected dingoes on a much higher proportion of 1 km segments than the other two, whatever the reading interval. The BM index came second and the FAS index last, at both sites.
• For example, read daily at the south site, 44% of segments were positive by the activity index, 28% by BM and 12% by FAS. Read every 4 days, the figures were 81%, 55% and 28%.

Behaviour seen through the indexes

• Few dingoes visited the scent discs, which the authors link to neophobia (wariness of new things), as seen in coyotes.
• Visits to meat stations tended to rise over the days, suggesting dingoes were learning where food was.
• After baiting, daily counts swung widely, which the authors suggest may come from surviving dingoes and neighbouring groups making exploratory forays into the emptied area. The work took place in May, the peak of the breeding season.
• Some dingoes inspected activity stations closely and crossed them several times; this was recorded as one animal. There was no sign that dingoes avoided the stations.

3. What they concluded

• All three indexes reflected changes in dingo activity, but with clear differences in sensitivity. The activity index was the most sensitive, with about 1.5 times the response rate of BM and three times that of FAS (in the authors’ words).
• The FAS index may attract mostly transient or non-territorial dingoes and so should be used with caution.
• Meat may artificially raise dingo activity over time, especially when the same stations, transect and bait are used for many days. Fresh meat is also hard to transport and keep in remote places.
• The activity index is unlikely to change normal dingo behaviour, but it is the most vulnerable to tracks being wiped out, because dingoes often walk along the wheel ruts that vehicles and cattle later cross. Separating superimposed tracks of several dingoes is difficult.
• Because dingo movement along roads relates to territory, comparisons between treatments should be made in the same season.
• To test the effect of baiting, baits should be spread over a wider area and post-baiting counts delayed until survivors return to normal patterns.
• Reading stations every 2 or 3 days smooths out daily counts but loses some sensitivity, because tracks fade and an observer cannot read older tracks as clearly as fresh ones.
• The higher number of baits visited but not eaten in the second baiting suggests the first baiting removed the bait-prone, naive dingoes, leaving the more wary, bait-shy ones.

4. How tracking was or was not used

All three indexes rest on reading dingo tracks on prepared ground. At FAS and BM stations, observers only recorded whether a dingo had visited, because dingoes scratched, rolled, urinated and generally wrecked these stations, making it impractical to separate superimposed tracks or count individuals. At activity stations they counted the dingo tracks crossing the raked strip each day. A corner mark on each station was used to judge whether rain, livestock or vehicles had wiped out the tracks. The paper does not describe how dingo tracks were told apart from those of other animals.

5. Tracker or observer certification

Not reported. The paper does not say who read the stations or what tracking experience they had. Wanda Glossop, Peter Cremasco and Diane Hopkins are thanked for technical assistance. All results depend on correctly identifying and counting dingo tracks.

6. Other technologies, skills or innovations

• Plaster discs impregnated with Fatty Acid Scent, prepared in a laboratory (vacuum-treated to remove odours, then soaked for 60 minutes).
• A simple corner mark on each tracking station as a check on whether tracks could still be read.
• A practical stopping rule for fieldwork: stop when the running mean changes by 10% or less from the previous day.

7. Implications for conservation (from the paper)

• Relative abundance indexes are used to measure the effect of control programmes and to compare populations over seasons; the method should be quick, simple and sensitive enough to show real changes.
• An index that relies on attractants may be biased towards some animals in the population (such as transients), which can confuse or mask what a study is trying to measure.
• Baiting may stimulate dingo activity for a time, so indexes taken straight after baiting can suggest more dingoes rather than fewer.