Disturbance bias when tracking Kalahari leopards Panthera pardus by spoor

1. What they did

Expert trackers following large predators by spoor in the sandy Kalahari had already been used to study lions, brown hyaenas and leopards. In the authors’ own leopard studies, a leopard’s tracks were followed day by day for up to 14 days. At the end of each day’s tracking the leopard was usually seen resting under cover, and it was left alone as soon as it was clear that the leopard was nearby. This daily contact with a tracker and a research vehicle could disturb the animals and bias the results, so the authors set out to check it.

They tested two possibilities: that over 7 to 14 days the leopards would either get used to (habituate to) the tracker and vehicle, or would flee further and further. Either effect would show up as a link between the number of days a leopard had been tracked and the distance it fled.

The day after each disturbance, before studying the leopard’s normal activities again, the trackers followed its flight step by step and recorded how far it went and what it did on the way. They assumed that a disturbed leopard would not rest while fleeing, so signs that it sat or lay down meant it was not unduly disturbed. To avoid differences between the sexes and the effects of temperature, they used only data for male leopards in summer, and no data for leopards resting at a kill. This gave 42 days of tracking, covering 37.4 km of flight, from nine leopards.

2. What they found

• Flight distances averaged 0.91 km (standard deviation 0.7 km). Because a few long flights pull the average up, the authors consider the most common range, 0.6 to 1.0 km (17 of the 42 flights), a more useful guide to the true flight distance.
• The longest flight was 2.7 km and the shortest 150 m.
• There was no significant link between distance fled and day of tracking, for any of the five leopards with enough data on their own or for all nine together. A curved line fitted no better.
• During the 37.4 km of flight, the leopards lay down to rest 37 times, sat down 16 times, crawled in and out of porcupine burrows eight times, and once clawed an Acacia luederitzii tree.
• Of 23 leopards seen at kills, only two did not return to their prey after being disturbed. In both cases the prey was small (a bat-eared fox and a porcupine) and almost completely eaten.

3. What they concluded

• If resting leopards are not disturbed, then the leopards studied do not appear to have been upset by the tracking and contact with people.
• The study found no sign that tracking made leopards either habituate or flee further over time.
• The authors are careful to add that their data show only an absence of evidence of tracking effects on flight distance, not clear evidence that there is no effect. They call for more detailed studies.
• They found no similar data in the literature to compare with.

4. How tracking was or was not used

Tracking was the method throughout. Trackers followed each leopard’s tracks day by day for up to 14 days, and found the leopard resting at the end of each day. Flight distances, and what the leopards did while fleeing (lying down, sitting, crawling into porcupine burrows, clawing a tree), were worked out by following the tracks step by step, as in the authors’ other studies of leopard movements. The study itself is a check on whether this kind of tracking disturbs the animals being followed.

5. Tracker or observer certification

Reported but not validated. The introduction describes the method as using “expert trackers”, and the acknowledgements thank “the various trackers used”, but the trackers are not named, and no certification or test of their skill is reported.

6. Other technologies, skills or innovations

• A research vehicle was used alongside the trackers.
• Statistical analysis with the General Linear Models Procedure of the SAS System.