Investigating the feasibility of a passive tracking index for monitoring wildlife in the Lower Omo Valley, Ethiopia

1. What they did

Wildlife managers in much of Africa have little money, equipment or trained staff, so they need monitoring methods that are simple and cheap but still show real changes in animal numbers. The Lower Omo Valley in south-west Ethiopia holds a great variety of wildlife. Conflict between local peoples has left a buffer zone where few cattle graze, the area is known for sport hunting, and anthrax outbreaks periodically kill large numbers of animals.

The authors tested whether a passive tracking index (PTI), already used to monitor carnivores, marsupials and hoofed animals in North America and Australia, could work there:

• Track plots. Twenty plots were placed at random along a little-used dirt road, at least 0.5 km apart. Each plot was raked and smoothed into a strip 1.5 m long across the road (about 3 m wide). The fine soil held tracks very well.
• Counting. Every 24 hours the plots were checked, the number of sets of tracks crossing each plot was counted for each species, and the plots were smoothed again. This ran for three consecutive days.
• Identification. A tracker from the local hunting concession identified the tracks.
• The index. For each species, the index is the average over days of the average number of track sets per plot, with a measure of its variability.

2. What they found

• A rainstorm on the first day may have wiped out some tracks, so that day may represent less than 24 hours of tracks. The authors calculated index values both with all three days and with only the two rain-free days.
• Index values were calculated for lesser kudu, Guenther’s dikdik, hyaena, baboon and guineafowl.
• Using the two rain-free days, the indices were: dikdik 0.350, guineafowl 0.275, hyaena 0.225 and lesser kudu 0.075. These were up to 50% larger than the values that included the rain day. Baboons had an index only for all three days (0.083).
• A genet, a caracal and a serval each crossed a plot once.
• There was no sign in the tracks that any species avoided or was drawn to the plots.

3. What they concluded

• The index worked for two hoofed species, a carnivore and a ground-feeding bird, which would already be useful for general management.
• Some species would need surveys timed to their migrations or placed in the pockets of habitat they use.
• These values could serve as a baseline for future monitoring, but permanent plot locations should be set up for following trends.
• Index values should not be compared between species, because two species with the same numbers can be active to different degrees. Trends over the same period can be compared.
• The method needs no expensive or high-tech equipment and no great technical expertise, and is unlikely to change how animals move. It suits sustainable sport hunting, human–wildlife conflict and tracking the impact of, and recovery from, disease.

4. How tracking was or was not used

The whole method rests on tracks. Prepared strips of soil across a road were checked each day, and a tracker from the hunting concession identified the species from the tracks and counted how many sets of tracks crossed each plot. The tracks also showed that animals did not seem to avoid or be attracted to the plots. No trailing was reported.

5. Tracker or observer certification

Not reported. The tracks were identified by “a tracker from the local hunting concession”. Nothing is said about the tracker’s experience or any test of their skill, although every index value depends on their identifications, and the hyaena tracks were not assigned to either of the two species named.

6. Other technologies, skills or innovations

• Raked and smoothed track plots on a dirt road, re-smoothed each day.
• A statistical approach (Engeman 2005) that gives an index and its variance without assuming that plots or days are independent, using SAS software.

7. Implications for conservation (from the paper)

• Lesser kudu and the other indexed mammals are hunted for sport, bringing licence fees (for example US$1500 for a lesser kudu) and concession income to the region. A simple index could support sustainable harvests and a stable income.
• Hyaenas take calves, sheep and goats from pastoralist families and occasionally attack people; baboons raid sorghum and maize, especially for the Karo. Monitoring can inform how these conflicts are managed.
• Anthrax killed wildlife and livestock in 2000 and 2001, and over 2000 lesser kudu carcasses were burned. Hyaenas and baboons were thought to be hard hit, but they tend to die in dens and thick cover. An index could show losses and recovery in species whose carcasses are rarely found.
• African cats are hard to monitor. Finding caracal and serval tracks suggests a larger survey might index them too.
• Changes in the intensity of conflict between local peoples would also show in the indexed species.