Monitoring rhinoceroses in Namibia’s private custodianship properties

1. What they did

Namibia holds about 28% of the world’s black rhinoceroses. Since 1993, private landowners in a Black Rhino Custodian Program have hosted and protected black rhinoceroses for the government, and they must monitor them and report regularly to the Ministry of Environment and Tourism (MET). White rhinoceroses in Namibia live mostly on private land and are the landowner’s own responsibility. Monitoring is costly, and many methods need aircraft or fitting animals with instruments. The authors, from the non-profit WildTrack, tested three cheaper ways of counting rhinoceroses from their footprints.

The pilot study ran in May and June 2018 on three custodianship properties chosen by the MET because they monitored their rhinoceroses well. Each custodian gave an estimate of their rhinoceros numbers beforehand. The field team (a team leader, field assistants and a tracker from the custodian) searched roads, game tracks and water points each morning and afternoon, photographed footprints, and followed trails. Each footprint photographed was first circled in the sand so it would not be sampled twice. Trails left by running rhinoceroses were not used.

The three methods:

• Full Identification Protocol (FIDP). Guided by the custodians’ trackers, the team matched sightings of rhinoceroses (known by ear notches, body features or group) to their fresh footprints, and followed fresh trails to a sighting. Rhinoceros feet have cracks in the pad that leave a pattern of heel lines in the footprint, unique to each animal. Trails were matched to each other by these heel lines, building “trail identities”, and then matched to known animals.
• Heel pattern only (HP). Co-author Sky Alibhai, who took no part in the fieldwork, matched the heel lines in the photographs off site, without knowing which animals they came from.
• Footprint Identification Technique (FIT). Heel lines and all other information were ignored. Only left hind footprints with clear outlines of all three toes were used. Points were marked on each image, measurements taken, and a statistical model grouped the trails into individuals.

They compared each method’s count with the custodian estimate and with each other, and compared footprint-based monitoring with other common methods.

2. What they found

Effort

• More than 1,500 footprints were photographed over five weeks: 608 of white rhinoceroses and 331 of black rhinoceroses at site C, 402 at site B and 300 at site A.
• There were 45 separate sightings. Of these, 23 came from following footprints; the rest began with a sighting from a vehicle.
• The team saw and identified every known rhinoceros at each site. At site A they got the first sighting of a recently born calf, previously known only from spoor, and so identified its mother. At site C they sexed the two most recent white rhinoceros calves.

Counts (Table 1)

Site A

Site B

Site C

Full Identification Protocol

4 black

8 black

17 white; 6 black

Heel pattern only

5 black

9 black

17 white; 6 black

Footprint Identification Technique

5 black

8 black

18 white; 6 black

Custodian estimate

4 black

8 black

17 white; 6 black

• Method 1 matched every trail photographed to a known rhinoceros and confirmed every custodian estimate.
• The heel pattern method added one animal at sites A and B. At site A, the extra “animal” was one trail photographed in the midday sun, which showed less heel detail in the photographs than the team saw in the field; the trackers knew it belonged to the bull. At site B it was the trail of a calf with its mother.
• FIT agreed with method 1 at site B and for the black rhinoceroses at site C. At site A it added one identity, a single trail known from tracking to belong to one of the cows. For the white rhinoceroses at site C, no trail of one cow with a calf was good enough for FIT; FIT recognized the other 16 but split off two single trails as separate animals, giving 18.
• Every false extra identity from methods 2 and 3 was a single trail. The error rate per animal fell as population size rose.

Comparing methods

• Method 1 was the slowest and most costly but the most accurate. The heel pattern method was fastest and cheapest, and FIT was in between; both had good accuracy (Table 2).
• The heel pattern method needs judgement and expertise; FIT is fully objective but strict about footprint quality. FIT could use fewer trails than the other two methods.
• In the authors’ comparison of five monitoring methods (Table 3), footprint-based methods rated medium for speed, high for accuracy and low for cost, where expert trackers are available and the ground holds clear footprints.

Other observations

• At site A, trackers sometimes assigned a trail to a rhinoceros from where it was, rather than from a careful look at the pad impression. The authors had seen this before.
• At site B, staff had seen footprints they could not identify; tracking and FIT showed they were from the younger bull.
• The black rhinoceroses at site C, recently introduced as a group of six, walked a lot along roads, apparently still exploring their new area.

3. What they concluded

• Every monitoring method has strengths and weaknesses. The best results come from looking at what a site has, especially skilled trackers, and combining methods to get the data needed in the time available.
• The false extra identities could likely be removed by stricter rules for photographing footprints. A single trail of poor quality that stands alone should be treated as suspect and followed up.
• The authors recommend a full identification survey (method 1) at each custodianship once a year if possible, with a quick heel pattern survey or FIT photographs at least monthly in between, combined with camera traps, foot patrols or waterhole counts so that every rhinoceros is seen regularly.
• Method 1 also gives custodians a reference set of footprint photographs for each animal, so they can keep monitoring individuals from their footprints.
• A tracker and a photographer, with cameras, a Global Positioning System (GPS) unit and rulers, can produce a reliable count for a typical custodianship in about a week.

4. How tracking was or was not used

Tracking was at the heart of all three methods. The team searched roads, game tracks and water points for rhinoceros footprints, judged fresh footprints (under 24 hours old) by their clean, sharp outlines, and followed trails from water points along roads to photograph footprints and, where possible, to find the animal. Of 45 sightings, 23 came from following footprints. At site C they followed white rhinoceroses from their grazing grounds to their resting sites. Individuals were identified from heel line patterns and footprint shape, and trails were matched to sightings. Field knowledge from tracking resolved the cases where the photograph-only methods went wrong. The authors note that footprints usually last at least 24 hours unless rain or high wind interferes, and that heel patterns and footprint shape may change as animals age.

5. Tracker or observer certification

Reported but not validated. The trackers were provided by the custodians, in most cases the people charged with monitoring the rhinoceroses, and are called “professional trackers” in the acknowledgements. Co-author Sky Alibhai, who did the heel pattern matching, is described as having years of experience examining rhinoceros footprints. No certification or test of anyone’s tracking skill is reported. The team’s identifications were checked against sightings of known animals in method 1.

6. Other technologies, skills or innovations

• Footprint Identification Technique (FIT) in JMP software: landmark points on footprint photographs, measurements of lengths, areas and angles, and a pairwise model that classifies trails as from the same or different animals. The authors report 95 to 99% accuracy for individual, age and sex in earlier work.
• Matching trails by heel line patterns, linking partial patterns across trails (if trail 1 matches trail 2 and trail 2 matches trail 3, all three belong to one animal).
• Photography tips: shading the footprint and using a reflector in harsh midday sun, though this did not fully work.
• WildTrack offers custodians free training and a JMP software licence to use FIT.

7. Implications for conservation (from the paper)

• Namibia needs a cost-effective, long-term way to monitor rhinoceroses; private custodians must pay for their own monitoring.
• Footprint monitoring is non-invasive and needs little equipment. It can use scouts already employed for anti-poaching or tourism, and makes use of trackers’ traditional ecological knowledge; engaging trainees could revive these skills.
• Including tracking in monitoring helps staff learn rhinoceroses’ movements, which animals share ranges, and whether one bull dominates others. Footprint libraries also draw attention to animals whose footprints stop appearing.
• Fitting collars, horn implants or anklets is the most expensive option, carries risks to animals and people, and counts only instrumented animals. The authors’ earlier work found that females immobilized repeatedly had longer gaps between calves. Waterhole counts can overcount when one rhinoceros visits several waterholes in a night.