Large herbivores

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Annual aerial wildlife census

We’ve carried out total area counts for elephant, buffalo, hippo, and sable, as well as sample counts for the more cryptic large herbivores occurring at Malilangwe annually during the hot dry season (September to October) since 1999.

These censuses are conducted using a helicopter with a pilot and recorder seated in the front, and two observers seated in the back. The helicopter is flown at 90 m (300 ft) above the ground, at an air speed of 40 to 60 kts, along pre-determined, parallel east-west orientated transects situated one km apart.

Transects are arranged systematically to cover the whole census area (Malilangwe, HVGS, and the Mhangula Triangle). Transects are flown morning and afternoon, for a maximum of three hours. The hottest part of the day is avoided because animals tend to rest in the shade at this time, making them more difficult to spot.

Markers are fitted to either side of the helicopter such that, when flying at 90 m, they demarcate the following distance classes on each side of the transect line: 0 –30 m; 31 – 90 m; 91 – 200 m; 201 – 350 m; 351 – 500 m

When animals are sighted, our observers call the species, the distance class of the sighting from the helicopter, and the size of the group to the recorder. The recorder manually captures the data using Cartalinx geographic information system (GIS) software and a notebook PC that is linked to a global positioning system (GPS).

 

The GPS allows automatic tracking of the flight path and manual capture of waypoints for each observation. When large herds of animals are spotted, they are counted by flying off the transect and circling the group. If the group is too large to be counted accurately, a photograph is taken, and counting is done in the office.

The location of the sighting is captured using the GPS, and then the helicopter is returned to the point of departure from the transect, and the census continued.

Double counting is occasionally a problem because animals that have been disturbed by the helicopter sometimes run into the next transect and are inadvertently recounted. To minimise this effect, probable double counts are deleted.

Buffalo, elephant, hippo and sable are relatively easy to see from the air, so their population estimates are taken as the total number counted. From 2001 onwards, the census area was flown twice. For this period, the number of each species counted was taken as the maximum of the two repetitions.

Population estimates of the more cryptic species are calculated using distance analysis because only a fraction of the actual number of these species are seen from the air. Distance analysis uses detection curves to estimate the number of animals that may have been missed by the observers.

 

Rhino populations and monitoring

Populations of black and white rhino are monitored by analysing sightings of individual animals. Each rhino can be identified by a unique pattern of ear notches. Ear notching of dependent calves (12 – 24 months old) is carried out biannually. Calves generally leave their mothers when they are two years old, and if they have not been notched by this time, it becomes difficult to keep track of their lineage.

Knowledge of lineage is important because it enables groups of unrelated animals to be selected as founder populations for new areas. Scouts record details of rhino sightings in field notebooks. The notebooks are collected monthly, and the sighting data are captured into a custom-built database.

Data for each sighting includes a GPS position, a sketch of the ear notches and horn profiles, age, sex, condition, behaviour, and the identity of other rhinos in the group. Sighting records are used to determine when new calves are born, and when calves are due to be notched.

Data accumulated over the years facilitates the construction of detailed life histories of individuals and monitoring of the demographics of the population as a whole.