Predation in the Namib

Large carnivores, like the lion, have an impact on their environment because they prey on other animals. It is important to understand the prey selection and predation patterns of lions, especially in the Northern Namib, where the killing of livestock by lions and the ensuing human-lion conflict is prominent. 

Predatory strategies are shaped by ecological constraints that may vary extensively between regions and habitats. The behavioural and ecological characteristics of predators are influenced by habitat and prey availability. More specifically, the density, distribution and richness of prey items in relation to habitat variations are the key parameters that affect group size, home range size and behaviour of social predators. Throughout their range lions are known to prey on a wide variety of species and the most abundant species generally form the mainstay of their diet.

In order to sustain itself, an adult lioness requires between 5kg and 10.3kg per day. The frequencies that lions capture prey to meet their required per capita daily food intake needs are highly variable and depend largely on their group size and the size of their prey. Scavenging, however, is also an important source of food for lions in many areas and they may scavenge as much as 40% of all their food items 27.

During observations over a 17-year period between 1999 and 2017, I established that, as expected, Desert lions have different predation patterns from their savannah counterparts. I observed 363 lion kills from 33 species (see above table showing a summary of prey species killed by lions. Carcasses that may have been scavenged are indicated in parentheses. Some carnivore species were killed, but not eaten (see footnotes)). Four of the most abundant species (gemsbok, zebra, ostrich and giraffe) contributed to 57% of their food items and 89% of the biomass they consumed. Even though the other 29 species that Desert lions utilised contributed to only 11% of the biomass they consumed, many of the species, such as porcupines, seals, cormorants and other birds are important as they sustained the lions during difficult times. Scavenging, in contrast to other studies, was an insignificant source of food for Desert lions as it contributed to less than 2% of their food items and bio­mass consumed. Livestock was also not an important source of food for lions. The unique ability of Desert lions to adapt to the extreme conditions imposed by the hyper-arid environment is demonstrated by the unusually wide range of prey species that they utilise.

In order to meet their daily food requirements, the frequency that lions capture prey depends on the size of the prey and the number of lions that have to share the food. Calculating the frequency that lions capture prey and their per capita daily food requirements is difficult and requires direct visual observations over an extended period.

During one continuous observation period of 30 days (721 hours) in the Hoanib area, a group of two lionesses captured mainly gembok and ostriches, and did so every six to eight days (N=18 kills).

During another observation period on the Hoanib Floodplain, two lionesses captured 27 ani­mals at a frequency of 6.96 days between kills (range: 3–16 days). The distances that these two lionesses travelled per night increased in a linear fashion with each sequential day following their last kill (see below table showing the relationship between the mean distance travelled per day, by two lionesses, and the time (days) since their last kill. Error bars indicate standard error of the mean).

On the fifth day since their last kill, the lionesses started moving further (12km per day) than the overall mean of 10km per day. The daily distances moved thereafter increased to 29km per day on the 15th day. As the lions became increasingly hungry with every passing day, they not only moved longer distances per day, but did so with more consistency. The variance about the mean, measured by % Coefficient Variance, dropped to below 50% on the 10th day, when the mean distance reached 20km per day, and decreased to 15% by the 15th day.

Observations on a single adult male over a period of 182 consecutive days produced comparable re­sults. The Terrace MaleXpl-68 captured 22 animals at a frequency of one every 8.3 days.

The daily per capita food intake was 10.8–12.1kg/day-1 for the lionesses during the two observation periods and 14.3kg/day-1 for the male. The low densities of prey in the Northern Namib and the amount of energy lions have to expend to find and capture prey can explain their higher per capita food intake when compared to lions elsewhere in Africa.

This is an excerpt from Vanishing Kings Lions of the Namib Desert by Philip Stander with Will & Lianne Steenkamp.