Butch Smuts worked in the Kruger National Park for many years, first studying what was causing a decline in zebra populations, and later performing intensive studies on the lion populations in the park, with a special emphasis on the central region of the park. Together with colleagues they developed mass capture protocols for lions that are still used today. During the course of this research, the first lion ever to be fitted with a radio-collar was captured and released to provide information to the curious scientists.
Over four years in the 1970s, the stomach contents of 257 lions were examined. 47 percent of the lions had empty stomachs. For the remaining lions, ten prey animals had been eaten by the lions. These were impala (30%), wildebeest (24%), giraffe (15%), zebra (11%), warthog (8%), waterbuck (5%), kudu and buffalo (2% each). A domestic goat (probably from outside the park) and an unidentified animal were also found. When statistical analysis based on the sizes of the animals was performed, giraffe was found to make up the greatest bulk of the animals' diet, followed by wildebeest and zebra.
Smuts and his colleagues performed a lion census in the mid 1970s, luring over 600 lions to call centres where the lions could be darted and marked to enable counting. During a five year period they managed to capture over 1 200 lions. He found that the central district of the Kruger National Park had over 700 lions, dispersed amongst sixty different prides. There was a sex ratio of two adult female lions to every adult male.
The largest pride contained 21 lions, and on average there were two males per pride, although this ranged from one to five males per pride. The lion density was worked out as 13 lions per 100km2. They also worked out that in Kruger at that time their was one lion per 110 prey items. This was a strong contrast to the Serengeti where there is only about one lion per 1,000 prey animals.