Resource competition between spotted hyaenas, Crocuta crocuta, (Erxleben 1777), and brown hyaenas, Parahyaena brunnea, (Thunberg 1820)

Abstract

Field data were collected and analysed on the feeding and spatial ecology of spotted hyaenas and brown hyaenas living in the Madikwe Game Reserve. Methods used to estimate the population of spotted and brown hyaenas include audio call-in surveys, photographic records and mark-resighting. The localized convex hull method was used on data collected from latrine surveys, radio-telemetry, sighting records, and camera-trapping to determine the spatial ecology of hyaenas in Madikwe. Faecal analysis and carcass observations were used to determine the prey consumption and dietary components of hyaenas. Population estimates of spotted and brown hyaenas in Madikwe using the NOREMARK method proved smaller than originally presumed by park officials. The brown hyaena population in Madikwe is critically small at 11 to 13 individuals and needs to be monitored. Spotted hyaenas are slightly more abundant at 20 to 30 individuals, but still merit monitoring of their numbers. The audio call-in survey method is effective when used for the first time or when surveys are separated by extended time periods during long-term monitoring. Hyaenas appeared to become habituated to successive repeated uses of the surveys and the numbers of hyaenas responding to the survey decreased accordingly. Hyaena responses to the audio call-in surveys also fluctuated with respect to the presence or absence of other predators, showing a decrease in response when lions responded to surveys. Range sizes of spotted hyaenas and brown hyaenas were large and covered nearly the entire reserve, and overlapped considerably with each other. The localized convex hull method is one of the most robust tools used in spatial analysis and was employed to determine the utilization distributions and range sizes of Madikwe’s hyaenas based on spatially fixed points of hyaena presence. Utilization distributions obtained from latrine surveys and camera-trap data indicated seasonal differences in the area use and range sizes of hyenas. Spotted hyaenas had smaller range sizes in the dry season, with larger range sizes in the wet season. Brown hyaenas had larger range sizes in the dry season, which contracted considerably in the wet season. Hyaena utilization distributions overlapped for 581.4km2 of the reserve, with an average overlap of 343.0km2. The overlapped area was significantly larger than areas which were exclusively used by spotted hyaenas (± 68.8km2) or brown hyaenas (± 92.3km2). Dietary analysis of hyaenas living in Madikwe depicted a near perfect overlap in food groups and prey remains. Brown hyaenas were shown to exploit a slightly wider dietary breadth than spotted hyaenas, utilizing birds and reptiles in their diets, but both hyaenas exploited larger mammals more often than smaller mammals. Impala and blue wildebeest were the most important food source for hyaenas in Madikwe and other less important food types were seasonally important. Invertebrates featured prominently in hyaena diets in the wet season, while seeds featured prominently in hyaena diets in the dry season. Spotted and brown hyaenas temporally and spatially avoided one another while foraging and at carcasses. Hyaenas often foraged alone or in small numbers in Madikwe, and were never observed to hunt large prey. The spotted hyaena population in Madikwe appears to be functioning relatively well and not under any immediate threat. However, the low numbers of brown hyaenas presents a concern as to the viability of the population. Competition for the same resources is significant between spotted and brown hyaenas, and efforts to reduce the number of spotted hyaenas through translocation to other reserves may be beneficial in ensuring that brown hyaena populations in Madikwe remain stable. As the lions in Madikwe provide much of the carcasses for hyaenas to feed on, future research may also look at the effect of lions in regulating the spotted hyaena population, and how this may or may not benefit the brown hyaena population.