Behavioural ecology and conservation biology of ground pangolins Smutsia temminckii in the Kalahari Desert

Abstract

Ground pangolins Smutsia temminckii are inconspicuous, mainly nocturnal mammals that occur at low population densities. As a result, there is scant information available on the ecology and physiology of this species. To date the handful of studies focussing on this species were centred in the mesic eastern regions of its range, with no attention being given to ecological and biological traits in arid environments. To address these data shortfalls, a study was undertaken in the Kalahari Desert in northwestern South Africa. Very High Frequency (VHF) transmitters or Global Positioning System (GPS) loggers were fitted to 16 ground pangolins and their ecology and physiology studied over a period of three years. Throughout its range the ground pangolin is increasingly endangered, predominantly due to anthropogenic threats. Previous studies have identified threats facing this species, but very few of these studies included quantitative data as to the extent of these threats. The present study suggests that the main threats to ground pangolins in southern Africa are electrocution on electrified fences, the traditional medicine trade, habitat loss, road mortalities and capture in gin traps. Although accidental poisoning has previously been viewed as a threat, a review of the available literature suggests that this is not the case and that these views stemmed from two isolated incidents of captive animals. Electrocutions probably pose the greatest threat to ground pangolins, with mortality rates of one pangolin per 11 km of electrified fence per year recorded during this study. Home range sizes of this arid-zone population are comparable to the home range sizes recorded in mesic populations. Study animals in the Kalahari had Minimum Convex Polygon (MCP) home range values of 10.0 ± 8.9 km² SD for adults and 7.1 ± 1.1 km² SD for juveniles, in comparison to the 0.17 – 23.38 km² MCP in Zimbabwe and 1.3 – 7.9 km2 MCP in mesic north-eastern South Africa. These results are surprising as arid-zone animals usually have larger home ranges than do their mesic counterparts. It is hypothesised that this discrepancy is due to the fact that ground pangolins in the Kalahari are on average 25 – 30 % smaller than their mesic counterparts. This smaller body size means that individuals require a smaller home range to meet their dietary requirements, which could be counteracting the trend of arid-zone individuals requiring larger home ranges. This research also found ground pangolins to be more active during the day in winter and nearly entirely nocturnal during summer. These changes in photoperiodicity are likely driven by adaptations to the extreme climatic conditions present at the study site rather than predation pressure or changes in food resources, although the latter may be playing a role as well. By being diurnal in winter, individuals avoid the extremely cold night-time temperatures, thus saving energy that would otherwise be spent on maintaining their body temperature. By contrast, becoming nocturnal in summer allows them to avoid the extreme daytime temperatures, thus conserving water. The results of this study reiterate previous findings that ground pangolins are entirely myrmecophagous and highly selective of the species that they eat. Study animals were recorded feeding on only four ant and two termite species, representing 7.5 % and 50 % of the total species richness of each of these families. This is similar to previous research in mesic savannahs where five ant one termite species constituted 97 % of the ground pangolin’s diet. No seasonal differences in prey selection were observed, although the species consumed did depend on the habitats that were available to individual ground pangolins. This study is the first to investigate the core body temperature (Tb) of a free-ranging pangolin. These data indicated that Tb fluctuated cyclically between 32 – 35 °C and reflected the activity periods of the animal, peaking when the animal was active. When the individual was inactive, Tb steadily decreased, suggesting that it used daily heterothermy to cope with the low food availability in this unpredictable environment. In summary, ecological parameters between arid and mesic ground pangolin populations are similar in some respects, but divergent in others. Arid-zone populations are smaller overall and show a higher degree of diurnal activity. Despite this smaller body size, home range values appear to be similar between arid and mesic populations. Although the prey species eaten by ground pangolins in the Kalahari differ from prey species in eastern South Africa and Zimbabwe, they belonged to the same genera and were of similar morphology and ecology. The core body temperature results confirm findings from previous captive studies that pangolin body temperatures are lower than those of other eutherian mammals of a similar size. Furthermore, these data indicate that core body temperature is a lot more variable than previously believed, and thus warrants further study. Overall ground pangolin densities in the Kalahari appear to be double those in eastern South Africa and Zimbabwe, although it is unclear whether this is genuine or whether it is an artefact of individuals being easier to locate in the Kalahari. This study also confirmed that electrocutions are probably the greatest threat to this species, and new threats such as accidental capture in gin traps and road mortalities have also come to light.