Movement patterns and habitat use by Namib golden moles (Eremitalpa granti namibensis Bauer and Neithammer, 1959)

Iipinge, Ndelimona

Movement patterns and habitat use by Namib golden moles (Eremitalpa granti namibensis Bauer and Neithammer, 1959)

Thesis / Dissertation

2023

Abstract

Linnaeus first documented the existence of Golden Moles (Chrysochloridae and Afrosoricida) in 1758 but little is currently known about the biology of most of the species. Namib Golden Moles (Eremitalpa granti namibensis) are small, blind insectivorous mammals that inhabit the Namib Desert dunes. They are a subspecies of Grant's Golden Mole, with the other subspecies, Eremitalpa granti granti, found south of the Orange River. These free-ranging small mammals consume a wide variety of predominantly sand-dwelling invertebrates, with termites (Psammotermes allocercus silvestri) making up more than 95% of the diet by biomass. In this study my primary aim was to investigate habitat use and foraging behaviour of a subpopulation of Namib Golden Moles (E.g. namibensis) within the Namib Sand Sea by following their tracks over a full calendar year at a single site. My secondary aim was to compare mole movement patterns and habitat use at the main study site with two other nearby sites that differ in habitat. I hypothesised that movement and habitat use will be non-random and influenced by the local distribution of prey resources namely, vegetation hummocks and dune slip faces. I further predicted that movement patterns would show seasonal variation linked to changes in ambient and sand surface temperatures. I followed mole tracks in the early morning for 3 to 14 consecutive days each month at the main study site and compared a subset of these data with two other sites in a single season. Along each track, I recorded GPS waypoints where the mole emerged, dipped its head into the sand to listen (head-dip), foraged (sand-swimming), and rested. I recorded both the microhabitat type (dune phase) and broad habitat (hummock or open) for each foraging and resting GPS waypoint. The area of each microhabitat available at each study site and the density of vegetation were calculated from drone images in QGIS using NGRDI and Field calculator respectively. Manly's alpha (αr) index was used to determine microhabitat and hummock preference. Home ranges were estimated using a 95% Kernel Density Estimation and were compared monthly and between the three sites. Key measures of movement and foraging behaviour were estimated for each mole track at all sites and the averages were compared monthly within the main site and for a single season between sites. Significant differences in movement and behaviour were evident both within the main site across months and between sites within summer. The track length was shortest but straightest with the lowest number of head dips at the main site which had the least hummocks and the most open habitat. Moles preferred to both rest and forage on or close to hummocks at all sites and preferred large hummocks. Within dune habitats, moles preferred avalanche bases and slip faces both of which are associated with higher prey density. Moles also preferred to forage and rest in large hummocks and the mean number of hummocks visited each day increased with track length and the number of head dips per track but decreased with track straightness. The best predictors of track length were season and sand surface temperature with track length being highest in summer and increasing with sand surface temperature. The results support previous findings that Namib Golden Moles have larger home ranges (mean = 5.08 ha) and move greater daily distances than other mole species, and furthermore that they both head dip and swim in the sand to first detect and secondly increase their chances of encountering prey. Novel findings include that mole track length is mostly affected by seasonal changes in sand surface temperature, and they resort to shorter, straighter, and mostly under-sand movement in winter. They prefer to forage in detritus trap zones (avalanche base and slip face) and foraging was not always associated with the extant hummocks.

Keywords

Biological Sciences

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