Going to extremes for sodium acquisition: use of community land and high‐altitude areas by mountain gorillas Gorilla beringei in Rwanda

Abstract

Space use in mammals may be influenced not only by their primary foods, but also by localized sources of physiologically critical resources such as sodium‐rich plants. We examined how sodium acquisition influences habitat use in mountain gorillas (Gorilla beringei) in Rwanda which have increased the amount of time they forage on community land outside of Volcanoes National Park (VNP), where eucalyptus (Eucalyptus spp.) tree bark is their most frequently eaten food. We measured sodium content in samples from 34 main dietary items and quantified sodium intake by 22 gorillas in three social groups over one year. On a dry weight basis, eucalyptus bark contains 3100 mg Na/kg. In contrast, the four herbs most frequently exploited for food inside the park are relatively sodium‐poor (<70 mg/kg each). Further, sodium intake rates were highest when the gorillas were on community land. Of the two groups that fed outside of the park, one obtained 73% and the other one 45% of their sodium in that habitat despite only feeding for minimal amounts of time there. However, one group that did not feed on community land acquired 78% of its sodium in the subalpine and alpine zones through the consumption of pith of giant lobelias and groundsels. Obtaining sodium thus likely creates an incentive for the gorillas to leave the park and make forays into high‐altitude habitat. Both strategies are not without risks: exiting their natural habitat and feeding on crops may increase human‐wildlife conflict and visiting high‐altitude areas may increase the risk of hypothermia.

Chimpanzee ranging responses to fruit availability in a high‐elevation environment

“…Thus, while high elevations can be harsh environments for primates, they can be an important part of a species home range when they provide a refugium for densely distributed, important food species. Similar behavior has been observed in mountain gorillas, who range at the altitudinal extreme of their range in Volcanoes National Park, Rwanda, to access sodium‐rich plant foods (Grueter, Wright et al, 2018).…”

Analyzing the popularity of YouTube videos that violate mountain gorilla tourism regulations

“…26,60]. Previous studies have demonstrated that several habituated gorilla groups in Bwindi range outside of the parks to feed on bananas-that may contain high sugar levels [61]-and eucalyptus trees that contain high sodium in both Bwindi and Virunga [61,62]. It is generally considered that such behaviors increased due to the habituation [60].…”

Importance of subterranean fungi in the diet of bonobos in Kokolopori

“…Bergstrom et al, 2019, Koops et al, 2019), and movement patterns (e.g. Grueter et al, 2018, McNaughton, 1988, Potts et al, 2015). In particular, it has been proposed that the availability of fallback food plays an important role in influencing the geographic and temporal distribution of many primate species (Grueter et al, 2009; Marshall et al, 2009), and the need to acquire specific nutrients can have important influence on their ranging and feeding behavior (e.g.…”

“…In particular, it has been proposed that the availability of fallback food plays an important role in influencing the geographic and temporal distribution of many primate species (Grueter et al, 2009; Marshall et al, 2009), and the need to acquire specific nutrients can have important influence on their ranging and feeding behavior (e.g. Bogart & Pruetz, 2011, Grueter et al, 2018, Hanson et al, 2003, Hohmann et al, 2019, Matsubayashi et al, 2011, Reynolds et al, 2009).…”

“…b The reference value for community (Kokoalongo/Ekalakala) is "Ekalakala. "T A B L E 3 Mineral content (mg/kg dry matter) of Hysterangium bonobo and Palisota ambigua in KP, in relation to plant food species that are frequently consumed in other ape populations (data extracted fromGrueter et al, 2018;Hohmann et al, 2019;Reynolds et al, 2009)…”