Daily Travel Distances of Unhabituated Grauer’s Gorillas (Gorilla beringei graueri) in a Low Elevation Forest

Abstract

To accurately determine the space use of animals, we need to follow animal movements over prolonged periods, which is especially challenging for the critically endangered Grauer’s gorillas (<i>Gorilla beringei graueri</i>) in eastern Democratic Republic of the Congo (DRC). As a consequence, we know little about Grauer’s gorillas, particularly from the lower elevational parts of their range. Between 2016 and 2018, we tracked unhabituated Grauer’s gorillas in lowland forests (500–1,000 m a.s.l.), at the community-managed Nkuba Conservation Area in Nord Kivu (DRC) to provide estimates of daily travel distances (DTD), daily displacement distances (DDD), and the linearity of recorded paths expressed as the Linearity Index (LI): DDD/DTD. We found an average DTD of ∼1.3 km (range 0.05–5.0 km), with temporal variation among monthly averages; specifically, an increase in travel distance over the June–August dry season resulting in peak travel distances at the beginning of the September–December wet season. Daily displacements showed similar temporal variation, which resulted in a lack of obvious temporal patterns in LI. We conclude that the movement patterns of Grauer’s gorillas in lowland forests, which are characterized by larger DTD than those of Grauer’s gorillas that inhabit highland habitats, show similarity to travel distances of other predominantly frugivorous gorillas. Moreover, the observed temporal patterns in space use may be tentatively linked to temporal changes in fruit availability or consumption. These observations have consequences for our understanding of the ecological role that Grauer’s gorillas play and provide baseline data to estimate current and future distributions, abundances, and carrying capacities of this highly threatened animal.

Diet of Grauer’s Gorillas (Gorilla beringei graueri) in a Low-Elevation Forest

“…To understand how human-induced changes in forest ecosystems may affect the food availability for GG, we first need to obtain baseline data on food resources for GG under "pristine" conditions. An overview of the food resources for GG could then be used as a starting point for the development of targets for forest restoration ("replant important great ape food trees" [Strindberg et al, 2018]) or other conservation and management strategies. Similarly, such data could feed into more in-depth research on patterns of food availability, the processes that influence food availability, and the links between food availability and various aspects of gorilla behaviour such as dietary flexibility [Fossey, 1977;Vedder, 1984;Kaleme et al, 1996;Plumptre, 1996;Yamagiwa et al, 1996;Grueter et al, 2013;Akayezu et al, 2019] and ranging patterns [Vedder, 1984;Kaleme et al, 1996;van der Hoek et al, 2021].…”

Anthropogenic Pressures on Gorillas: A Case of Grauer’s Gorillas in Maiko National Park, the Democratic Republic of Congo

“…Despite their significance, Grauer's gorillas are likely more threatened by anthropogenic activities than any other class of primates [52]. For instance, the large tracts of forest home to the gorillas have been destroyed throughout the DRC, and the remaining forests are fragmented [36].…”

“…Given the severity of threats to the remaining population of Grauer's gorillas, our knowledge of the variables affecting their conservation status must be recorded and effective communication tools must be employed to strengthen conservation efforts among all stakeholders. Despite their significance, Grauer's gorillas are likely more threatened by anthropogenic activities than any other class of primates [52]. For instance, the large tracts of forest home to the gorillas have been destroyed throughout the DRC, and the remaining forests are fragmented [36].…”

Isolated Grauer's gorilla populations differ in diet and gut microbiome

“…Grauer's gorillas are herbivores, consuming a large diversity of plants and plant parts (Yamagiwa et al, 2005). However, due to political instability throughout their range, very little is known about the ecology of different populations (but see van der Hoek, Binyinyi, et al, 2021a; van der Hoek, Pazo, et al, 2021b).…”