Nesting Behavior of Gorilla gorilla diehli at Kagwene Mountain, Cameroon: Implications for Assessing Group Size and Density

Abstract

We recorded nesting data at 569 fresh night nest sites, comprising 7032 individual nests, of Cross River gorillas inhabiting the Kagwene Mountain in western Cameroon. The mean night nest group size was 12.4. Overall, 55% of night nests were constructed on the ground and 45% in trees. Significantly more arboreal nests were constructed in the wet season (69%), vs. the dry season (19%). Day nest construction was common at Kagwene (n=260 nest sites, mean nest group size= 5.98) and we encountered significantly more day nest sites in the wet season. Nest site reuse was also common (35%), though not related to season. Our results of nesting habits concur with those from other western gorilla studies, in which rainfall influences arboreal nesting. However, we encountered wet season arboreal nesting, day nest construction, and overall nest site reuse more frequently than reported for other sites. Our observations have considerable implications when estimating group size and density using traditional nest count data. The gorillas at Kagwene inhabit the highest altitudinal range of all Cross River gorilla subpopulations and rainfall is also high; therefore other subpopulations may demonstrate different nesting characteristics. However, one should consider our findings when attempting to estimate Cross River gorilla density at other localities through nest site data.

Applying resource selection functions at multiple scales to prioritize habitat use by the endangered Cross River gorilla

“…This study relied on indirect sampling methods (Doran et al, 2002;Rogers et al, 2004;Sunderland-Groves et al, 2009). Specifically, we recorded CRG nest sites, trampled vegetation, dung and feeding sign (chewed, broken and discarded vegetation) and estimated the approximate date of use by the CRG for each sign.…”

Subpopulation range estimation for conservation planning: a case study of the critically endangered Cross River gorilla

“…CRGs in Cameroon avoid humans, making direct observation nearly impossible, and the potential for habituation has been rejected due to risks associated with hunting vulnerability and habitat fragmentation (Sunderland-Groves et al 2009). Therefore, this study relied on indirect sampling methods to gain insight into the ranging patterns of this relatively unknown subspecies (Doran et al 2002;Rogers et al 2004;Sunderland-Groves et al 2009).…”

“…Therefore, this study relied on indirect sampling methods to gain insight into the ranging patterns of this relatively unknown subspecies (Doran et al 2002;Rogers et al 2004;Sunderland-Groves et al 2009). Gorillas live in social groups and all weaned group members construct nests in close proximity to one another each night, forming 'nest sites' (Ganas et al 2008;Schaller 1963;Williamson 1988).…”

“…Home range should ideally be calculated for individual groups, rather than subpopulations. However, using cluster analysis, nest counts, and approximate nest dates, I was unable to determine if the study site consisted of one or multiple groups, likely due to the flexible grouping patterns, high home range overlap, and frequent re-use of nest sites observed in CRG (McFarland 2007;Sunderland-Groves et al 2009). Therefore, for this study, I included all CRG signs found in the region to calculate the subpopulation range, rather than individual group home ranges.…”

A Thermodynamic Comparison of Arboreal and Terrestrial Sleeping Sites for Dry‐Habitat Chimpanzees (Pan troglodytes schweinfurthii) at the Toro‐Semliki Wildlife Reserve, Uganda

“…When chimpanzees are sympatric with gorillas, they adjust their SP siting strategy by sleeping in tree species bearing ripe fruits rarely eaten by gorillas [Basabose & Yamagiwa, 2002]. Gorillas construct arboreal SPs significantly more often during the wet season [Sunderland- Groves et al, 2009;Tutin et al, 1995]. In addition, among bonobos, nests are clustered in larger numbers when fruits are abundant [Mulavwa et al, 2010].…”