Arboreality in Wild Western Lowland Gorillas ( G. g. gorilla ) at the Mondika Research Center, Republic of Congo

Although primates are typically considered arboreal, tree use varies widely. Among great apes, gorillas are the largest-bodied and generally the most terrestrial, yet arboreal behavior varies within and between species. We investigated arboreal behavior in one group of wild western gorillas (n = 1831.2 h of focal observation; 334 individual-days from 1 male and 4 females) at Mondika Research Center, Republic of Congo, to determine how tree strata use, activity, and food choice vary among individuals and fruit seasons. Compared with published studies, this group spent less time above ground than western gorillas at Loango, more than Virunga mountain gorillas, and approximately the same amount as Bwindi mountain gorillas. The four females were more arboreal than the male and spent proportionally more of their arboreal time resting/socializing than he did. Overall arboreality did not vary by season, but tree-strata use did, with seasonal patterns differing among individuals. Although less arboreal, the male frequently used high strata when in trees. As fruit availability increased, gorillas used lower strata more frequently and shifted from feeding primarily on leaves/bark toward fruit/flowers. These findings show that gorilla arboreal behavior reflects resource availability, forest structure, and individual characteristics, emphasizing that comparisons of vertical space use across primate populations must account for local ecology and within-population variation. Moreover, our results emphasize the importance of incorporating complex climbing structures into captive enclosures to support the health and welfare of western gorillas.