Assessing the Impact of Seasonality on Cross River Gorilla Nest Construction at Kagwene Gorilla Sanctuary, North-West Cameroon: An Advanced Study

The Cross River gorilla, one of the most endangered subspecies of western gorilla (Gorilla gorilla) is
endemic to 12 to 14 sites at the Cameroon-Nigeria border, where it is facing enormous threats from
habitat loss, bush meat trade and minor climate changes (seasonal changes). In a strive to reduce the
enormous stressors on this subspecies, this study assesses the impact of seasonality on nest
construction by Cross River gorillas in the Kagwene Gorilla Sanctuary with the objective of evaluating
the impact of seasonal changes on the nest construction. To achieve this goal, the study employed a
hunter guided survey team, as well as guides/trackers of the Wildlife Conservation Society. This team
regularly tracks and searches the forest for gorilla signs using vegetation trails, food prints, dung, and
feeding signs which are subsequently followed onwards to the nesting site. Data were collected from
January to December 2014. A total of 268 fresh gorilla nest sites were observed containing 1813
individual nests. Out of the 1813 nests recorded, 39.6% (N=718) of the nests were on the ground
and 60.4% (N=1095) on trees. The frequency of each nest type varied significantly among months
(P =0.4433). There was a significant effect of season on nest category. Ground categories (bare
earth, herbaceous, woody and mixed) were more common in the dry season (74.9%) than in the wet
season (25.1%). On the other hand, tree nests were more common in the wet season (77.4%) than in
the dry season (22.6%). Mean nest diameter for the two seasons (dry and wet) was 1.1 and 1.3 m,
respectively. The mean nest height was 12.5 m for both seasons. Cross River gorillas showed higher
preferences for tree nests within the height class interval of 11 to 15 m (49.6%). The distribution of
nests across gradient of altitudes did not vary significantly between seasons (P>0.05), and nests were
most common on steep slopes (n=810). Seasonality did not significantly affect the choice of slope
(P>0.05). There was a significant difference in the habitat types (primary forest, light gap, secondary
forest and rock) used for nesting, with primary forest being most preferred. Nest site distribution was
predominant in the northern section of the sanctuary. This study reveals that, both temperature and
rainfall play an important role in nest construction by Cross River gorilla at Kagwene.