Female Efi Using Trunk as a Stabilizer during Food Processing at Mbeli Bai

<p>The top photo shows the intact trunk shortly before Efi manipulated it (visible to the left of female Fulani). The trunk was then detached by female Efi with both hands (middle), pushed into the ground, and used as a stabilizing stick while dredging aquatic herbs towards her with her other hand (bottom).</p

Food bouts recorded from Group Kingo, N = 580.

<p>Food bouts recorded from Group Kingo, N = 580.</p

Spectrogram of humming.

<p>Spectrogram of humming.</p

Spectrogram of singing.

<p>Spectrogram of singing.</p

Food bouts recorded from Group Buka, N = 247.

<p>Food bouts recorded from Group Buka, N = 247.</p

Overview of descriptive results.

<p>Overview of descriptive results.</p

Foods of the gorilla diet between July and September 2012.

<p>Total call frequency and call rates per feeding session are indicated. All fruit was ripe.</p

Female Leah Using a Walking Stick while Crossing Bipedally through an Elephant Pool at Mbeli Bai

<p>Female Leah first looked at the new elephant pool and the branch she later used as the walking stick, and entered the water without the tool (not shown). After re-entering the pool and taking the branch with her right hand, she walked bipedally 8–10 m into the water, frequently testing water deepness.</p

Rout_MalesReachAdulthood_Final

Generalized linear mixed model (GLMM) to compare the probability that males reached adulthood in a breeding group (versus a non-breeding group or solitary)

Rout_HaremSizeAverages_Final

Analysis of variance (ANOVA) to test whether the number of adult females per group is larger for mountain gorillas than western gorillas