Surprising findings

What they found deepened the understanding of these endangered small apes. "Their adaptability to environmental changes is better than we expected," Fan said.

Their research compared the daily behaviors of the gibbons in the black cardamom forests and the nature reserve, focusing on their eating habits in different seasons, time allocation, home range, daily travel distances each month, reproductive patterns and group sizes.

"By analyzing data derived from these parameters, we could understand the gibbons' adaptation to the cardamom forests, evaluate the long-term suitability of these habitats for gibbons and offer tailored conservation strategies," Fan said.

The study revealed differences in food choices between the two populations of Skywalker hoolock gibbons. While the gibbons in the nature reserve primarily consume fruit, those in forests with black cardamom had to adjust their diet by consuming more leaves, and occasionally nuts during October and November.

"This shift isn't driven by a preference for certain food," Fan explained.

"Rather, it's because they had to broaden their menu to deal with the scarcity of fruit."

Interestingly, he said, the gibbons in the cardamom forests exhibited more active behavior, spending an average of 9.2 hours per day moving within the forests, 0.6 hours more than their counterparts in the nature reserve.

"The gibbons in the caoguo forests allocate an additional 0.7 hours to foraging compared to those in the reserve," he said. "After all, compared to such 'energy bombs' as fruit, leaves are just 'low-calorie food'. It naturally takes them more time to eat their fill."

However, despite the challenges of limited resources, both populations maintained similar daily routines — spending most of the time resting after moving and foraging.

"Noteworthily, the gibbons in both habitats spent similar amounts of time in social intercourse — grooming and playing with each other," the zoologist said.

Another finding is that despite some habitat disturbance, the gibbons in the black cardamom forests did not expand their home ranges or increase their daily travel in most months compared to those in the nature reserve.

More interestingly, in times of fruit scarcity from June to August, they reduced travel distances and focused on leaf consumption to conserve energy, he said.

In the black cardamom forests, the female gibbons in a study group gave birth in 2008 and 2012 but did not reproduce afterward, possibly due to aging. And the other two groups in the cardamom forests had average reproductive intervals of 6 years and 3 years.

Another group in the reserve had average reproductive intervals of 3 years.

"Between 2017 and 2023, we conducted field surveys on 17 Skywalker gibbon groups, nine of them living in the cardamom forests while the remaining eight inhabited the primary forests," Fan said. "There were no obvious differences in group sizes between the two populations."

Overall, the study indicated that the cardamom forests could support gibbon reproduction and maintain group sizes, with no significant differences compared to those living in the reserve's primary forests.