Capacity for recovery in Bornean orangutan populations when limiting offtake and retaining forest

Aim:

We assess the potential long-term viability of orangutan populations across Borneo, considering the effects of habitat loss, and various forms of population reduction, including hunting, retaliatory killings, and capture and translocation.

Location:

The study focused on the island of Borneo, a region that has experienced substantial deforestation over the past four decades, resulting in the degradation and fragmentation of its lowland forests, thereby threatening the island's unique biodiversity, including orangutan populations.

Methods:

To evaluate the long-term viability of orangutan populations, we employed a spatially-explicit individual-based model. This model allowed us to simulate various scenarios, including the impact of removing habitat fragments or individuals from the population.

Results:

Our findings revealed that small forest fragments facilitate orangutan movement, thereby increasing the number of individuals settling in non-natal patches. Crucially, orangutan populations proved highly vulnerable to even small levels of offtake. Annual removal rates exceeding 2% diminished the positive role of small forest patches in sustaining population connectivity, the long-term viability of populations and prospects for recovery.

Main Conclusions:

Our results suggest that orangutan populations in Borneo could potentially recover from recent declines if removal of orangutans by hunting, retaliatory killings, capture and translocation is reduced, and habitat connectivity is maintained within human-modified landscapes. These findings emphasize the urgent need for conservation strategies that mitigate negative human-wildlife interactions, and/or help preserve habitat and fragments as stepping stones. Measures could include promoting coexistence with local communities and translocating orangutans only in rare cases where no suitable alternative exists, to ensure the long-term survival of orangutan populations in Borneo.