A systematic review of the impacts of El Niño-driven drought, fire and smoke on non-human primates in Southeast Asia

During the El Niño phase of the El Niño–Southern Oscillation, much of Southeast Asia experiences intense droughts and surging temperatures, exacerbating wildfires and creating a blanket of hazardous haze across much of the region. These patterns are predicted to worsen with climate change, further increasing the vulnerability of the region’s primate species, 94% of which are threatened with extinction. Here, we report findings from a systematic search of the literature and synthesize the current state of knowledge regarding the impacts of El Niño-driven heat, drought, fire and smoke on non-human primates in Southeast Asia. Our review shows that habitat loss and degradation driven by El Niño-induced drought and fire cause changes to diet, activity patterns, social interactions and physical condition, and lead to population crowding, reduced group sizes, increased infant mortality, displacement of individuals and local extirpation. Furthermore, prolonged exposure to smoke alters behaviour and worsens the health of primates. Two studies presented evidence for the recovery of primate populations in habitats damaged by fire if forest is allowed to regenerate. We highlight significant gaps in our understanding of the impacts of El Niño on non-human primates, particularly the need for research that considers the interconnected effects of rainfall, temperature, fire and smoke, as well as long-term effects on reproduction and mortality. Because of the unpredictable nature of El Niño, we acknowledge the difficulties of planning research in this area and emphasize the potential of long-term research sites to add to our understanding of this key conservation issue.