Chimpanzees are rarely active at night after building their nests. So, it was a surprise for me and other volunteers at Chimp&See to see them on our camera trap videos at almost all sites at least occasionally walking in the darkness. We decided to tag and collect those videos. While only a tiny fraction of videos at Chimp&See show what we call the “nightchimps”, it is an interesting phenomenon and leads to questions about what general or site-specific environmental circumstances might cause more or less nocturnal activities.
After starting and curating the Chimp&See “nightchimps” collection, we got the chance to join the project to get a different perspective on the science part and support the science team beyond our regular Chimp&See moderators’ tasks.
Using the nighttime video clips identified and tagged by our volunteers and video material from other PanAf research sites, as well as associated data from environmental surveys of these sites, this study provides a first comprehensive analysis of nocturnal chimpanzee activity in the wild spanning their range and all four subspecies. The study shows that chimpanzees indeed are active at night on the terrestrial camera trap videos at almost all sites (18 out of 22 in the study), but only infrequently, making it a rare behavior still. From all observed chimpanzee activity in the videos only 1.8% occurred at night, but this amount differed from site to site considerably, from 0 videos to more than 8% of all observed chimpanzee activity at one site. The video material shows chimpanzees mostly traveling during these times, but also some social activities and feeding.
The researchers then tested whether different environmental factors like percentage of mature forest at a given site, the abundance of predators (lions, leopards, and hyenas), the abundance of other large mammals (buffalos and elephants), average daily temperature, rainfall, observed human activity, and the percentage of moon illumination on a given night affect the probability of observing chimpanzee nocturnal activity. Only three of these factors showed an effect on increased night activity: lower levels of human activity, more forest coverage of the site, and higher day temperatures – as we’ve seen at the Chimp&See site “Dry Lake” during the dry season.
As data was collected exclusively via camera trap videos, the authors speculate that these initial data might underestimate the amount of nocturnal activity. When more camera trap videos become available in the future – including at Chimp&See – they hope to find more evidence for nocturnal behaviors and its relevance for conservation and also human evolution.
This study demonstrates the unique advantage of using camera traps to find and investigate new and rare behaviors in chimpanzees and other animals, here especially those occurring at night. While it is possible to watch chimpanzees by staying at the nesting site all night, this can only be done at one of the few sites with habituated chimpanzees and a dedicated nocturnal field team. Moreover, the huge collaborative effort of the PanAf program provides the first opportunity to compare sites, environmental factors, and different populations to learn more about the evolutionary drivers of chimpanzee behavior.
- Watch the Chimp&See “nightchimps” collection here.
- More information about the Pan African Programme: The Cultured Chimpanzee and its mission.
- Original publication: Tagg, N. et al. “Nocturnal activity in wild chimpanzees (Pan troglodytes): Evidence for flexible sleeping patterns and insights into human evolution” American Journal of Physical Anthropology, 166(3), 510-529.
If you want to join Chimp&See helping us to find more exciting chimpanzee videos and, for instance, contribute to the leopard mini-project please visit www.chimpandsee.org!
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