New publication using Chimp&See data investigates nocturnal activity in wild chimpanzees

The Pan African Programme: The Cultured Chimpanzee (PanAf) in collaboration with Dr. Nikki Tagg Nama (PGS Cameroon, Royal Zoological Society of Antwerp) have just published a research paper investigating the nocturnal activities of wild chimpanzees. Using data from camera trap videos annotated on Chimp&See and from the PanAf collection, the researchers have been interested in the influence of different environmental factors that could lead to more nighttime activities of chimpanzees and possibly disturb their sleeping patterns.

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!

Chimpanzees at night

It’s the 21st of December – Winter solstice in the Northern hemisphere – and with over 16 hours of darkness the longest night here in Europe. These “dark times” motivated us to talk about chimpanzee activity at night and what you can see about it over at Chimp & See.

Chimps are not really known for any nocturnal behavior – in fact, not much is known about it at all in the wild, as research teams observing chimp communities during the day usually leave the group after the chimpanzees have made their nests for the night. Nightly vocalization (e.g., long distance calls) and other activity indicators had been recorded in the wild and in captive (zoo) apes, but the reasons for staying up late or even waking up and any possible activities lie mostly – well – in the dark.

Usually, it is assumed that chimpanzees mostly sleep through the night. In areas where chimpanzees live, sunset and sunrise varies not much seasonally and the length of the night (defined as the dark period between sunset and sunrise) is between 11 and 13 hours with only small changes during the year. Because of relatively poor night vision (like us humans) and with known predators (like leopards) active during the night, it is assumed that chimps generally stay in the safety of their nests through the nighttime hours from dusk until next day’s dawn. Given these considerations, we expected it to be very rare to see the chimpanzees at night.

An adult male balancing across a small creek at 5.33 a.m. (Muddy Frost 7)

Nonetheless, at almost each research site up at Chimp & See until now we have seen at least on one occasion what we call the “nightchimps” – chimpanzees that are caught on camera while it is dark. At most sites, these “nighttime” chimp activities (mostly traveling, some feeding) are during the early hours of the day (just before 6 a.m.) and are not considered very unusual. Depending on the distance to a desired feeding patch (e.g., fruit trees), chimps will get up early enough to reach them – or reach them first if feeding competition is an issue.

This chimpanzee infant is very tired on mom's back at 1.46 a.m. (Dry Lake 11)

But at the current site Dry Lake – the first in a dry savannah habitat in West Africa – we could collect significantly more “nightchimps” videos and several of them with time stamps very late at night. Currently, it is wild speculation why the chimps are active so late and why there are considerably more videos from the very early hours of the day than from other sites. One obvious reason might be the hot climate with day temperatures of over 40 °C during the dry season. Almost all “nightchimps” videos found until now have date stamps from March to May (in 2013) with hot temperatures and numbers of recorded “nightchimps” both peaking in April. The chimpanzees may just avoid the very hot day temperatures and feed and/or travel during the cooler morning and late evening hours. They might also need to forage longer or in a bigger area to find enough food. Other factors (like human pressure and domestic animals) may play a role but need to be analyzed and compared with other research sites. Certainly, something the science team will look into.

A family of three at 8.59 p.m. (Dry Lake 11)

• If you want to see more “nightchimps” please look into this collection: http://talk.chimpandsee.org/#/collections/CCPS000162
• Currently, we try to match some of the “nightchimps” to previously identified chimpanzees at this research site, which is even harder than expected as facial features, fur coloration and other traits appear very differently in the infrared cameras. You can follow our discussion here: http://talk.chimpandsee.org/#/boards/BCP000000o/discussions/DCP0000l2z