Monday, January 25, 2016

Chimps as individuals

At Chimp & See, we ask our volunteers to accomplish two different tasks. First, we need their help classifying many hours of video material from camera traps in Africa in terms of the species and number of wild animals they contain. Secondly, if one or more chimpanzees are found in a video, we want to identify them in order to better estimate population size and answer other ecological and behavioral questions (like association patterns and cultural transmission).

While other citizen science projects like Snapshot Serengeti and WildCam Gorongosa are similar in terms of annotating all animals present, Chimp & See is one of the first projects (another one is Whales as Individuals) to attempt identifying individual animals from camera footage. In the beginning, the science team was not sure if volunteers would be able to identify individual chimps, but is happy that it works very well. We now know that with a bit of effort and guidance many can learn this skill.

Identifying (i.e., matching) chimpanzees means finding out whether a chimp in two different situations (video sequences) is the same chimp or not. The matching is considerably harder than classification itself as everyone in the project can tell. First of all, we are mostly observing chimp communities that are unhabituated to human presence. Little is known about the individual chimpanzees at each research site and so we cannot compare them to a well-lit high-resolution picture and a list of his/her features known in advance. These chimps are new to all of us – and with each site progressing, we try to get to “know” them better and recognize features that enable us to identify them as individuals. A second level of difficulty arises from the chimps themselves. The chimps hardly ever stand still in front of the camera to allow a good look at all sides of their body and face and show the specific individual traits we can rely on.

Achenar is a male adult chimp with a boxy head missing his right ear.
The traits should ideally be permanent, but temporary ones like wounds might be recognizable at least a few days or maybe even weeks. Basically every distinctive feature can be seen as a trait and support the match, starting with general body size and build, missing limbs, fur color, bald spots, number of digits (fingers and toes), and pigmentation of face, hands, and ears. The face can be narrow, round, triangular. Small or bigger scars can be visible on body and face. Ears can be bent, have cuts, or be missing altogether. A recurrent topic is the distinctiveness of the baldness pattern on the forehead that is partly already seen in infants. More behavioral traits like a special gait (how a chimp walks) or handedness are often hard to compare, as camera perspectives are rarely the same, but observing it can support a difficult match. For all these and many more features one could think of, it does not matter whether the volunteers know the correct scientific term or can provide a full list of features the chimp has. A lay description is sufficient to discuss with others and the science team. The wisdom of the crowd generates very good results.

Female chimp Esme is quite old and has a badly damaged left ear
Once an individual chimp is identified, a volunteer who has participated in the matching discussion can propose a name for this chimpanzee. Up to now, we identified and named more than 100 chimps at different research sites.

During the year, I will introduce individual chimps and show how we came up with a specific match. Following is irregular series, you can learn what to look for when comparing two chimps, how to deal with different camera angles and black-and-white footage, and how hard it is to identify infants and often even juveniles.

A first example: Timur

This old and weathered looking male from Quiet Wood (a site in Central Africa) has been identified as part of our “throwback” initiative that aimed to take a second look at the very first research sites up at Chimp & See after some months of experience with the video footage.

Timur helped us a lot with his identification as he always stopped in front of the camera and stayed there for some invaluable seconds just looking around. Even with different lighting – including black-and-white footage from evening twilight – his facial and bodily features were clearly seen: a flat head, pointy and undamaged ears, straighter brows, big eye sockets, and the flat nose with long nostrils. In some footage, the lips look lacerated and an underbite has been discussed. In addition to quite a lot of gray fur at the lower back and legs he has a unique pink patch on the right side of his butt. It is not clear whether this is a wound, scar or something else, but the footage spans over several months and it does not go away.

Full screen picture here
Full screen picture here
Back views (two months apart): same pattern of gray
and a pinkish patch on the right side of his butt.
Timur has been named (by me ) after confirmation of the proposed match by the science team. He has been seen in three different video sequences over the course of four months.
You can join the matching discussions at Chimp & See!

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