Survival skills of injured chimps
Chimpanzees accidentally snared in cruel traps have an amazing ability to compensate for severe and permanent injuries sustained, according to two University of St Andrews psychologists.
Emma Stokes, working as a postgraduate with Professor Dick Byrne at the School of Psychology, spent the last two years in the Budongo forest in Uganda, East Africa and has revealed that serious injuries in chimpanzees, including loss of limbs, may result in severe disability but not necessarily severe handicap. Byrne has found the same in mountain gorillas, another species of great ape; but there are no reports of monkeys surviving such horrific injuries in the wild.
Chimpanzee injuries, caused by accidental snaring, are widespread in Africa with up to 25% of all adults suffering permanent upper or lower limb injuries. The traps are mainly set for other mammals on the forest floor such as duikers and bushpigs but, due to their curiosity, young chimpanzees are particularly prone to becoming accidental victims.
Most chimpanzees are injured early in life, before they develop the complex skills needed for eating some plants. Emma has found that they learn the same overall sequence of steps in the feeding technique as their mothers, implying that they pick up this knowledge by imitation. However, they develop novel ways of performing actions in order to achieve each step, depending on the nature of their injuries.
As well as furthering the understanding of the cognitive underpinnings of ape behaviour and evolutionary origins of human thinking and intelligence, the project provides a systematic investigation into snaring, a serious conservation threat to chimpanzees.
Emma first looked at manual feeding skills in able-bodied chimpanzees; then at how individuals compensate in the face of extreme limb injury, to find out how their feeding technique differs from that of their able- bodied counterparts; and finally, at how effective this compensation is in terms of feeding efficiency.
Emma said, “We looked at a variety of different food types, but one of the most interesting was the leaves of paper mulberry, a major food type for chimpanzees which is particularly tricky to process. There are two main techniques, with several steps in each, that able-bodied chimps use to prepare the leaves. When injured chimps feed on this plant, they use both of the two main techniques, but they have to develop some novel actions to achieve each step.”
The exact action they choose depends on the type of injury. For example, Tinka, an adult male studied, had severe injuries to both hands. The only normal functioning part of his hand was the thumb.
Emma explained, “Tinka was unable to strip up a whole bunch of leaves because he could not move any of the fingers of his hand. Instead he stripped the leaves with his lips by gripping the blade above the petiole with his mouth and then manoeuvring them into the hand to get a good enough grip. Once stripped off, he could eat the soft blades as normal, leaving the tough petioles behind. This way, he effectively bypassed the tricky part of stripping up the leaves with his hand but still managed to keep the efficiency of eating lots of leaves at once rather than one at a time. Instead of discovering a new method that particularly suited his disabled hands, he relied on the same overall technique as the able- bodied individuals (i.e. strip up lots of leaves at once, remove petioles and eat blades together), which he most likely learnt from his mother. But he used his own special ways to achieve each step of the process. Impressively, when we compared feeding efficiency between injured individuals and able-bodied chimpanzees, we found that injured chimpanzees were not significantly slower at processing paper mulberry than able-bodied ones – in other words, they appear to have effectively compensated for their injuries.”
The research was carried out by following the chimps on a daily basis with the help of a Ugandan field assistant. Emma recorded the details of every feeding action used, while her assistant noted the activity of all individuals in view every 15 minutes, to see if injured chimps fed less or more on some foods than able-bodied individuals. Feeding rate was recorded on a hand-held computer using a programme which automatically timed the intervals between successive mouthfuls.
Professor Byrne added, “We know that humans are just as impressive as these chimpanzees, when it comes to compensating for injuries in clever ways and thereby often attaining a good quality of life despite quite shocking impairments. There seem to be no cases of monkeys managing so well, so we suspect that the remarkable ability to compensate for these motor impairments is to do with the much larger cortex of the brain in great apes, including ourselves, compared to other primates.”
NOTE TO EDITORS – Emailable photographs of an injured chimpanzee from Budongo and an injured gorilla from Rwanda available from Claire Grainger – contact details below. Interview requests should also go to Claire Grainger.
Issued by Beattie Media on behalf of the University of St Andrews For more information please contact Claire Grainger on 01334 462529/2530, 07730 415 015 or email [email protected] Ref: chimps- injured/standrews/chg/5march2002