Sciency Thoughts: Crop raiding behaviour by Chimpanzees in southwest Uganda.

Chimpanzees, Pan troglodytes, like all the Great Apes, face increasing conflict with Humans throughout their range, driven by logging, poaching, mining, the illicit trade in wild animals and agricultural incursion into their territories, all of which are ultimately driven by sharply rising human populations (the Human population in the tropics is growing twice as fast as elsewhere, but rising populations in other parts of the world also drive Human consumption of tropical products). Chimpanzees can be particularly badly hit by logging, which removes essential fruit-bearing trees from their territories, causing them to seek out alternative food sources, which in turn brings them into conflict with human agriculturalists.

In a paper published in the journal PLoS One on 22 October 2014, a team of scientists led by Sabrina Krief of Eco-anthropologie et d’ethnobiologie, Hommes, Natures, Sociétés at the Museum national d’histoirenaturelle in Paris and the Projet pour la conservation des grands singes at Kibale National Park in Uganda report the results of a camera trap study by the Sebitoli Chimpanzee Project, into crop-raiding by Chimpanzees on the western fringe of Kibale National Park.

The project focused on a maize field on the western edge of the park. This is separated from the park itself by a trench 2 m wide and 2 m deep, dug by the Uganda Wildlife Authority to prevent Elephants crossing from the park into agricultural land, but crossed at one point by a fallen tree, known to be used as a highway by Chimpanzees entering the field. The Sebitoli Chimpanzee Group comprises about 80 individuals, 26 of which show deformities caused by snares associated with poaching activity, with eight individuals missing parts of limbs.

The local population of Batooro and Bakiga farmers do not eat Chimpanzees, but actively defend their crops (the lead male of a neighbouring Chimpanzee group was severely injured by a spear), and are themselves facing pressures due to rising a population and limited land availability (due to logging, tea plantations and designated parkland), causing them to farm right up to the borders of the park, and the field is actively defended by Human farmers, who have guard huts within the field manned day and night and also keep Dogs in the field. However Chimpanzees are highly adaptable, and the Sebitoli Group have long experience of dealing with Humans, with a territory that shares 32 km of border with human communities (out of a total of 39 km of border) and which is crossed by a tarmac road.

A Chimpanzee in the Kibale National Park. Kabarole Tours and Safari.

Krief et al. predicted a number behavioural traits and adaptations that would be observed in the Sebitoli Chimpanzees, based upon prior observations of Chimpanzees foraging on agricultural land. Typically when staging raids into agricultural land or the territory of rival Chimpanzee groups the raiding parties are smaller than typical foraging parties, and led by dominant males from within the group (who are more prone to high risk activities). Chimpanzees taking part in raiding activities are usually more cautious and vigilant than at other times, spending more time scanning for threats and producing less noise; they have also been known to make use of moonlight when moving about near potentially hostile humans, taking advantage of the full moon. Finally Chimpanzees taking part in high-risk activities typically show signs of stress, such as increased scratching or even attacks of diarrhoea.

Uganda-Kibale National Park-Sebitoli area, home-range and maize field monitored (location of the guarding huts, thefallen tree and the video-trap). Krief et al. (2014).

Surprisingly the Chimpanzees of Sebitoli showed few of these behaviours. The raiding parties were slightly larger than typical foraging parties for the group, and were often led by females. Members of the group that would typically be considered vulnerable, such as young infants, disabled adults, and even a juvenile with an unhealed broken limb took part in the raiding parties, and only the loudest vocalizations were avoided; on one occasion two Chimpanzees were observed copulating at the edge of the field. The Chimpanzees did not appear overly concerned about Human or Canine guards in the field, and while they would retreat if threatened or chased, often simply waited out of view before retuning to foraging in the field.

On defensive behaviour they did exhibit, and which was completely unexpected, was switching the time of day at which they were active, often foraging after dark and favouring nights around the new moon, when light levels are lowest, rather than around the full moon, when light levels are high. This is surprising, as while Chimpanzees are highly adaptable, they are not usually considered to be nocturnal animals, and have not previously been shown to alter their foraging times to avoid humans.

Only one previous study has shown Chimpanzees targeting a human crop at a particular time of day, when a group of Chimpanzees were found to be more likely to consume Cassava later in the day. However Cassava is considered to be a low preference food for Chimpanzees, and it is thought that these animals were only seeking it out after attempts to locate other food sources had failed. The Sertoli Chimpanzees were, in contrast, clearly switching to a highly atypical foraging schedule in order to access a high preference food (Maize), which shows a considerable degree of pre-planning.

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Monday, 10 November 2014

Crop raiding behaviour by Chimpanzees in southwest Uganda.