126 different kinds of fruit consumed!

After a period of habituation to her presence, facilitated by the frequent visits of groups of tourists to that part of the national park, Aurélie Albert monitored a troop composed of two to three males, a dozen females, twenty juveniles and some subadult males. Mixing with this very discreet group (on the ground), or following it by means of binoculars in the different forest strata, the young researcher was able to identify more than a hundred types of fruit species - 126  to be exact - consumed by the macaques. What was surprising was not so much this quite large range, typical of the profusion of plants in the tropical zones, but the array of techniques used by the primates to handle the seeds,  and as a result, their effectiveness in dispersing them. “Within their home range, the pig-tailed macaques move around mostly where they are guaranteed to find large quantities of seeds according to the high fruit abundance period for each tree species, this means that their foraging movements are guided by the knowledge they have about the period of high abundance of their preferred fruit species in accordance with the seasonal variation”, explains Aurélie Albert.

In order to achieve these results, the researcher monitored her troop of primates from dawn to dusk for a thousand hours, checking their movements by GPS every half an hour. To obtain a sample of the distribution of trees frequented by the animals, transects (imaginary lines) one kilometer long and twenty meters wide were drawn across their home range, equivalent to about 27 hectares. In total, nearly 12,000 trees comprising 228 species were tagged by GPS and with a label placed on each trunk. With the help of a local assistant, the phenology of 183 species of trees was regularly monitored: budding, flowering, fructification, maturing of fruit etc. “I divided the home range of the animals into cells of 110 meters long on each side. For each of those cells I calculated the fruit abundance index which I then crossed with the animal movements. While proximity to the macaques is a particularly pleasant aspect of the work (provided that contact with them is avoided in order to avoid methodological biases), monitoring and observing them during the rainy season is particularly difficult: leeches invade the entire forest cover. As for the monkeys, they move around very little at that time, seeking refuge very high in the trees where they are even more discreet than usual.”