First long term study of primate crop-raiding in Asia published
A study which took place on Buton Island, Indonesia on the crop-raiding behaviour of the Buton macaque has found that some troops spend up to a third of their time feeding on crops in farmers’ fields. They raid the farms, which are a mix of annual and perennial crops, in a highly co-ordinated way in terms of how they enter the farm and which crops they target. Farms are a risky place to be for the macaques as they tend to be quite open, with mostly ground cover crops and, of course, full of farmers!
Crop-raids are led by adult males who tend to be more willing to engage in risky behaviour than adult females, particularly those gestating or with infants. Work on risk taking behaviour predicted that juveniles may also be amongst the first to enter the farm, but in this study juveniles raided the farm when they could but neither took the initiative nor hung back.
Understanding how and when the monkeys crop-raid is essential for conservation
The monkeys’ behaviour varies depending on how far they venture in to the farm. When deep in the farm they rest, groom and socialise, whilst they show the most vigilance behaviour on the edges of the farm. This is most likely due to the fact that the monkeys only venture deep into the farm if they think it is safe to do so, ie when farmers are not actively deterring the monkeys. Safety in numbers is also important. The more monkeys present in a raid, the longer the raid lasted. What we don’t yet fully understand is whether the presence of more individuals enabled longer raids, or the longer raids encouraged more individuals to enter the farm.
Ten year study
This study began in 2002 and represents the first long term study of primate crop-raiding in Asia, and one of the longest in the world. Understanding how and when the monkeys crop-raid is essential for conservation. It provides vital information about the monkeys’ behaviour which can be used to develop management strategies and continue to promote tolerance towards the monkeys from the local people.
Patterns of crop-raiding varied throughout the study, with more raids taking place in the early years of the study. There were an average of 21 raids per farm in 2003 during the two month study period, decreasing to an average of one raid per farm in 2009 . The recent decrease in raids may be due to changes in wild fruit availability, farm layout and crops planted, crop yield or climate variables.
Advice given to local farmers from the study may also be having an impact. Farmers were advised on deterrence strategies such as fencing and the use of dogs to scare off monkeys, and crop-planting strategies (planting more vulnerable crops further from the farm edges) which may also have played a part; however, in 75% of raids no human (or canine) deterrence was witnessed.
Finally it’s possible that the number of monkeys in the area could have declined. In earlier years the monkeys were forced into raiding as their forest habitat was converted to farmland; if the monkey population subsequently collapsed (suggested by a decrease in the number of troops in the area), then there will be fewer monkeys in the area to raid. Only one troop in the area is habituated and that troop has declined in population size by 50% during the study, due in the main to a poisoning event by the local farmers.
Currently the levels of tolerance of the Buton macaque in this area are relatively high and there is some level of slightly uneasy co-existence going on. It’s therefore vital that we try to manage this situation before it escalates to a conflict situation.