Three critically endangered Sumatran elephants were poisoned to death within an palm oil plantation on the island of Sumatra, reports the Associated Press. Rono Wiranata of FAKTA, an Indonesia NGO, said the three elephants were found in two locations on a state-run oil palm plantation in Aceh province. It appears the elephants had eaten poised palm fruit. Plantation workers told Wiranata more elephants may die due to the poison. The deaths come less than a month after another elephant was killed in the same district. Its tusks were removed, presumably for to sell in the lucrative ivory market. Environmental group WWF called for an investigation into that killing. Conflict between villagers and elephants is increasingly common as forest habitat shrinks in Sumatra due to agricultural expansion and establishment of pulp and paper plantations. Some conservationists are taking a controversial approach to pacify remaining elephants by introducing semi-domesticated elephants into wild herds. The idea is to teach the elephants not to raid croplands and plantations or move through their former migration corridors. In other parts of the world, especially Africa, conservationists have grown chili peppers to dissuade elephants from entering agricultural areas. It\'s unclear whether that tactic would work with Sumatran elephants. Less than 3,000 Sumatran elephants remain in Sumatra. The population is down by roughly half since 1985 according to the International Union for Conservation of Nature (IUCN).