no longer present on the island were shown to have existed at some time there. These plants included a giant palm, the Rapa Nui Palm, that showed signs of being the largest palm species in the world, eclipsing the size of the Chilean Wine Palm if it were not extinct. There are also signs of Easter Island's once possessing a far more diverse collection of fauna. The skeletal remains of 25 different species of nesting bird have been located on the island, but have since been reduced to 16. This trend of extinction and extirpation is a common occurrence when humans populate a new area, because of tendencies to overhunt and overexploit resources. Deforestation would have caused a decrease in crop yields due to soil erosion, loss of wood as a resource to construct fishing boats, among other things, and would have necessitated a halt to the construction of the moai erected around the island. Diamond hypothesizes that resource scarcity may have led to brutal civil war, creating a drop in population. He further hypothesizes that there were about 7,000 individuals pre-war, a number which fell to the 2,000 whom missionaries met when they showed up in the 19th century and conducted the first census of the island. In recent years this decline has been increasingly implicated upon the arrival of Europeans to the island and the diseases that commonly came with them like smallpox, with several researchers having instead noted that pre-colonial Rapa Nui society was rather stable. Agriculture Agriculture on Easter Island shows signs of intensification before European arrival, necessary because of its climate which had an excess of wind and a low amount of rainfall for the area. Archaeological finds show a multitude of composting pits and irrigation systems. Large boulders were also stacked to serve as barriers against the wind. In the fields, a system of agriculture called lithic mulch was employed. In this method, farmers would lay rocks out in patterns in their fields, forcing the plants to grow in certain areas. This method is known to increase soil moisture while decreasing soil erosion from wind, effectively combating the climate conditions. Crops grown on Easter Island included sweet potatoes, yams, taro, bananas and sugarcane. Chickens were the sole domestic animal, though the "chicken coops" carved of stone which still dot the fields of the island were most likely tombs from which the chickens obtained calcium