Till the Last Drop: Honey Gathering in Nigerian Chimpanzees

Various populations of chimpanzees attack beehives to obtain honey, often with the help of wooden tools. However, little is known about how honey abundance in tropical habitats fluctuates with season and how chimpanzees respond to this. For a woodland-savannah habitat inhabited by the Nigeria-Cameroon chimpanzee subspecies, we analyzed monthly proportions of flowering trees and vines as a proxy for honey production. We found a strict negative correlation between flowering and rainfall, probably because pollination benefits from dry conditions. Honey-gathering behavior of the Gashaka-Kwano chimpanzee community was reconstructed from tools abandoned at extraction sites. The apes use sturdy digging sticks and more slender probes, sometimes successively as a tool set, to access honey from subterranean and tree-dwelling colonies of stingless bees and honeybees. Chimpanzees exploited beehives throughout the year. However, during the dry season, when colonies had presumably hoarded more honey, hives were targeted with a greater number of tools. This was not because chimpanzee foraging party sizes had increased. Instead, individual apes used more probes during a given honey-gathering event – suggesting that dipping remained worthwhile for longer. In this situation, as tool tips become soft and unsuitable after prolonged dipping, the chimpanzees need to source new implements that possess hard tool points. The apes did not obtain them by breaking previously used tools into fragments, as these would be too short for successful insertions. We assume this because the average length of tools did not decrease with the increased number of apes that worked a hive. This indicates that each tool is sourced individually from raw material in the surroundings of the extraction site. Chimpanzees thus adjust the use and manufacture of tools to honey abundance, reflecting that the sugary fluid is a sought-after resource.