https://phys.org/news/2018-05-mongooses-reward-friends.html

Senior author, Professor Andy Radford from Bristol's School of Biological Sciences, said: "Humans frequently trade goods and can track the amount they owe using memories of past exchanges. While nonhuman animals are also known to be capable of trading cooperative acts immediately for one another, more contentious is the possibility that there can be delayed rewards."

Lead author, Dr. Julie Kern, also from Bristol, added: "There have been hardly any suitable experimental tests on wild animals, especially non-primates. By working with groups of dwarf mongooses habituated to our close presence, we could collect detailed observations and conduct experimental manipulations in natural conditions."