Bonobos and chimpanzees can recognize photos of former group members, even those they haven’t encountered in over two decades. This suggests that these primates boast the longest social memory observed in any animal besides humans.
Renowned for their cognitive prowess, great apes, including gorillas, chimpanzees, and bonobos, have demonstrated impressive memories.
Some chimpanzees, for instance, can recall the precise locations of specific fruit trees in a forest and anticipate events in previously viewed films.
Laura Lewis at the University of California, Berkeley, notes that researchers observed signs of recognition and remembrance when revisiting ape populations studied in the past.
To delve into the duration of social memory in apes, Lewis and her team conducted experiments involving 12 bonobos and 15 chimpanzees residing in zoos across the UK, Japan, and Belgium.
Each animal was presented with side-by-side photos of two different apes on a screen for three seconds—one of a former group member from at least a year ago and the other of a stranger.
Utilizing eye-tracking technology, the researchers discovered that all participants gazed at images of former group members approximately a quarter of a second longer, on average, than they did at pictures of strangers.
Notably, for former colleagues with positive relationships, as indicated by zookeepers, the apes lingered even longer in their photos.
The findings suggest that these apes retain memories of acquaintances even after extended periods of separation.
Christopher Krupenye of Johns Hopkins University likens the experience to unexpectedly encountering a schoolmate while walking down the streets of a major city and experiencing that double take.
In an extraordinary case, according to Lewis, a bonobo named Louise appeared to recognize her sister Loretta and nephew Erin after more than 26 years of separation, marking the longest long-term social memory recorded in a non-human animal.