When it comes to short-term memory, animals have very short ones indeed. A new meta-analysis examined more than 90 memory experiments carried out on 25 species encompassing birds, mammals, and bees. Researchers at Stockholm University and Brooklyn College found that for dogs, events are forgotten after about two minutes—and that's on the long end of the spectrum. The average memory duration for all animals studied is 27 seconds, with chimps' memory as short as 20 seconds; that's a length of time that rats beat, reports National Geographic. Humans subjected to similar studies have had no problem remembering a sample stimulus they had seen as many as two days prior. In fact, based on these findings, "we think humans' ability to remember arbitrary events is unique," one researcher says.
Animals' memories can be broken into two categories—short-term and longer-term "specialized" memories, reports the University of Stockholm. And while animals can have excellent specialized memories (think birds remembering the exact locations of previous nests), memories of specific events tend to disappear in a span "ranging from a few seconds to several minutes," per the researchers' findings, published in December in Behavioural Processes. That said, one researcher not involved in the study pointed out that some animals have shown the ability to capture episodic memories the way humans can—great apes have been shown to do so for days, if not years—while another cautioned that "it might be too early to argue that humans are the only ones who are able to mentally travel back and forward in time." (Dolphins, meanwhile, can recall whistles 20 years later.)