Remember the Titans: Long-term memory of social competitors among male northern elephant seals

Long-term memory of conspecifics underpins complex social relationships in many mammals, including humans. A diversity of taxa rely on individually unique vocal signatures to enable recognition of social partners over time. Given that longitudinal studies are often difficult to conduct with animals with extended lifespans, the nuances of these acoustic memories and their role in stabilizing relationships remain largely unexplored. We examined long-term vocal recognition in male northern elephant seals (Mirounga angustirostris), a species with marked dominance hierarchies and intense male-male competition. At the beginning of the breeding season, we exposed adult males to calls from three sources: a familiar dominant rival from the prior season, a familiar subordinate rival from the prior season, and an unfamiliar alpha male from a distant colony. Calls produced by familiar rivals from the previous season elicited faster and more frequent postural changes than unfamiliar calls. Specifically, seals retreated from the calls of familiar dominant rivals and approached familiar subordinates from previous years, but showed minimal movement in response to unfamiliar dominant males. These findings reveal that male elephant seals remember familiar competitors after long periods of separation, which reduces the cost of aggression and stabilizes dominance relationships among males over time.