An observation of potential altruism by a male northern elephant seal (Mirounga angustirostris)

Abstract

Altruism, the behavioral assistance of another in need, has ancient origins in mammalian evolution (Preston, 2013).An individual is thought to behave altruistically when its actions result in the reduction of its own survival or reproduction to benefit the fitness and survival of another individual (Kay et al., 2020). Allo-parenting (adoption of orphaned young), a type of altruistic behavior, is commonly reported in social birds as well as mammals (Konig, 1997). Allo-maternal care (nonmaternal care of young) has been noted in numerous pinniped species including in both Phocidae and Otariidae (Arso Civil et al., 2021;Gemmell, 2003). Male altruism, though, has rarely been described in marine mammals, including pinnipeds (Acevedo-Gutierrez, 2009). Generally, polygynous marine mammal males infrequently engage in parental care, but rather devote their time and energy to mating with many females (Berta et al., 2005). Here, we document a novel exception to that general depiction with a possible altruistic act by an adult male northern elephant seal (Mirounga angustirostris) that responded to a young pup in distress at a colony at Point Reyes National Seashore, California.Elephant seals gather annually at numerous colonies along the eastern Pacific, ranging from British Columbia south to Baja California, to give birth and suckle their young onshore (Lowry et al., 2014). The breeding season throughout their range extends from December through March when mostly adult males and females gather onshore. The sexes are extremely sexually dimorphic, exhibiting a dominance hierarchical polygynous mating system (Le Boeuf, 2021). Adult females are capital breeders that gather in harems onshore and remain in close proximity with pups for approximately 30 days, at which time they come into estrus, mate, and shortly thereafter depart the colony. Suckling and unweaned pups are unable to swim well, and infrequently venture into the water until they wean, though they do cool off at the tidal edge (Codde et al., 2016). Dominant males also spend little time in the water and are mostly preoccupied with either defending their position near or attempting to mate with females. Dominant males, though, occasionally may herd or escort females arriving or departing between harems onshore and deep water to prevent subordinate males from attempting to harass or mate with them (Le Boeuf, 2021), and both sexes will retreat to wet sand and shallow water to cool off during warm weather. Both males and females fast during the breeding season relying on stored energy reserves,