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, with some males fasting up to 4 months, and correspondingly, experience exceptional weight loss (Deutsch et al., 1990). Consequently, males tend to avoid energetically costly actions, especially minimizing movements unrelated to reproduction (Le Boeuf, 2021).

Elephant seal females generally remain close to and are protective of their pups from conspecifics and other species, and if separated, will vocalize with a “pup attraction call” to locate and encourage reunion (Riedman & Le Boeuf, 1982). Females occasionally assist pups and prevent their drowning when high tides and surf swamp colonies, by encircling their pups with their bodies to form a “U” shape, and thereby shelter them from waves (P. A. Morris, personal communication, February 2023; S.G.A., personal observation, January 1998). In contrast, Reiter (1996) described the male relationship to pups in the harem as “nonexistent,” and that male behaviors do not include protection or even recognition of pups.

Two of us (S.G.A. and M.J.L.) observed and describe here the separation of a female and her pup by tidal wash and waves, and the ensuing male response to the pup in distress at Drakes Bay in Point Reyes National Seashore, California on January 27, 2022 (Figure 1). The elephant seal colony at Point Reyes (38.0178°N, 122.9913°W), established in 1981, has grown since inception, and recently expanded along an 8 km beach in Drakes Bay, where seals are usually protected from large surf and high tides (Allen et al., 1989; Codde et al., 2016). Surveys at the Point Reyes colony consist of counting all seals, grouping seals by age class, and opportunistically documenting seals marked with flipper tags or hair dye (Adams et al., 2006). The weather on January 27 was sunny, mild, and windless with temperatures of approximately 17°C recorded. We first noted the pair mid-day at the low-tide water's edge on wet sand when we were hiking west along the beach while surveying seals. The pup was <2 weeks old and was resting by the side of the female, approximately 20 m from a small harem of <40 females. An alpha bull was present by the harem on dry sand and there were a couple of subordinate males nearby (age classes described by Le Boeuf, 2021). On our return trip at about 14:15 PDT, as the tide was rising and in about the same location as the pair we noted earlier, we observed a female on the water's edge and a pup being washed out by the undertow of waves. We presumed that this was the same pair noted earlier because of the female's position in relation to the harem at about 25 m distant. The pair were separated by about 15 m, and waves of approximately 1–2 m continued to draw the pup out. We noted that the pup was unable to swim as it struggled to keep its head above water, calling. The female moved into shallow water but remained on firm sand and did not venture beyond the tidal wash. She called to the pup with an urgent pup attraction call but did not pursue as the pup was drawn further out beyond the surf. A male, which we identified as the alpha of this small harem, was in the wave wash approximately 10 m from the female. We presumed that this adult male was the same one that we observed earlier when he was closer to the harem. The male approached the calling female, briefly touching his nose to her left flank. The female rebuffed the male with open mouth, and continued to look towards and vocalize to her pup. He then instantly turned and charged across wet sand and into the surf, swimming swiftly out to the struggling pup. Meanwhile, pup and female continued to exchange calls. The pup at this point was beyond the breaking waves approximately 40 m from the female, and likely in 3 m depth. The head of the pup was barely above the surface, and its rear flippers twisted in the air but were not used for swimming. The male, whose head seemed larger than the pup, did not attempt to seize the pup in his mouth, but instead positioned his body so that he was gradually and gently pushing the pup with his head and body while swimming towards shore. When waves drew back, he physically assisted the pup by providing shelter and an anchor with his body, and thus preventing it from being drawn out to sea again. We did not observe, though, whether the male supported the pup underwater with his flippers. Slowly but steadily, the male gently pushed the pup to shore until it could touch bottom within 4 m of the female. The pup and female moved towards each other while the female continued to call. After nearly 20 min from our initial observation, the reunited pair moved higher up on the beach beyond the tidal wash. The female subsequently bellowed in a voice usually directed towards males, and within seconds, the male trumpeted and then rested on the wet sand. We noted during our observation that no other adult males were within 50 m of the harem and that there was no disruption of the females of the harem in the alpha male's absence. We then terminated observations at approximately 14:35 PDT and continued on our survey.

While at the water's edge, dominant males often are attracted to females vocalizing while being harassed by peripheral adult and subadult males. The alpha male's response to the female call in our observation appeared to be a similar response; although, the female call was a pup attraction call rather than one directed towards harassing males. His subsequent behavior of pursuing the pup and pushing it to shore, might be interpreted as misdirected sexual behavior, where dominant males frequently herd and escort females to shore to thwart harassment by other males. However, we propose that the actions were intentional, where the male redirected his attention from the distressed female to that of the pup; appearing to take deliberate action, sprinting out beyond the surf at considerable distance away from the female and his harem. His subsequent herding actions were different from those of escorting females because he gently pushed the pup until it reached solid sand and intentionally blocked it from waves and undertow. When the female bellowed after reuniting with her pup, he did not respond by approaching her, but rather trumpeted and remained in the tidal wash.

We believe that our novel observation meets the definition of an altruistic act (Kay et al., 2020): the pup benefited from the male retrieving it from being swept out to sea and drowning because it was too young to swim, and the male expended energy at a critical time that had the potential to impact his fitness. For an alpha male, this cost might be substantial because he would need to conserve energy while fasting for several months, defending his position against other males, and mating with many females (Deutsch et al., 1994). In our observation, the effort lasted approximately 20 min, which is likely not insubstantial. Half the breeding season was still ahead on January 19, and consequently, a fasting alpha male might already have expended considerable resources to secure and retain his position (Deutsch et al., 1990), but also would have a significant number of females that could be inseminated if able to retain his alpha position. In his absence, the harem was exposed to potential harassment by subordinant males; although we counted subordinate males earlier near the harem, during our return, we did not see any in the immediate vicinity at the time of the event. We speculate that the male's trumpet after the female bellowed, may have been directed either towards the female or to reinforce his dominant position to potential lingering rivals. Importantly, an alpha male benefits genetically if the female stays to wean her pup and mates with him; whereas if the pup is lost, she might leave his harem before coming into estrus.

Kin selection (genetic relatedness; Trivers, 1985) has been proposed to explain altruistic behavior in stable social groups, and specifically in pinnipeds such as harbor seal (Phoca vitulina; Arso Civil et al., 2021), Hawaiian monk seal (Neomonachus schauinslandi; Boness et al., 1998); Antarctic fur seal (Arctocephalus gazella; Gemmell, 2003), and gray seal (Halichoerus grypus; Pomeroy et al., 2000). Le Boeuf and Briggs (1977) speculated that kin associations might be even more pronounced for northern elephant seals because the species experienced severe genetic bottlenecks which resulted in depressed genetic diversity. Elephant seals present at Point Reyes are also closely related, based on data collected from marked seals (Allen et al., 2012). We cannot confirm kinship of the male and female that we observed, though, because we have no genetic data. Nevertheless, it is possible that the male and female were present on the same beach in previous years. Le Boeuf (2021) reported that some males at Año Nuevo were beachmasters for consecutive years, as we also noted at Point Reyes (S.G.A., personal observation of marked seals).

Examples of male altruism in pinnipeds are exceptionally rare, and in only one incidence, was it documented in the scientific literature. Elorriaga-Verplancken and Acevedo-Whitehouse (2017) reported a male California sea lion (Zalophus californianus) exhibiting intersexual altruistic behavior with an ill adult female. They speculated kinship between the male and female might explain the behavior, though acknowledged that they had no genetic data to confirm relatedness. Possible altruistic behavior of male elephant seals has not been previously reported or observed by colleagues at other seal colonies in the region (P. A. Morris, personal communication, February 2023).

Harem density may have contributed to the novel male behavior that we observed. In a large and dense colony, the opportunities for altruistic behavior towards pups may diminish because alpha males likely would be focused on the increased presence of competitive males, and hence, would expend more energy in vigilance and fighting. In a colony of southern elephant seals (Mirounga leonina), Lloyd et al. (2023) reported that colony density was linked to age-specific life history traits of males and that the cost to survival was lower for dominant males from smaller harems than from dense ones. At Drakes Bay, a fairly new subcolony at Point Reyes, the seals are not crowded, and small harems are sparsely distributed over several kilometers (Allen et al., 2012). With reduced colony density, competition and associated energy demands among males may be much diminished, allowing for increased survivorship and time to engage in such altruistic behaviors.

Perhaps, some examples of behavior labelled as male sexual behavior directed at pups might be similarly altruistic behaviors. On occasion at Point Reyes, we have noted male seals preventing pups from being washed out during storm driven waves by cupping their bodies around them, similar to that of female protective behavior (S.G.A., personal observation, January 1998). Possible altruistic behavior rather than misdirected sexual behavior may also explain the actions of subdominant males that attend weanlings as female substitutes when they form “weanling pods” on the periphery of harems (Rose et al., 1991; S.G.A. & S.A.C., personal observation at Point Reyes).

Kay et al. (2019, 2021) noted that the processes surrounding the evolution of altruism remain unresolved, though, they asserted that scientists mostly agreed that genetic relatedness has a central role. Preston (2013) proposed that nonmaternal altruistic behavior such as offspring retrieval was based in part on the evolution of neural-hormonal feedbacks that reinforced a behavior to solve a problem. Novel behavior such as we observed, if repeated over time, might provide insights into how altruistic traits develop or are learned; though, to achieve even a glimmer of understanding of altruistic trait development would require intensive, long-term studies involving genetic relationships of known individuals within a colony.

Sarah G. Allen: Conceptualization; validation; writing – original draft; writing – review and editing. Matthew J. Lau: Conceptualization; visualization; writing – original draft; writing – review and editing. Sarah A. Codde: Data curation; funding acquisition; project administration; writing – review and editing.