Travel – Antarctic on Le Lyrial (Days 12-17)

Aggressive play in juveniles

Young elephant seals engage in a variety of social interactions that appear to be forms of play but serve as preparatory training for adulthood. These interactions are critical for learning dominance behaviors and social ranking.

Types of play-fighting in young Elephant Seals

Juvenile males (and occasionally females) engage in structured play that mimics adult battles but is significantly less violent. These interactions include:

• Mock Charges – Young seals lunge at each other but rarely make contact.
• Neck Wrestling – They push against one another, trying to overpower their opponent.
• Open-Mouth Displays – Gaping and mock-biting are common intimidation behaviors.
• Mimicked Vocal Threats – While they do not yet have the full resonance of adult males, they practice the distinctive threat calls.
• Pushing and Shoving – Using their bodies and forelimbs, they attempt to unseat their opponent.

These play interactions are highly structured and appear to follow social rules. The “loser” of these juvenile contests often submits by retreating or flattening their body against the ground to signal non-aggression.

While these activities are common in both sexes, males are significantly more engaged in them, indicating that these behaviors serve as early training for future dominance battles.

Adult male aggression

Dominance and polygyny

Elephant seals are among the most sexually dimorphic mammals, with adult males reaching up to 4,000 kg, whereas females rarely exceed 900 kg. This extreme size difference is the result of intense male-male competition for access to harems. The breeding season (typically from December to March for M. angustirostris and from August to October for M. leonina) is when aggression among males is at its peak.

Hierarchy establishment

Male elephant seals operate within a highly competitive, hierarchical system:

• Alpha Males (“Beachmasters“) – These are the dominant bulls that control harems of up to 100 females.
• Beta Males – Subordinates who may challenge the dominant male or attempt to sneak matings.
• Peripheral and Satellite Males – These lower-ranking males remain on the outskirts of the colony and usually do not breed.

Combat and threat displays

Dominance battles among males are some of the most brutal in the animal kingdom. These contests involve:

• Inflated Proboscis Displays – The characteristic enlarged nose of the male allows for deep, resonant bellows that establish dominance and deter rivals.
• Roaring Contests – Males bellow at each other in a vocal duel. Often, weaker males back down without engaging in physical fights.
• Chest-to-Chest Clashes – If vocal displays fail, males rear up and slam their upper bodies into one another.
• Biting and Wounding – Serious fights involve deep gashes, puncture wounds, and torn skin. Despite their thick blubber providing some protection, severe injuries can lead to death.

Fights can last from a few minutes to over an hour. The dominant male asserts control by physically overpowering his rival, who will eventually retreat.

The behaviour of losers

When a male loses a dominance battle, his actions depend on his status and the severity of the defeat:

1. Submission – A losing male will often lower his head, retreat, and flatten his body to avoid further aggression.
2. Peripheral Positioning – Defeated males may remain at the edges of the harem, waiting for another opportunity to challenge.
3. Sneaky Mating Strategies – Some losers adopt a “sneaky” tactic, attempting to mate with females when the dominant male is distracted.
4. Exile and Wandering – Severely beaten males may leave the breeding beach entirely, recovering in solitude before attempting to challenge again in the next season.
5. Death – In some cases, males suffer fatal injuries from battle, particularly those inflicted on the throat and shoulders.

Older or permanently defeated males often abandon competition altogether, instead living in isolated areas or congregating with other non-breeding males.

Why did Elephant Seals become so large?

The extreme size dimorphism seen in elephant seals (males reaching up to 4,000 kg, while females rarely exceed 900 kg) is a result of both natural and sexual selection.

Deep-diving and energy efficiency

One of the main factors driving large body size was adaptation to deep-sea foraging:

• Large size reduces metabolic rate per unit of body mass, allowing for longer dives and greater energy storage in the form of blubber.
• Elephant seals routinely dive 500–1,500 meters deep in search of squid and fish, staying underwater for up to 2 hours.

This size advantage allowed them to exploit food sources unavailable to smaller marine mammals.

Sexual selection and competition

The enormous size of males is not just for survival. It is a direct consequence of intense competition for mates.

• Elephant seals evolved a polygynous mating system, where a single dominant male mates with dozens of females.
• Males that were larger, stronger, and more aggressive had higher reproductive success.
• Over millions of years, this led to runaway sexual selection, favouring massive body size and hyper-aggressive behavior.

Why are male Elephant Seals so aggressive?

The extreme aggression of elephant seals is primarily due to their reproductive strategy, which is based on male dominance and harem defense.

High-stakes reproduction

• Elephant seal males have one of the most skewed reproductive ratios in mammals.
• In a given breeding season, only a small percentage (~5%) of males will mate, while others never reproduce.
• Since mating success is monopolised by dominant “beachmaster” males, intense aggression and violent combat evolved as the primary means to secure reproductive opportunities.

The evolution of ritualised combat

Male aggression is not random. It follows highly ritualised patterns that evolved to minimise unnecessary injury while still enforcing dominance. This involves vocal threats, posturing and displays, bite-based battles, and loser submission.

These behaviors are the result of millions of years of selection pressure, where only the most aggressive, dominant males left offspring.

Aggression in females: a different evolutionary path

While male elephant seals are famous for their aggressive dominance battles, female elephant seals exhibit distinct social and aggressive behaviours of their own. Their comportment is shaped by factors such as breeding, pup-rearing, social hierarchy, and interactions with dominant males. Unlike males, female aggression is often centered on maternal investment and intra-sexual competition rather than mating access.

Social structure and hierarchy

Female elephant seals live in harems controlled by a dominant alpha male during the breeding season. However, within these harems, females have their own social hierarchy. Although not as violent as male interactions, female competition can be intense.

• Dominant Females (“High-Ranking”) – Older, more experienced females often have priority access to better pupping spots and show greater aggression toward lower-ranking females.
• Subordinate Females – Younger and smaller females occupy less favourable positions and are more likely to be displaced by dominant females.
• Peripheral Females – Some females remain on the edges of harems, sometimes to avoid male harassment.

Hierarchy among females is primarily determined by age, size, and prior breeding experience.

Aggressive behaviour among females

Although less dramatic than male-male fights, female elephant seals engage in aggressive encounters, particularly in high-density breeding environments.

Forms of female aggression

• Threat Displays – Females use open-mouth displays and vocalisations (high-pitched screams) to assert dominance or warn intruders.
• Biting and Body Shoving – Direct physical confrontations occur when females dispute space, often leading to superficial wounds.
• Maternal Aggression – Nursing mothers are particularly aggressive toward intruding females or threats to their pups.

Most aggression among females arises from competition over:

1. Space in the Harem – Closer proximity to the centre provides more protection from the elements and dominant males.
2. Pup Defense – Mothers actively fend off other females that come too close to their young.
3. Food and Resting Sites (outside of breeding season) – While at sea, females are generally more solitary but may compete over resting spots.

Unlike male fights, female conflicts are usually short-lived, with the loser quickly retreating.

Mating and male interactions

Male harassment and avoidance strategies

• During the breeding season, females are often subjected to forced copulation by males, particularly lower-ranking ones who cannot secure a harem.
• To minimise harassment, females may use group positioning, staying close to dominant males for protection from sneaky males.
• Some females attempt to escape forced mating by moving toward the water, though this is rarely successful.

Estrus and mating Behaviour

• Females come into estrus about three weeks after giving birth.
• They generally have little control over mate choice, as the dominant male dictates breeding.
• If an alpha male is preoccupied, subordinate males may seize mating opportunities.

Maternal behaviour and pup rearing

Elephant seals have an extreme maternal strategy characterised by intense but short-term care.

Maternal investment

• Females give birth to a single pup per year (twins are rare).
• They nurse their pups for about 3–4 weeks, during which time they do not leave to feed, relying on stored fat reserves.
• During this period, they lose up to 40% of their body weight.

Maternal aggression

• Mothers aggressively protect their pups, lunging at intruding females or overzealous males.
• If an orphaned pup attempts to nurse from another mother, it is usually rejected aggressively.
• Occasionally, “supermothers” will adopt an abandoned pup, but this is rare.

Weaning and abandonment

• After the brief nursing period, the mother abruptly abandons the pup, leaving it to fend for itself.
• The weaned pup joins a “weaner group”, where it learns social behaviours through play-fighting and vocalisation.

Behaviour outside the breeding season

Unlike males, which spend months fasting and fighting for dominance, females spend most of their lives at sea.

• Solitary Deep-Diving Foraging – Female elephant seals travel vast distances to feed on squid and fish.
• Minimal Aggression at Sea – Unlike their breeding-season behavior, females generally avoid direct competition while at sea.
• Navigation and Site Fidelity – Many females return to the same breeding beach each year.

Competition for breeding space

• Harem areas are limited, and females must compete for prime pupping spots.
• Older, dominant females displace younger ones, leading to intra-female aggression.

Maternal investment and pup protection

• Since females only produce one pup per year, they evolved aggressive maternal instincts to protect their offspring.
• High female aggression toward intruding individuals ensures their pup has the best chance of survival.

Why didn’t other seals evolve the same way?

Elephant seals are unique in their combination of extreme size, deep-diving foraging, and highly aggressive mating systems. Other seals took different evolutionary paths based on their environments:

• Leopard Seals (Hydrurga leptonyx) evolved to be solitary apex predators.
• Weddell Seals (Leptonychotes weddellii) focus on cooperative group living.
• Harp Seals (Pagophilus groenlandicus) have a monogamous or promiscuous mating system, reducing male aggression.

Elephant seals’ evolution was driven by their need to monopolise resources and mates, leading to extreme aggression and size dimorphism.

This combination of evolutionary pressures resulted in the hyper-aggressive, hierarchical behaviour we see today. While it is an efficient strategy for reproductive success, it comes at a cost since most males never reproduce, and some die from fighting injuries.

Why do male Elephant Seals have a large, inflated nose?

The distinctive proboscis (enlarged, trunk-like nose) of male elephant seals is one of their most recognisable features. This exaggerated structure evolved through sexual selection and vocal communication as a key adaptation for dominance and reproductive success. 

The proboscis as an evolutionary adaptation

The proboscis of male elephant seals evolved due to the species’ highly polygynous mating system, where a small number of dominant males control access to harems of females. This feature provides several evolutionary advantages related to aggression, communication, and mate competition.

Acoustic amplification for threat displays

One of the primary functions of the proboscis is vocal enhancement. The large nasal cavity allows males to produce deep, resonant bellows that serve as a threat display to rivals.

• These vocalisations are low-frequency sounds that travel long distances.
• A larger proboscis creates a deeper, more intimidating call.
• Roaring contests often determine which male retreats before physical combat occurs.

Why is this advantageous?

• Males save energy by scaring rivals away instead of fighting.
• Stronger, deeper calls signal larger body size, preventing unnecessary battles.
• Sound transmission is particularly effective in crowded, noisy breeding environments.

Visual signal of dominance

The proboscis is a secondary sexual characteristic, meaning it evolved due to female preference and male-male competition.

• A larger nose signals higher dominance rank among males.
• Younger or weaker males have smaller, less developed noses, making it clear who holds social power.
• This allows rapid assessment of rivals without immediate physical conflict.

How did the proboscis evolve?

The development of the elephant seal’s proboscis is an example of sexual selection through male competition, similar to the evolution of antlers in deer or the mane in lions.

Sexual selection and runaway trait development

• Early elephant seal ancestors likely had smaller nasal structures.
• Over generations, males with larger, louder noses outcompeted others for mates.
• Females indirectly favoured dominant males, reinforcing the evolution of larger noses and deeper vocalizations.

This is an example of runaway selection, where a trait becomes exaggerated over evolutionary time because it gives an advantage in reproduction.

Hormonal influence on growth

• The proboscis only develops fully in sexually mature males (~3–5 years old).
• It grows in response to testosterone during the breeding season.
• Older males have more pronounced noses, further reinforcing social rank.

Why don’t females have large noses?

Female elephant seals do not engage in male-male combat or harem defence, so they did not evolve an enlarged proboscis.

• Female selection pressures favour smaller, more streamlined bodies for deep diving and energy conservation.
• Since they do not need to produce loud, long-distance calls, there was no evolutionary benefit to developing a large proboscis.

Do any other animals have similar adaptations?

Yes! Several species evolved nasal structures for dominance and communication, including:

• Proboscis monkeys (Nasalis larvatus) – Males have large noses that amplify vocalisations and attract mates.
• Walruses (Odobenus rosmarus) – Use deep bellows and tusks for male-male combat.
• Moose (Alces alces) – Have nasal chambers that help in vocalising during the rut.
• Saiga antelope (Saiga tatarica) – Have an enlarged nose that acts as a sound filter and temperature regulator.

These examples highlight convergent evolution, where different species develop similar traits for dominance and communication.