Social Structure and Behavior

Social Structure and
Behavior of
Marine Mammals
Group living
Evolution of social behavior has been
shaped by a number of factors
Where they give birth

Where they forage
What they eat
Predation risk
Level of sociality in marine mammals

varies considerably among taxa and may
vary with season as well
Costs and benefits of groups

Benefits
Reduced risk of predation through a variety of
mechanisms
Reduced risk of non-socially transmitted parasites
(remember the cookie cutter shark)
Cooperative foraging
Increased access to food or space
Reduced male harassment (e.g. southern sea lions)
Costs
Parasite transmission
Increased competition for limiting resources
Geographic vs Social Philopatry

Unlike many mammals, both male and female
marine mammals, especially odontocetes, may
remain in locations where their mothers are
In male bottlenose dolphins, philopatry is
geographic they rarely interact with mothers
Male killer whales exhibit both they remain in
natal areas and stay with natal group for life
Land-breeding pinnipeds may show strong
breeding-site fidelity but not necessarily familybased interactions
Social relationships
Based on pattern of interactions between
individuals over time
Individuals have relationships with other
individuals; the network of relationships results in
a social structure
Even solitary species have relationships
Maybe aggressive interactions with individuals in
adjacent territories
Social bonds are relationships that include
consistent affiliative component
Bonds are a social tool for increasing
reproductive success
Bonds may vary with ecological conditions, age,
sex, social position, and tactics of other individuals
Affiliative behaviors
Used to strengthen bonds, repair damaged ones,
or reduce tension, or obtain needed service
Dolphins in Shark Bay (and other odontocetes)
Petting, fin overlaps, rubbing
Synchronous surfacing events
Greeting ceremonies when killer whale pods
unite
Affiliative behaviors reported in species without
bonds
Nuzzling in male manatees
California sea lion males maintaining physical
contact or prolonged side-by-side swimming
Aggression and agonistic displays

Wide variety of vocal and physical threats including
growling, opening mouth, jerking heads, lunging, and
charging
Male California sea lions shake heads side to side
vigorously while Stellers males shake up and down
Pop vocalizations of male dolphins in Shark Bay
Jaw claps, bubble blowing also common
May escalate into physical conflicts of biting and ramming
Tusks and modified teeth (e.g. beaked whales) for
combat
In many species, blows to the body are more lethal and
fatalities occur with no external injuries
Sociosexual behavior
Non-conceptive sexual behavior common in birds and
mammals
Reported from northern fur seals, manatees, right whales,
and many odontocetes
Some delphinids may rival bonobos
T. aduncus in Shark Bay

Many combinations observed, most common in immature
individuals
In adult males, may involve affiliate behaviors or
dominance interactions depending on context
Group Formation
Most obvious phenomenon of social life
Occur in groups with individuals moving in coordinated
fashion and maintaining little interindividual distance
Groups imply that individuals of a species come together
to derive benefits from interactions resulting to proximity
Groups may serve social foraging, predator avoidance or
defense against predators
Group Formation in Cetaceans
Groups of Cetaceans
Pods closely spaced and close-knit groups of cetaceans
Schools large aggregations that appear to coordinate their
movements for long periods
Whales
Predation by large sharks and killer whales is one important factor

for group formation in whales and dolphins
Scarring is an evidence of predation
Spotted dolphins benefit the most from this protection and may also
benefit from group foraging
Effects that play a role in the protection of an

individual by a group
Dilution effect
Reduces the chances of an individual to be attacked by a
predator who has noticed the group
Confusion effect
Many individuals rushing back and forth through the visual
field of an attacking predator
Geometry of the selfish herd
Animals in the middle of a group can in effect use other
individuals around to shield them from predators as there are
others geometrically closer to the predator attacking them
Uses other members for protection
May also partly protect individuals against PARASITES
The advantages of grouping using the abovementioned do not depend
on individual recognition or social bonds among individuals in a group
but also in a totally anonymous group.
Advantage of gaining protection in the group will be counteracted by
increasing food competition among individuals of a large group which
determines the upper size of the group
Killer Whales
Groupings offers additional option to defend smaller,
more vulnerable individuals against predators by
taking them in the middle of the group
Involves bonds between individuals in a group
Individuals defending each other are kin to each other or it
may represent mutualistic cooperation
Advantage of groupings to a predator

Small groups (3) are more efficient in detecting and
catching prey than single animals or duos
Competition is less than in a large group
For more evasive prey, larger groups may be successful
because more animals are better at intercepting prey
Intentional Stranding
Lunging
Deep Diving

Social Structure and Behavior

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Social Structure and Behavior

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Social Structure and

Where they give birth

Level of sociality in marine mammals

Costs and benefits of groups

Geographic vs Social Philopatry

Aggression and agonistic displays

T. aduncus in Shark Bay

Group Formation in Cetaceans

Predation by large sharks and killer whales is one important factor

Effects that play a role in the protection of an

Advantage of groupings to a predator

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