chapter 12: ecology of group living and social behaviour

group living

3 main ecological factors fro evolution of social behaviour

  • where they give birth - e.g. seal colonies

  • where they forage - e.g. deep sea / sperm whales: baby sitting

  • what they eat - abundant food (e.g. fin whales that feed on euphasiid (krill) prey)

benefits of living in groups

  • predation risk

    • individual avoidance at sea

      • elephant seals avoid killer whales by diving deep

      • nearshore dolphins, baleen whales hide in river mouths or surf zones or kelp beds

      • pigmy and dwarf sperm whale - reddish cloud to confuse predator

  • predation risk most important factor to build groups

  • dilute predation risks fro individuals, e.g. mixed dolphin groups

  • warning / alert others / defend against predators (e.g. sperm whales “margarite formation”)

margarite formation

  • non-socially transmitted parasites: dilution effect (cookie cutter sharks)

  • cooperative feeding (killer whales, humpback whales, dolphins cooperate with fishermen…)

  • environmental factors 8keep warm, protection …)

  • forced aggregations: when resources are clumped

    • individuals do not necessarily benefit from each other’s company

    • examples: belugas gather in warm tidal creeks during annual moult or pinnipeds are forced together on small haul out places

costs/risks of living in groups

  • risk of transmitting parasites socially (e.g. bacteria infections, parasite fish)

  • competition for limited resources (share food, haul-out places, mates…)

philopatry (the behaviour of remaining in, or returning to, an individual’s birthplace)

  • natal philopatry → returning to birth place, extreme in pinnipeds - territory of male northern fur seals rarely shift more than 10 m

  • sexually dimorphic philopatry: to avoid inbreeding (e.g. sperm whales - male dispersion)

    • “sexually” over here means that the males and females return to their birthplace differently

    • females return to their natal area

    • males disperse more widely, leaving their natal area to breed more elsewhere. This helps avoid inbreeding and increases genetic mixing

  • but most aquatic marine mammals have huge home ranges that overlap many conspecifics: differs between geographic and social philopatry

    • geographic philopatry → the tendency of animals to return to or remain in a specific geographic location for critical life events such as breeding, pupping, or nesting

    • social philopatry → the tendency of animals to remain within or return to their natal social group or social structure, rather than a geographic location

    • some geographic but not social philopatry:

      • bottle nose dolphins remain in their natal home range but rarely interact with their maternal relatives

    • both geographic and social philopatry:

      • killer whales - no dispersion of either sex, they interact with their relative throughout their life - but mate outside their kin group

social marine mammals

interactions, relationships, and social structures

affiliative (friendly) behaviour

  • strengthen bonds

  • mend damaged bonds

  • reduce tension

  • need service from another

  • dolphins / sperm whales

    • rub body parts, mutual stroking, fin touching, “greeting ceremonies” in killer whales, synchrony

    • but also skin / parasite removing

aggression, agonistic displays and dominance

  • growling, open mouth, head jerking, lunging, charging another

  • sounds: ‘pop’ sounds in dolphins, growls in seals

  • ‘toothrake’ marks from fights (male beaked whales, narwhal 3 m tusk (but mostly sensory organ), elephant seals)

  • headbutting (bottlenose dolphins, pilot whales)

  • but most non lethal, except infanticide / killing of harbour porpoises by bottlenose dolphins

  • agonistic interaction not necessarily aggressive

sociosecual behaviour

non-receptive sexual behavior

  • common in marine mammals: fur seals, baleen whales, toothed whales, manatees… for communication, relationships, bonding…

  • dolphins - bonobos

    • role dominance or affiliative behaviour / greeting, forming social bonds, conflict resolution and post-conflict reconciliation

    • alliances in male bottlenose dolphins - dominance /affiliative

  • test the social bonds

  • immature animals ‘play or practice of herding others’

female social structures

1. matriarchal groups

  • female leader in a groups with group members that are relatives and non-relatives

  • few examples in humans: the Mosuo culture, which is in China near Tibet

  • bonobos female groups within a fission-fusion society (type of social organisation where the size and composition of animal groups change overtime depending on factors like food availability, social needs, or reproductive status), sons inherit the status of their mothers, often life-long bonds

2. matrilineal groups

  • offspring line from one female, several matrilines can be in a group, that are either related (sister groups e.g. killer whlaes, pilot whales) or not (e.g. sperm whales and elephants)

  • example:

    • matriarch A has two daughter B and C

    • B has offsprings and eventually creates her own matriline

    • so B is the matriarch of her line

    • however B still has a matriarch, that is A

    • the same can happen with C forming another matriline.

    • this is how there can be multiple matrilines in a matrilineal group

3. matrifocal /matrilineal groups

  • one matriline with a female and her offspring, no offspring dispersal by neither gender: Bisexual philopatry - killer whales (single matrilines) and pilot whales (multilevel matrilines)

  • bisexual philopatry → both males and females of a species remain in or return to their natal area or group

  • matrifical groups → the social structure of a species group revolves around the mother and her offspring. the mothers are the cores of the group. They can help other whales take care of their offspring if the parent has to leave for a little to forage.

  • so a species can be both matrilineal and matrifocal

  • in summary:

    • matrilineal = who you’re related to through your mother

    • matrifocal = who the group revolves around socially - the mother(s)

bonding startegies in odontocetes

females bonded, males rove alone

sperm whale (elephants)

  • females: matrilineal (ca 10 individuals) stable groups in tropical areas but can split after 5-10 years (not all females are related)

  • cooperative offspring care, babysitting, communal feeding (allomothering)

  • males: bachelor groups / old males solitary

    • migrate away from females to higher latitudes to feed

    • mature later than females (delay breeding to become larger to compete with others)

    • rove alone around females, but bonds among younger males possible

roving male allinaces, weak female-female bonds

bottlenose dolphins and bottlenose whale:

  • fission-fusion societies (change in size and composition)

  • male-male bonds can last for a lifetime

  • male allinaces work alone or with other alliances to capture females

  • as strong as mother/offspring bonds

  • social female bonds - looser nertwork among several females

roving with natal kin

bisexual bonds in killer whales and pilot whales

  • matrifocal units (killer whales: 2-9 individuals, 1-4 generations mother and offspring; pilot whales: 60-200 animals, multi-level sister group)

  • natal philopatry of both gender

  • bonds between mother and sons strong

  • bonds between brothers - scouting/mating

  • bonds between sisters/mothers - offspring care

adoption of non-related animals

  • killer whales accept non-related animals, even feed them when ill or incapable. Special case in Norway an adopted orphaned handicapped female born 1995 seen with more than 5 different groups

  • crippled bottlenose dolphin was seen with sperm whales

  • iceland 2023: killer whales raised a long-finned pilot whale calf - adoption or abduction?

ecological factors in evolution of bonding strategies

  • females bear cost of parental care

  • female reproductive and bonding strategies determined by access to food and saftey from predators (some cases males: infanticide)

  • female philopatry (non social factors such as resource distribution and prey behaviour or social factors such as cooperative defence of offspring or resource

  • bisexual philopatry due to low cost of locomotion - large home and feeding ranges in which they encounter other non related mates, e.g. killer whales and pilot whales

  • cetecean offspring are followers, not tied to a breeding site

  • male mating and bonding determined by distribution of females but also presence of predators: bottlenose dolphins in scotland dont form alliances, shark predation is low compared to australia, where they form allinaces