The Bottlenose Dolphin

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The Bottlenose Dolphin

• Social Relationships in a Fission-Fusion Society
  (91)

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General Information

• Tursiops Truncatus
• Found in temperate and tropical waters worldwide
• 2 longest-running field studies in Sarasota Bay,
  Florida and Shark Bay, Western Australia
• Fission-fusion grouping individuals associate in
  small groups that change in composition, often on
  a daily or hourly basis -May depend on the
  social context whos there and whos not
• Intra- and interpopulation variation in foraging
  techniques -Use of tools

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Appearance

• Medium-sized delphinid
• Slate gray to charcoal
• Speckles- increase in coverage and density with
  age after sexual maturation
• Regional variation in body size -Larger body
  size associated with colder water temperatures

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Systematics

• Two main questions
• 1) Whether there are several species or
  subspecies of Tursiops or a single species,
  Tursiops truncatus with marked geographic
  variation -2 separate species
• 2) Whether the genus is monophyletic
• More complications- inshore versus offshore
  bottlenose dolphins- based on morphology,
  hematology, cranial morphology and parasite
  faunas -Found nuclear and mitochondrial genetic
  differences between near-shore and offshore
  populations in west North Atlantic

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Field Studies

• 1970s begin of longitudinal studies
• Recognition based on1) Scars2) Shape of dorsal
  fin
• Determining sex of individuals difficult
  because -Lack of obvious dimorphism -Ventral
  genitalia mammary slits are hidden from
  researchers therefore, sex determination
  limited to females because of consistent presence
  of small calf

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Field Studies

• Longest study 1970 identifiable individual
  dolphins across 4 generations (Sarasota, Florida)
• Mean group size 5-140 individuals -Variation
  attributed to differing definitions of group
• Use of different methods complicates our attempt
  to compare bottlenose dolphins across study sites
  

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Life History

• Bottlenose dolphins are long-lived -Females in
  Sarasota can live for more than 50 years and
  males for more than 40
• Females begin breeding at 5-13 years
• Age of maturity for males 8-13 years
• Sarasota females reach asymptotic length of 2.5m
  at age 10, males continue to grow -Reach
  asymptotic length of over 2.6m, and are 33-39
  heavier than females

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Reproduction

• After 12-month gestation period, bottlenose
  dolphins give birth to a single offspring that
  remains with its mother for several years -Young
  attempt to nurse up to age 3-5 in Shark Bay -3-4
  ½ in Sarasota -Duration of dependency can be
  considerably longer
• Differences in body size or nutrition levels may
  account for variation within and among habitats
• Health differences may also explain variation in
  the age at which females give birth

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Reproduction

• Mortality may be high for infants of primiparious
  females
• Exhibit diffuse seasonal reproduction with a
  single or bimodal birth season centered in
  spring/early summer and fall
• Tursiops is a spontaneous ovulator and seasonally
  polyestrous, producing 2 to 7 ovulations per year
• Cycle length estimated to be 30 days

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Feeding and Foraging

• Feed on a wide variety of fish, as well as some
  cephalopods (squid and octopus) and shrimp
  (sometimes)
• Often circle around fish schools, with one or few
  individuals at darting into the school to eat
• Often reported to swim upside down while chasing
  fish near the surface
• Georgia and South Carolina pursue prey onto mud
  banks and slide back into the water
• Stun or kill fish by whacking them up to 9m
  into the air with their flukes
• Arch their peduncles or lift their flukes as they
  dive increase the angle of descent as they
  travel to bottom
• Carry conical sponges over their rostra protect
  the rostra as they probe the bottom for prey

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Feeding and Foraging

• 1) Dolphins employ a diverse repertoire of
  behaviors during feeding that reflect variation
  in prey strategies to avoid detection or captures
• 2) May use both social and solitary feeding
  strategies
• 3) Variety of feeding methods underscores the
  potential for studies of individual foraging
  specializations in bottlenose dolphins,
  especially the role of learning of foraging and
  feeding techniques
• Most complete record of the feeding habits of
  bottlenose dolphins comes from the analysis of
  stomach contents of individuals caught
  incidentally in nets

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Predators

• Dolphins that survive shark attacks bear evidence
  of the encounter in the form of distinctive
  crescent-shaped scars -sharks might kill over 2
  of the Natal dolphin population annually
• 4 most common predators on dolphins were bull
  shark, dusky shark, tiger shark and great white
  shark
• Observed avoiding hammerhead sharks, too
• Killer whales may occasionally threaten coastal
  and offshore bottlenose dolphins

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Interspecific Associations

• Commonly found in mixed-species groups in pelagic
  waters -Of 40 of mixed-species groups were made
  up of bottlenose dolphins and short-finned pilot
  whales -Poorly understood relationships
• Variety of interactions between Atlantic spotted
  dolphins and bottlenose dolphins in the
  Bahamas -Contact behavior as well as sexual
  aggressive behaviors
• One of few mammals known to direct lethal,
  non-predatory aggression at other mammalian
  species -Harbor porpoises (play and competition
  for prey)

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Habitat and Group Size

• Dolphin species that inhabit more open, pelagic
  habitats generally form larger groups -Factors
  risk of predation in open habitats and a
  transition from solitary prey items on reefs or
  shallow sea grass beds to schooling fish in the
  pelagic environment
• Median group size 10
• In the Pacific, aggregations found in the
  thousands

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Day Range

• Day range is highly variable
• Sarasota dolphins typically travel within a
  40kim long home range at 2-5km per hour

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Home Range and Migration

• Sarasota Bay bottlenose dolphins are long-term,
  year-round residents of a home range of about
  125km -Includes shallow estuarine bay waters and
  channels inshore of a north-south series of
  barrier islands
• April-September concentrate in inshore waters
• Remainder of the year dolphins spend more time
  in the Gulf coastal waters

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Social Behavior and Communication

• Dolphins social interactions are repeated over
  days, months, and years
• We know this due to Observations of captive
  dolphins in the 1940-60s

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• Express affiliation by physical contact and
  synchronous movement
• Closely bonded males swim side-by-side less than
  a body length apart and surface at the same time
• Mothers and calves also do this
• Contact swimming one dolphin rests its pectoral
  fin against the other
• more passive form of behavior

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Dolphins in Monkey Mia
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• Active forms of behavior Stroking another
  dolphin with pectoral fin
• Rubbing against another
• Rub body part on another individual
• Occurs with closely bonded individuals
• I.e. mother and calf

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Socio-sexual Behavior

• This form is non conceptive
• Can mediate social relationships
• Serve as a communicative function
• I.e. mounting of one male by another to express
  dominance
• In Shark Bay male calves will mount older males
• Older males will mount calves
• Females pregnant and immature females mount
  other females
• Less common

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• Goosing rostro-genital contact
• One dolphin rubs rostrum in genital area of
  another
• Genital inspections (in Shark Bay)
• one animal brings rostrum close to, but not in
  contact with genital area
• -sometimes they echolocate
• -this might provide the dolphin with information
  about reproductive states

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Aggression

• Jaw clap rapid opening and closing of jaws
• Like a quick snap
• Example of this in one of the videos in class
• Head jerk involving rapid lateral or vertical
  jerk of the head
• I.e. Flipper

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Physical Violence

• Biting
• Tooth raking (less severe than sharks)
• Striking with rostrum, pectoral fins, peduncle
  and flukes
• Peduncle starts just behind the dorsal fin and
  ends where it meets with their tail fluke.
• aggression can include a number of these
  behaviors

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Fighting

• dolphins can face each other head-to-head
• Jerk their heads up and down
• Produce low frequency vocalizations
• Can escalate into fighting with biting and
  strikes
• Ram another with rostrum
• I.e. dolphin was ramming into Robin Williams
• In captivity dolphins have killed small sharks
  by ramming and striking them
• Harbor porpoises have been battered to death with
  this technique

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Displays

• Done on surface where easily observed
• Either sex can perform range of displays
• Can reflect excitement
• Slap part of body on water surface
• Rostrum
• Flukes
• Belly
• Side or back

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• Rooster strut done by single males or
  simultaneously by 2 or 3 males
• Done side-by-side
• Head arched above surface and bobbed up and down
• Butterfly 2 males around a female Males make a
  figure 8, forming wings
• Female is the body of the butterfly
• These vary based on size and shape of figure 8s
  and order performed
• Some complex displays are only seen once
• Scientists argue that males dont have set
  repertoire of displays
• These displays may function to advertise health
  and vigor to females and other males
• This is not seen in females
• But they do have synchronized surfacing  or
  breaths

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Association Patterns and Relationships

• Determining sex of individual is difficult
• Sex specific association patterns only in Shark
  Bay and Sarasota
• Used survey method researchers travel through
  study area and record groups during encounters
• Scientists recorded how many times 2 individual
  dolphins were found in the same party and how
  many parties there were.

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Female-female relationships

• Shark Bay and Sarasota
• Females have a large networks of association and
  are linked are to others in another area through
  mutual association or occasional occurrence
• Most females associate with a smaller group of
  other females in bands
• Within these bands, females with calves of
  similar ages tend to associate with each other
• Extended family Some females dont belong to any
  band
• Loners

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Female Sociability

• In Shark Bay and Sarasota
• Some females more solitary
• Others found in groups
• Scientists not exactly sure why
• It may be related to feeding strategies
• If a dolphin is spending a lot of time foraging,
  there is less time for socializing

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Hannah

• Downside
• Hannah was a solitary bottlenose dolphin
• She hung around bridges and places that other
  dolphins didnt frequent
• In 1989, her 5 month old calf was attacked by a
  shark
• Calf survivorship is related to group size and
  stability in Sarasota
• Females in bands have higher probability of
  successful rearing their calves

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Advantages

• Pros to living in bands
• Protection from sharks
• Bonds with other females
• Cooperation against harassing males

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Male-male relationships

• In Shark Bay
• 2 levels of alliance formation
• 1. Males in pairs and trios
• 1st order alliances
• Cooperation to consort with other females
• Very strong
• Some observed up to 13 years
• 2. teams of 2 or more alliances
• 2nd order alliances
• To take females from other alliances or to
  protect from these attacks
• More unstable
• Larger groups, with dolphins switching often

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• Alliance formation not as prevalent in Sarasota
  as in Shark Bay
• More solitary adult males in Sarasota
• No long-term adult male trios recorded
• In Shark Bay, males participate in attacks on
  rival alliances to help other alliances obtain a
  female
• This is not to get a female for themselves
• Why?

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Altruism

• Reciprocal altruism or pseudo-reciprocity
• Reciprocal altruism individual helps out another
  even if theres a cost
• Pseudo-reciprocity performed to increase chance
  of receiving benefits that are a by-product of
  selfish behavior of recipient
• So, even though another alliance has a female,
  they are still able to mate together when the
  alliances were together
• Just a theory
• Relations between alliance partners are both
  cooperative and competitive

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Male-Female Relationships

• In both Shark Bay and Sarasota
• Affiliations are strongly associated with a
  females reproductive states
• Association will increase when a female is
  cycling than during pregnancy
• Solitary males occupied smaller areas heavily
  used by female bands and were observed with more
  receptive females
• Males in pairs occupied areas far beyond those
  used by female bands and rarely observed with
  receptive females

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Herding Females

• Consortship can last from a few minutes to over
  a month
• females herded
• Often begins with a chase, aggression, or
  displays by males
• Male will either capture a female when alone or
  isolate her
• Consortship is over when female leaves
• Successful escape
• Swimming away with no reaction from males

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Herding Females

• Males may produce a distinct, low frequency pop
  to warm female to stay nearby
• Aggressive
• Head jerks
• Charges
• Hitting
• Travel behind the female or side-by-side and
  slightly behind her
• Aggression is not always observed, and perhaps
  not always needed
• Could also be a form of mate guarding
• males were also seen associating with females
  outside the Sarasota community

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Mixed Sex Groups

• Common in Shark Bay
• 50 of groups had males and females combined
• 31 of groups had males and females in Sarasota
• Males and females forage together
• Travel and rest together
• Basically a chance for male and female
  relationships to develop beyond courtship

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Shark Bay Dolphin and Calf
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Mother-Calf Relationships and Development
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• Sexual maturity Males 7 12 years of age.
  Females 5 10 years of age.
• Gestation period Approximately 12 months.
• Calf size Length 35 50 inches (90 130 cm).
  Weight 30 90 lbs (13.5 41 kg).

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Nursing

• Nursing process Female dolphins posses two
  mammal glands which produce a rich milk to
  nourish her young.
• Calf feeds on milk by placing its rostrum against
  one of the two mammal slits located on the
  ventral surface of the mother's body. It then
  cups its tongue around the nipple which lies
  beneath the mammary slit. 

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• A tight seal is formed between the calf's tongue
  and the mother's nipple.  The mother can
  physically eject milk into the calves mouth to
  help speed the nursing process.  This is very
  helpful since the whole process takes place under
  water while both animals hold their breath.    
• Nursing period Young calves may begin eating
  fish within a few months after birth, but may
  continue to nurse for 1 to 2 years or more.

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• Number of calves Normally one per pregnancy.
  Twin fetuses have been reported -- very rare and
  none are known to have survived.
• Maternal bond and experience are important to
  calf survival
• Infant survival is much lower with very young
  and/or inexperience mothers.

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Allomaternal Care

• In some circumstances other female dolphins
  provide care for a calf that is not their own.
• Leads to more successful rearing of the young.
• Helps inexperienced animals learn how to be
  parents. Research indicates that epimeletic
  behavior (care-giving behavior) is common among
  bottlenose dolphins.
• Group members often guard or physically help an
  injured dolphin. S
• Suggested (but not proven) that dolphins exhibit
  reciprocal altruism, manifested by mutual
  assistance in combat, in feeding, and various
  protective measures (Reynolds et al., 2000).

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The New Born Period

• Characterized by echelon swimming infant close
  and parallel to mother
• Respiratory synchrony
• Frequent rubbing and touching
• Behaviors decline over the first two months
• Gaining Independence

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Growing Up!

• First two weeks- most social interaction with
  mother, rubbing against head region
• Three weeks- display chin slaps , spyhops, jaw
  claps and belly slaps
• Several months for fishing
• May take years to be nutritionally independent
• Mother and calf about 10 meters apart

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Moments of Separation

• Mother separates with infant to get food
• 20 of their time with other immature
• Mann and Smuts 1993
• Coo and Smoo

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Mother-calf Communication

• Infants whistle depending on distance of
  separation more than duration of separation
• Under stress they both whistle
• In captivity high rate of whistling for both
• Help to identify identity, location, and
  motivational state of whistler

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Fission-Fusion Society

• Calves who separate more often from their mother
  have a higher rate of survival
• Separation allow infants to learn to hunt and
  socialize independent from their mother
• Immature dolphins spend most time in social
  groups
• 10 years as adolescents/adults

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Mating Strategies

• In most mammal, most or all parental investment
  is performed by the female pg 118
• Female invest in offspring
• Male invest in obtaining mates
• Herding
• 1) Force Copulation
• 2) War of Attrition
• 3) Females prefer multiple males
• 4) Prevent mating with other males or monopolize
  females females can escape to mate

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The Ecology of Social Relationships

• Female reproduction is limited by access to
  resources
• Male limited by access to mates
• Social groups may be focused on searching for
  food and maintaining social bonds
• Social bonds why individuals and populations vary
  in their patterns of bond formation

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Female-Female Relationships

• 1) vigilance
• 2) cooperative defense
• 3) male harassment
• 4) competition with other females over resources

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Male to Male Relationships

• Usually form pairs or travel alone
• Why form alliances?
• 1) Mating
• 2) Predators
• 3) Resources

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Individual variation

• Male alliances versus alone
• Being alone may have a better payoff
• More independence
• Alliances allow male to corner female

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Future Directions

• Most studied
• Conservation
• Pollution
• Boat traffic
• Commercial and recreation fisheries
• Habitat alteration

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• A Production by
• Eryn
• Shannon
• Lori