Cetacean Social Systems

environmental role in social behavior

behavior and availability of prey — solitary/small groups of prey is better for individuals or small groups to hunt; widely dispersed but clumped better for large groups

exposure to predators — large cetaceans are more solitary (bigger so less predation risk), inshore species are less exposed than offshore

space is more limited inshore

types of social systems in odontocetes

orcas (and pilot whales) — most stable groups, matrilineal, males leave to mate with females

sperm whales — matrilineal, alloparenting (care by nonparent), male nursey groups for 4-6 yrs then bachelor groups 21-28 yrs but sexually active males alone

bottlenose dolphins — fusion-fission, matrilineal bands, nursery groups of females with calves, bachelorette groups, males as pairs

spinner dolphins — fusion-fission groups

smaller species have less long-term, stable groups

types of social systems in mysticetes

usually solitary or in small groups

only associations usually during breeding or feeding

no real need for sociality to feed because of large size and eats entire school of prey

humpback whale exception — forms temporary social groups for cooperative feeding (think bubble nets)

fission-fusion school and which species use it

fusion — night, offshore feeding following the DSL

fission — separate groups, day, inshore resting

spinner and bottlenose dolphins

duration of reproductive cycle relationship with social system complexity

delayed maturity, long life span, long period of dependency, long gestation, long lactation, long inter-calf interval — long term groups for better calf care

longer reproductive cycle = stronger social structure

pilot whale and sperm whale — longest cycles and most complex

harbor porpoise and bottlenose dolphin — shorter cycle and less complex

differences between mysticete and odontocete reproductive cycles

odontocete — delayed maturity, long life span, long period of dependency, long gestation, long lactation, long inter-calf interval

mysticete — short gestation, short lactation interval, young weaning age, short inter-calf interval, higher milk fat than odontocetes

group cohesion through acoustics

communication

dolphins — signature whistle, individual, learned, broadcast identity, recognize others (mimic), males more similar to mothers because they leave

larger odontocetes (orcas) — pod-specific dialect, distinct pattern/call type/punctuation, codas (sperm whales, clicks in order)

leaps as means of communication to provide status/location

characteristics of dolphin signature whistles

unique, learned, permanent, females different from mothers and males similar to mom, mimic others