Cooperative Hunting:

Schooling dolphins search for food together, but one they find their prey there are two methods they use to actually hunt. They can either spread out and hunt more individually or work cooperatively to school the fish together fore easier feeding. In one study, cooperative hunting was only observed in 6 of 94 feeding sightings, so it is not the most common hunting technique. However when group hunting was used, it was used repeatedly with 79 bouts in those six sightings. Schools of about 11 dolphins swim swiftly in a line abreast one an other towards the fish. Those dolphins at the ends of the line swim fastest and eventually encircle the prey in a large loose circle. All the cooperative hunters would swim towards the center of the circle synchronously until the circle was about 8-10m in diameter. This technique aggregates the fish into a higher density in a small area, making feeding easier. All would then feed for about 3 to 5 min, then reorganize for another encircling bout. Only certain dolphins were observed to use this hunting method. It was observed that dolphins captured encircled prey easily so this hunting method works, but may not be the most efficient method because it was utilized less frequently than solitary feeding (Rosenbach 1999).

 

Cooperative Mating:

Male dolphins are known too cooperate in order to mate. Kinship is generally the fundamental link that drives cooperation in animals through inclusive fitness. Helping ones relatives to reproduce is a means of getting ones genes into the next gene pool, although it is only sometimes beneficial for very close relatives due to decreasing degree of relatedness in diplo-diploid organisms. Genetic analysis of bonded males showed no patterns of relatedness. There was no preference to form bonds with maternal kin or other close relatives. Dolphins do have the ability to distinguish relatives through signature whistles which are maternally influenced and individual. The lack of brother-brother bonds is likely due to the long interbirth interval of at least 2 to 3 years. Male bonds generally form while the males are still infants and grow stronger as they reach maturity. Dominance between male dolphins is based heavily on age, size, and weight. A male dolphin who had to wait a few years to get smaller, weaker, but more related male to pair with would be at a disadvantage.

Male cooperation could be based upon mutualism or reciprocal altruism which both benefit unrelated individuals. If reciprocal altruism was the mechanism that drives males to form pair bonds, when they single out a receptive female, one should mate and the other should wait for his turn with the next female. This is not the observed case though. Males in coalitions have been reported to synchronously mount and mate with their isolated female. This suggests mutualism because both males get to mate with the female and are able to defend/prevent her from mating with other male groups so they effectively decrease the competition of their sperm to only their partner male (Moller 2001).

 

Allomothering:

Allomothering occurs when a dolphin takes care of another's offspring. Females of various ages baby sit infants or allow them to swim in echelon position beside them. This helping behavior can be rationalized by looking at it with a cost/benefit perspective from each of the three players, the mother, the infant, and the alleomother. To the infant, the costs of being allomothered include risk of disease, increased chance of predator attraction, and the risk of poor care under a possibly unskilled allomother. The infant benefits from the allomothering through hydrodynamic advantages that reduce the costs of speeding. The surrogate could defend the young from small predators. Just staying with a group and being in contact with an other individual for an extended period of time gives the infant a more varied social experience and improved social skills. The social skills and bonds are the greatest benefit to the infant.

Mothers have many of the same costs and benefits as infants do because the loss of their infant reduces their reproductive success. Mothers often agnostically interact with allomothers who try to take their offspring. The aggressive behavior needed to deter allomothering when it is not wanted is also a cost to the mother. This 'kidnapping' phenomena is called bolting wherein the allomother swims swiftly past the calf and the infant instinctually follows the allomother. Maternal aggression followed the bolting attempt every time for the first three days of the infants life. This could be an evidence for imprinting, allowing the infant a three day sensitive period.

Allomothers actively seek out other female's infants to mother so it is likely they benefit highly from 'babysitting.' Allomothers invest energy and risk agnostic encounters with the mother, males, and predictors. The benefits to the allomother vary with degree of relatedness and parenting experience. The escorts are more likely to be other infants or inexperienced females and were not necessarily related to the mother or infant. Experienced females only cared for others infants when the infants were close kin (Mann 1998). From a selfish behavior perspective this makes sense because the unrelated individuals gain needed parenting skills but females with experience benefit through kin selection by only helping their relatives.

Photograph courtesy of Captain Samone http://www.artfuldolphin.com/gallery/page2.html