Bottlenose Dolphin

Males in some areas have been observed in continuous close contact with one (and occasionally two) other males. These males form strong bonds and their groupings are called alliances. Alliances have been observed to remain constant over 14 years. The primary objective of the alliance, and the probable reason for its initial evolution, is to gain access to females. Typically, an alliance will herd a female, either with or without force, and attempt to mate with her. These herding events can last from hours to a few weeks, with both males mating with the female. Researchers noted a preference among alliances for females that could be in estrus (neither pregnant or with young calves), although all types of females were herded (Connor, et al. 1992). Initial genetic tests conducted in Sarasota Bay, Florida, indicate that there is not a high degree of relatedness between males in these bonds. Males begin to form these bonds before they achieve independence from their mothers (Connor, et al. 2000). Living in a pair may have benefits other than mating for the male dolphins, as males continue to associate in alliances when not herding females (Connor, et al. 1992). Males that live in groups live longer lives than solitary individuals from the same area. Reynolds, et al. (2000) hypothesize that this increased longevity is not due to a decrease of predator attacks (pairs actually have a higher number of scars from shark attacks), but because the pair can work together, both to fight off a predator and to help each other recover. Although the alliances help both males, each individual is involved in the alliance for selfish reasons: increased mating potential and increased survivorship.

The male dolphins form two types of alliances: first-order and second-order. First-order alliances are the type described above, between two or three dolphins that form a stable relationship. Second-order alliances occur when two to three first-order alliances join together to cooperate against another, separate alliance. Typically, one alliance in the second-order coalition is attempting to either prevent a kidnapping or conduct a kidnapping from a third alliance. Researchers have two different hypotheses for the reasons behind second-order alliances. The first is that, by helping kidnap or protect alliance 1's female, alliance 2 will receive potential mating opportunities with this female while alliance 1 retains control of her. The second hypothesis is that alliance 1 will repay the favor at some point in the future, either by helping to kidnap or protect a female that alliance 2 is interested in. In four second order alliance kidnappings involving the same two first-order alliances, the first-order alliances alternated which pair kept the female. For example, during the first kidnapping that alliance A and B worked together, alliance A kept the female. During the second interaction, alliance B kept the female. These observations support the second hypothesis and indicate that this behavior may be an example of reciprocal altruism (Connor, et al. 1992). Dolphins do meet several other criteria necessary for reciprocal altruism (repeated interactions within a small group and symmetrical exposure to the situation). More research is necessary to determine if the second-order alliances meet the other criteria of reciprocal altruism (identification of cheaters and withholding benefits from those individuals).

BOTTLENOSE DOLPHIN (Tursiops truncatus) Social System: Fission-Fusion Society
Bottlenose Dolphin Home		Dolphin social organization has been described as fission-fusion by researchers, indicating "societies in which individuals associate in small parties that frequently change in composition and behavior" (Connor, et al. 2000). Groups stay in the same general area, but individuals within the community travel between groups. The movement is very fluid, with no set distinction between neighboring communities. These larger groups can contain more than 400 individuals, with the mean ranging from 5 to 140 individuals, depending on the area and the definition of "group" (Connor, et al. 2000). The primary hypothesis for the evolution of group society is the added protection that group living provides. Dolphins may attract more predators in groups, but they also have more individuals to warn of a predators approach and to fight off a potential predator (Connor, et al. 2000). Also, if a dolphin does become injured or ill, others in the group can help it recover (see epimeletic behavior) (Lilly 1963). The Moray Firth, Scotland, dolphin community provides an opportunity to test the predator hypothesis for the formation of groups because shark predators do not exist in this area. Such a study is currently in progress (Connor, et al. 2000). Within their larger community, dolphins typically associate in smaller, single sex subgroups (Samuels and Gifford 1997). Females and young groupings have smaller home ranges within the center area of the community, while males have larger home ranges on the outside area of the community. Females probably prefer to be close to the center of the group for added protection, while males possibly get additional mating opportunities by being closer to other communities. Both males and females tend to keep their natal area within their adult home range . Female subgroups, or bands, may have a relatively high degree of relatedness members(Connor, et al. 2000), although genetic information is unavailable in many areas where dolphins are studied (such as Shark Bay, Australia). In some areas, males form tightly bonded groups with one or two other individuals, called alliances (Connor, et al. 1992). Dolphins can form strong bonds within their subgroups, particularly between male alliances and mother-offspring pairs. Bonds are strengthened with petting and other contact. Socially bonded animals, particularly males, have been observed practicing synchronized behavior. Females will often surface in synchrony, while males may exhibit elaborate displays of jumps in synchrony (Connor, et al. 2000).
Basic Information
Social Systems
Social Spacing
Mating System
Epimeletic Behavior
References

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Biology Department
Biology Department		Despite their preference for remaining in a group, groups cannot stay together all of the time because the food source is both limited and widely distributed. Therefore, dolphins have evolved fission-fusion societies that attempt to maximize group time and provide ample opportunities to gather sufficient nutritional resources (Connor, et al. 2000). Occasionally, individuals are solitary. Researchers have offered no full explanation for these occurrences, only that interest in social behavior differs among individuals. Many of these solitary dolphins interact strongly with humans. An example is the solitary dolphin, "Pita," that lives off of the coast of Belize and actively solicits human interaction. Pita has exhibited both aggressive and sexual behavior towards humans and is advertised as a tourist attraction by some in the area (Dudzinski, et al. 1995).	Photo by David Hofmann. Used with permission.
Animal Behavior Homepage			Photo by David Hofmann. Used with permission.
	Male Alliances Males in some areas have been observed in continuous close contact with one (and occasionally two) other males. These males form strong bonds and their groupings are called alliances. Alliances have been observed to remain constant over 14 years. The primary objective of the alliance, and the probable reason for its initial evolution, is to gain access to females. Typically, an alliance will herd a female, either with or without force, and attempt to mate with her. These herding events can last from hours to a few weeks, with both males mating with the female. Researchers noted a preference among alliances for females that could be in estrus (neither pregnant or with young calves), although all types of females were herded (Connor, et al. 1992). Initial genetic tests conducted in Sarasota Bay, Florida, indicate that there is not a high degree of relatedness between males in these bonds. Males begin to form these bonds before they achieve independence from their mothers (Connor, et al. 2000). Living in a pair may have benefits other than mating for the male dolphins, as males continue to associate in alliances when not herding females (Connor, et al. 1992). Males that live in groups live longer lives than solitary individuals from the same area. Reynolds, et al. (2000) hypothesize that this increased longevity is not due to a decrease of predator attacks (pairs actually have a higher number of scars from shark attacks), but because the pair can work together, both to fight off a predator and to help each other recover. Although the alliances help both males, each individual is involved in the alliance for selfish reasons: increased mating potential and increased survivorship. The male dolphins form two types of alliances: first-order and second-order. First-order alliances are the type described above, between two or three dolphins that form a stable relationship. Second-order alliances occur when two to three first-order alliances join together to cooperate against another, separate alliance. Typically, one alliance in the second-order coalition is attempting to either prevent a kidnapping or conduct a kidnapping from a third alliance. Researchers have two different hypotheses for the reasons behind second-order alliances. The first is that, by helping kidnap or protect alliance 1's female, alliance 2 will receive potential mating opportunities with this female while alliance 1 retains control of her. The second hypothesis is that alliance 1 will repay the favor at some point in the future, either by helping to kidnap or protect a female that alliance 2 is interested in. In four second order alliance kidnappings involving the same two first-order alliances, the first-order alliances alternated which pair kept the female. For example, during the first kidnapping that alliance A and B worked together, alliance A kept the female. During the second interaction, alliance B kept the female. These observations support the second hypothesis and indicate that this behavior may be an example of reciprocal altruism (Connor, et al. 1992). Dolphins do meet several other criteria necessary for reciprocal altruism (repeated interactions within a small group and symmetrical exposure to the situation). More research is necessary to determine if the second-order alliances meet the other criteria of reciprocal altruism (identification of cheaters and withholding benefits from those individuals).

		Dominance Dominance interactions in bottlenose dolphins are not fully understood. There is a definite separation between the dominance hierarchies of males and females. All males are dominant over all females. Males appear to have a flexible dominance relationship, changing the hierarchy depending on the immediate situation. Aggressive interactions are common, but no common characteristics consistently exhibited by the winner have been determined. Female dominance is relatively stable and is based on age (and not body size) of the individual. Females do not usually display aggressive behaviors towards one another. When a new female is introduced to a group, interactions increase between females as the hierarchy position of the new female is established. Male/female aggression did increase during the spring and the fall. Though this initial study was conducted in captivity, it reflects behavior observed in the wild (Samuels and Gifford 1997). Dominance has been studied by observing interactions between individuals and recording which dolphin "wins" the interaction. Aggressive behaviors include both displays (such as threatening with an open mouth and jerky head movements and snapping jaw shut or pursuit) or contact (ramming (using rostrum or melon), hitting, or biting). Submissive postures include flinching and fleeing (Samuels and Gifford 1997). Researchers have also noted that more dominant dolphins are closer to the surface of the water than less dominant dolphins(Gubbins, et al. 1999), possibly because of decreased predation at the surface of the water.

This webpage was completed by Wendy Adams in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester of 2002. For comments and questions, please email at vecase@davidson.edu