This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

Contribute Thoughts | Search Serendip for Other Papers | Serendip Home Page

Biology 202
2004 First Web Paper
On Serendip

Alliance Strategies in Bottlenose Dolphins

Emma Berdan

Dolphins have long been considered some of the smartest animals next to humans. They exhibit complex behaviors such as: social hierarchy, formation of alliances, what appears to be suicide(1) and cooperative behavior.(2) This paper will deal with alliance formation in particular. Why do dolphins form these alliances? Is it simply helpful for survival or is it more complex? How do these alliances compare with human behavior?

Researchers have been studying the bottlenose dolphins (Tursiops sp.) in Shark Bay, Western Australia for quite a long time because they are tame. They have observed male-male alliances that seem very stable. Male alliances are usually groups of two or three males that can last many years. The association coefficient for some pairs of males is in the same range as those found for mothers and their nursing calves(3).

So why do males form these alliances? The answer seems to greatly reflect human behavior: to get women. Male alliances typically "herd" females for anywhere from a few minutes to months(4) These herding events are not usually enjoyed by the females. Herding is often forcible with escape events and violence involved.(3) In a herding event males will surround the female or chase her. Aggression toward the female is common and can include: hitting with the tail, head-jerks, charging, biting, or body slamming.(3) Should the female try to escape, which often happens, the males will chase her more often than not. Of course the ultimate goal of a herding event is sex and the males in the alliance will take turns to make sure everyone has an equal share. If the alliance has three members, only 2 will herd the female and the third will stay behind. However, the individual who is left behind changes with every herding event so again all members have an equal chance at mating. (3)

What has just been described is a primary alliance. However, bottlenose dolphins also form secondary alliances. Once again these are between males.(3) Let us say we have a primary alliance A consisting of 2 males. They may have a secondary alliance with another primary alliance B which has 3. Now there is a third primary alliance that is not affiliated with A or B called C which has 3 males. If C has just herded a female that alliance A or B wants then A and B will join together and forcibly take that female.(3) If A or B took on C alone it is unlikely that they would succeed because they would be evenly matched. But if they work together then its 5 against 3 and the secondary alliance will succeed. Both primary alliances do not mate with the stolen female. Perhaps alliance B will claim her this time but this means that next time alliance A will get the female.(3) Again we see equal sharing of the "spoils". Now in a reverse situation let us say that perhaps alliance C has come to reclaim their female from alliance B. B will call upon A and A will help defend the female from alliance C. (3)

I will briefly touch on the third type of alliance, the super alliance.(5) A super alliance is made up of stable alliances and labile alliances.(5) Stable alliances are like the primary alliances described above. Labile alliances are ones in which males change partners frequently. The observed super-alliance consists of 14 males. Each male of the alliance has 5 to 11 alliance partners from within the super alliance.(5) Although theoretically the males should have no preference of one male over another for alliance formation, in reality there are preferences and avoidances.(5) The super alliance is another example of the social complexity found in these dolphins.

We know the dolphins form these alliances to get women but are they looking for sex or to reproduce? Alliances are likely to herd non-pregnant females that are likely to be in estrus.(3) So we can assume that although fun may be had, the overall goal is reproduction. Since there is equal sharing of the female, according to the theory of fitness we would expect males in an alliance to be related. If the males are related, than a member of the alliance would increase his own fitness when one of the other alliance members took their turn with the female. Research shows that males in a primary and secondary alliance are likely to be somewhat related.(4) However, males in a super alliance are not usually related at all.(5) Why then would a male choose to be in the super alliance? One answer could be that since the super alliance is so big they can basically take on all of the primary and secondary alliances and steal many females. Therefore the males in the super alliance would have more access to females. Perhaps that would make up for what fitness is lost by not allying with related dolphins.

Do these revelations mean that dolphins may be closely related to man on an intelligence level? We can definitely say that dolphins have complex social structures. In fact, nested alliances are quite rare and are really only found in dolphins and humans. Also, a lot of the dolphin social behavior and structure is similar to primates, which again suggests that dolphins are close to the human intelligence level.(5) But let us look at relatedness of these alliances with human society. In human society both males and females do form alliances with each other(friendships) and these alliances can last for long or short periods of time. In dolphin society it's only that males that form these alliances. In human society one of the many things that these alliances do is approach members of the opposite sex. The same is true in dolphin society except that dolphins often approach the females aggressively, while the same behavior in humans(gang rape) is much less common. In dolphins, alliances that go after females are likely to be related, in humans this is less common.

Finally, the last issue I will address is the idea of sex for fun. In my opinion, an animal that has sex for purposes other than reproduction is probably more likely to be related to humans intellectually. Earlier I stated that alliances are more likely to herd non-pregnant females. So reproduction is one of the goals. But it has been proven that dolphins do enjoy sex. Dolphins have been recorded having homosexual sex and there is no chance for reproduction there.(6) So perhaps the dolphins in the alliances are also having sex for fun but since they don't have the worries of fatherly duties they may as well have sex with non-pregnant females.

In conclusion, dolphins are remarkably social, intelligent, and complex animals. Their social complexity indicates that they may be near the intelligence plane of human beings. I think that the more we study these animals the more we will realize that they are closer than we think.


References

1)Dolphin fact page

2)Seaworld Bottlenose Dolphin Fact Sheet

3)Connor, R.C., Smolker, R.A, & Richards, A.F. 1992a Two levels of alliance formation among male bottlenose dolphins (Tursiops sp.). Proc. Natl. Acad. Sci. USA 89:987-990

4)Krutzen et al. 2002 Contrasting relatedness patterns in bottlenose dolphins(Tursiops sp.) with different alliance strategies. Proceedings of the Royal Society of London series B. 270:497-502

5) Connor, R.C., Heithaus, M.R., & Barre, L.M. 2001 Complex social structure, alliance stability, and mating access in a bottlenose dolphin 'super-alliance'. Proceedings of the Royal Society of London series B 268:263-267.

6)Gay Marine Animals


| Course Home Page | Course Forum | Brain and Behavior | Serendip Home |

Send us your comments at Serendip

© by Serendip 1994- - Last Modified: Wednesday, 25-Feb-2004 09:37:25 EST