Why Do Adult Males Form Pair Bonds?
By Edward Owen, PhD

Male pair Racing Stripe and Otter in Sarasota Bay 12 July 2001. Paired males are often synchronous in their surfacing patterns.

In December 2003, I completed my dissertation through the Ocean Sciences Department at the University of California, Santa Cruz under the guidance of Dr. Randall Wells. The focus of my research was to understand why adult male dolphins form pair-bonds. These pair-bonds are extremely strong, second only among the Sarasota dolphins to mothers and calves in the amount of time individuals spend together, and they are the longest lasting relationships in the Sarasota dolphin community. One pair of males, Norman (FB26) and Jimmy Durante (FB48) were pair-bonded for at least 22 years! During the course of their lifetime, the majority of males form pair-bonds, typically with a similar-aged male (within 4 years).

With geneticist Dr. Debbie Duffield at Portland State University, I investigated how related these pair-bonded males are to one another by comparing their DNA, extracted from blood samples taken during the health assessment program. We wanted to know whether kinship could be used as an evolutionary explanation for pair-bond formation. We found that while some pairs form between close kin (half-brothers), on average, pair-bonded males are no more likely to be related to their partners than to males which are not their partners. Factors other than kinship, such as having a previously established social relationship with a prospective partner and being close in age, seem to be more important when selecting a partner.

Another component of my research was to use both data that I collected and long-term data-sets maintained by SDRP to test hypotheses regarding the function of the pair-bond. It has been hypothesized that males may form these bonds: 1) to increase access to females for mating or 2) to provide other ecological benefits such as enhanced foraging success through cooperative foraging or increased predator detection and protection. I found evidence that one of the advantages of having a partner is being able to stay close to a female for a longer period of time, which in all likelihood provides more mating opportunities. Males in pairs may be able to do this because they can act in a coordinated fashion to better control female movements and guard her against other males (see photo). I also found some evidence for enhanced predation detection and protection and for enhanced foraging ability (although more data are needed to explore these benefits further). Thus the data strongly suggest that males form pair-bonds to gain greater access to females for mating, and they may also gain additional ecological benefits from these relationships.

This work has important conservation implications because it enhances our understanding of the mating system of bottlenose dolphins. Though captive breeding success has improved dramatically in recent years, success has not been universal. Information on male breeding patterns leading to their reproductive success is crucial for developing optimal breeding situations in captive colonies, thereby reducing pressure for collecting from wild populations, and for evaluating probabilities for replenishment of depleted stocks.

This work has been supported by NOAA Fisheries and the Disney Wildlife Conservation Fund.