Revisiting Le Boeuf 1974

In 1974, Burney Le Boeuf published a paper in American Zoologist that described his field behavioural studies on the role of competition in determining reproductive success of elephant seals on Año Nuevo Island, California. Forty-two years after the paper was published I asked Burney Le Boeuf about the origin of this study, his recollection of field work and what we have learnt since then about seal reproductive behaviour. 

Citation: Le Boeuf, B. J. (1974). Male-male competition and reproductive success in elephant seals. American Zoologist, 14(1), 163-176.

Date of interview: Questions sent by email on 3rd August 2016; responses received on 27th September 2016


Hari Sridhar: Your early research was on rats and then on dogs. What was your motivation to start working on seals? At what stage in your career did you start this work?

Burney Le Boeuf: I was a graduate student in a lab at the University of California at Berkeley that conducted research in reproductive endocrinology (major professor: Frank A. Beach).  It was experimental and reductionist.  I did my thesis on dogs in a large outdoor enclosure that was halfway between the lab and the field, i.e., experiments in a rather natural setting.  As I completed my PhD work I became increasingly interested in fieldwork and functional explanations of behavior that put me on a track to evolutionary biology.  When I interviewed for an assistant professorship at the University of California at Santa Cruz, I was asked if I would be interested in studying the seal colony at Año Nuevo, about 30 km up the coast.  I answered yes, knowing next to nothing about seals.  When I visited the colony in December 1967, I was captivated.  I asked questions that could not be answered.  Males were fighting in the middle of a large group of females.  It seemed like a dominance hierarchy as had been observed and reported in barnyard chickens.  But dominance hierarchies were not considered important at the time because most studies were in the laboratory and males were forced to fight to produce a winner.  The hierarchy was contrived.  But it was obvious on first sight that the male elephant seals I observed exhibited something like a dominance hierarchy.  But one had to mark the males to really tell what was going on.  I immediately wrote a research proposal on male-male competition.  It was funded and I started doing fieldwork on elephant seals.  This was the beginning of a long-term project that lasted 40 years (it is still going under the direction of others; I am retired).  I started this project after a one-year post-doctoral position at the University of California at Davis, and one year after obtaining my PhD.


HS: Could you share with us the origins of this paper and the specific work presented in it? Was the work motivated by natural history observations?

BL: This research began during the 1967-1968 breeding season at Año Nuevo Island.  We marked males with paint or dye and recorded their threats, fights and matings throughout the breeding season.  We showed that individuals achieved status by fighting and stereotyped threat displays.  The higher the social status (dominance status) of a male the more frequently he copulated with females; 4% of the males in attendance copulated with 85% of females present.  The alpha male mated with more females than any other male.  We concluded that this was an extreme form of polygyny and that a social system such as this might have important genetic consequences for the species, especially if the same males dominated for multiple breeding seasons.  The paper was published in Science (1969 vol 163).

This paper (Amer. Zool. 1974, vol 14) was designed to determine whether the same males dominated breeding over multiple years.  That is, to determine how males maximized their reproductive success and just how extreme was the polygyny.  We marked and tagged virtually all males associated with the colony and recorded their behavior throughout six consecutive breeding seasons – 1968 through 1973.  The study revealed a number of things: 1) Less than a third of males mated; a few of them were responsible for the majority of copulations; 2)  Male reproductive success (RS) was limited by females present, males in competition and the setting; 3) As the harem size (number of females present) increased over the years, young males had a better chance to sneak occasional copulations; 4) Copulation frequency was highly correlated with dominance status; 5) Males copulated in 3 or 4 consecutive years; one male dominated mating for 3 years in a row (shown to be 4 consecutive years in a follow-up study) and most males died within a year or two of their most successful year of mating; 6) The RS of most males is nil because they die before reaching peak years; some mature, peak, reach old age and die without ever mating; 7) Males that achieve high status when females begin to come into estrus usually prevail for the entire breeding season, i.e., there are individual strategies that best position males to save energy and dominate and maximize breeding for the entire breeding season.  This study showed that males are under strong selection pressure to achieve high social status and breed with as many females as possible.  Elephant seals display a social system characterized by a high degree of polygyny.

The work was based on behavioral observations in a natural settings where interference from the observers was minimized, that is, what we recount and present is what the seals normally do.

I would add one more point.  There was a final paper in this series that measured lifetime reproductive success (see Le Boeuf and Reiter 1988 at the bottom of this piece).  Whereas the first paper showed what went on in a single breeding season, the second showed relationships over six consecutive breeding seasons, the last paper measured the reproductive success of both males and females during the course of their lifetimes.  It showed, not surprisingly, that males have more variation in RS than females; most males never mate; most females that live mate but only a few times.  Subsequent observations showed that a few females may live up to 22 years.


HS: Can you give us a sense of what fieldwork was like during this time – what kind of place did you stay in; did you mostly work alone (you mention Ron Whiting in the acknowledgements – who was he and how did he help); did you have a vehicle; what was a typical day like etc.?

BL: I conducted this research with the assistance of six undergraduates.  They were students in a class that I taught, Field Studies in Animal Behavior, the duration of which coincided with the elephant seal breeding season.  I trained them to read tags (from a blind) and observe the behaviors under study (who dominates whom, who fights and wins and loses, who mates, etc.)  With this crew, we made observations every day during the breeding season.  I spent every weekend on the island study site (Thursday or Friday to Monday) and lectured during the week.  We had bunk beds and cooking space in two buildings on the former, abandoned lighthouse on the island.  We carried in our own water and food.  We used an outdoor privy (with a great view).  We crossed the dangerous and harrowing channel in an Avon inflatable raft powered by a 15 hp outboard motor engine.  We got to the launching site in an old 4 wheel former military truck that John Wayne might have used.  Ron Whiting was one of the students that was very smart, intuitive and capable.


HS: You say these seals “breed on remote islands that are relatively free of human disturbance”. Does that still remain the case? Or have these islands changed a lot since this paper was published? When was the last time you visited Ano Nuevo island?  Do you continue to work there?

BL: Yes, these seals breed on remote islands relatively free of human disturbance.  It remains that way.  In the early years (1968 to 1975), the elephant seals at Año Nuevo bred only on the island.  In 1975, they started breeding on the adjacent mainland (and animal preserve and park) and soon the mainland colony surpassed the colony on the island in size.  The seals are protected from disturbance on the mainland by rangers; the mainland has become a popular seal viewing site (highly controlled).  I last visited the island five years ago.  I relish the time I spent there as well as on the various other island colonies in the range.  I still write about seals but I don’t get my hands dirty; there are younger others to do that.


HS: You say the seal population was “expanding throughout the study period” and the number of pups born annually has increased”. What has happened to this population since then? Does the tagging program continue even today?

BL: The northern elephant seal population continues to increase.  The entire population (US and Mexico) was estimated at 210,000 to 239,000 individuals in 2010 (see Lowry et al. Aquatic Mammals 2014, vol 40).  The elephant seal colony at Año Nuevo peaked in the mid-1990s and then started to decline before leveling off in about 2010.  The main reason is that immigration of females from southern California decreased because the females went to a closer new colony, Piedras Blancas (see Le Boeuf et al. Aquatic Mammals 2011, vol 37).  The tagging program continues today and is directed by my former student Dr. Richard Condit.


HS: Would you remember how long the writing of this paper took and when and where you did the writing? 

BL: No I don’t remember.  It took as long as was necessary to have the presentation come up to the data (which is always the challenge and the goal).  I wrote the paper at my computer at home or in my office.


HS: Did this paper have a relatively smooth ride through peer review? Was American Zoologist the first place this was submitted to?

BL: Yes, smooth ride through peer review.  Few changes.  American Zoologist was the first and only journal to which the paper was submitted.


HS: How was the paper received when it was published? Did you anticipate at all that it would have such a big impact on the field? Would you know what it mostly gets cited for?

BL: Well, I was proud of it.  I thought it was a great contribution to the literature.  It stamped me as an expert on elephant seals, a prime exponent of long-term field studies, and a key player in studies of social behavior and evolution.


HS: What kind of an impact did the paper have on your career and the future course of your research?

BL: Well, as I said it put a stamp on my career standing.  It helped me to get tenure at my institution.


HS: Today, 42 years after it was published, would you say the main conclusions still hold true, more-or-less?

BL: Yes, the conclusions still hold.  After all, this was a point in time.  What we reported was what was observed at this time.  If one went to the same site and repeated the study in 2016, the details would be different because the numbers and context is different, but the generalities would be the same.  There would be a high positive correlation between dominance hierarchy and mating success and relatively few of the males in attendance would dominate mating.


HS: If you were to repeat this study today would you do anything differently, given the advances in technology, theory and statistical techniques?

BL: I might use drones to census the animals and determine the presence or absence of individuals bearing tags or marks.


HS: You say “The factors which determine a female’s success in leaving progeny have not been studied systematically”. Has that happened since this study?

BL: Yes, a great deal of research has been done on what makes for female RS.  See the list of references at the bottom.


HS: In this paper you hint at individual personalities and behavioural syndromes in male elephant seals (e.g. time of arrival on rookery). Did you investigate this in more detail in subsequent research?

BL: No, I don’t think we added to this. It is pretty subtle and one has to spend a great deal of time on site observing to document this.


HS: Have you ever read this paper after it was published? If you compare this paper to papers you write now are there any striking differences?

BL: Yes, I have read and have referred to it many times.  Striking differences?  No.


HS: Among all the papers you have published, would you count this as one of your favourites?  If yes, why?

BL: I think it is among the favorites because of its importance at the time.  Also because the long-term data are solid and the interpretation is not based on vogue theory that is apt to change.


HS: What would you say to a student who is about to read this paper today? What should he or she take away from this paper written 42 years ago?

BL: I don’t think this paper is time-locked.  It could be done today on a remote island with a similar population of seals.


Subsequent papers by Burney Le Boeuf on seal reproductive behaviour

Costa, D. P., B. J. Le Boeuf, A. C. Huntley, and C. L. Ortiz. 1986. The energetics of lactation in the northern elephant seal, Mirounga angustirostris. Journal of Zoology, 209:21–33.

Cox, C. R. and B. J. Le Boeuf. 1977. Female incitation of male competition: a mechanism in sexual selection. The American Naturalist, 111:317–335.

Le Boeuf, B. J. and D. E. Crocker. 2005. Ocean climate and seal condition. BMC Biology, 3:9.

Le Boeuf, B. J. and C. L. Ortiz. 1977. Composition of elephant seal milk. Journal of Mammalogy, 58:683–685.

Le Boeuf, B. J. and J. Reiter. 1988. Lifetime reproductive success in northern elephant seals. In T. H. Clutton-Brock, editor, Reproductive Success, chapter 22, pages 344–362. University of Chicago Press.

Le Boeuf, B. J., R. J. Whiting, and R. F. Gantt. 1972. Perinatal behavior of northern elephant seal females and their young. Behaviour, 43:121–156.

Reiter, J., K. J. Panken, and B. J. Le Boeuf. 1981. Female competition and reproductive success in northern elephant seals. Animal Behaviour, 29:670–687.

Ortiz, C. L., B. J. Le Boeuf, and D. P. Costa. 1984. Milk intake of elephant seal pups: an index of parental investment. The American Naturalist, 124:416–422.

Reiter, J., N. L. Stinson, and B. J. Le Boeuf. 1978. Northern elephant seal development: the transition from weaning to nutritional independence. Behavioral Ecology and Sociobiology, 3:337–367.

Riedman, M. L. and B. J. Le Boeuf. 1982. Mother-pup separation and adoption in northern elephant seals. Behavioral Ecology and Sociobiology, 11:203–215.





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