Revisiting Petrie et al. 1991

In a paper published in Animal Behaviour in 1991, Marion Petrie, Tim Halliday and Carolyn Sanders showed, through an observational study, that: 1. mating success of male peacock was related to the number of spots on their tails; 2. the relation between mating success and number of tail spots was a result of female choice, i.e. females preferentially mated with males with a greater number of tail spots. Twenty-five years after the paper was published, I spoke to Marion Petrie about the making of this study and what we have learnt since about the tail of the peacock.

Citation: Petrie, M., Tim, H., & Carolyn, S. (1991). Peahens prefer peacocks with elaborate trains. Animal Behaviour, 41: 323-331.

Date of interview: Questions sent by email on 1^st July 2016; responses received by email on 21^st September 2016

 

 

Hari Sridhar:  In the Introduction of your paper you cite only three references. One is Darwin. The other two are studies that manipulated a male character and measured mating success. What role did these studies play in motivating your work?

Marion Petrie: Although Darwin first suggested that the peacock’s train had evolved as a result of female choice, no one had tested this idea. I was working at Whipsnade Park on a study of Chinese Water Deer, and, whilst staying overnight in the park, noticed the free-ranging peacocks displaying in groups (lekking).  I thought that it would be feasible to study the peacocks at Whipsnade (that it would be relatively easy to catch and mark them) and test Darwin’s hypothesis.  The beauty of a lek mating system is that the process of active female choice is directly observable.

HS: This paper has three authors. How did this group come together and what was the contribution of each author? Who did most of the writing?

MP: Tim Halliday held a lectureship at the Open University, which was the closest University to Whipsnade Park, and had an interest in mate choice.  I met Tim at a conference and talked about studying the peacocks at Whipsnade.  We wrote a grant application to the Natural Environment Research Council (NERC) to start the study together. This grant included provision to appoint field assistants for the breeding season and Carolyn Sanders acted as my most excellent assistant on the project. The paper was written after the field season and Carolyn was not involved with writing.  It is hard to recall exactly who wrote what, but looking through my files it looks like I produced a first draft which Tim then improved and added to. Tim is also a talented artist and drew all the lovely figures.

 

HS: What is the history of the “free-ranging, feral population of blue peafowl at Whipsnade Park”? When were peafowl brought there and what for?

MP: Whipsnade Park belongs to the Zoological Society of London, and I am afraid that I know very little about the history of the population of the peafowl, although it had been in existence for at least 40 years when I started working there. I know that peafowl born in captivity at London Zoo were brought to Whipsnade, and that Whipsnade provided a home for other peafowl from other sources. The keepers at Whipsnade sometimes caught and sold peacocks.  So my impression was that there were movements in and out of the population, and that this had been going on for some time.

 

HS: Have you ever had the opportunity to observe peafowl in their natural range?

MP: I have been to India twice for short filming trips during the peafowl mating season, and had the opportunity to watch peafowl there, although they were not ringed.  It was possible to observe a “lek” and courtship, and, although I didn’t see an actual mating, it was fairly easy to observe peacocks displaying close together in Sariska National Park. One of the aims of the filming trips was to film tigers and peafowl, so I also went to Ranthambore National Park. I can remember seeing peacocks in flight there…a fabulous sight!  Although I didn’t note any obvious differences in behaviour between Indian and UK birds, there was an obvious phenotypic difference: the peacocks in India tended to have longer legs, and, as a result, held their trains further up from the ground.

 

HS: What was a typical day like when you were doing this work? Did you do the trapping and banding and lek observations yourself? Who was Nigella Hillgarth, who you acknowledge “for help in marking and measuring the birds”?

MP: I don’t think I can describe one typical day because they would vary so much over the year. But some tasks would predominate at particular times of the year. I was heavily involved in catching birds in the months prior to the breeding season, and took all the measurements myself, whilst Nigella held the birds (to make sure the same person took all the measurements).  My memories of this was that it was very cold as we had a small unheated shed to work in, and under these adverse conditions, Nigella and I became great friends.  Sometimes we had large numbers of birds to process all at once, so we would work very long hours. At the time, Nigella was a PhD student working on pheasants in the Zoology Department in Oxford, and Bill Hamilton was her supervisor.  Nigella was interested in the ecto-parasites of peafowl, and as part of her work, we recorded the number of feather mites drinking at the eyes of the peafowl in a time period. Nigella and I are still in touch, and she is now the president and CEO of the New England Aquarium.

During the mating season, I was heavily involved in watching the birds. The lek watching started in mid-April and continued until the end of May; Tim and Carolyn also covered some of the watches.  The aim was to arrive at the lek early in the morning, before peacocks left their roost sites, and continue until the males stopped displaying, around the middle of the day. This could mean very early starts for me, as I was living in Norfolk at the time, and it was a 100 mile drive to the Park. We would watch from a small canvas hide, sitting on a small canvas chair, but sometimes we had to kneel to move round the hide, in order to follow females moving between males situated around the hide.  Watching the birds was extremely interesting and stimulating.  There was always something new to see, and many observations would make you ask ‘why are they doing that’? Some observations would provoke analyses that contributed to a paper.  An example of this was the observation that certain females would sit by particular males and engage them in courtship at times when another female tried to approach them.

After the mating season I was involved in data analysis and writing up, preparing to give talks at summer conferences, applying for grants and jobs!  This went on until Christmas and then the cycle would begin again.

 

HS: The observations ended in May 1988 and the paper was submitted on 8 July 1989. Can you give us a sense of what happened in the intervening one year?

MP: Whilst the observational work ended in May 1988 for this paper, we were still working at Whipsnade. In April and May 1989, I had four field assistants and we watched at four leks within the park.  After the end of the observation season in 1988 there was a period of analysis and writing the paper first for Nature and then for Animal Behaviour.  The referees requested changes so the paper needed to be revised before it was eventually published in Animal Behaviour On a more personal note my second child was born on 1st August 1989.

 

HS:  Was the term “hoot-dash” used for the first time in this paper? Is it still used when describing peafowl mating?

MP: No, hoot-dash was in the literature and is still used as far as I know.

 

HS: Was the photo in Fig. 2 of the “hoot-dash” taken in Whipsnade park? Was Chris Pierpoint a professional photographer?

MP: Yes it was, and Chris was one of the four excellent field assistants working in 1989 and was a very good photographer.

 

HS:  Did this paper have a smooth ride through the publication process? Was Animal Behaviour the first place you submitted it to?

MP: We first submitted the paper to Nature but it was rejected, so we rewrote the paper for Animal Behaviour.  Nature has a very strict word limit, so the first draft of the paper for Nature was a lot less expansive than the Animal Behaviour version.

 

HS: You acknowledge Morris Gosling and Robert Gibson for “comments on an earlier draft”. Could you tell us who these people were and how you knew them?

MP: Morris Gosling and I worked together on Chinese Water Deer at Whipsnade and on lekking in Topi in Kenya.  He is also my long-suffering husband.  Robert Gibson is a colleague who has done some outstanding work on mate choice and lekking in sage grouse.

 

HS:  How did the collaboration with Alan Grafen, for the female choice null model, come about?

MP: I gave a talk at the Zoology department in Oxford and presented the data on the sequence of males and females visited.  Alan attended the talk, came up to me afterwards and kindly offered to analyse the data as it is now presented in the paper.

 

HS: You say “a large part of the variance in mating success can be attributed to train morphology and that females choose to mate with those males that have the most elaborate trains of those sampled”. You also say “Our data do not suggest that competition between males is an important determinant of mating success”. Today, 25 years after the paper was published, do these statements still hold true for peacock mating behaviour?

MP: I do think that there is good evidence for these statements from the data that we collected at that time.  Whether it is ‘true’ for all peafowl everywhere is a different question, and whilst some studies have found the same positive relationship between train morphology and mating success, at least one Japanese study claims that no such relationship exists (although, they did find a non-significant positive correlation).  Of course, if females do not prefer peacocks with elaborate trains it does raise the question of why the peacock’s train has evolved, and I haven’t seen any good data that support any alternative hypothesis.

 

HS:  In the Discussion, you highlight many questions for future research – how females assess males, why do females choose males with more elaborate trains, what determines whether males obtain a display site, how do males choose leks – have these questions been addressed since? 

MP: I do think we are further ahead with these questions: how females assess males has been looked at in a nice study where the researcher attached eye-trackers to peahens and showed that peahens do look at the train.

Why females choose males with more elaborate trains formed the basis of much of my future peacock work, after the publication of this paper.  I removed peacocks from Whipsnade and bred from them in captivity.  This was a controlled breeding experiment, where each Whipsnade cock was mated with 4 females, and the subsequent eggs removed from pens and artificially incubated and hatched in separate compartments, so we knew the sire for all the offspring produced.  The young were reared in large groups and monitored regularly to record growth.  When the offspring were old enough, they were released into Whipsnade Park and we observed their subsequent survival and future behavior.  We found improved growth and survival of offspring of peacocks with more elaborate trains.

We also followed the male offspring of the release experiment through to sexual maturity and looked at where males started to display. We found that males would set up display sites close to their sibs or half sibs (even though they were not reared together). We also found from DNA fingerprinting that male leks in general consist of relatives.

 

HS:  Your study was entirely observational and with a small sample size (N = 10 males). Since this study, have you had the opportunity to repeat these tests with larger sample sizes and in an experimental way?

MP: Yes, I looked at the relationship between train elaboration and mating success in a much bigger sample from four lek sites.  I have also removed eye spots of peacocks and shown a change (reduction) in subsequent mating success.  This paper was published in Behavioural Ecology and Sociobiology but this has not been cited nearly as widely as the Animal Behaviour paper.

 

HS:  Did this paper create a buzz – within academia and outside – when it was published?

MP: My memory is that there wasn’t a huge amount of buzz around this paper, although it did get some attention. Other papers that I have published created a bigger response in the media, such as the paper in Nature 1994 showing evidence for improved growth and survival of the offspring of males with more elaborate trains.

 

HS: How important has this paper been in your career? Has it had a major influence on the course of your future research?

MP: I think that the peacock work has had a huge impact on my career and it was certainly critical in my obtaining a NERC advanced research fellowship which I held in Zoology at Oxford and which provided the wherewithal to do a further 5 years of pure research.

 

HS: Have you ever gone back and read this paper after it was published? When you read this paper now, what are the aspects about it that strike you first?

MP: I did have a look at the paper again recently, in response to your questions, and it does seem like something from a different era, where natural history and simple field observations were considered to be important.  Times have changed enormously in academia, and it is now extremely difficult to obtain money to do this sort of work.  This is a shame, to say the least, as there is so much that we don’t know about the natural world.

 

HS:  If you compare this paper to papers you write today, are there any differences, e.g. in writing style?

MP: I am not sure how my writing style has changed, if it has at all, but how you produce papers has changed.

As you become more senior in academia your job changes from being one where you do everything yourself (from collecting data to analyzing and writing papers) to one where you spend a lot of time applying for grants for other people to work as part of a team.  Your job becomes contributing ideas, reading other people’s work and contributing to that, rather than writing your own papers from scratch.

 

HS: Have you had the opportunity to go back to your study site after the paper was published? Are any of the birds you banded still around?

MP: I wrote a number of papers on peacocks after this one was published in 1991, and this involved doing several years more field work at Whipsnade. However, in 1996, I moved to a new post at Newcastle University, and once I moved to the North-East, it was logistically difficult to continue working at Whipsnade.  I continued to work on peacocks at a peacock farm in Norfolk.  I have been back to Whipsnade once, a few years ago, and saw very few peafowl.  Apparently, there was a big cull when there was an avian flu scare in the UK, as the keepers were worried that avian flu could be passed from the free-ranging peafowl to other animals in their collection.  I saw one of my marked birds, and it was begging at one of the restaurants in the park.  Flint pit paddock still exists, but it is no longer full of peacocks.

 

HS:  This paper has been cited 360 times (Google scholar) as of today. Do you keep track of these citations, and do you know what this paper gets cited for, mostly?

MP: I do not look at the citations of this paper very closely nowadays, but think it is usually cited as evidence for female choice. Although this is not universal, and in my experience, what people actually cite in a paper sometimes has more to do with what they are trying to say, than what you have actually said!

 

HS: What would you tell a student who is about to read this paper today? Any caveats? What should he or she takeaway from it?

MP: Probably the most important parts of the paper are the data on individual females.  These show two things: one is that females don’t mate with the first male that they approach; they always look at more than one male and this is very good evidence for female choosiness.  The second is that they mate with the male that has the highest eye-spot number of those visited.   This suggests that the male’s train has something to do with their choice, although it is not necessarily eye-spot number that is being assessed, and it may be something that is related to eye-spot number. It may also explain why males with relatively few eye-spots obtain matings (by being the best of those sampled), and that this doesn’t always result in a high correlation between train characteristics and mating success either within a lek or across several leks.

 

HS: Among all the papers you have written, is this your favourite?

MP: I wouldn’t say that this paper is my favourite. The first paper I wrote from my PhD work will always have a special place in my heart and that is Female moorhens compete for small fat males which was published in Science in 1983.