Revisiting Møller 1988

In 1988, Anders Pape Møller  published a paper showing that male barn swallows (Hirundo rustica) with experimentally-lengthened tails obtained mates quicker that males with shorter tails. While this wasn’t the first experimental demonstration of the function of male secondary sexual ornaments, what made this study important was that it was the first in a monogamous species. Twenty-eight years after it was published, I spoke to Anders Møller about his motivation for doing this study, and what we have learnt about mate choice in barn swallows since then. 

Citation: Møller, A. P. (1988). Female choice selects for male sexual tail ornaments in the monogamous swallow. Nature, 332(6165), 640-642.

Date of interview: 9th July 2016

HS: This is not your first piece of work on barn swallows. You had, already at this time, done quite a lot of work on this species. Can you tell us how you got interested in them?

AM: Well, in actual fact, this year is the 46th year when I am studying these birds. It’s, almost, an embarrassingly long time I have dedicated to this species. But then, as you know, people in biology study all kinds of organisms for very long periods of time – Drosophila in animals, and for people who are studying plants, it is Arabidiopsis. I started getting interested in the behaviour of animals – free-living animals, outside the windows, in the real world – many many years ago. When I was studying biology at university, I was a little bit frustrated that there were so many people studying animals and plants in the lab, under conditions that might not have very much to do with the conditions under which they live in nature. So the motivation really was to try to understand how animals behave in the free world.

I have studied many different kinds of organisms over the years, because I can’t make up my mind. Different kinds of organisms are suitable for different kinds of questions. The reason why I study barn swallows, and why many other people have joined this effort, is because they are extremely abundant, very easy to handle, very easy to observe and very easy to catch. This might not seem like important advantages to a non-biologist, but, believe me, there are very few organisms where you can catch individuals and follow them throughout their lives. There are many organisms, including Drosophila, where you can’t do this. They might be the wrong size, or if they are the right size, you never see them again once you have captured and tagged them. In summary, I think you can even call it laziness, to choose a species that is easy to study. But if you want to get robust results you have to pick a model system that is easy to work on.


HS: Right from the beginning, was understanding the reproductive behaviour of this species one of your interests?

AM: Yes, already when I was a master’s student I was studying these birds. I grew up in the countryside. My father was a farmer and I was also a farmer for several years. And in the countryside there were swallows everywhere. In Europe, as well as in North America and Asia, it’s a species that signals the arrival of spring. There are many superstitions about this bird – if you don’t take care of this bird you can have problems of running your farm, your animals might die and so on. All these kinds of superstition.


HS: When did you get interested in sexual selection?

AM: This was around 1985-86, when I had just finished my PhD and obtained an assistant professorship at the University of Uppsala in Sweden. The way I looked at sexual selection in those days was very influenced by what Charles Darwin had written about it in his book about sexual selection. He emphasized that in species where males could attract one or more females, the males that were more adorned would have, on average, more mates and produce more offspring. This is easy to understand for a species like the peacock, but for a species like the barn swallow, which is socially monogamous, it’s more difficult to understand. If there is an even sex ratio in the population, which is usually the case, then there is a partner for everybody.  There is no variation in mating success and therefore you shouldn’t expect any traits to be exaggerated. If you look at barn swallows, with a few exceptions, all morphological characters are the same size in males and females. One of these exceptions is the length of the outermost tail feathers, which is considerably longer in males than in females, and also much more variable. The puzzle was that you have this exaggerated character but there appears not be to be much variation in mating success. How can this come about?


HS: What was your PhD dissertation on?

AM: I wrote a thesis on the costs and benefits of social behaviour in barn swallows. If you start studying this species you will notice that quite a few individuals are completely solitary – only one male and one female breeding in a particular site – and in some places you get 200-300 pairs breeding in one single barn. I was interested in finding out why there is this huge variation in sociality and what are the costs and benefits associated with that kind of behaviour.


HS: In the abstract of your paper you cite five references, four of which are theoretical papers. The fifth is Malte Andersson’s paper. Can you tell us about the influence of that paper on your work?  

AM: Yes, I can easily do that. As I said before, Charles Darwin said that in many species you can easily have exaggerated secondary sexual characters – exaggerated morphological traits, vocalizations, smells – because there is so much variation in male success. This was Charles Darwin’s intuition that led to this conclusion. Subsequently, there was not much done in this area. That’s really a strange feature of sexual selection – for decades and decades and decades nothing was done in terms of empirical research. And Malte Andersson, at the University of Gothenburg in Sweden, was the one who changed that. He had been to Kenya and he had seen widowbirds. Male widowbirds are almost as exaggerated as peacocks. They have extremely long tail feathers, which they display in flight. The females are smaller, inconspicuous looking birds, which take care of the offspring and build their nests in grass. These females, according to Darwin’s theory, should be most interested in males with the most exaggerated traits. What Malte Andersson did was to simply bring a pair of scissors and superglue and, by cutting off a piece of the tail feathers from some individuals and adding this to the tails of other individuals, change the variation in exaggeration of these traits. The prediction was very simple – you should have more females aggregating on territories of males with experimentally elongated feathers. This was what Malte Andersson was able to show, subsequently.

However, there were still some outstanding questions. And one of them was that if you go out and look at the natural variation in tail length of these widowbirds, you should find that individuals with naturally longer tails should be more attractive to females. But Malte Andersson was not able to show that in his field study. So, this was really a puzzle. You could manipulate these feathers and that would have a consequence for mating success of males, but then if you look at natural variation in length of males, there was no effect of tail length whatsoever. Malte Andersson writes about this, in one of the final notes in his paper, but it was still hanging in the air and it was kind of puzzling why there was this inconsistency in the results.


HS: Was your study aimed at examining this further?

AM: Yes, I had two objectives. One of them was to test what could be the mechanism behind the evolution and the maintenance of exaggerated secondary sexual characters in monogamous species. One solution to this problem was proposed by Ronald Fisher, who said that if it is the case that some individuals are in better condition than others – and there are many reasons for expecting that to be the case – then you would have some individuals that breed early and some that breed late. The ones that breed early should be the ones that are most attractive in the population. And therefore, for a monogamous species, one would expect an association between the degree of exaggeration of these secondary sexual characters and timing of breeding. So if you manipulate tail length the timing of breeding would change. The second objective was to measure the lengths of the outermost tail feathers and investigate if natural variation in this character was associated with timing of breeding. So that’s what I set out to do and I did it.  Of course, it’s much easier again to do this on barn swallows than on widowbirds. Malte Andersson did this in the field in Kenya where he was always surrounded by perhaps 200 locals, 75 to 100 of whom were screaming children. It was not an easy task. He doesn’t mention this in his paper, but he told me subsequently. I had a much easier deal. I rarely had more than one person attending these events. It was also easier in another respect – the barn swallow has only two exaggerated feathers so it’s much easier to make this manipulation.


HS: In the Acknowledgements, you also thank Malte Andersson for some advice on the glue you used to stick the feathers. Can you share with us what this was?

AM: Well, the glue we used was simply a super glue. Today you can buy this in any store anywhere in the world. Its glue that basically turns very hard as soon as it interacts with the air and so the feathers will never break in that particular spot. Sometimes feathers break in other places but that’s another story. I think like with most of these inventions, this glue was something that was invented by the military industry in the US. The brand we used was, I think, called Loctite.


HS: Was your sampling design different from Andersson’s?

AM: Well, in fact, if you read Andersson’s paper carefully, you will see that he really doesn’t measure reproductive success as the number of females that each male could attract. He went out to the field and recorded the number of nests in the territories of the different males. But if you have ever been to the savannah in Africa, you would have noticed that this is not an easy task to do. The grass is very tall and the nests are camouflaged and inconspicuous. And because of this it is very difficult to record accurately. Also, in Andersson’s design, he recorded the number of nests before he did the experiment, then he cut and glued the tail feathers and then, after some time, he went back to recount the number of nests in the territories. So his measure of success was the number of nests after minus the number of nests before. What I did was to manipulate the tail lengths of males and then record when the females were attracted to the territory. But I also recorded the exact date when these females started laying their eggs. So, in that way, I could show that if you elongate the tail feathers, the males and female partners started breeding earlier, because the females in better condition were attracted to these males with elongated tails. This has a strong consequence for reproductive success because, not only in swallows, but virtually in all different kinds of animals, those that reproduce earlier are more successful in reproduction.  In seasonal environments, at the end of summer if the offspring are not fully independent they will die. So you can only achieve high reproductive success by starting out early. In the barn swallow case the birds can produce from one to 3 clutches per year. But you can only do that if you start out early. For that reason, the males with elongated tails reproduce much earlier than those with shortened tails and this resulted in a more than two-fold difference in reproductive success.


HS: You did these experiments in a place called Kraghede in Denmark. What kind of a place was this? Do you continue to work there?

AM: Yes, this is the place where I grew up, so I know all the farmers in these farms since I was a small boy. In fact now I think none of those farmers who were there when I started this study are still around. Many years have passed and most of them have passed away.

Kraghede is not a particularly interesting place. It’s an open country site with a few farms and few trees around the farms. The swallows, as I said, breed mainly inside buildings and barns. Therefore they are very easy to catch. I catch them using mist nets. You can simply put the nets in the doors and windows and eventually you will catch all of them. As I said before, there is this advantage with this bird that, not only can you catch all of them, but if you are interested in measuring long-term consequences of these kinds of experimental manipulations, you can also catch all the survivors in subsequent years, because they return to the site where they were produced.


HS: Did you do all this work on your own or did you have people to help you?

AM: I often had some of my friends joining me, but usually, after some weeks, most people think it is too boring. In fact, for many years, I have always brought my children with me to the field. I remember, one morning some years ago, after we had been in the field for, I think, six or seven weeks in a row, my son Pierre standing outside the car and saying “Dad, I don’t want to see any more swallows!”


HS: How old was he?

AM: I think he was 4.


HS: What was being grown in these farms?

AM: Well, in the 70s and 80s it was mixed crops – grain and grass and hay for the cows and so on. But nowadays it is mostly wheat all over.


HS: Do you continue to work in Kraghede?

AM: I have just come back to Paris after spending six weeks in that site. I have just captured all the birds, found out where they were living , who has survived from last year, how many eggs they have laid, how many young they produced during the first clutch.


HS: 28 years after this study!

AM: Yes, and 46 years since I first started working there.


HS: Has the site changed a lot since you worked there in 1987?

AM: Yes, because in those days it was much more diverse and now it’s a monoculture. Just one or two crops everywhere. The reason why the swallows like the farms and the farm buildings is that they eat the flies that live in the surroundings of the farms. But now, because most farmers have given up keeping cattle, there are many fewer insects for the swallows to eat.


HS: Have the arrival dates of these swallows changed since the time you did this study?

AM: In my study area, the birds now arrive, perhaps, 2 – 2.5 weeks earlier in spring, than some years ago. This is also one of the reasons why I am still working on these birds. There are very few long-term studies that go beyond 10-20 years. I have been looking at the effects of climate change on sexual selection and found that the effects are quite strong. Like I said earlier, males with long tails attract good-condition females earlier in the season, breed earlier and have more time to sire a second clutch. But with the advancing of spring arrival, this advantage for long-tailed males is not so big anymore, because even the short-tailed males now have time for a second clutch.


HS: You have also made some behavioural observations in the study, in the context of “female rejection”? What time of the day were those observations made?

AM: Well, this is the other reason why most people are not very keen to join this fieldwork. I usually start very early in the morning. At sunrise. And in northern latitudes like Denmark, it starts getting light very early – around 3.30-4 – in the morning. And that’s the time when the birds are most active. The males are displaying their tails to the females, to attract them to their small territories, where they eventually will construct the nest.


HS: In a couple of places in the paper, you mention a “manuscript in preparation” One is where you say “More than 90% of all pairs remained together during both first and second clutches in the same breeding season, whereas mate fidelity between years was low, primarily due to high overwinter mortality” and the other is where you say “Male tail length was not related to territory size nor to his investment in nest building, mate guarding or the feeding of nestlings.” When and where were these eventually published?

AM: They were published in Animal Behaviour in 1990 So if you take the last point first, Darwin was puzzled by sexual selection in many different ways. He wrote explicitly about the peacock, that it was a bird that kept him awake many many nights, puzzling about how can something like that evolve and be maintained. He felt the peacock was the largest objection to this theory of evolution. This was simply because he had difficulty understanding why should it matter so much to these females if they were associated with one male or another. So the small note that you just read was one of the ideas that Darwin thought about. He felt that perhaps males with more exaggerated traits were better fathers, who provided more food for the offspring. But that is not the case in the peacock, because the peacock after copulating with the female never sees the offspring. He doesn’t feed them at all. In the barn swallow it’s a little bit different. Males contribute approx. half of the food to the offspring. About the note that you just mentioned – I followed the birds and recorded how often they fed their offspring. It turns out that, in fact, it’s the long-tailed males, the attractive males, who are the lazy fathers. They provide less food, not more food, which makes it even more puzzling. Why do females accept this cost?

Subsequently, I also looked at other explanations. One of them was the explanation put forward by William Hamilton and Marlene Zuk in Science in 1982, where they suggested that what could be running these circles of sexual selection in all these different species could be that some individuals are more resistant to deleterious diseases and parasites. If that is the case, it is not difficult to imagine that such males with exaggerated traits would be healthier and, for that reason, females would be out looking for such males because they will also gain this advantage.


HS: Just is an aside: In one place in the paper there is a reference to citation no. 22, but the paper has only 21 citations.

AM: Maybe it is a citation in one of the figures, because usually those come at the end.


HS: But this one comes in the middle of the paper, so maybe it’s a typo. It comes where you say “It has been suggested that sexual selection may occur in apparently monogamous systems if females engage in extra-pair bond copulations with favoured males”?

AM: Let me just check this. Yes, that was the other issue that came up much after Darwin and Fisher. Darwin had a rather Victorian view of nature and relationships.  He thought that females would always be monogamous. But that is not necessarily the case. In fact, Table 1 in the paper, and also our subsequent DNA fingerprinting studies (ref1, ref2), showed that individuals with lengthened tails were more attractive in two ways: not only did they have more offspring in their own nest, they also fathered more offspring in the nests of other individuals. Because of this you need to look at variation in number of partners as an additional mechanism that would generate variation in mating success.


HS: How long did the writing of this paper take?

AM: I am an old man now and soon I will retire. I have come to the conclusion that one of the most important skills for a young scientist is to be able to write clearly and precisely. Surprisingly, this skill is usually not taught in universities. Or if it’s taught, it is only because of the initiative of individual supervisors who try to help their students.  What I have done in the last few years, not only here in France but also in Spain, Italy and China, is to give courses to students on how to write papers in an efficient way. And my take on this is that if you understand the questions and understand the results, you can write the paper in one day! You can look at this in a different way.  All journalists have a deadline. They have to quickly write something that interests the readers of their newspaper, otherwise they will get kicked out by the editor of the newspaper. I can’t see much difference between writing a paper or an article for a newspaper. So I usually recommend to students that they put down as much as possible in one single day. Today, with all the software and computers, you can start editing immediately, and after a few days or a week you will have made very good progress. And it is not just something I say. When I give these courses I take out my computer and start writing a paper in front of the students and finish in less than one day. I do that to show them that it’s possible. You can teach many things, but if you can show it with a good example it’s so much more powerful.

This paper too, took very little time, because I had been thinking about these questions for a long time and had already collected all the data. It was just a question of putting it down. As you know, the paper is not very long, so it was more a question of trimming it and cutting off small pieces that were perhaps not so relevant. I think I typed everything for this paper in one day. Of course, this first version is quite different from the published version. But you have to start somewhere. I know many students who, when they start writing their paper, start with the title, then write an abstract, but then they think the title is not very good, so they come up with another title. In this way, after an hour or two, they are still at the title stage. So, I usually try to put everything down immediately and not think much about whether it’s perfect or not.  That’s something you will have to improve subsequently.


HS: When I start writing a paper, I have already decided that it is going to take a few months at least, so I am always working with that timeline at the back of my mind.

AM: I don’t look at it that way. Many people say that scientists and artists are two different kinds of human beings. I don’t agree. If you have done a study that is very close to your heart, you want to get it out on a piece of paper and show it to everybody as quickly as possible. This is not so different from the feeling of an artiste who is trying to write a poem. I usually say to my students when I give this kind of course: you should feel that if you can’t get it out now you will die!


HS: Did this paper have a smooth journey through peer-review?

A: Nothing is easy. It is always very hard to publish papers. You need to be working on the right subject at the right time. You need the right referees who are not too ruthless. I always say that it is possible to reject any paper. Any paper! If you have three positive reviews and the fourth is extremely critical, it’s done. You can do whatever you want and it will not change anything. You will have to look to another journal.


HS: But this paper seems to have had a fairly easy ride: it was submitted in December 1987 and accepted in two months.

AM: Yes, but I think it went through two rounds of review.


HS: Did it change a lot from the first draft?

AM: Not really, just some details needed to be specified. In general, the reviews were very favourable. The fact that the study was experimental, that it addressed this old question of Darwin and Fisher, and had these interesting results in Table 1 on extra-pair copulations – all of these made the reviewers think that it was a reasonably large step forward in this field.


HS: In the Acknowledgements you thank someone called A. Ulfstrand for the drawings. Was this for the numerical figures or the drawings of the swallows?

AM: Both. In the old days there were no software, so all the illustrations were made by hand. A. Ulfstrand was the wife of the head of our department. In fact, I am still in contact with my former head of the department and his wife. I still see them every now and then and we talk about swallows and the old days.


HS: Do you still have the original drawings?

AM: Yes, I still have them in a folder in my office.


HS: Can you tell us about the other people you acknowledge in the paper?

AM: Lars Gustafsson, Jacob Höglund and Arne Lundberg were colleagues from my department in Uppsala. Staffan Ulfstrand was the head of the department. Jonathan Waage was a US scientist on sabbatical in Uppsala in those days. Tim Birkhead was a colleague of mine; we were collaborating on many different projects in those days, so it was natural that I asked him. Bob Montgomerie was another North American scientist who was on sabbatical in Uppsala at that time. Andrew Pomiankowski was a theoretical evolutionary biologist from the UK.


HS: Was the grant you acknowledge awarded, specifically, to study sexual selection in barn swallows?

AM: Yes, it was.


HS: When the paper was published, did it attract a lot of attention, within academia and in the popular press?

AM: Well, this has changed a lot since those days. Today if you publish a paper like this, you will have lots of people contacting you. In those days that was far from the case. There was a “News and Views” piece in Nature about the paper by Peter O’Donald.


HS: This paper has been cited so many times. At the time when it was published did you anticipate that it would have such a big impact and become such an important study in the history of sexual selection?

AM:  No, certainly not. I think there are very few people who do research in order to attract attention.  I think most scientists do it because they want to know, want to satisfy their curiosity. At least to me, personally, it doesn’t matter if it’s cited or not. This perhaps sounds a little bit odd, but the most important thing is that you learn something, you get some answers to some pressing questions you’ve been thinking about for a long time. For me the main benefit is to be allowed to do this kind of work, to go out and check if this is really how things are.


HS: Do you have a sense of what this paper gets cited for, mostly?

AM: Well, I have to admit, this is not really something I am checking. Of course, I can go to the Web of Science for example, or on ResearchGate and look up who cited it. But that does not really interest me. There are so many more interesting things to do. Sorry about that.


HS: Did this paper have a big impact on the future course of your research?

AM:  Yes, I actually published another paper in Nature the year after, which was a continuation of this study. And I was able to do that only because I was studying swallows and not widowbirds. As I said in the beginning, barn swallows are unique because all survivors return to the same site where they originally recruited. Therefore, I could go out in the subsequent year and check if the experimental manipulation had an effect on their survival. And indeed it had. There were survival costs of increased tail lengths. So this way I could show that sexual selection had life history consequences. This was yet another step towards solving some of those old puzzles that had bothered Darwin and other people for a long time.


HS: Do you work on sexual selection on barn swallows even today?

AM: Yes, together with my colleagues in Italy, I have just got a review paper accepted, where we looked at all the studies of sexual selection in barn swallows. It might not sound like a big review but, in fact, there are more than 100 papers on this subject from different parts of the world – from Japan and China to Europe and North America.  What this review shows is that there are many characters involved in sexual selection, and which character is important differs among populations in different parts of the world. This in turn suggests that characters involved in sexual selection in different populations might have had a role in speciation.


HS: It’s been 18 years since this paper was published – would you say that the findings are still, more-or-less, true?

AM: Yes, I would say that. There have been several other studies since then, using a similar experimental technique, both in barn swallows and in other species, and, by and large their conclusions are the same.  The results in Table 1 about effects of tail manipulation on extra-pair copulations have also been vindicated in several subsequent studies of paternity, in barn swallows and other species. So many of the relationships we established in this paper turned out to be very general.


HS:  Today, do we have a better idea of why females choose long-tailed males in barn swallows?

AM: Yes, I think so. Starting with Darwin and subsequently followed up by Fisher, there was this belief that attractive males would be very good fathers. It turns out they are lousy fathers. And that’s true of many other species too. So today it looks like resistance to parasites, or the ability to raise strong immune-responses against parasites, is an important mechanism in many different animal species. Some studies suggest that’s perhaps the case even in humans.


HS: And that’s the case in barn swallows as well?

AM: Yes. I have done a number of different experiments investigating the abundance of parasites and micro-organisms, like bacteria and fungi, and found clear relationships with tail length. And different components of immunity – T-cells, B-cells and several other responses of the immune system – are also strongly correlated with tail length. And with experimental manipulation of tail length.


HS: Another unknown you indicate in your paper is whether the females that mate with long-tailed females are also of better quality. Do we know more about that now?

AM:  Yes, that is also generally the case. This was Ronald Fisher’s idea that attractive males would mate with females in better condition because females in better condition could start reproducing earlier. This way an attractive male would also be able to start reproducing earlier. That is clearly the case in barn swallows, as shown by several studies. In this first study, I made the treatment before the males had obtained a female. I went out early in spring and tried to catch birds every day so they didn’t have a chance to mate before I had caught them. That way I could measure how long it took for males with different treatments to obtain a female. But it is also possible to make the same kind of experimental manipulation after the pairs have become established. And the surprising thing is that if you change tail length when males have already obtained a female, they don’t give up on the female they have obtained. But the female adjusts its reproductive effort – how many clutches it lays, how many eggs it lays etc. – to this manipulation. This could also account for Malte Andersson’s findings. We know that in his study the female birds were already on these territories. So, it’s possible that in his study the birds were already mated, but some females were reproducing and other females were just hanging around waiting for better conditions. In other words, his manipulation was more a manipulation of female parental investment.


HS: Do we also know how natural variation in male tail length correlates with reproductive success in the barn swallow?

AM: Yes, there is data on this from more than 10 populations and they all show the same general relationship.


HS: Is this from your own work?

AM: Yes, this is from my work, from the work of my former postdocs, and from the work of some of my colleagues. We are now a group of scientists working in Spain, in northern Africa, in Ukraine, in Italy, in Poland and other places. As I said before we just had a large review paper accepted in Biological Reviews, in which we summarise this.


HS: Have you ever read this paper after it was published?

AM: It’s a little bit embarrassing but I am not sure I have. It reminds me of what I said earlier about the similarity of scientists and artists.  It’s like writing a poem. You have put your heart into it and written it down, but then you don’t want to look at it again. You have moved on to other things, you are thinking about something else.

Occasionally, I go back to what I have written when somebody sends me an email with a question about a particular study. Then I go back to check what was actually done.


HS: If you compare this paper to papers you write today do you find differences?

AM:  Sometimes, I am a little surprised about how well it was written, because in those days it was much harder. It was the dawn of email. Okay, we had the first versions of Microsoft Word, so it was starting to get easier. Today, in most countries of the world, scientists have all the papers at their fingertips, but in those days, I remember, it sometimes took several months for a paper to arrive at your desk, after you have ordered the paper in the library.


HS: Has your writing style changed?

LK: I didn’t have any training in scientific writing. Also, though I studied English in high school, it was for a total of six years. Not much. But now, even though I have been living in France for 21 years and speak French fluently, I mostly converse in English. My wife and I speak English to each other and we speak English to the children. So I think my language has improved over the years for these reasons.


HS: What would you say to someone who is about to read this paper today?

AM: Usually, what I encourage my students to do is to read carefully and be critical. When I say critical, I don’t mean that the students should read it and say this is rubbish, but that they should always think how they can improve this. Are there ways in which we can do this better? If that’s the case, the student hasn’t wasted his or her time reading the paper.


HS: Do you think there are ways in which this experiment could be improved?

AM: We have done these kinds of experiments, perhaps, 20 times now. And we have changed the design. One thing we have done for example is to paint the outermost tail feathers white, instead of cutting them. That way, the bird’s flight is not affected but yet, the tail looks shorter to the female. We find that this modification also affects the reproductive output and mating success of these males. Another thing we have done is to paint over only the white spot in the outermost tail feathers. This white spot is a weak spot because the feather easily breaks there. In fact, ectoparasites, such as chewing lice, like to chew on this white spot. It’s intriguing why there is such a weakness in a character that is so important for mating success. So what my student Mati Kose from Estonia did was he painted over these spots in some birds, but not in others, and found that this also affects the mating and reproductive success of males.


HS: Have there been any advances in technology that might allow you to do these experiments better today?

AM: Well, at a certain stage I was wondering if we should simply make some simple video recordings of birds and show the video screens to females. I am sure this will work, but the main problem is that if you catch birds that feed on insects and bring them indoors very quickly deteriorate in condition So that’s been the main reason why we haven’t done that yet.


HS: Is this one of your favourite papers?

AM: I think it was a nice study. I don’t know if it’s one of my favourites though. Often it seems like my favourite papers never get published. The papers that I like the most, reviewers don’t like at all! I have a computer full of such manuscripts. There is a Finnish journal which I think is Journal of Negative Results.  I have been wondering whether, perhaps, we should establish a Journal of Unpublished Results!









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