In 1999, Rebecca Kilner, David Noble and Nick Davies published a paper in Nature showing how the common cuckoo exploits the sensory predispositions of its host, the reed warbler, to obtain the same amount of care that the latter would give a brood of its own chicks. Seventeen years after the paper was published, I spoke to Rebecca Kilner about her motivation for doing this work and how it influenced her subsequent research.
Citation: Kilner, R. M., Noble, D. G., & Davies, N. B. (1999). Signals of need in parent–offspring communication and their exploitation by the common cuckoo. Nature 397: 667-672.
Date of interview: Questions emailed on 26 July 2016; responses received on 31 August 2016
Hari Sridhar: After completing a PhD on “Parental investment in canaries and zebra finches” in 1996, you started working on the cuckoo-warbler system. What was your motivation to switch to this system?
Rebecca Kilner: My PhD work was mainly an experimental analysis of the way in which nestling birds signal to their parents for food. I chose the canary as a model study system because I could breed it in captivity and so subject it to manipulations that wouldn’t have been possible in the field (at that time). It was a natural extension of this work to turn my attention to cuckoo begging behaviour. We wanted to know whether cuckoo chicks tapped into existing rules of communication between nestlings and parents, or whether they had a special trick for extracting care from their hosts. It turns out they just tap into the existing rules.
HS: This paper has three authors. How did this group come together and what did each person bring to this project?
RK: I started working on cuckoos when I was briefly employed by Nick Davies, in the months after finishing my PhD and before I started a research fellowship. He is arguably the world expert on cuckoos, and natural history and behavioural ecology in general, and he already had a post-doc, David Noble, working with him on a different grant.
Nick and Dave did most of the hard work in the field, finding and checking hundreds of nests. My job was to design the experiments, to measure begging behaviour in the lab and to carry out the provisioning experiments with Nick.
HS: What was a typical day like for you during the summers of 1996-1998? Did you have help in field? Who was M. de L. Brooke who you thank for help in finding nests?
RK: These were some of my happiest days as a biologist, mainly due to the wide-ranging discussions Nick and I had about biology as we sat for long hours in our deckchairs and counted provisioning rates at the warbler nests. I also spent a lot of time in a shed used by the ringers at Wicken Fen. This was less fun, but made more enjoyable by regular visits from Ralph, an old Fen man who kept geese and ducks in the neighbouring field and who always had a good story to tell (“Saw a baby mink today. Got it with my pitchfork”). The shed was also well-positioned for access to the ice-cream van.
Mike Brooke is the Strickland Curator of Ornithology at the Cambridge University Museum of Zoology. He did the field experiments on cuckoos and reed warblers with Nick Davies in the 1980s that have now become classic papers in the field of co-evolution, setting the benchmark for quality in this research area and laying the foundations for all the cuckoo work done since. Mike helped out by finding nests and letting me sit in his freezing cold kitchen to measure nestling begging behaviour (The chicks were fine because we kept them in heated nests but I had to keep popping outside to warm up!). He also collected some of the provisioning data we used in our analyses during his time working with Nick in the 1980s.
HS: In the Methods you say you used “old Turdus nests” placed over the reed warbler nest in the brood size manipulation experiment. Where did you source these Turdus nests from?
RK: Nick found them in his garden and in the Botanic Gardens in Cambridge.
HS: Does Wicken Fen still serve as a field site for brood parasitism research? When was the last time you visited this site? Has the place changed from the time you did this study?
RK: Yes, Nick still works there every summer. I go from time to time with my family. It has changed a bit since we worked there. It’s much larger and more managed. There are boat rides on the Lode and a teashop now as well. It was more rustic when I worked there.
HS: You acknowledge “C. Thorne and the Wicken Fen group for research facilities”. Can you tell us a little more about who these people were and how they helped?
RK: These people ring birds regularly at Wicken Fen and allowed us to use their shed as a field lab for measuring begging behaviour (see above).
HS: Who did most of the writing for this paper? How long did the writing take?
RK: I’m probably biased but my memory is that I did a lot of the initial writing and drafting. It was greatly finessed by Nick, though, and we spent quite a while discussing how to bring the different parts together to tell the story. We planned the broad outline of the story before the field season in 1998, and spent that season filling in the gaps. We finished collecting the data at the end of July and submitted the paper in November.
HS: You thank a number of people for commenting on the manuscript. Can you tell us how you knew each of these people?
RK: The people we thanked were: Fiona Hunter, who I shared an office with and who is an outstanding field biologist; Naomi Langmore, a talented behavioural ecologist, who was a post-doc at the time in Cambridge – I started working with her on Australian cuckoos in 1999 and the collaboration continues to the present day; and Rufus Johnstone who is a theoretical biologist and whose work has been hugely influential in shaping the way we think about the evolution of animal signals. He was a post-doc in Cambridge too at the time, and his papers inspired a lot of our experimental work.
HS: You thank B. Grenfell for producing Fig. 7. Can you tell us who this was?
RK: This is the eminent epidemiologist Bryan Grenfell FRS. He was a lecturer in the Department of Zoology in Cambridge at the time – he is at Princeton now.
HS: Did the paper have a smooth ride through peer-review?
RK: Yes, amazingly.
HS: Was Nature the first place you submitted this to?
HS: How different was the published version from the original submitted version?
RK: Not that much, as I recall
HS: How was the paper received when it was published?
RK: Well, I think. I gave a few seminars about the work which went down well and it got some nice coverage in the media in the UK
HS: Did this paper have a major influence on your career?
RK: Almost certainly. It was very exciting to get a Nature Article published when I was 27. It will probably never happen again! It helped me take the next steps in my career towards becoming a tenured academic.
HS: How did it impact the course of your future research?
RK: In two very obvious ways. First, it made me wonder why cuckoo hosts don’t reject cuckoo chicks given that they can reject cuckoo eggs. This is the problem I worked on next with Naomi [Langmore]. We discovered that some Australian cuckoo hosts can actually reject cuckoo chicks (a complete shock at the time). We still don’t know exactly why reed warblers don’t do this too, but I think we are closer to solving this problem.
Second, it made me wonder why other brood parasitic chicks, like cowbirds and vidua finches, don’t kick out host chicks in the way that the common cuckoo does. To answer this question I teamed up with Joah Madden and Mark Hauber. We did some field experiments which showed that host young can help the cowbird attract more food from the host parent – this is why they aren’t kicked out at hatching. The cuckoo can’t afford to do this. Unlike cowbirds, it is much larger than its hosts and would probably starve if it shared food with the host nestlings.
HS: In the paper you say “the amount of food supplied by parents to young is likely to be the source of a conflict of interests between the two parties”. Did this paper in some way motivate your later work on parent-offspring conflict?
RK: My work on parent-offspring conflict started with my PhD research, in fact, and still dribbles on…
HS: Its now 17 years since this paper was published. Would you say that its main conclusions are still, more-or-less, correct?
RK: I think so. One exciting subsequent finding by a Japanese team was the discovery that Horsfield’s Hawk-cuckoo nestling has a different trick for overcoming the handicap of being alone in the nest. Rather than calling like a brood of chicks as the common cuckoo chick does, it displays fake gapes – bare patches of skin on its wings that simulate the gapes of other nestlings. So it faces the same problem we identified in the common cuckoo, but has evolved a different signalling solution.
HS: If you were to redo these experiments today, would you do anything differently, given the advances in technology, ecological theory and analytical tools?
RK: I’d probably analyse the data in a more sophisticated way
HS: In this study, you derived two regression equations experimentally – 1. Relating chick need to begging signals; 2. Relating begging signals to parental behaviour. This, you said, provided, in principle, a way to test the prediction that parents supply chicks with exactly the food they demand, but which wasn’t possible then because the “the analysis is beyond our reach”. Is such an analysis possible today?
RK: No, unfortunately. The problem is that the equations are not in the same units and so cannot be directly related to one another. I can’t see a way round that.
HS: You conclude the paper by saying “the constraints of eliciting a high provisioning rate alone, or of losing food in sibling competition, may mean that we never see brood parasites being fed at the high rate we might predict”. Is this still the case?
RK: I think so – and our cowbird work supports the concept of this trade-off.
HS: Do you know what this paper mostly gets cited for?
HS: What would you say to a student about to read this paper today? What should he or she take away from it? Would you add any caveats?
RK: I hope mainly that they are excited by the natural history. And that they can see it is possible to reach some quite sophisticated conclusions by thinking clearly rather than simply using fancy techniques or analyses.
HS: Have you ever read the paper after it was published?
RK: No, I can’t bear to read anything I have written! I spend a long time working on each paper, but once it is gone, it’s gone for good and it’s time to think about the next problem.
HS: Would you count this as one of your favourite papers, among all the papers you have published?
RK: I like this paper because we had so much fun collecting the data and working everything out bit by bit. We ended up with a very different set of thoughts to those we started with. I very clearly remember working out how to start thinking about multiple signals with these data – I was in the shower of all places. And the excitement of putting that idea into practice still dripping wet and barely clothed.
I don’t have a favourite paper, but the ones I like most combine these ingredients – fun designing experiments and collecting the data, puzzling patterns that don’t make sense at first, the thrill of the penny dropping when you realise what is really going on, and the excitement of writing it up and sharing your excitement with others.