Revisiting Krebs et al. 1977

In a paper published in Animal Behaviour in 1977, John Krebs, Jonathan Erichsen, Michael Webber and Eric Charnov showed experimentally that whether great tits (Parus major) are selective or not about prey choice depends only on the supply rate of the more profitable prey, and not of the less profitable prey. These findings partially supported a model of optimal foraging that they had developed. Twenty-four years after the paper was published, I spoke to John Krebs about the making of this study and what we have learnt since then about foraging decisions of great tits.

Citation: Krebs, J. R., Erichsen, J. T., Webber, M. I., & Charnov, E. L. (1977). Optimal prey selection in the great tit (Parus major). Animal Behaviour, 25, 30-38.

Date of interview: Questions sent by email on 10 August 2016; responses received on 10 August 2016


 Hari Sridhar: What was your motivation to do the experiments presented in this paper?

John Krebs: To test a model of optimal prey selection


HS: This paper has four authors. Could you tell us how this group came together and what each member of the group contributed to this study?

JK: Erichsen designed the apparatus, Charnov did the modelling, Webber and I ran the experiments and the analyses.


HS: Who were the two observers – one who replenished the food and the other who watched the video monitor – during this experiment?

JK: Sometimes Krebs and Webber, and sometimes Krebs and Erichsen.


HS:  How did you come up with the idea of using a conveyor belt apparatus for this experiment? Would you know whether the apparatus that you used still exists?

JK: Erichsen had designed the apparatus for another purpose. I doubt that it still exists


HS:  Where and by whom were the four great tits caught? How did you find the fifth bird, which was raised from an age of 12 days?

JK: They were caught by Krebs at Wytham Woods, the fifth was hand raised by Krebs.


HS: Could you share with us what the codes ‘bw’, ‘gbw’, ‘ro’, ‘yy’ and ‘pw’ stand for?

JK: Colour ring codes: blue, white, green, red, orange, yellow, pink


HS: During the writing of this paper, how did the authors share, discuss and edit drafts of the manuscript? Would you remember how long the writing took?

JK: Don’t know how long it. Krebs wrote the draft and others commented


HS: Did this paper have a relatively easy ride through peer-review? Was Animal Behaviour the first journal you submitted this to? 

JK: We didn’t submit it elsewhere.  I don’t recall how the referees commented on it


HS: Were these results considered controversial soon after they were published? Did this paper receive a lot of attention from peers?

JK: The results weren’t controversial. The paper was, I think, well-received.


HS: Did this paper play a role in influencing the future course of your research career?

JK: It was one of our early papers on foraging theory, which formed a major research focus of my group for the following decade.


HS: Today, 39 years after it was published, would you say that the main conclusions of this study still hold true?

JK: I have no reason to doubt the results, but Rechten et al. 1981 Anim. Behav. 29, 1276-77 corrected the theory, and Berec et al. 2003 Can. J. Zool. 81, 780 were unable to repeat the results in toto.


HS: If you were to redo these experiments today would you do them differently?

JK: Yes.


HS: In the paper you say “it will be impossible to distinguish between ‘mistakes’ and ‘deliberate sampling’ until we have devised a specific predictive sampling model”. Was such a model developed subsequent to this paper?

JK: Yes.



HS:  You say that “our failure to find this [a step change from no selection to selection for profitable prey] in our experiment is likely to be a general result”. Was this statement borne out by future research? 

JK: See Rechten et al 1983, Anim. Behav. 31, 576-584


HS: In the 39 years since it was published, have you ever had to go back and read this paper for any reason?

JK: I did in the early days but not recently


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

JK: It was one of our early papers testing optimal foraging models.  In hindsight the theory and experiments could have been improved


HS: What would you say to a student about to read this paper today? What should he or she take away from this paper written 39 years ago?

JK: I would say it is a good example of how to link theory and experiment, but also that by today’s standards it is not a very sophisticated piece of work and much has been done since then to develop both the theory and experimental techniques.

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