Revisiting Gill and Wolf 1975

In a paper published in Ecology in 1975, Frank Gill and Larry Wolf examined the costs and benefits of feeding territoriality in the golden-winged sunbird, a species found commonly in the montane regions of Kenya. Gill and Wolf found that maintaining territories was beneficial when the nectar levels are low but the costs of territory maintenance outweigh benefits when nectar levels are high. Forty-two years after the paper was published, I asked Frank Gill about his collaboration with Larry Wolf, his motivation to do the study, and what we have learnt since about the economics of territoriality.

Citation: Gill, F. B., & Wolf, L. L. (1975). Economics of feeding territoriality in the golden‐winged sunbird. Ecology, 56(2), 333-345.

Date of interview: Questions sent by email on 8th December 2017; responses received by email on 11th December 2017.


Hari Sridhar:  I would like to start by asking you about your collaboration with Dr. Larry Wolf. Correct me if I’m wrong, but your first paper with Dr. Wolf seems to have been in 1961 – a note on flocking behaviour in gulls. After that, for 14 years you didn’t write any papers together, before a series of co-authored papers on foraging in hummingbirds and sunbirds. Could you share with us how you got to know each other and how you decided to work on sunbird/hummingbird foraging together? I notice that you cite some of Dr. Wolf’s earlier papers on hummingbird foraging, but this paper seems to be his first, too, on sunbirds. How did the idea to work on sunbirds in Africa come about?

Frank Gill: We were undergraduate roommates and birding pals at the University of Michigan. Hence the 1961 note, my first publication.  Larry went out to Berkeley for graduate work and I finished my Bachelor’s degree there, then surveyed birds, especially seabirds, of the Indian Ocean region in 1963-64. Larry finished his thesis on Aimophila, then got into hummers with Gary Stiles in Costa Rica. My thesis field work on Reunion Island included attention to a white-eye (Z. olivaceus) that had evolved into a nectar-feeding sunbird.  We reconnected; Larry was looking for a post-doc project and I a follow-up to my thesis on white-eyes.  We decided that we should do something together on behavioural ecology of nectar feeding birds. Had to decide between sunbirds in Africa and honeyeaters in Australia. Chose sunbirds. Wrote an NSF proposal, which was funded. The rest is history.


HS:  Stepping back a bit, could you tell us how you got interested in birds? 

FG: At about 6 years old. My grandfather showed me a Song Sparrow at our yard birdbath, through binoculars. I was hooked and started down the path unknowingly to professional ornithology


HS: This paper is now a textbook example for costs and benefits of territoriality (e.g. the Behavioural Ecology textbook by Krebs & Davies). Was this planned as a project on territoriality right from the beginning? 

FG: Don’t think so. Our NSF proposal was a rather general statement about measuring costs and benefits in behavioural ecology. Jerram Brown‘s papers were seminal.


HS:  How did you choose to work in “the vicinity of Hell’s Gate near the southern edge of Lake Naivasha (altitude 1,930 m), 16 km sw of Naivasha, Kenya”? When was the last time you visited this place? Could you give us a sense of how it has changed since the time you worked there? Are golden-winged sunbirds still common in this patch?

FG: Early 80’s, I think. Initially, I planned to find a field site in Uganda, but Brit colleagues warned me about Idi Amin and the turmoil there. So I reoriented to Kenya. I was looking for field sites in Kenya and a birder friend mentioned seeing lots of sunbirds at Hell’s Gate, so I went there and the rest is history. The fields of Leonotis there were converted to commercial ornamental flowers in the late 70’s


HS:  If you think back to the days when you did fieldwork for this project, what are your most striking memories? 

FG: Too many to list. I loved Africa, its people, its wildlife and my Golden-winged Sunbirds.


HS:  Would you remember who drew the figures for this paper and how they were drawn (especially the lovely map of feeding territories that is Fig. 3)? 

FG: I think I did; not sure


HS: You acknowledge a number of people at the end of your paper. Could you tell us a little more about how you knew them and their contribution to this paper:


  1. A.D. Forbes-Watson – My friend and host at the museum in Nairobi
  2. R. Leakey – Head of the museum who helped me get permits
  3. Leo Mackay – ??
  4. Ray & Barbara Terry – Logistics support and residence managers in Gilgil
  5. R. Faden ??
  6. J. Gillet  ??
  7. S. Peters – field assistant
  8. W. Ewens – statistical consultant
  9. W. Moss – statistical consultant
  10. J. Hendrickson – analysis consultant
  11. F.R. Hainsworth – Larry’s colleague – expert on hummingbird physiology
  12. G. Pyke – shared interest in nectar feeding bird models


HS: How long did the writing of this paper take? When and where did you do most of the writing? 

FG: Don’t recall; was at the Academy of Natural Sciences of Philadelphia.


HS: Today, 42 years after it was published, what would you say about the main conclusions of the paper? 

FG: Just a peek into the advanced statistical feeding behaviour of birds.


HS: What kind of influence did this paper have on your subsequent research? I notice that you continued working on foraging in hummingbirds till the late 80s. Have you kept track of how research has progressed on this topic, i.e. territoriality in nectar-feeding birds? 

FG: Yes, shifted to traplining Long-billed Hermits in Costa Rica to explore the extreme opposite of territoriality.


HS: In the paper you say that the phenomenon of pair-defence of territories in golden-winged sunbirds requires further study. To what extent has this happened?

FG: Don’t know


HS: In the paper you assume sunbirds visit flowers randomly with respect to previous visits and also say that you have some preliminary evidence for it. Was this a topic you researched further?

FG: See 1977. Nonrandom foraging by sunbirds in a patchy environment.  Ecology 58: 1284-1296. (F.B. Gill and L.L. Wolf).


HS:  In the paper say that the energetic costs of non-territorial foraging strategies are poorly understood and suggest that understanding the energetic consequences of body size might be a fruitful avenue of future research. To what extent do you think this has happened? 

FG: Don’t know, but see 1988. Trapline foraging by hermit hummingbirds: competition for an undefended, renewable resource.  Ecology 69: 1933-1942.


HS:  Have you ever read this paper after it was published? If yes, in what context?

FG: Long time ago! Not for many years. Attention went elsewhere.


HS:  Would you count this paper as a favourite, among all the papers you have written? 

FG: One of them.


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? Would you add any caveats? 

FG: Follow your creative research whims and wait patiently for recognition and influence.


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