By Jacob C. Cooper
Linked paper: Multiple lines of evidence indicate ongoing allopatric and parapatric diversification in an Afromontane sunbird (Cinnyris reichenowi) by Jacob C. Cooper, J. Dylan Maddox, Kellie McKague, and John M. Bates, Ornithology
Five years ago, as I was settling into my new life as a graduate student at the University of Chicago and the Field Museum, I explored the giant specimen cabinets of the Field Museum’s ornithology collection to familiarize myself more with the birds I hoped to study. It didn’t take long before I came across one of my favorite birds from previous trips in Equatorial Guinea and Cameroon, the Northern Double-collared Sunbird (Cinnyris reichenowi). These small sunbirds, part of a larger radiation of so-called double-collared sunbirds, vary from being hyperabundant to surprisingly scarce at different montane localities. As I looked at these specimens, I was immediately surprised by the fact that two specimens appeared to be a slightly different shade of green and noticeably shorter-billed amongst the Cameroonian specimen series. This confusion deepened when I noticed that both of these birds were from the interior of Cameroon and both had a name I was not familiar with—Cinnyris genderuensis—inscribed on the label. I showed the birds to Ben Marks, the Field Museum collections manager, and asked what he thought. He smiled, and quipped something along the lines of That’s interesting—it couldn’t hurt to sequence them! I didn’t know it at the time, but that casual suggestion would evolve into a chapter of my dissertation and gratifying investigative work in multiple countries.
Throughout their range, Northern Double-collared Sunbirds are almost wholly montane (above 1500 m), but they reach much lower elevations on the seaward side of Mt. Cameroon and have populations in the lower elevation, relatively xeric regions of the interior of Central Africa and in parts of East Africa. These birds possess a large range disjunction that is shared by many other Afromontane birds, occurring in the highlands of Central Africa and also in the highlands of East Africa. While Northern Double-collared Sunbirds are one of the only Cinnyris sunbirds in the mountains of Central Africa, the eastern part of their range is shared with many more species of Cinnyris sunbirds. I began to read through the literature and found that the name I did not recognize—genderuensis —was a name applied to Northern Double-collared Sunbirds found in the interior of Cameroon, whereas coastal Cameroonian birds with the longer bills were given the name preussi. Confusingly, birds on the island of Bioko, Equatorial Guinea, were also described as separate and given the population name of parvirostris, in part because of their shorter bills. As more specimens were obtained throughout the range of this species, taxonomists eventually agreed that only two populations existed within a single species of sunbird: a western preussi and an eastern reichenowi.
I set out to test this assumption that all western birds belong to the same population using existing collections* to build an extensive morphological database of Northern Double-collared Sunbirds across their range, including from all subpopulations of the western preussi. In all, I visited ten collections in the U.S. and Europe for this project (as well as other projects), and I began to learn more, not only about the birds but also about the history of ornithology in the region. Deep dives into the literature and collections inspired in me a newfound sense of appreciation for these resources, but also made me intimately aware of the history and circumstances behind some historical collections. In one particularly sobering moment, I found a bird collected by Emin Pasha—offering a case study in how some cherished scientific resources are inextricably linked to colonialism in Africa.
By combining collections data with genetic data (some of which was derived from 80-year old specimen toe pads!), we found that eastern and western populations of Northern Double-collared Sunbird are distinct, and further, that genderuensis is a distinct population undergoing diversification and not merely a synonym of other western populations. Conversely, we did find that Bioko birds, while a little smaller billed than their mainland counterparts, are not a separate population genetically, illustrating the complexities that can exist at the tips of lineages.
I’m very thankful that I had the opportunity and privilege to study these sunbirds, as well as the incredible opportunity to work in Africa. I’m eternally grateful to the local people, communities, governments, researchers, and others who enabled this research, while fully acknowledging the painful history behind some of these historical collections. I’d also like to thank the many museums I visited, my co-authors and collaborators, and the reviewers and editors of Ornithology for supporting the publication of this research.
*I used existing collections for this project, but I have also had the opportunity to participate in museum inventories and survey trips myself.