a web page by Don Roberson
  • 5 species in Africa
  • DR personal total: 1 species (20%), 1 photo'd

The Sugarbirds are a small family of African passerines. Traditionally there were just two species of sugarbirds (genus Promerops) endemic to southern Africa, but molecular research suggests that three more drab 'thrush-like' birds are closely related, so for now, they are tentatively assigned here. It is possible that the three 'extra' species currently assigned to Promeropidae should be in their own family [Arcanatoridae]; more on that below.

Turning to the traditional two species of sugarbirds, perhaps the best known is Cape Sugarbird (male [left] and female [below]). Males have dramatically long tails that blow in the breeze; females also have long tails but nothing like the very long tails of males. They have brush-tipped tongues to consume nectar, and overall they resemble a very large and long-tailed sunbird.

Cape Sugarbird is a resident endemic in the Fynbos biome, centered on the Western Cape Province of South Africa, extending eastward into the Eastern Cape Province. The range of the other sugarbird — Gurney's Sugarbird Promerops gurneyi — extends from the mountains of the Eastern Cape Province, South Africa, to eastern Zimbabwe and adjacent Mozambique.

Both sugarbirds "live in close association with protea scrub, where they are dependent on nectar for food. The genus Protea belongs in the Protaeceae, a plant family virtually confined to the Southern Hemisphere. Africa is home to well over 100 species of protea, 91 of which grow naturally in southern Africa" (de Swardt 2008). The close association of these sugarbird species to specific plants recalls the close association of various hummingbirds with New World flowering plants.

In the distant past, sugarbirds were thought to be related to Australasian honeyeaters because they both fed on nectar. Anatomical studies suggested a relationship to thrushes. Early egg-white protein studies — the forerunner to the DNA-DNA hybridization studies of Sibley & Ahlquist (1990) — found potential links to either specialized starlings or to sunbirds. It is now known (e.g., Beresford et al. 2005) that sugarbirds are an ancient basal lineage among the Passeroidae, with no close ties to any other major lineage in the group.

Molecular research (Beresford et al. 2005, Johansson et al. 2008) found that three disparate 'thrush-like' birds might be the sister group to the traditional Sugarbirds. These species are
  • Spot-throat Modulatrix stictigula of montane forests in the eastern arc mountains in north Malawi, north Mozambique, and eastern Tanzania.
  • Dapple-throat Arcanator orostruthus, also of the eastern arc mountains from eastern Tanzania to north Mozambique [Usambara Mts., et al.]
  • Gray-chested Kakamega [aka "Gray-chested Babbler"] Kakamega poliothorax of montane forests from Cameroon to western Uganda

These three birds from sub-saharan Africa had been considered babblers, but they aren't. At various times in the past, Spot-throat was thought to be a thrush or a bulbul, Dapplethroat had been placed with chats or bulbuls, and Kakamega had been considered a thrush. The apparently belong in Passerida, next to the sugarbirds (Beresford et al. 2005).

Whether the "Spot-throat" set should be placed in the Sugarbird family or in their own family [Arcanatoridae] is a more difficult question. All the primary research is now 8-10 years old and there has been no published follow-up so far. It is not clearly known when this "Spot-throat" group split from the Sugarbirds. Beresford et al. (2005) estimated the split at between 28 and 39 million years ago [mean 28 mya]. In another radiation within the Passerida, Fjeldså et al. (2010) estimated that the Cinnamon Ibon Hypocryptadius cinnamomeus of montane Mindanao, Philippines, split from the other Old World Sparrows about 31 mya. Yet, among all the global checklists, I am the only one to split the Ibon as a family [Hypocryptadiidae]. Why is this? Why, for example, does the IOC split Arcanatoridae as a family, at around 28 mya divergence, and not Hypocryptadiidae, at around 31 mya divergence?

One problem may be that the methodology used ten years ago to estimate age of divergence among related clades is not as accurate as more recent methodologies. We need newer and better evidence on the time of divergence on both the Spot-throat set and on Cinnamon Ibon. Until that is accomplished, I remaining conservative and just following Beresford et al. (2005), who place the Spot-throat set among the Promeropidae. There is some doubt, though, that they are even sister clades. Depending on which Bayesian consensus tree one cites among the options set out in Johansson et al. (2008), one can argue either side of that issue.

In short, we need more certainty about the age of divergence of the proposed "Arcanatoridae" and we need to better understand the full set of species that might belong to that clade. Gray-chested Kakamega [aka Gray-chested "Babbler"] was added to the clade in 2008. Are there more species to be included?


Photos: The photos of Cape Sugarbird Promerops cafer come from vicinity of Walker Bay, South Africa, in March 2005.

      All photos © Don Roberson; all rights reserved.

Bibliographic note: There is no "family book" but a nice introduction to the traditional two species of sugarbirds, with some good photos, is in de Swardt (2008).

Literature cited:Family book:
Robert A. Cheke, Clive F. Mann, and Richard Allen. 2001.
Sunbirds: a Guide to the Sunbirds, Flowerpeckers, Spiderhunters, and Sugarbirds of the World. Christopher Helm, London.

This is a very nicely done "family book" — actually, a three-family book — in the Helm Identification Series. In standard format, the first half of the book is color plates with facing text on plumage characters and i.d. points, plus a good showing of subspecific variation. The second half is the main text with range maps, detailed descriptions, full discussion of subspecies, habitat, food, and breeding biology. All these topics are given in short summary fashion, but provide a fine overview. The two sugarbirds are a very small part of this book, and they did not anticipate that the spot-throat et al. might be related, but this was before molecular evidence was available. Overall the paintings are crisp, clear, and useful, and the text a good summary on many topics.

Literature cited:

Beresford, P., F.K. Barker, P.G. Ryan, and T.M. Crowe. 2005. African endemics span the tree of songbirds (Passeri): Molecular systematics of several evolutionary `enigmas'. Proc. Royal Soc. B 272: 849–858.

Cheke, R.A., C.F. Mann, and R. Allen. 2001. Sunbirds: a Guide to the Sunbirds, Flowerpeckers, Spiderhunters, and Sugarbirds of the World. Helm Identification Guide. C. Helm, London.

de Swardt, D.H. 2008. Family Promeropidae (Sugarbirds), pp. 486–497 in Handbook of the Birds of the World (del Hoyo, J., A. Elliott & D.A. Christie, eds). Vol. 13. Lynx Edicions, Barcelona, Spain.

Fjeldså, J., M. Irestedt, P.G.P. Ericson, and D. Zuccon. 2010. The Cinnamon Ibon Hypocryptadius cinnamomeus is a forest canopy sparrow. Ibis 152: 747–760.

Johansson, U.S., J. Fjeldså, and C.K. Bowie. 2008. Phylogenetic relationships within Passerida (Aves: Passeriformes): A review and a new molecular phylogeny based on three nuclear intron markers. Mol. Phylog. Evol. 48: 858–876.

Sibley, C.G., and J.E. Ahlquist. 1990. Phylogeny and Classification of Birds: a Study of Molecular Evolution. Yale Univ. Press, New Haven, CT.




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all text & photos © Don Roberson, except as otherwise indicated; all rights reserved