• 2 species in African tropics
• DR personal total: 2 species (100%), 2 photo'd

In central and west Africa there is a stocky, medium-sized "warbler" that frequents the undergrowth of forests from lowlands to mountains, known as Green Hylia or, sometimes simply as Hylia — derived from its monotypic genus Hylia (left). [An old colonial name was "Yellow-throated Warbler."] Of this bird, Barlein (2007) wrote: "Affinities uncertain: firm plumage, somewhat robust build and strong, slightly decurved bill atypical for a warbler, and voice unique. Has often been placed in sunbird family (Nectariniidae), mainly on account of certain anatomical features (brush-tipped tongue, flattened hyoid horns), but general behaviour and nest are not typical of a sunbird. Has also been classed as a tit (Paridae) and as a weaver (Ploceidae). Further, has been treated together with the remizid Tit-hylia (Pholidornis rushiae) in a separate family, Hyliidae, placed next to Nectariniidae. Recent mitochondrial DNA evidence indicates that these two species represent one lineage with the diverse assembly of Old World warblers, and are not closely related to nectariniids Retention of present species in current family provisional, pending further study."

Considering this lineage to be a Family is still provisional, but the evidence is getting strong, and it seems worth highlighting at this time.

The other member of the Hyliidae is Tit-hylia (right, a nice shot of a tiny bird by Arthur Grosset). It is Africa's smallest bird, but shares the slightly decurved bill and general range with Green Hylia. It, too, ranges in forests from west Africa to central Africa. It has been assigned to various families over the years, but has recently been often placed among the penduline-tits (Remizidae).

Sefc et al. (2003) used mtDNA to determine the relationships of three Africa enigmas, including both Green Hylia and Tit-hylia. They considered the various families in which these had traditionally been placed, and conclusively ruled out any close relationship with sunbirds (Nectariniidae), estrilid finches (Estrildidae), or honeyeaters (Meliphagidae). They found strong support for a "sister relationship" between Green Hylia and Tit-hylia — meaning that they appear to be each other's closest living relative.

Therefore, although most world checklists still place them in totally different families for traditional reasons, Tit-hylia (below) and Hylia should be considered together.

No modern study has yet undertaken that task. However, Fregin et al. (2012) included Hylia within their molecular study of the broader superfamily Sylvioidea. The used one mitochondrial DNA marker and six nuclear gene markers to provide a much more robust phylogeny of this group. They placed Hylia in a clade with the Long-tailed Tits [family Aegithalidae], but the divergence between Hylia and the Long-tailed Tits appears to be quite ancient (Fregin et al. 2012 do not give time estimates).

The family Hyliidae Bannerman 1923 was initially proposed for Green Hylia in the 1930s (Bates 1930, Bannerman 1939, Fregin et al. 2012). Now that we know of its close relationship with Tit-hylia — and where Hyliidae would appear in a phylogeny, next to Aegithalidae — it may be time to provisionally accept this Family. Additional research is needed and much anticipated, but it certainly seems possible that the Hyliidae will be a more widely accepted family in the future. At the moment, as a world birder, you needs to assure that you have this one "in the bag" during any visit to west or central Africa.

Green Hylia gives a loud, high-pitched double note: peee-peee. It occurs singly, in pairs, or in family parties, and often joins mixed-species flocks. Nests may be domed structures with a side entrance, or a fragile structure with an opening at the top. Its peculiar tongue, with frayed tip, was the reason it was proposed as a family in Bates (1930).

Photos: The Hylia Hylia prasina was at Buhoma, Bwindi-Impenetrable Forest NP, Uganda, in July 2002. Arthur Grosset photographed the uppermost Tit-hylia Pholidornis rushiae in Kakum NP, Ghana, in May 2011, and I photographed the next one at Brimsu Reservoir, Ghana, on 1 Dec 2013. Photos © Don Roberson except the upper Tit-hylia © Arthur Grosset, and used with permission; all rights reserved.

Arthur Grosset has many superb photos, especially from tropical forest around the world, on his website.

Bibliographic note: There is no "family book" but an introduction to Hylia prasina is in Barlein (2006).

Literature cited:

Bannerman, D.A. 1939. The Birds of Tropical West Africa with Special Reference to those of The Gambia, Sierra Leone, the Gold Coast, and Nigeria. 5th ed. Crown Agents for the Colonies, London.

Barlein, F. 2006. Family Sylviidae (Old World Warblers), pp. 492 –712 in Handbook of the Birds of the World (J. del Hoyo, A. Elliott, & D.A. Christie, eds.). Vol. 11. Lynx Edicions, Barcelona.

Bates, G.L. 1930. Handbook of the Birds of West Africa. Bale, Sons and Danielson, London.

Fregin, S., M. Haase, P. Alström, and U. Olsson. 2012. New insights into family relationships within the avian superfamily Sylvioidea (Passeriformes) based on seven molecular markers, BMC Evol. Biol. 12: 157

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