Green hylia

The green hylia (Hylia prasina) is a monotypic genus widespread in tropical Africa, where it mostly inhabits the understory and mid-stratum of moist forest. It is a canopy insectivore which had been tentatively placed within the family of Cettiidae warblers, but in 2019 its assignment to a new family, the Hyliidae, was strongly supported.

Hylia prasina is a monotypic songbird that has proven difficult to place within the phylogenetic tree. Connections between Hylia and other genera have been attempted by comparing DNA sequences, physical similarities and even behavioural characteristics. None of these links have been sufficiently proven to allow definite classification of the green hylia.

The green hylia belongs to the order Passeriformes and the superfamily Sylvioidea, however the classification at family level is under dispute. The species is often attributed to the family Cettiidae (bush warblers) along with Scotocerca, Erythrocercus, Tesia, Cettia and Abroscopus. Investigation into indels does not support a strong relationship between Hylia and the Cettiidae.

Anatomically, the green hylia has similarities to sunbirds and warblers. Characteristics shared with sunbirds include a long hyloid with flattened epibranchial horns, a brush-tipped tongue and membrane-covered nostrils. Similarities to some warblers include very comparable colouring. The relationship between the genera Hylia and Phylloscopus (leaf warblers) has been examined but seems to have low empirical support. A sister relationship between Hylia and Aegithalidae (long tailed tits) was similarly poorly supported. Close relationships with Nectariniidae (sunbirds), Estrildidae (finches) and Meliphagidae (honeyeaters) have also been rejected.

The sister relationship between Hylia and Pholidornis (tit hylia) is strongly supported, based on mitochondrial data and physiological similarities. It has been suggested that both genera should be placed in a new family 'Hyliidae', pending further confirmation. It is likely that the green hylia, along with other closely related species, have an uncertain position in the phylogenetic tree as a result of rapid radiation of the families within the Sylvioidea.

The green hylia has dark brown irises, a black bill and olive green feet. This species is small, weighing approximately 14 g. There is no noticeable difference in colour between the sexes, however males are generally larger.

There are two subspecies, H. p. prasina and H. p. poensis, which differ in the colouring under the throat. H. p. prasina has an olive green chin and throat and olive-grey underbelly while H. p. poensis has a white-grey throat and underbelly.

The green hylia uses several different calls, the most common being clear whistles (kee kee) or dry scolding rattles (trrit trrrit). It is known for its recognisable, pure, two-note song. Alarm calls used to warn of nearby predators are short as this makes it difficult for predators to locate exactly where the call is coming from.