Green hylia

Appearance

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 genders, 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.

Distribution

The green hylia occurs in a wide range throughout most of tropical Africa. The subspecies "H. p. poensis" can only be found on islands in the Gulf of Guinea. "H. p. prasina" is much more widely distributed throughout the Guineo-Congolian forest and is found from western Gambia to western Kenya.

Habitat

The green hylia is a common forest generalist, occurring at forest edges and gaps between vegetation as well as forest interiors. Its preferred habitat is mostly intact, semideciduous moist forest. Green hylia habitat includes plant species such as "Elaeis guinensis", "Celtis zenkeri", "Cola gigantea", "Acalypha ornata", "Markhamia platycalyx", "Coffea canephora", "Albizia" sp., "Fagara macrophylla", "Funtumia elastica", "Pycnanthes angolensis", "Musanga cecropioides" and "Xylopia aethiopica". Liana and "Scleria" species provide suitable habitat as they tangle amongst other vegetation, providing nesting materials and a supply of food. Analysis of carbon sources in green hylia food, indicating the origin of the consumed insects, showed that carbon present derived exclusively from C3 plants, which are mostly forest plants, and not C4 plants as might be found in farmland crops, even when these areas border forest habitats.The green hylia is a foliage-gleaning insectivore of the canopy and forest understory, usually foraging at a height of about 10 metres. Its diet includes insects, ants or butterflies which are accessible in its feeding area, on the underside of leaves or amongst forest litter. The species is considered a forest generalist as it is capable of surviving in a wide range of environmental conditions.

Reproduction

The green hylia is usually observed alone or in a mating pair. Mating pairs roost together in their nest. The eggs are white and otherwise not very distinctive. The nest is built a few feet from the ground in a suitable location, such as the vertical forks of young palm trees. The nest is oval and domed in shape with a 20 mm circular opening at the side of the top. Nests are crumbly and friable, the bulk being made up of loose tufts of plant matter which are not fragmented, interwoven or compacted. The outside is covered by a fine layer of fibrous strips topped with the occasional leaf skeleton. The nest measures 150 mm from top to bottom and 90 mm side to side and front to back. It differs from that of other sunbirds in that it is positioned in forks of vegetation and not suspended in the air.

Predators

The green hylia is currently classified as Least Concern by the IUCN based on large population numbers and wide distribution. The species is however likely under pressure from habitat destruction. While the green hylia as a forest generalist is not as sensitive to habitat disruptions as other species, understory and leaf litter clearance does affect its opportunities for foraging and nest building. A significant decline in green hylia population has been observed in plantation areas where these habitat components are absent.

The scarp forest habitat of the green hylia is increasingly being cleared for charcoal production and to make way for agriculture. The entire forest understory in certain areas is being cleared through slash and burn techniques to make way for the farming of crops such as bananas, maize or beans. These crops do not support species such as "Hylia prasina" as they do not possess sufficient understory environments. It is currently unknown how quickly the destruction of these habitats is occurring. While the green hylia has so far not been observed to be affected by this type of habitat clearing, many species with shared habitat requirements are in decline.

Parasites in African habitats may affect the species. "Plasmodium parahexamerium" was identified as infecting the green hylia in 2009, with as yet unclear ramifications. This parasite was thought to only inhabit New World hosts, thus its appearance in an Old World bird is both interesting and concerning. Despite this, parasites are not known to be a significant threat to the species as a whole.