Bird habitats and communities in Vietnam

A large proportion of Vietnam’s bird species, including nearly all of the endemic species, are associated with forests. In terms of bird community composition, forests mean bird habitats in Vietnam may be divided into five broad categories: evergreen forest, semi-evergreen forest, deciduous forest, limestone forest and coniferous forest. Of these, the most widespread is evergreen forest, accounting for around 64% of the total natural forest cover of Vietnam.

Evergreens forest

Evergreen forest occurs in areas with high year-round rainfall and a relatively short dry season, and is dominated by broadleaf tree species that remain in leaf throughout the year. Evergreen forest is the natural vegetation type in many lowland areas in northern and central Vietnam, and in most mountainous areas. Low elevations support a range of lowland evergreen forest formations, characterised by a high diversity of tree species, with no one family dominating.

Typical members of the lowland evergreen forest bird community include Brown Hornbill (Anorrhinus tickelli), Coral-billed Ground Cuckoo (Carpococcyx renauldi), Ratchet-tailed Treepie (Temnurus temnurus), and a number of endemic galliformes.

At elevations around 1,000 m asl, lowland evergreen forest undergoes a transition to montane evergreen forest. Montane evergreen forest can be divided into lower montane evergreen forest, which is distributed at elevations up to c.1,700 m asl, and dominated by members of the Fagaceae, and Lauraceae families, and upper montane evergreen forest, which is distributed at elevations above c.1,700 m asl, and characterised by the presence of Rhododendron spp.

The bird communities of lower and upper montane evergreen forest are fairly similar, with a high diversity of thrushes, nuthatches, babblers and warblers, although the bird community of upper montane evergreen forest is generally less species rich and includes several upper montane specialists, such as Chestnut-tailed Minla (Minla strigula), Golden-breasted Fulvetta (Alcippe chrysotis) and Stripe-throated Yuhina (Yuhina gularis). Montane evergreen forest also supports a number of endemic laughingthrushes.

Semi-evergreen forest

Semi-evergreen forest, sometimes referred to as mixed deciduous forest, has a higher proportion of deciduous tree species than evergreen forest, and occurs in areas with greater seasonality. Semi-evergreen forest has a limited distribution in Vietnam and is largely restricted to parts of the Central Highlands and the lowlands of southern Vietnam. The bird community of semi-evergreen forest is very similar to that of lowland evergreen forest.

Deciduous forest

Deciduous forest, sometimes referred to as dry dipterocarp forest, is a low, open forest type, with an understorey dominated by grasses, and a canopy dominated by deciduous trees in the Dipterocarpaceae family. Deciduous forest is distributed in areas with an extended, pronounced dry season.

In Vietnam, deciduous forest is confined to the Central Highlands and small parts of the coastal zone of south-central Vietnam. Bird species richness is markedly lower than in evergreen and semi-evergreen forest, due to the greater seasonality and the lack of a well developed understorey.

The bird community is characterised by a high diversity of woodpeckers and parakeets, and the presence of such species as Rufous-winged Buzzard (Butastur liventer), White-rumped Falcon (Polihierax insignis), White-browed Fantail (Rhipidura aureola), Small Minivet (Pericrocotus cinnamomeus) and Common Woodshrike (Tephrodornis pondicerianus).

Limestone forest

Limestone forest is essentially an evergreen forest formation developed on a limestone karstsubstrate. While the plant community of limestone forest is quite dissimilar to that of evergreen forest, the bird community is quite similar.

There are, however, a few birds restricted to limestone forest, including Limestone Wren Babbler (Napothera crispifrons), Streaked Wren Babbler (N. brevicaudata), Sooty Babbler (Stachyris herbeti) and an undescribed taxon of Phylloscopus warbler. The global ranges of the latter two taxa are restricted to limestone forest areas in central Vietnam and Laos.

Coniferous forest

Coniferous forest refers to forest dominated by conifers. There are also a number of mixed broadleaf and coniferous forest formations in Vietnam but the bird communities of these formations are similar enough to those of evergreen forest not to warrant separate consideration.

In Vietnam, natural coniferous forest largely comprises Pinus kesiya forest, a fire-climax formation widespread on the Da Lat plateau. There also exist significant areas of pine plantation throughout the country, although these are of marginal importance for bird conservation.

The bird community of natural coniferous forest is generally less species rich than that of other natural forest types, due to the relatively simple forest structure. However, this habitat supports a small suite of species not found in other forest types, such as Slender-billed Oriole (Oriolus tenuirostris), Red Crossbill (Loxia curvirostra) and the endemic Vietnam Greenfinch (Carduelis monguilloti).

Other terrestrial habitats

Other terrestrial habitats in Vietnam include natural grassland, secondary grassland and scrub, agricultural land, and human settlements. Of these habitats, natural grassland is of the greatest significance for bird conservation.

Natural grassland was once widely distributed in Vietnam, along rivers, around the borders of seasonal wetlands and in areas where edaphic conditions prevented the development of forest. However, this habitat has now been extensively converted to agricultural land and is restricted to a few remnants.

Some members of the grassland bird community have adapted to secondary habitats but others are largely restricted to remaining areas of natural habitat, for example Bengal Florican (Houbaropsis bengalensis), Rufous-rumped Grassbird (Graminicola bengalensis) and Jerdon’s Bushchat (Saxicola jerdoni), all of which must be considered on the verge of extinction in Vietnam.

Wetlands

In addition to terrestrial habitats, Vietnam supports a wide diversity of wetland habitats. Inland, freshwater wetlands include rivers, lakes and seasonally inundated grasslands. Slow-flowing, forested rivers support a distinctive community of birds, including River Lapwing (Vanellus duvaucelii), Masked Finfoot (Heliopais personata) and White-winged Duck (Cairina scutulata).

However, these rivers have been a focus of human settlement throughout Vietnam, leading to the loss of this bird community from most areas, and the presumed national extinction of at least one breeding species: Black-bellied Tern (Sterna acuticauda). Lakes are a potentially important habitat for migratory waterbird species, particularly ducks and other waterfowl species. In terms of habitat loss, lakes are one of the least threatened habitats in Vietnam, as, although there are few natural lakes, a large number of artificial lakes have been formed over recent decades following dam construction.

Despite the presence of large areas of suitable habitat, the importance of lakes for migratory waterbirds is currently low, due to uncontrolled hunting at most sites. Seasonally inundated grasslands are an important habitat for a number of large waterbird species, including Sarus Crane (Grus antigone) and Painted Stork (Mycteria leucocephala).

Seasonally inundated grasslands were once widespread throughout the Mekong Delta but have now been reduced to small fragments, and even these are under continued threat of conversion to agriculture and aquaculture.

Coastal and marine wetlands include mangroves, intertidal mudflats and offshore islands. Mangroves are the natural vegetation type along a large proportion of the coastline of Vietnam, particularly in the coastal zones of the Red River and Mekong Deltas.

However, as a result of wartime spraying of defoliants in the south of the country, unsustainable fuelwood collection, and widespread enclosure within aquacultural ponds, most areas of natural mangrove have been lost.

While few bird species in Vietnam are restricted to mangrove, it is an important habitat for many migratory waterbirds and, in the Mekong Delta, supports a number of important waterbirdcolonies. Intertidal mudflats have an uneven distribution along the coastline of Vietnam, being concentrated at the mouths of major rivers.

They are one of the most important habitats for migratory waterbirds in Vietnam, as they provide important feeding areas for a range of waders, gulls and terns, including the globally threatened Spoon-billed Sandpiper (Eurynorhynchuspygmeus), Spotted Greenshank (Tringa guttifer), Saunders’s Gull (Larus saundersi) and Black-faced Spoonbill (Platalea minor). Unfortunately, these habitats are subjected to high levels of disturbance, due to shellfish collection and other human activities, and are threatened in many places by mangrove afforestation.

Larger, forested offshore islands, such as Con Son, support two forest species adapted to offshore islands: Pied Imperial Pigeon (Ducula bicolor) and Nicobar Pigeon (Caloenas nicobarica). Smaller, rocky islands are important sites for breeding seabirds, such as terns and boobies, although there has been little ornithological study of these habitats in recent years.

References

Tordoff, A. W. ed. (2002) Directory of Important Bird Areas in Vietnam : key sites for conservation. Hanoi : BirdLife International in Indochina and the Institute of Ecology and Biological Resources

Stattersfield, A. J., Crosby, M. J., Long, A. J. and Wege, D. C. (1998) Endemic bird areas of the world: priorities for biodiversity conservation. Cambridge, UK: BirdLife International