SummaryAn annotated compendium of all those bird species known to have occurred in the lowland “Man and Biosphere” Beni Biological Station (B.B.S.) reserve is provided. Previous checklists are reviewed, together with sightings accumulated over the 1992–1995 period during which approximately 70 new species have been added to the reserve inventory, bringing the total to 478. Occurrence across the 12 delineated habitats, relative abundance and sighting documentation are given for each species. The avifauna of the B.B.S. is mixed biogeographically; in addition to a substantial component of lowland birds widespread throughout South America, it is composed of Amazonian, cerrado and chaco elements also. Representation from the Bolivian Yungas is minimal. Significantly, no less than four threatened and 15 near-threatened species have occurred, including the little known Bolivian endemic Unicoloured Thrush Turdus haplochrous, and the enigmatic White-winged Nightjar Caprimulgus candicans, known until recently only from Emas National Park (Brazil). Short accounts are provided detailing records of all of these species. Birds of the reserve core, consisting largely of humid tropical forest formations inundated during the austral summer, appear not to be subjected currently to any serious environmental degradation, although some subsistence clearance by Chimane Indians in the northern reaches of the reserve gives some cause for concern. Of much greater import, however, are changes occurring outside the confines of the B.B.S. These include increasing urbanization immediately to the west (and associated road upgrading) and forest fragmentation to the south brought about by logging. The latter is especially worrying because linkage of the B.B.S. forest block to surrounding forest is already physically tenuous, and therefore it is imperative that future logging activities be geared to minimize isolation occurring and the damaging restriction of gene flow. Monitoring in rainforest immediately south of the reserve should become routine to warn of putative avifaunal impoverishments. Extensive surveying of the 2,500-ha El Porvenir éstancia (savanna and related forest islands) due to be assimilated shortly into the B.B.S., which constitutes less than 2% of the area under consideration, has shown that it is used by no less than three threatened and up to nine near-threatened species. In the absence of data relating to other savanna areas (c. 15%) at present, the exact status of each species at the B.B.S. remains imprecise and begs for further research to be undertaken. Unfortunately, present management of the El Porvenir savanna is not conducive to the long-term maximization of populations of these species, several of which have local strongholds in this part of Beni. We recommend that the current policy of cattle ranching adopted by this éstancia should cease or be reduced dramatically, to minimize grazing and trampling damage, and that measures should be taken to reduce incursions of fires started wilfully in neighbouring properties. The Academia Nacional de Ciencias de Bolivia, which administers the reserve, should be encouraged to safeguard and enhance the savanna complement further by ensuring that the impending ratification of El Porvenir proceeds as quickly as possible, and by purchasing additional tracts of land to the south of the present southern reserve boundary, where feasible. Such actions should not only secure the future of the biota of the savanna habitat within the B.B.S. but also should ameliorate the degree of isolation which has occurred already by preserving the “curiches” (former river beds) and forest islands which act as access corridors for forest-dwelling and other birds.
The avifauna of the Vietnamese Mekong Delta
