The avifauna of the Belalong forest, Brunei Darussalam

Abstract

The areas explored were the full length of the East (Main) Ridge to the summit of Bukit Belalong and down to Sungai Temburong and Sungai Belalong, the length of the West Ridge from the Field Centre back to Sungai Belalong, much of Sungai Belalong from Kuala Belalong almost to the project boundary, and Sungai Temburong from Kuala Belalong to a little beyond Sungai Babi. 24-hour periods of mist netting were carried out, 10 periods at Pondok Bujat, one in an alluvial forest close to Sungai Babi, and another along Sungai Belalong at the Field Centre. Netting was carried out twice at the summit of Bukit Belalong. A total of 218 individuals of 58 species were captured, of which 214 of 57 species were ringed, the others being net casualties. Moult and weight were recorded, along with any changes in retraps, as were signs of breeding activity. 198 species were recorded in the project area, with three others identified to genus only. 25 species recorded are not forest dependent, and a further 15 are also likely to be found outside forest. During the expedition, 20 definite cases of breeding were discovered involving 16 species. Within the area three zones were recognised, namely riverside (Zone 1), slopes and ridges up to about 460 m (Zone 2) and slopes and ridges above 460 m (Zone 3). No true montane species were found. Bird species demonstrate vertical stratification in tall tropical forest, with four levels being recognised, with a fifth category for aerial feeders: ground level (leaf litter foragers) — 20 species, nine exclusive to this stratum; understorey — 76 species, 11 exclusive; mid levels — 95 species, 10 exclusive; canopy — 75 species, 44 exclusive; aerial — three forest-dependent species are exclusively aerial, whereas one other is also found in the canopy. Nine species are tied to waterways, of which two (Enicurus spp.) are also litter foragers on land, and another (Ceyx erithacus) may also be found some distance from water. 128 (116 forest dependent) species were found in the riparian zone (Zone 1); 139 (136 forest dependent) species were found on the lower slopes (up to c. 460 m, Zone 2) and 121 (114 forest dependent) on the higher slopes (above c. 460 m; ridge-top pole forest — Zone 3). 14 species of palaearctic migrants were recorded, together with two others, viz. Ninox scutulata and Muscicapa daurica, which have resident and migrant populations. Moult cycles were calculated to last from 100 to 220+ days.