Effects of distance from forest edge on upper storey birds in Ayer Hitam Forest Reserve, Malaysia

Tropical rainforest has lost much of its natural biodiversity due to deforestation. This activity leads to the creation of numerous forest patches and thus causes edge effects. Although several studies have examined the effects of edges on bird populations, little is known about effects of the forest edge on the upper storey birds in the isolated forest especially in tropical rainforest. Thus, a study was conducted in the isolated Ayer Hitam Forest Reserve (AHFR), Puchong, Selangor to; (i) examine the species composition, abundance, density and diversity of the upper storey birds at different distances from forest edge, (ii) detect any correlations in the upperstorey birds with microhabitats and microclimates factors, (iii) to identify which group and species of the upper storey bird that was affected by the edge effects and iv) to determine which micro-environmental factors have strong effects on the upper storey birds. This study was conducted in a 1,248ha of isolated AHFR for about 20 months (December 2006 – July 2008). The information on the upper storey birds and micro-environmental variables were recorded using point sampling method. Altogether a total of 113 species from 3,226 observations of birds were recorded of which 61 species (45.86%) and 1,618 observations (50.15%) were classified as the upper storey birds. Results showed that 48 species (78.67%) of the total upper storey birds observed were considered as rare species, while four species namely Phaenicophaeus javanicus, Calyptomena viridis, Dinopium rafflesii and Psittinus cyanurus are among the rarest forest interior species. Feeding guild analysis indicated that sallying insectivore, arboreal foliage gleaning frugivore and arboreal foliage gleaning insectivore/frugivore showed a significant difference at different distances from the forest edge. The density of upper storey birds along edge-interior gradient showed that the forest interior had a higher density of the upper storey birds compared to the forest edge. Based on response of the upper storey birds to the micro-environmental variables, number of trees between 10-20cm dbh, 30-40cm dbh, > 60cm dbh and humidity had a positive correlation with the group of barbets, broadbills, flycatchers and malkohas. The observations of these groups were higher at the forest interior compared to the forest edge. Results from this study indicated that large sized of the upper storey birds such as barbets, broadbills and malkohas tend to forage at the forest interior and infrequently observed at the forest edge. Changes in microenvironmental variables such as number of trees, light intensity, temperature and humidity had a significant effect on the upperstorey birds. Therefore, the upperstorey bird populations and their habitats in the isolated AHFR should be monitored and conserved since most of them depended on the forest interior to survive especially the ‘extreme rare species'.

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