Ornithol Sci 5: 121–125 (2006) ORIGINAL ARTICLE Bird species richness and diversity in relation to vegetation in Bavi National Park, Vietnam Vu Tien THINH# Department of Wildlife, Forestry University of Vietnam, Xuanmai, Chuongmy, Hatay, Vietnam Abstract I studied the relationships between bird community and vegetation in ORNITHOLOGICAL Bavi National Park, Vietnam, during August and September 2004. Bird species rich- SCIENCE ness and bird species diversity were correlated to physiognomic variables of the tree layer, in particular canopy closure and tree basal area. Shrub layer characteristics and © The Ornithological Society floristics, expressed here as tree species richness and tree species diversity, were less of Japan 2006 correlated to bird species richness and diversity. Key words Bird species diversity, Bird species richness, Tropical forest, Vegeta- tion, Vietnam Vegetation has long been thought to be a major STUDY AREA AND METHODS factor in determining bird community composition (Terborgh et al. 1990; Wiens 1992). Many studies 1) Study area have found physiognomic attributes of vegetation The study was conducted in BNP, which is located such as foliage height diversity, foliage volume, in the northwest quarter of Hatay province, Vietnam, and percent vegetation cover to be correlated with about 50 km west of the capital, Hanoi. The 7,377-ha bird species richness and diversity (MacArthur 1961; park was established in 1991. Forty-six study points Balda 1969; Karr & Roth 1971). However, our under- were established in a succession from shrub to old standing of how vegetation determines bird commu- forest. In order to reduce the impact of the edge effect nity composition in tropical regions, especially in and maintain independence among points, these Southeast Asia, is still limited. points were located at least 100 m from the edge and Given its diverse topography and climate, Vietnam 200 m between points. is blessed with a rich and abundant biodiversity (Cu 2002). Ten percent of mammal, bird and fish species 2) Bird counts of the world are found in Vietnam and more than Avian communities were surveyed using the point- 40% of its plant species are endemic. Unfortunately, count method, which is well designed for surveying biodiversity in Vietnam has been declining at a rapid birds in structurally complex vegetation, such as the rate due primarily to habitat degradation, especially tropical forest in BNP (Bibby et al. 2000). This tech- in natural forests (Nhat 2001). The vegetation cover nique is more efficient than transect methods in esti- in Bavi National Park (BNP) is considered represen- mating the relationship between bird species richness tative of changes to natural forests in Vietnam in re- and habitat, because the survey points were located to cent decades. Past anthropogenic activities have cre- correspond exactly with a vegetation survey. The ated uniform vegetation in BNP. Species richness and counts were conducted under favorable weather con- diversity studies of the bird communities in BNP are ditions during August and September 2004 (within urgently required. The goal of this study was to ex- the breeding season in the study area). Points were amine the avian community in this tropical region in visited twice each. The first survey was conducted relation to vegetation characteristics. from sunrise to 10:00 and the second from 15:00 to sunset when birds are most active. To avoid distur- bance caused by the observer’s arrival, counts were (Received 9 May 2005; Accepted 5 December 2005) begun one minute after reaching the survey point. A # E-mail: [email protected] count duration of 15 minutes was used. During this 121 V. T. THINH time, the number of individuals of each species heard stepwise model selection method was used. A 0.05 or seen in a circle with a radius of 12.5 m around significance level was used as a criterion for variables each point was recorded. Birds flying above the plots to be added to or remain in the model. Outliers were were not recorded. In order to avoid inter-observer checked by Studentized residuals. bias, bird counts throughout the surveys were done by one observer. RESULTS 3) Vegetation measures A total of 65 species belonging to four orders (Ac- Vegetation measures were also conducted in Au- cipitridae, Passeriformes, Piciformes, Trogoniformes) gust and September 2004. Vegetation was sampled in was recorded during the two survey periods. Of a 25ϫ20 m plot that was centered around the bird- these, 51 species were in the order Passeriformes (ac- count point. In each plot, the following vegetation counting for 78% of the total number of species) and variables were estimated: (1) mean tree diameter at nine (14%) were in the order Piciformes. Among the breast height (DBH, cm), (2) tree basal area (BA, Passeriformes species belonging to 15 families were m2/ha), (3) canopy height (CH, m), (4) canopy clo- recorded, of which Muscicapidae, Pycnonotidae, sure (CC, %), (5) tree density (TD, trees/ha), (6) tree Sylviidae, Timaliidae, Turdidae were most frequently species richness (TSR), (7) tree species diversity observed. Four species: Red-whiskered Bulbul Pyc- (TSD), (8) shrub cover (SC, %), (9) shrub height nonotys jocusus, Black Drongo Dicrurus macrocer- (SH, m), (10) heterogeneity of shrub height (HSH) cus, Brown Bush Warbler Bradypterus luteoventris, (see Erdelen 1984; Bibby et al. 2000). and Magpie Robin Copsychus saularis, were abun- Canopy closure (CC) and shrub cover (SC) were dant. estimated by using a sighting tube (2 cm diameter). The tree layer structures were most closely corre- For each variable, the sighting tube was used 20 lated with BSR and BSD (Table 1). The correlation times at each vegetation survey plot. To investigate coefficients of tree layer variables with BSR and BSD shrub cover, five quadrats of 1ϫ1m were established ranged from about 0.5 to 0.7. The floristic attributes, in the plot (four at the corners and one at the center). expressed as TSR and TSD, were weakly correlated In each 1ϫ1m quadrat, the height of the shrub layer with BSR and BSD. was measured at five random points. The shrub layer was found to have little influence HSH is the coefficient of variation in SH. Individ- on birds (Table 1). SH and HSH had small correlation ual tree basal area was calculated based on diameter coefficients with BSR and BSD. Only SC had a mod- at breast height, and basal area (BA) was obtained by erate negative correlation probably reflecting the ef- summing the basal area of individual trees and divid- fect of CC. ing it by the vegetation plot area (0.05 ha). The relationships between BSR and BSD and physiognomic variables of the tree layer are pre- 4) Data analysis Bird species richness (BSR) and tree species rich- Table 1. The Pearson coefficients of correlations between ness (TSR) were calculated for each plot by deter- avian variables and tree vegetation variables in Bavi National mining the total number of species observed at each Park, Vietnam (Nϭ46). point. Bird species diversity (BSD) and tree species diversity (TSD) were obtained by the Shannon- Variable BSR BSD Wiener information index (Magurran 2004). DBH 0.56*** 0.59*** Canopy closure and shrub cover were transformed BA 0.61*** 0.70*** with the arcsine square-root transformation to CH 0.50*** 0.49*** strengthen the normality of the variables. Other vari- CC 0.63*** 0.66*** ables were analyzed using the original data, because TD 0.56*** 0.64*** the statistical assumptions were met. TSR 0.43** 0.45** The correlations between BSR, BSD and vegeta- TSD 0.36* 0.36* SC Ϫ0.37* Ϫ0.41** tion variables were examined respectively. Multiple SH 0.15 0.15 regressions among variables were examined by SAS. HSH 0.18 0.16 In order to select vegetation variables that can accu- rately predict avian species richness and diversity, the *PϽ0.05, ** PϽ0.01, *** PϽ0.001 122 Bird-vegetation relationships versity and the floristic composition of the tree layer, expressed as species richness and diversity, were poor predictors of bird species richness and diversity. Nev- ertheless, floristics, expressed as the abundance of some specific tree species or group of tree species may be useful in explaining the distributions of cer- tain bird species or bird guilds (Rice 1983; Douglas et al. 1992). Most tropical forest birds are dependent on forest canopy for nesting or foraging. Therefore, canopy volume may be a good predictor of avian community indices. However, due to the lack of accurate meth- ods for measuring canopy volume, the relationship between canopy volume and avian community in- Fig. 1. Relationship of BSR to canopy closure in Bavi Na- dices was not analyzed. Though canopy closure is not tional Park, Vietnam. as good as canopy volume, it can be used to reflect the extent of forest canopy. In my study, CC was one of the variables most strongly correlated with bird species richness and diversity. Other structural vari- ables, though they do not directly influence most birds’ lives, were correlated with avian community indices because these variables are stongly associated with canopy volume and canopy closure. Of these variables, BA was more closely associ- ated with BSR and BSD than DBH, CH and TD. This may be because BA is most closely associated with canopy volume and can reflect the forest structure better. It was not always the case that plots with high DBH and CH values were in old forest (some plots in shrubland have a few huge trees). And, it was not al- ways the case that plots with high TD values were in Fig. 2. Relationship of BSD to tree basal area in Bavi Na- old forest (some plots in regrowth forest have many tional Park, Vietnam. small trees). BA incorporates both TD and DBH in one variable, making it better able to reflect the forest sented in Fig.