INTRODUCTION

Wetlands are widely recognized as highly important ecosystem with diverse attributes including a distinctive avifauna (Burger, 1985). Freshwater wetlands hold more than 40% bird species of the entire world and 12% of all animal species (Kirsten and Brander, 2004). The gradual losses of wetland habitats and degradation have caused declining of many bird species (Taylor and Pollard, 2008). Many of them are under heavy pressure and at risk due to degradation of breeding sites, water level destabilization, sedimentation, contaminant and nutrient inputs and invasion of exotic plants and animals (Scott and Poole, 1989).

Freshwater wetlands provide suitable breeding and foraging sites for more than one quarter of the regional avifauna and most of them are nongame species (Naugle et al., 2000). Various globally threatened and non-threatened bird species depend on wetland to fulfil the daily requirements such as food, water and shelter (Ishikawa et al., 2003). Wetland birds are diverse and often show different behavioural tactics to explore the wetland areas and reflect the ecological conditions of a particular area. Nevertheless, the information on the population parameters and ecology of wetland birds is scare (De Leon and Smith, 1999).

Malaysia is blessed with a total of 3.5 to 4.0 million ha of natural wetland areas which is equal to 10% of the total land area (Aik, 2002). Malaysian wetlands are divided into ten major types namely mangroves, mudflats, nipa swamps, freshwater swamp forest, peat swamp forest, lakes, river systems (nearly 100 river systems), fresh marshes and wet rice paddy fields (Malaysian Wetland Working Group, 1986). These wetland areas serve as important habitats and refuges for wide array of migratory and threatened bird species (Asmawi, 2007; Min, 2007).

To date no population study has been done to compare between waterbirds and terrestrial birds in freshwater wetland of Malaysia. Very little is known about the bird assemblages and population trends in freshwater wetland habitats. The main objective of this study was to determine and compare the density and diversity of waterbirds and terrestrial birds at Paya Indah Wetland Reserve, Selangor Peninsular Malaysia.

In this study the term water birds refers to bird species that entirely depend on wetlands for variety of activities such as foraging, nesting, loafing and moulting (Rajpar and Zakaria, 2009). Whereas the term terrestrial birds refers to bird species that do not totally depends on the wetland habitats but may use the wetland areas in search of food, shelter and loaf. The species diversity is the number of different bird species in a particular area while species density is a number of birds per unit area.

MATERIALS AND METHODS

Study site: Paya (swamp) Indah (beautiful) wetland reserve encompasses of 3050 ha out of which 450 ha are under the administration of the Department of Wildlife and National Parks, Peninsular Malaysia. The study area is located adjacent to Malaysia's administrative centre Putrajaya within the quadrant of 101° 10' to 101° 50' longitude and 2° 50' and 3° 00' latitude (Fig. 1).

Bird surveys: Bird surveys were carried out at Paya Indah Wetland Reserve, Peninsular Malaysia using distance sampling point count method to determine species composition, diversity and density within November 2007 to January 2009. Sixty one point-count stations 300 m interval distance apart from each other were established within the study area. The main reason of using 300 m interval apart between point count stations was to avoid double counting of the same birds at more than one station. The birds were surveyed fifteen consecutive times at monthly interval for each station to obtain reliable estimates and to reduce bias. The replication of point count stations increased precision and provide reliable results (Petit et al., 1995; Smith et al., 1993).

The survey was done early in the morning from 0730 and 1100 h. The detections of birds within each point count station were done for ten-minutes.

Fig. 1:	Location map of paya indah wetland reserve, selangor peninsular Malaysia

Ten-minute count enables to record sufficient number of individuals with minimal efforts and disturbance (Lee and Marsden, 2008; Jimenez, 2000; Lynch, 1995; Gutzwiller, 1991). During each survey all bird species and individuals seen or heard and the distance from the point station to the birds were estimated. The flushed birds with known original position were included in the analysis while flying birds were omitted due to unknown original position. The methodology was followed as described by Nadeau et al. (2008), Aborn (2007), Buckland et al. (2004) and Bibby et al. (2000).

Data analysis: The density of bird species was determined using Distance Software (Version 4.1) by Buckland et al. (2004). The bird density of those species whose numbers of detections were below five were not analyzed due to low number of sample size. The methodology was followed as described by Marsden (1999). The diversity indices such as species diversity, richness and evenness were determined using Community Analysis Package Software (CAP, Version 4.0) by Henderson and Seaby (2007).

RESULTS

Species composition: Distance sampling point count method detected a total 13872 bird individuals that belong to 100 species and 38 families at Paya Indah Wetland Reserve, Selangor Peninsular Malaysia. Out of the total number of species, 25 bird species were belongs to water birds (3088 detections; 22.26%) and 75 bird species were belongs to terrestrial birds (10784 detections; 77.74%) (Appendix 1 and 2).

Overall bird density: The density analysis shows that the bird density of Paya Indah Wetland Reserve, Peninsular Malaysia is 83.92±4.53 birds ha^-1 that ranged from 75.40-93.41 birds ha^-1 (95% confidence interval). The results also show that the terrestrial birds have higher density (70.26±4.48 birds ha^-1) as compared to water birds (13.09±1.78 birds ha^-1) (Table 1).

Water bird density: The five highest waterbird species density was recorded for Purple Swamphen (5.05±0.89 birds ha^-1) followed by Lesser Whistling Duck (4.66±1.12 birds ha^-1), White-breasted Waterhen (3.02±0.35 birds ha^-1), Yellow Bittern (2.84±0.62 birds ha^-1) and Cotton Pygmy Goose (2.63±0.11 birds ha^-1). The five lowest waterbird density was recorded for Little Grebe (0.35±0.12 birds ha^-1), Black-crowned Nightheron (0.33±0.12 birds ha^-1), Ballion's Crake (0.31±0.13 birds ha^-1), Pheasant-tailed Jacana (0.26±0.12 birds ha^-1 and Grey Heron (0.13±0.05 birds ha^-1). In addition, the densities of four water birds namely Common Kingfisher; A. atthis, Great Egret; C. albus, Little Egret; E. garzetta and Slaty-breasted Crake; G. striatus were not analyzed due to very low detections (< 5 observations) (Table 2).

Table 1:	The density of water birds and terrestrial birds of paya indah wetland reserve, peninsular Malaysia

Table 2:	Ranking of water bird density at paya indah wetland reserve, peninsular Malaysia

Table 3:	Ranking of terrestrial bird density at paya indah wetland reserve, selangor peninsular Malaysia

Terrestrial bird density: The five highest terrestrial bird density was recorded for Yellow-vented Bulbul (12.97±1.05 birds ha^-1) followed by Pink-necked Green Pigeon (11.4±1.15 birds ha^-1), Peaceful Dove (9.85±0.96 birds ha^-1), Eurasian Tree Sparrow (7.85±2.17 birds ha^-1) and Rufous-tailed Tailorbird (7.54±1.43 birds ha^-1).

Table 4:	Comparison of bird species diversity of terrestrial birds and water birds at paya indah wetland reserve, selangor peninsular Malaysia

The five lowest terrestrial bird density was recorded for Black-throated Sunbird (0.41±0.19 birds ha^-1) followed by Rufous Woodpecker (0.40±0.14 birds ha^-1), Greater Coucal (0.39±0.15 birds ha^-1), Little Spiderhunter (0.34±0.12 birds ha^-1) and Ashy Minivet (0.31±0.18 birds ha^-1). In addition, eighteen bird species were not analyzed due to small sample size (<5 observations) (Table 3).

Diversity: Diversity is a major aspect of species structure in avian community. Principal Component Analysis Software (CAP Version 4.0) by Henderson and Seaby (2007) was used to determine and compare the diversity of water birds and terrestrial birds in the study area. The result shows that terrestrial birds have the highest species diversity i.e., Shannon’s index (N₁ = 20.83), species richness i.e., Margalef’s index (R₁ = 7.97) and species evenness i.e., McIntosh’s index (E = 0.73) was recorded in terrestrial birds compared to water birds (Table 4).

DISCUSSION

Freshwater wetlands are highly important habitat for wide array of waterbirds as well as terrestrial birds and their importance depends on size, diversity of vegetation, water quality, food resources and topography. Birds are most conspicuous and significant component of freshwater wetland ecosystems and their presence or absence may indicate the ecological conditions of the particular areas.

The growing pressure on wetland resources due to human activities, climatic and edaphic changes has caused great threats to wetland fauna especially water birds throughout the world (Greenwood et al., 1995; Laurance, 1999). Determining the accurate population size and population fluctuation of different birds in wetland habitats is highly important to understand the bird community structures and population status of existing species in the dwelling area (Thompson, 2002; De Sante et al., 2005; Kaminski et al., 2006).

Paya Indah Wetland Reserve is a natural wetland and extremely variable in vegetation structures, vegetation composition and productivity (food resources, nesting sites and shelter). The recording of 25 water bird species and 75 terrestrial bird species using point count method shows that this wetland reserve is a highly important habitat and support diverse water birds and terrestrial birds in order to perform multiple activities such as foraging, breeding, loafing and roosting. The occurrence of higher number of species could be due to vegetation diversity such as trees, shrubs, emergent and submerged vegetation, reeds and sedges, ferns, grasses and herbs that provides multiple microhabitats. The different strata of vegetations also have attracted different bird species through offering optimal combinations of food, water and shelter resources that satisfy the daily requirements of bird species to maintain their populations.

The results of this study show that the highest water bird density was recorded in Purple Swamphen followed by Lesser Whistling Duck and White-breasted Waterhen. This may be due to diversity and richness of aquatic vegetation such as emergent vegetation (i.e. Eleocharis dulcis, Nelumbo nucifera, Nelumbo pubescens and Philydrum lanuginosum), grasses (i.e., Scirpus olneyi, Panicum maximum and Imperata cylindrical), sedges and rush (i.e., Scleria purpurascens and Spartina alterniflora), ferns (i.e., Stenochlaena palustris, Cyclosorus interruptus and Lycopodium cernuum), reeds (i.e., Phragmites karaka and Typha angustifolia), submerged (Myriophyllum spicatum, Salvinia minima, Creatophyllum demersum and Elodea sp.) and herbaceous plants (i.e., Cyperus sp., Junicus effuses and Panicum repens) that created suitable habitats and offer abundant food resources, safe breeding sites and hiding cover from predators and weather. Heterogeneity of aquatic vegetation also provides a dwelling area for different invertebrate assemblages such as Oligochaeta, Turbellaria, Hirudinidea, Pelecypoda, Arachnida, Insecta and Crustacea (Kostecke et al., 2005). These invertebrates are an important food sources for waterbirds (Anderson and Smith, 2000). The greater abundance of invertebrate are closely related to dense aquatic vegetation due to higher habitat structural complexity (Gray et al., 1999; De Szalay and Resh, 2000).

Water birds are closely associated to wetland aquatic vegetation to complete their life cycles and often select the most available microhabitats in different ways depending on their behaviour or spatial location (Nudds et al., 1994; Green, 1998; Hag et al., 1998). Vegetation composition and structure (Isacch et al., 2005), habitats characteristics and food resources (Murkin et al., 1997; Farmer and Wiens, 1999; Ashley et al., 2000) and surrounding landscape are the key factors that influence the distribution, diversity, density and habitat selection of bird species (Pearson, 1993; Koopowitz et al., 1994; Vos and Stumpel, 1995).

Factors that influence the habitat selection may vary from species to species. For example; species morphology, foraging behaviour (e.g., visual vs. tactile foragers) and prey availability (i.e., prey density and vulnerability to capture) may affect the distribution and reproduction success of water birds (Gawlik, 2002). Hattori and Mae (2001) stated that the highest species richness and density of water birds occurs in reed bed of aquatic vegetation where the water level is 20 to 65 cm in depth. Fairbairn and Dinsmore (2001) and Kushlan (2000) also reported that water bird density is associated with habitat variables such as vegetation cover, food, safe nursing and loafing sites. This study indicated that waterbird populations are directly influenced by the amount and quality of available foraging habitats and they select wetland areas with surface water that supply suitable prey organisms for foraging.

The highest terrestrial bird density was recorded in Yellow-vented Bulbul followed by Pink-necked Green Pigeon, Peaceful Dove, Eurasian Tree Sparrow, Scaly-breasted Munia and Baya Weaver. This could be due to the presence of different habitats such as marsh swamp, lotus swamp, open water body, dryland and patches of shrubs and availability of abundant food sources such as variety of fruits, insects, seeds, grains, safe roosting and breeding sites. These similar observations have been recorded by Zakaria et al. (2009) and Rajpar and Zakaria (2009). The distribution of scatered trees and patches of shrubs created different layers of vegetation that serve as potential foraging and nesting sites for them. Vertical layering and complexity of vegetation has increased the foraging surfaces for terrestrial insectivore and frugivore bird species. The adjacent areas such as oil palm plantation and forest reserve may also influence the distribution of bird species. Petit and Petit (1996) and Cody (1985) reported that bird density is positively correlated with habitat heterogeneity and preference.

The results of diversity analysis show that bird species diversity may vary from terrestrial birds to water birds. The higher bird diversity, richness and evenness were recorded in terrestrial birds as compared to water birds. This may be due to difference in habitat richness and diversity of vegetation such as trees, shrubs, emergent vegetation, grasses, sedges, rushes, ferns, reeds, submerged and herbaceous plants. The terrestrial birds seem to be capable of using all available habitats within the wetland area. Unlike the water birds which are highly dependent on the water based or water related habitats such as marsh swamp, lotus swamp and open water body. In most instances, bird diversity is parallel to habitat diversity as suggested by Buffington et al. (1997) and Jobin et al. (2001) studies.

In addition, other factors such as weather (rainfall), social interactions and predators such as Water Monitor Lizard (Varanus salvator), Monitor Lizard (Varanus begalensis), Python (Python reticulates), King Cobra (Ophiophagus hannah), Cobra (Naja naja) may also affect the distribution and habitat selection of water as well as terrestrial birds in the wetland reserve. These findings were consistent with other studies in similar types of habitat (Zakaria et al., 2009).

CONCLUSION

This study indicated that Paya Indah Wetland Reserve is highly important habitat for waterbirds as well as terrestrial birds. The wetland bird richness is closely associated with vegetation structure and composition, size of wetland, diversity and abundance of food resources and shallowness of water. Habitat structural diversity provides refuge from predators.

ACKNOWLEDGMENT

The authors would like to thank Department of Wildlife and National Parks, Peninsular Malaysia to allow conducting this research study at Paya Indah Wetland Reserve. This research was partially funded by Fundamental Grant Research Scheme 01-10-07-291FR and Forestry Sector Research Division Project, Pakistan Forest Institute, Peshawar Pakistan.

APPENDIX

Appendix 1:	List of water bird species recorded using point count method at paya indah wetland reserve, peninsular Malaysia

Appendix 2:	List of terrestrial bird species recorded using point count method at paya indah wetland reserve, peninsular Malaysia