Abstract: This research investigated the effects of urbanization on bird communities, in which bird assemblages of different land use, namely urban and suburban, agroforestry and forest areas were compared. Point counts were applied to record all birds within a radius of 50 m and all birds detected visually and acoustically within 15 min were recorded. Although, the different of number of species among land use types was negligible, results showed that the diversity of bird communities were highly different. Bird diversity in urban environment was lower than those in forest but higher than in agroforestry. Urban environment with high landscape heterogeneity promoted by human supported a diverse bird species. The composition of bird communities was also very different among the land uses, because each species has different ranges of habitat optimal for them. Surprisingly, the value of conservation index of urban environment was the highest, because all of three endemic bird species can survive in urban environment. The evidence that urban area can have high conservation value must be considered by urban planner.
INTRODUCTION
The studies in the United States showed that among the leading causes of species endangerment the interactions of native with non-native species ranked highest, followed by urbanization and agriculture (Czech et al., 2000). In many cases, introduction of exotic species can lead to rapid extinction of indigenous species. For example, introduction of exotic species by European have been the primary cause of extinction of many bird species in Australia (Primack, 1995). Urbanization threats wildlife directly by replacing natural habitat with infrastructure facilities and housing and by depleting resources necessary for wildlife to support urban development (Czech et al., 2000). The world’s urban population will grow substantially over the next 25 years (1.80% annually). In 2005, world’s urban population was 3.15 billion people or 48.7% of the world’s population and it is projected to increase to 4.9 billion people by 2030, roughly 60% of total human population (United Nations, 2006). Based on this prediction, the pressures of urbanization processes on the survival of wildlife is expected to increase. Extreme change of landscape composition and configuration of initially agriculture and natural land uses to urban environment will represent a major threat to regional and global biodiversity (Clergeau et al., 2006).
The rapid process of urban development and change of human lifestyle, make deep understanding of the ecological processes operate in urban environment especially necessary for sustainable land-use planning (Palomino and Carrascal, 2006) and for conservation of biodiversity (Cornelis and Hermy, 2004). Urban areas are area excellent for ecological study (Whitten et al., 1996). However, until recently little thought has been directed to conservation of urban habitate and wildlife (Bolen and Robinson, 2003). Especially in the southern hemisphere, urban ecosystem has been poorly studied when compared with those in northern hemisphere. Usually, urban environment is considered as area of low diversity with large populations of few species. However, there is mounting evidence that urban and suburban forests can contain relatively high level of biodiversity (Alvey, 2006). Urban forest and green space are a key means of preserving and promoting biodiversity in the urban ecosystem. Management of wildlife in urban area with the greatest human pressures and other resources in short supply is very challenging, because in this area the concept of multiple-use of land reaches to its maximum application (Bollen and Robinson, 2003).
Often, avian fauna was used to evaluate the impact of urbanization on wildlife or as an indicator of urban sustainability (Clergeau et al., 2006; Donnelly and Marzluff, 2004; Fernándes-Juricis, 2000; Hostetler, 1999; Hostetler and Knowles-Yanez, 2003; Palomino and Carrascal, 2006; Melles, 2005; Sandström et al., 2006). Birds are sensitive indicators of environmental change because they are high in the food chain. Thus, they reflect changes to plants and animals that are their food. As birds are highly mobile they sum up changes over large areas and because birds have a short life spans, environmental changes will be quickly indicated by change of their populations. Furthermore, native bird species have proved a popular indicator of care for nature and effective nature conservation (London Sustainable Development Commission, 2004). To increase the quality of life in cities, the World Health Organization (WHO) has recommended a minimum of 9 m2 of green space per person (Whitten et al., 1996). In the urban landscape the composition and species diversity of birds are mainly affected by local factors such as age of vegetation and the size of urban forest. Isolation from species gene pool does not appear to exert any significant influence on community assembly of birds (Fernándes-Juricis, 2000).
Urban areas can be divided into three zones (Van Druff, 1979). The metropolitan centre is the densely populated inner-city or down town area. This area has little room for vegetation and wildlife. The second zone is suburbia, which less densely developed than the inner city. More green area is available here and wildlife may present in remnants habitat of former natural communities interspersed among human habitations. The third zone is rural-urban interface, which is the least developed and opportunity to save important habitate is still available. To understand the role of urban environment on conservation of bird diversity, comparison of composition of bird community in the urban and in other land uses was conducted. The main goals of this research are to study the effects of urbanization on the bird communities by comparing their composition and diversity in urban and in natural environments.
MATERIALS AND METHODS
Study area: The study was conducted in Yogyakarta province in Java island, Indonesia. It is located in the central part of the island. Java is one the most densely populated island in the world with 114 millions inhabitants on an area of 132,000 km2, or at average the human density is 864 people km-2. Yogyakarta province covers an area of 3185.8 km2 with an average human density of 1,011 people km-2. The most densely area is the city of Yogyakarta with more than 12 thousands people km-2, surrounded by sub urban areas with an average human density of 1,600 people km-2. Hence, human pressures on the natural environment are very high leaving little space for natural and semi-natural habitats. In this province, state forests count for approximately 171 km2, or only 5.4% of the total area. Further conversion of agriculture and green spaces and transformation from rural to urban are expected to continue, because annual population growth of suburban areas is still high (1.5% year-1).
To study species composition of bird in different land use system ten locations were selected. They are consisted of eight metropolitan centres and suburbia areas (U1-8), one agriculture system (A1) and one forest environment (F1). The study area is in total 737 ha and composed of 137 ha urban, 300 ha agroforestry and 300 ha forest areas. Table 1 provide further details on each habitat type.
Bird survey: The survey of animal was conducted between July and September 2006. Point counts were used to record all birds within a radius of 50 m from the centre of point transect (Bibby et al., 1995). Points were visited between 06:00 and 09:00 h and all birds detected visually and acoustically within 15 min were recorded. The distance between points was 150 m. A rangefinder was used to measure and estimate distance and all observation beyond 50 m were excluded from the analysis. Field guide to bird species of Sumatra, Java, Bali and Kalimantan provided by MacKinnon et al. (2000) and the encyclopaedia of birds by Perrins (2003) were facilitated species identification.
Data analysis: Shannon-Wiener index (H’) and the reciprocal form
of Simpson index (1/D) was used to measure the diversity of bird species in
each habitate types. It is calculated from the equation (Ludwig
and Reynolds, 1988; Magurran, 1988):
| Table 1: | Description of study sites in Yogyakarta |
The significant different of species diversity between habitat types was calculated by using t-test provided by Hutcheson (1970) as follow:
The similarity of bird assemblage between land uses was quantified with percent of similarity (PS) introduced by Bray and Curtis (1957):
The index of conservation important was calculated for each habitat type. This index allows the comparison of bird communities not only based on their species composition and abundance but also based on the species conservation status of observed species in each habitat types. The IUCN assessment system and endemic status was used to assign species value for each species. Species of no conservation concern will have a score (v) of 1, vulnerable species will have a score of 2, endangered species will have a score of 4 and critically endangered species will have a score of 16. Endemic but non threatened species will have a score of 4 and those that possess threatened status will have a score of 16. The index of conservation important was calculated for each habitat type as follow (Petit and dan Petit, 2003):
where, Ij is the relative conservation important of habitat j, vi is the vulnerable score of species i, n is the number of species in habitat j and pij is the relative preference by species i for the habitat j.
The habitat preference of a species for habitat j is calculated as the proportion of the total number of individuals of species i observed in habitat j. Consequently, for each species, the value of pij ranges from 0 to 1 within a land use type and sum to 1 across all land uses.
RESULTS
Results of this research showed that the number of bird species recorded in the study area was 55 species and 23 families with the value of pooled diversity index was H` = 2.85. Three species were listed as endemic to Java and Bali, namely Orthotomus sepium (Olive-backed Tailorbird), Padda oryzivora (Java Sparrow) and Halcyon cyanoventris (Javan Kingfisher). Olive-backed Tailorbird occurred in urban and agroforestry area and Java sparrow was found only in urban area, while Javan Kingfisher was present in all habitate types. Classification according to their guilds showed that 25 species were insectivore, nine omnivore, eight granivore, four carnivore, three frugivore and granivore, three insectivore and carnivore, two nectarivore and one insectivore and granivore. Most birds were generalist species with a broad habitat range from secondary forest, agriculture area to semi open and urban environment. No bird was known as forest dependent species. The list of species found in the study area was shown in Table 2.
In comparison with other habitat, agroforestry area has the highest number of species with 33 species and 18 families, followed by urban environment with 31 species and 17 families. Surprisingly, forest area has the lowest number species with only 30 species and 17 families. On the other hand, the highest density of individuals occurred in urban environment followed by forest and agroforestry. However, the calculation of diversity index with Shannon-Wiener Index, Simpson Index and Shannon-Evenness Index showed that forest consistently has the highest diversity. The t-test showed that the diversity of bird species between agroforestry and forest (t = 7.32; p<0.01; df = 2375), between agroforestry and urban (t = 6.02; p<0.01; df = 1864) and between urban area and forest (t = 2.78; p<0.01; df = 2474) differed highly significantly. Total number of individual per km2 and the value of diversity index were shown in Table 3.
The composition of bird species among the habitat types was very different
as shown by the calculation of community similarity. The similarity percentage
between urban and agroforestry bird community was the lowest (27%), between
agroforestry and forest was 34. 74% and the highest between urban and forest
(35.17%). The conservation value of each habitat with bird species as determinant
factors showed that urban environment possessed the highest value of conservation
index (27.21) followed by agroforestry (18.46) and the lowest forest (18.33).
According to BirdLife International (2008) Checklist version
1 published by Birdlife International all species recorded in the study area
were classified as low concern of conservation priority. Therefore, the conservation
value of each habitat types was determined mainly by the number of species and
the number of individuals.
| Table 2: | List of observed bird species and their density in each habitat types |
| *C: Carnivore, F: Frugivore, G: Granivore, I: Insectivore, N: Nectarivore, O: Omnivore | |
| Table 3: | Value of index diversity of bird community fore forest, urban and agroforestry area |
DISCUSSION
The finding of this study showed that although, the difference of the number of bird species among the habitats was negligible, the composition of bird communities was significantly different showed by low value of percentage of community similarity among the habitats. Among 55 species, only thirteen species occurred in all habitat type. The only family that occurred only in urban environment was Ardeidae (Heron family). Member of this family recorded in this research included Ardea cinerea (Grey Heron), Ardeola speciosa (Javan Pond-Heron), Nycticorax nycticorax (Black-Crowned Night-Heron) and Bubulcus ibis (Cattle Egret). Herons and egrets were mobile birds. Most individuals moved significant distances, not only from day to day but also hour to hour (Perrins, 2003). As roosting trees they selected big and tall tree, where the presence of predators and disturbances were at a minimum level. In urban environment they preferred arboretums to build nesting colony. The birds spent much of the non feeding portion of the days at roost. They typically formed a mixed segregation of species at the same tree.
The similarity between forest and agroforestry was, not as expected, lower than those between urban and forest. It was because the urban green areas have more big trees than agroforestry area, which was dominated by crops and small tree. Therefore, the environmental condition between forest and green area in urban area was more similar. In addition, although the number of recorded bird species in forests was the lowest, the value of diversity index was the highest, because in the calculation of diversity index not only the number of species was considered but also the evenness that is how equally abundant the species are (Magurran, 1988). The higher value of diversity index for forest bird community was evidence that the abundance of bird was more equal in forest than in urban environment and in agroforestry area. In general, the value of diversity index for urban, agroforestry and forest indicated the moderate status of ecological diversity (Jørgensen et al., 2005). This research did not support finding that urban environment are generally less diverse than forest and agroforestry (Palomino and Carrascal, 2006). However, this finding was not unique. Kühn et al. (2004) reported that in Germany city grids were more divers in plant species than non-city grids. The same results were also reported by Araújo (2003) that in Europe urban areas had a higher level of biodiversity in comparison to unpopulated area. There was also evidence of positive association between human population density and species richness of bird, mammal, snake and amphibians in Africa (Balmford et al., 2001). Urban and suburban areas can maintain high species richness, if they are composed by different semi-natural habitats (Cornelis and Hermy, 2004). Some possible explanation about the positive relationships between species richness and human population were proposed by Araújo (2003). First explanation was that the areas suitable for human were also generally suitable for other species. Second, human activities might increase the diversity of area through introduced species and promoted landscape heterogeneity.
The results of the research showed that the density of bird species in the urban area was higher than in any natural habitat in the surrounding area was supported by other research (Palomino and Carrascal, 2006). It was because in urban environment resources required by bird such as, foods and shelters were more abundant than in natural habitat. Moreover, several species are well adapted to urban habitat. The research showed that urban environment had higher conservation value than forest and agroforestry area, because all recorded endemic species were present. On the other hand, no forest-dependent species were recorded in forest as well as in the agroforestry area, which would increase the conservation value of these areas. The results of this study was an evidence that urban environment can maintain high level of diversity of non forest dependent species. The city and forest planner must maintain urban forests and green areas as well as street vegetation in adequate size to preserve diversity of bird species as high as possible.
ACKNOWLEDGMENTS
This study was funded with research grant provided by the Faculty of Forestry and Department of Forest Resource Conservation, Gadjah Mada University through PHK-A2 grant 2006. We thank all members of Bird Watcher Club at the Faculty of Forestry for helping with data collection. Also, many thanks for the manager of Wanagama Teaching Forest and Local Governments of Sleman and Saptosari, Yogyakarta, who permitted the authors to conduct this study in their territories.