Avifaunal diversity and bird community responses to man- made habitats in St. Coombs Tea Estate, Sri Lanka

Author Details: Mr. J. Dananjaya Kottawa-Arachchi is a research officer and he has conducted research on biodiversity in tea plantations and birds of montane ecosystems in Sri Lanka. He is the vice president of Hill Country Environment Association and secretary of Friends of Horton Plains, Sri Lanka. Mr. Rajika N. Gamage is a wildlife photographer and author of illustrated guide to the Butterflies of Sri Lanka. He is a photographer at Tea Research Institute and has conducted research on butterflies of Sri Lanka. He is the president of Hill Country Environment Association and committee member of Friends of Horton Plains, Sri Lanka.


INTRODUCTION
Sri Lanka is a tropical island (65,610km 2 ) located in the Indian Ocean, off the southern tip of the Indian peninsula. A growing human population in Sri Lanka has resulted in the reduction of natural habitats as natural forests have been converted to human settlements, agricultural lands, industrial areas and other related infrastructure development. A large scale destruction of natural forests took place especially during British occupation in order to establish plantation crops such as tea, coffee and rubber. These activities marked the beginning of environmental problems and large scale biodiversity erosion in the country (Anonymous 1999). Even in the present day scenario, existing protected forests in the wet zone that are rich in biodiversity, continue to degrade due to illegal encroachment, suffering further fragmentation.
The systematic study of the avifauna of Sri Lanka began in the mid-18 th century with major contributions from naturalists such as J.G. Loten, R. Templeton, E.L. Layard, E.F. Kelaart and V. Legge (Weerakoon & Gunawardena 2012). Sri Lanka supports a rich avifauna diversity that stands at 453 species at present. This includes 237 species of birds that are known to breed in Sri Lanka, of which 33 are endemic species (Rasmussen & Anderton 2005). Further, 21 species that are listed as breeding residents, also have migrant populations, which include migrants of different races of the species that occur in the country. The remaining 216 species are migrants of which 72 species are encountered rarely and therefore considered as vagrants (Weerakoon & Gunawardena 2012).
Studies on flora and fauna of economically important crop plantations such as tea, rubber and coconut are very scarce in Sri Lanka. Further, the role of human-altered landscapes in biodiversity conservation has been greatly neglected. Extensive studies on ecology and distribution of birds of Sri Lanka have so far been conducted in and around protected areas such as Sinharaja World Heritage site (Bambaradeniya et al. 2003), Lower Hantane (Gunaratne & Gunatilleke 2003), Wilpattu National Park (Weerakoon & Goonatilleke 2007), Galoya National Park (Hettige et al. 2000), and rarely in human-altered habitats such as at Buttala (Surasinghe & Alwis 2010). For plantation crops, a detailed avifaunal diversity survey was done by Kottawa-Arachchi et al. (2010) in Mattakelle tea estate, Talawakelle where 61 bird species were recorded in seven different habitats.
Therefore, this study was focused on estimating bird diversity and classifying important habitats for avifauna in tea plantation ecosystems in Sri Lanka.

STUDY AREA
The present study was conducted in St. Coombs tea estate (6 0 55'N & 80 0 40'E) in the up-country wet zone of Nuwara Eliya District, Sri Lanka (Fig. 1). This tea estate is under the management of Tea Research Institute (TRI) of Sri Lanka. It is situated in the Agroecological region WU2a (Panabokke & Kannangara 1996) falling under the montane wet zone. The mean annual precipitation is 2250mm and the annual average minimum and maximum temperatures are 14.2 0 C and 24.8 0 C, respectively. The average elevation is 1382m. The estate covers an area of 237ha of which 128ha is under tea cultivation.
The agro-ecosystems in St. Coombs tea estate are dominated by Tea (Camellia sinensis) plantations with low shade trees such as Erythrina lithosperma and Calliandra calothrysus, and high shade trees Grevillea robusta and Eucalyptus spp. A small segment of the land is under multi-species cultivation of vegetables, managed by the estate community. Among the tree species, Avocado Persea americana, Mango Mangifera indica, Guava Psidium guajava, P. littorale, Jackfruit Artocarpus heterophyllus and Annona squamosa could be found in home gardens. Kahakona Cassia spectabilis, African Tulip Tree Spathodea campanulata and Fern Tree (Jacaranda mimosifolia) were found along roadsides as ornamental trees.
The objectives of the study were to identify the habitats, which are beneficial to bird life in tea plantation ecosystems, quantify the present status of avifaunal diversity, behavioral patterns of birds and the identification of ecosystems in St. Coombs tea estate for threatened bird species. This information could be of importance in formulating effective strategies to conserve the agro-ecosystems, to develop further studies and in particular to understand the beneficial effects of the natural avifaunal diversity to the tea plantations.

METHODS
A thorough field survey was undertaken to identify different habitats in St. Coombs tea estate and based on the complexity of habitat structure, five habitats (home garden, wetland, tea plantation, Eucalyptus plantation and small scale reservoir) were chosen for threatened and 16 nationally threatened bird species were identified. Seventeen bird species were observed in all five habitats (Table 1) and the most encountered bird species was the Sri Lanka White-eye Zosterops ceylonensis (Image 6). Sometimes, it was observed in large flocks of 100-250 individuals.
Species diversity of different floral and faunal components of Sri Lankan home gardens depict that a wide variation exists in species assemblages of different geographic/agro-ecological regions (Pushpakumara et the present study (Images 1-5). This was followed by the field observations on birds for a period of five years from January 2008 to December 2012. The line transect method was used in this study. The intensity of observations was two days per month. Bird counts were made along a 200x20 m line transect and 30 minutes were spent in each habitat (06.30-07.00 hr or 16.00-16.30 hr) and the same methodology was repeated in all habitats selected for the study. The time of monitoring of each habitat was planned in such a way to ensure that each habitat was monitored both in the morning as well as in the evening. The activities of birds, feeding habits and food recourses were also observed and recorded.
A pair of 7x35 binoculars (Nikon) was used to observe birds. Popular field guides including Kotagama & Fernando (1994), Harrison & Worfolk (1999) and Warakagoda et al. (2012) were used for bird identification. A pre-designed data sheet was used for the purpose of recording.

RESULTS AND DISCUSSION
During the study period, a total of 87 species of birds including 11 species of endemics and 11 species of migrants were recorded. Among them, one globally The results indicated that home garden as a habitat showed the highest bird diversity (63 species, 75% of the total recorded). The Shannon index (H') was 3.38 and evenness (E) was 0.40. This was expected as the home garden habitat was well-structured and heterogeneous with different plant species, including woody lianas and grasses that provided more niches and food sources for birds. The avifaunal diversity was comparatively low in other habitats and their Shannon index (H') is given in Koel Eudynamys scolopacea, which are very rare in the Agro-ecological region WU2a, were also recorded but only once in the home garden. The wetland habitat is a hydrologically influenced wood-land, which is prone to regular floods during the south-west monsoon. A total of 40 bird species was recorded in this habitat (Fig. 2). The Cattle Egret Bubulcus ibis, Indian Pond Heron Ardeola grayii, Whitethroated Kingfisher Halcyon smyrnensis and Barn Swallow Hirundo rustica were very common at this site. Blyth's Reed Warbler Acrocephalus dumetorum, Ashy Prinia Prinia socialis, Plain Prinia P. inornata, Common Tailorbird Orthotomus sutorius and Scaly-breasted Munia Lonchura punctulata were also frequently recorded in this habitat. Soh et al. (2006) suggested that the poor canopy cover in the tea plantation was probably the main factor On the other hand, large numbers of insectivores were observed during the study period. For example, 45 out of 87 of the bird species were insectivores. The study revealed that most of the insectivores fed on flying insects. The high number of avifaunal observations made on the shade tree species of Calliandra calothrysus, Grevillea robusta and Spathodea campanulata could be due to the fact that they are wide spread throughout the plantation and provide micro habitats for the various needs of the avifauna.
During the study period, two nests (tree holes) of Crimson-fronted Barbet and Yellow-fronted Barbet were observed on the dead branches of avocado P. americana and Ficus trees in home gardens, respectively. Few nests of Scaly-breasted Munia Lonchura punctulata were observed throughout the year in home gardens. Two adults of Oriental Magpie-Robin Copsychus saularis were seen carrying food material in September 2012. A juvenile of Greater Coucal Centropus sinensis accompanied by two adults were seen in Home gardens. Two nests of Sri Lanka White-eye Zosterops ceylonensis were noticed in the tea plantation and the nests were seen on the fork of tea C. sinensis bushes at a height of about 1m. The nests were built by the fibres and leaves of various grasses. Two adults of Plain Prinia Prinia inornata with two juveniles were recorded in the wetland habitat.

Threats to the avifauna of the region
Nearly one-third of all the resident birds in Sri Lanka are forest birds, including all the endemic species. Out of the endemic birds, more than 60% are restricted to the forests in the wet zone (Weerakoon & Gunawardena 2012). These forests are being rapidly depleted to support the needs of the burgeoning human population. Therefore, loss of forest cover and fragmentation of forests are the main threats faced by the birds of Sri Lanka. Narayanan et al. (2011) also revealed that landscape alteration, hunting, felling of nesting trees and pesticides are the major detrimental factors for the survival of birds.
A considerable extent of habitat destruction and modifications were observed during the study period in St. Coombs tea estate. Most wetlands and seasonal streams of the study area, which provided habitats for waterfowls, grassland birds and egrets, have been converted to agricultural lands. Setting fire to grasslands and scrub vegetation were observed during the dry season. These activities adversely affected the migratory birds such as warblers and Pitta by reducing available roosting and foraging areas as well as food. Dead trees in home gardens and tea fields which could be used to make holes by barbets and woodpeckers for nesting are being removed for firewood regularly. Furthermore, it could directly affect the nesting sites of resident avifauna.
Regular human movement through tea fields and noises from vehicles may have affected the behavior of forest birds. These activities may have caused to reduce such species in tea ecosystem, when compared to natural forests. On the other hand, the population of the Jungle Crow Corvus macrorhynchos drastically increased as a result of garbage accumulation. It was observed that groups of crows extensively predated on birds including their eggs and juveniles. They were also responsible for destroying bird nests.
An increase in plant diversity with native nectarine species and fruit-bearing plants was observed in home gardens and road sides which could have improved avifaunal diversity. Thus, the importance of maintaining large natural forest cannot be overemphasized in order to conserve the diversity of forest birds. In this context, plantations with a mixture of indigenous tree species may serve well to compensate for the loss in forest areas, as their bird species richness and community composition closely resembled natural forests (Farwig et al. 2008). Increasing plant diversity with native species in the abandoned lands, home gardens and road sides and creating awareness of the detrimental effects of excessive use of agro-chemicals among the estate community would certainly bring the necessary beneficial changes to these ecosystems. Further studies are needed on ecology, behavior, population dynamics and interaction with human activities in plantation ecosystems.

CONCLUSION
Out of the five habitats selected for this study at St. Coombs tea estate, home gardens stand out as the best site for birds, followed by the small scale reservoir. The current study shows that home gardens support bird diversity including a large proportion of endemic bird species thereby enabling these findings to be used as guidelines in long term conservational practices. Several conservation measures such as increasing plant diversity, introduction of shade trees and prevention of fire are recommended to protect and conserve avifaunal