Sinharaja is a Rain Forest and a biodiversity hotspot which is located in south west lowland wet zone within Sabaragamu and Southern provinces of Sri Lanka. Sinharaja rain forest is the country’s last viable area of primary tropical rain forest. It covers an area of 11,000 Ha of primary and secondary forests. This narrow strip of rolling site comprises of a series of ridges and valleys. More than 60% of the trees are endemic to Sinharaja Forest and many of them are considered rare. There is much endemic wildlife, especially birds but the reserve is also home to over 50% of Sri Lanka’s endemic species of butterflies & mammals and also many kinds of insects, reptiles and rare amphibians. This is one of the main reasons that UNESCO declared Sinharaja Forest as a UNESCO World Heritage in 1988 under the name of Sinharaja Forest Reserve. In 1936 Sinharaja Forest was first recognized as being the only considerable patch of virgin tropical rain forest in the Island. Sinharaja forest was accepted by UNESCO as a biosphere reserve in 1978. Recognizing the need for maximum possible 4 protection the site in near declared as a National Heritage Wilderness Area. Being the habitat for rare and endangered species and an outstanding site for study of the process of biological evolution. Sinharaja Forest is the best place to watch mixed species bird flocks. According to a study carried out on the mixed species bird flocks, 42 individual birds occur in the flocks on average which makes this the world’s largest mixed species bird flock. The mixed species Bird flock study of Sinharaja forest has been continuing since 1981 and is considered as the World’s longest bird flock study.