The Bird Community at Pasoh: Composition and Population Dynamics
Pasoh Forest Reserve (Pasoh FR) has been the site of several bird population studies, starting in the late 1960s and continuing through the present. So far, at least 220 species of birds have been reported using the primary forest in Pasoh FR, with an additional 13 species in the regenerating forest and edge habitats. Of these, about 184 species are residents that are likely to breed within the primary forest. Estimated population densities for several common babblers were 11~70 individuals per 100 ha suggesting total populations of 200~1,500 individuals within Pasoh FR. However, most species were much less common, many with only a few pairs per 100 ha, or in some cases only a few pairs in Pasoh FR. Such populations are assumed to be too small to be viable in the long term without immigration from outside Pasoh FR. Many species were long-lived, with representatives of 14 species having been captured at least 10 years after initial ringing. The longevity record so far, is held by a Rufous-collared Kingfisher (Adenoides concretus) that was ringed as an adult in 1972 and recaptured 21 years later. Apparent survival rates for 14 resident species, after correcting for lower returns of newly ringed birds, averaged 77% per year. As such, populations could persist for many years even if breeding were impaired. Because Pasoh FR is now surrounded on three sides by oil palm plantations, and is too small to support viable populations of many species in isolation, the future of the bird community may be at risk. Further research, to estimate population densities of all species and possible movements to and from the adjoining hill forest, would be valuable to determine which species are most at risk, and to try to identify mitigating measures. Such research would also be of considerable value for understanding the relationships between extinction risk, population movements, population dynamics and rarity.