Malcolm C. K. Soh

Undesirable aliens: factors determining the distribution of three invasive bird species in Singapore

Biological invasions are a major environmental concern due to their negative impacts on biodiversity and economics. We determined the population sizes and habitat-abundance relationships of the three most successful invasive bird species in Singapore: the house crow Corvus splendens, white-vented myna Acridotheres javanicus and common myna A. tristis. Estimated population sizes of the three species between February 2000 and February 2001 were between 106 000-176 000, 122 000-155 000 and 20 000-29 000, respectively. Population size of the house crow grew dramatically (>30-fold) in the last 15-16 y while that of the white-vented and common myna declined. Habitat-abundance relationships suggest that house crows are highly dependent on anthropogenic food. Their abundance was also positively related to proximity to coast. The common myna associated closely with agricultural areas while the white-vented myna probably preferred urban greenery among residential buildings. Our study shows that the three invasive bird species associated with different aspects of human-modified environment.

Nest site selection of the house crow (Corvus splendens), an urban invasive bird species in Singapore and implications for its management

The house crow (Corvus splendens) has reached pest proportions in Singapore and requires an integrated system of population control measures. One such crucial component, possibly reducing its breeding success, was the focus of our study. We compared the nest sites (n=30) of the house crow with randomly selected sites (n=30) to determine which environmental variables, if any, are indicative of preferred nest sites. The chi-squared test revealed the yellow flame tree (Peltophorum pterocarpum) to be the preferred tree species used for nesting. We formulated our model based on 11 preselected variables using binary logistic regression and evaluated the strength of support for each model (relative to all other models) using the second order model selection criterion AICc. The results indicate that house crows selected nests in areas that were more urbanised and open, with higher disturbance, nearer bin centres and food centres, and nested in trees that had larger crown volume, density and diameter. Based on these results, we suggest that urban managers can alter the landscape characteristics to make them less conducive for nesting crows. Such measures might include minor adjustments to the design of existing bin centres to prevent crows from entering, planting alternative, less suitable tree species in future, and regular pruning of trees with larger and denser crowns.

Abundance and projected control of invasive house crows in Singapore

The Indian house crow (Corvus splendens) has successfully invaded tropical and subtropical regions well beyond its native range, reaching pest proportions in many areas. The invasive population of house crows in Singapore (Southeast Asia) has increased at least 30-fold since 1985 and now numbers in excess of 130,000 birds. To understand the population ecology and behavior of the house crow in Singapore, we undertook regular population size and roost surveys, dissections of birds shot (to provide age structure and breeding status), detailed nestsite observations, and monitoring of coastal dispersal. Using a discrete-time, density-dependent population model to synthesize this information, we demonstrated that at least 41,000 crows will need to be culled in the first year of a control program, and equivalent effort committed each year thereafter, to be confident of suppressing the Singapore population from its 2001 density of 190 birds/km(2) to the management target of <10 birds/km(2) within a 10-year period. This figure drops to 32,000 if culling is combined with other management strategies such as resource limitation and nest destruction. Complete eradication of the house crow from Singapore may be an unrealistic goal due to potential difficulties in detecting crows at IOW population densities and influx of migrants from neighboring Malaysia. Our study has implications for pest-bird management in other cities in Asia, Africa, and the Middle East, and presents it surrogate population-dynamics management tool for use in regions where the house crow has become established as a pest species, but where limited local field data is available.

Persistence of lowland rainforest birds in a recently logged area in central Java

Summary In 2001 and 2002, we assessed avian richness in Linggoasri (central Java) where almost all lowland rainforest had been cleared 3 years previously. Bird surveys were carried out in a selectively-logged forest, two regenerating forests and one pine Pinus merkusii plantation. A comparison with a bird list complied at least 3 years prior to logging in Linggoasri showed that 10 lowland bird species may have been extirpated from this area following logging. However, further surveys will be needed to validate these extirpations. A comparison with a list of lowland forest birds of Java shows that only 37% of these occurred in Linggoasri. From the lowland avifauna of Java, sole frugivores and insectivores were less likely to be present in Linggoasri. Smaller, generalist-feeding lowland species, endemic to Java, were more likely to be present in this area. Persisting lowland bird species, however, did not appear to be seriously affected physiologically by habitat degradation, showing no significant loss of body condition or reduction in survival and reproduction. There is an urgent need to preserve the few remaining lowland forest patches of Java and, given the alarming rate of deforestation throughout Southeast Asia, it is critical to conserve adequately large primary lowland forests (e.g. >5,000 ha) if we are to preserve existing lowland avifauna.

Up in the Clouds: Is Sustainable Use of Tropical Montane Cloud Forests Possible in Malaysia?

Perched atop misty mountains, tropical montane cloud forests are one of Earths most imperiled and neglected ecosystems. More than half of these forests occur in Southeast Asia; those in Malaysia are considered some of the best studied in the region. Malaysia has numerous mountains that are exceptionally rich in biodiversity and sustain numerous locally endemic species, but they are also threatened by expanding forestry, agriculture, infrastructure, and global warming. Malaysia serves as an excellent case study to illustrate the issues and challenges associated with tropical cloud forest conservation. We critically assess the current status of Malaysias cloud forests—focusing on their biological uniqueness and prospects for long-term survival—and propose conservation strategies for agricultural, forestry, tourism, and policy sectors to help conserve these endangered ecosystems. It is our hope that decisionmakers around the region can use our review to evaluate and improve their national strategies related to cloud forest conservation.

Blood parasite prevalence and abundance in the bird communities of several forested locations in Southeast Asia

ABSTRACT Parasites were studied qualitatively and quantitatively from the blood of 859 birds mist-netted between 1998 and 2003 in Singapore, Peninsular Malaysia (Cameron Highland, Frasers Hill, Pasoh and Johor), East Malaysia (Sarawak) and Indonesia (Java). The total prevalence and relative abundance of haemoparasitic infection in the birds were evaluated by location (study area) and habitat type (e.g. primary forest). Over 50% of the examined bird species were parasitized by more than one species, in some up to five. The greater research effort was invested in Fraser and Cameron, yielding the largest numbers of birds (340) and species (55), and contributing the largest share of the recovered haemoparasites. The Frasers Hill collection yielded the highest prevalence. The prevalence in Cameron Highlandss birds varied annually. In the latter area, Leucocytozoon infection was consistently more prevalent than Haemoproteus. In the remaining study areas, the overall prevalence was considerably lower, usually not exceeding 20% and predominated by Haemoproteus. The overall infection in Pasoh and Singapore did not exceed 6%. In the rest of the study areas Leucocytozoon prevalence was 0–3%. Our prevalence data seemed to fluctuate between years, but their magnitude could be evaluated without multi-annual studies. No particular preference in the efficacy of transmission could be demonstrated for either primary or secondary forests.