Insectivorous bats are a highly diverse yet vulnerable component of vertebrate diversity in Old World rainforests. 22 insectivorous species were recorded on Buton Island during the preliminary work conducted by the Operation Wallacea survey in 2000 and the list is almost certainly incomplete. Despite this extraordinary diversity, these insectivorous bats are highly susceptible to environmental disruption. Vulnerability is conferred by life history traits that combine low fecundity, prolonged maternal care and slow development; all adaptations for life in stable, predictable habitats, and where populations are maintained close to the carrying capacity of the environment (Kunz and Pierson 1994). Of particular conservation concern are the insectivorous bats of the rainforest interior, which number at least 15 species in Kakenauwe Forest Reserve, Buton. Not only are they affected by quantitative loss of habitat as forests are fragmented and degraded, but they also experience qualitative habitat changes as edge effects alter the forest microclimate (Saunders et al. 1991), and impact insect availability (Johns 1997).

The susceptibility of bats in the forest interior to disturbance events is further heightened by specializations of wing morphology and echolocation signal-design that equip them to forage in the dense clutter of the forest understorey, but greatly constrain their ecological flexibility. These species may glean insects from surfaces such as the ground, bark and foliage, or take airborne prey in the cluttered air-space inside stands of vegetation. In doing so, they face two key ecomorphological challenges. First, echolocation signals must be designed so that the bat can distinguish echoes returning from prey items from those returning from the surrounding vegetation. Flutter detection in the Hipposideridae and Rhinolophidae, and precise target localization and spectral discrimination in the Kerivoulinae and Murininae (subfamily Vespertilionidae) are two very specialized but effective responses that have evolved as a solution to this problem (reviewed in Neuweiler and Fenton 1988; Kingston et al. 1999) and work well in the cluttered environment of the forest interior where prey densities are relatively high. However, their efficacy in more open habitats, where prey densities are lower, is greatly reduced; the effective operating range of the echolocation signals is very limited in some cases (Kerivoulinae, Murininae, high frequency rhinolophoids) and unsuited to the detection of distant prey items distributed at low density.

Second, bats capable of foraging in a cluttered environment need to be highly manoeuvrable. Manoeuvrability is conferred by low wing loading, rounded wingtips and low aspect ratio (Norberg and Rayner 1987). However, this manoeuvrability comes at a price; flight is slow and energetically costly, precluding the fast, efficient flight necessary to exploit low prey densities in open habitats.

It is this combination of clutter-resistant echolocation capable of distinguishing prey items from the background and energetically costly but highly manoeuvrable flight that confines many insectivorous bats to the rainforest interior. They are ill-suited for prey detection and/or capture in the more open habitats that tend to arise from disturbance events such as fragmentation and degradation, and thus are highly dependent on intact expanses of forest. As a consequence, they are likely to experience a severe decline in diversity as forest habitats are lost and fragmented.

Work in the Neotropics has demonstrated that bat species respond differently to land-use changes (Fenton et al. 1992; Estrada et al. 1993; Ochoa 2000; Schulze et al. 2000). The few studies conducted in South East Asia so far also support this prediction. Zubaid (1993) reported that Kuala Lompat (Krau Wildlife Reserve, Malaysia) supported a higher species diversity of insectivorous bats than a fragmented secondary forest site, and he attributed this to lower insect abundance in the disturbed site (after Johns 1986) and changes in forest profile. Extensive urbanization in Singapore has reduced bat species from the forest interior to only four, all of which are endangered (Pottie 1996). Similarly, Danielsen and Heegaard (1995) found that species richness of insectivorous bats in Sumatra was reduced by logging. Initial work on the forest interior insectivorous bat species at Kakenauwe Forest Reserve, Buton, in 2000, revealed some apparent community differences in forests with different levels of disturbance. The least disturbed sites contained a greater range of species including Rhinolophus philippinensis, Hipposideros diadema and Phoniscus jagorii. The more disturbed sites contained fewer species, with a different community structure. 

1. To determine whether insectivorous bat community structure can be used as an indicator of the level of forest disturbance. Specific predications we will test:

• Species richness in undisturbed forest is greater than in disturbed forests.
• Species found in disturbed forest are not a random sample of the regional species pool but represent a subset of those found in undisturbed forest i.e. there is a deterministic, predictable sequence of species lost from disturbed forests and this relates to differential extinction or immigration rates among species (nested subset hypothesis – Patterson & Atmar 1986).

2. To identify those species most vulnerable to disturbance (following 1b). These species will be the target of future autoecological work that will attempt to identify the morphological and ecological correlates of this vulnerability.

Captured bats were held individually in cloth bags and identified from external features based on information in Corbet & Hill (1992), Payne & Francis (1985), Flannery (1995) and Bonaccorso (1998). However, field identification from external features proved highly problematic in the 2000 field season. Many specimens collected during this work have exhibited divergence from current species descriptions or are possible new records for the area. Definitive identification will require access to large comparative series of specimens, including type material. The most comprehensive US collection is held by the American Museum of Natural History, but I also propose to visit collections at the Smithsonian, British Museum of Natural History and the Bogor Museum. Further voucher specimens were collected (approximately 54 individuals) for later identification.

Echolocation recordings were made using an Ultra Sound Advice bat detector and a portable ultra sound processor. Morphologically similar but acoustically divergent cryptic species may be common in some families. Echolocation recording can confirm species identification and ensure that this hidden diversity is not missed. Tissue punches were taken from up to 10 individuals of each species to determine taxonomic status and generate phylogenetic information.

A paper entitled ‘Bat species of Buton and Kabaena Islands’ will be produced by Dr. Tigga Kingston (Boston University), Dr. Stephen Rossiter (Queen Mary and Westfield, University of London) & Dr. Boeadi (Museum of Zoology, Bogor), by May 2003. Additional data from this project will be incorporated into further publications after next year’s work.

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