Distribution and behaviour of echolocating bats as assessed with bat-detectors in Indonesia

This is an overview of some of the bat-detector observations I have made since March 2009 in Indonesia, using a Batcorder (SF: 500kHz) and a Pettersson D240X (SF:375kHz). The observations were made by me unless specified otherwise. If bats were captured that were not horseshoe bats or Hipposideridae, they were recorded in free flight, outside in an open environment. Mostly, these recordings served to confirm the identity of previously recorded freely hunting bats. The accompanying table of Indonesian bats on this website tries to capture the extremes of each species in both open and dense habitats, which is why I never take averages of hand-released bats.

Rhinolophidae and Hipposideridae general
So far, I haven't been able to discover clear differences in flight behaviour and foraging behaviour between different species of rhinolophids in Indonesia. In both the Hipposideridae and Rhinolophidae large species tend to use perch hunting more than small species. In Rhinolophidae, small to middle-sized species are often found flying at 0.3-2 m height, following paths in the forest and also following forest edges. Because of this flight behaviour they are easily trapped in mistnets and appear to be more common than Vespertilionidae in many areas, which is unlikely to be true. To Rhinolophidae, flying insects look like a flickering light that is clearly visible even with many bushes around. They are experts in scanning corridors and / or tunnels of vegetation. Some species may also scan the ground in particular. Except for Hipposideros ater, I have only been able to observe small Hipposideridae hunting during the early evening hours when their hunting grounds may be different from those under complete darkness. It may be that later in the evening, small and medium sized Hipposideridae choose more open environments than Rhinolophidae, or at least hunt higher above the ground where they are not easily detected by an observer. However, it is still possible that some species of Hipposideridae may be more capable of following insects into dense vegetation than horseshoe bats are, even if they generally tend to fly further away from it.

Hipposideros ater
Distribution: The species was seen in Sulawesi, but also occurs in Papua, down to Australia. The species calls extremely high and soft so that it is mostly missed (or even too high for some detector types) by the observer. It may be fairly common throughout its range. This tiny bat will often fly towards the observer at 0.2-1.5 m altitude to inspect him / her. The species often uses small paths in forests (as horseshoe bats) so the observer often gets a glimpse of this bat in the flashlight, mostly while failing to record anything. Once, an individual started spinning around me at knee-height for 10 seconds, nearly touching my trousers. Occasionally, one sees the bat diving into vegetation that is so dense that one suspects the bat to have crashed there. It may be that this bat species is more adapted to hunting in extreme clutter than most other bats including gleaning Myotis, Kerivoula, Murina and all horseshoe bats. So far, it has only been seen in intact forests.

Pipistrellus javanicus
Distribution: Very common in west-Java (probably commonest species), but may be somewhat rarer towards the east. In Bali mainly in forests, only occasionally in towns. Status in Flores unclear, but certainly not common. Does occur on Sulawesi, but not everywhere and mixed with other pipistrellus species. In west-Papua replaced by P papuanus. Hunting behaviour looks identical to P pipistrellus in Europe, although P javanicus may be slightly more adapted to open space. Can be seen over water bodies, in forests (below canopy), cities, street lamps, sometimes in groups. Very rarely uses social calls, except for when visiting special "swarming locations", such as the 1000 islands off Jakarta. Similar species: Pipistrellus papuanus (echolocation virtually identical), Scotophilus collinus on Flores uses echolocation very similar to P javanicus.

Pipistrellus papuanus
Distribution: Common in west-Papua (commonest species), rest of Papua and Moluccans not yet surveyed. Common everywhere including cities and forests. May sometimes be the only microbat species in cities. Numbers of hunting pipistrelles in Papua are comparatively low, though. Hunting behaviour as P javanicus, but maybe spread over a larger area / trajectory. Social calls, so far not heard in free flight.

Pipistrellus tenuis (not 100% sure)
A species of pipistrelle bat using a QCF-frequency between 45 and 49 kHz has been found, but is yet to be identified by means of capture. Here, it is tentatively referred to as Pipistrellus tenuis. Distribution: This species has so far only been heard in Kuala Lumpur (Malaysia), lake Tamblingan on Bali (1-3 specimens) and Sulawesi. It is most common in SW-Sulawesi and even the only pipistrelle-species heard in Makassar, where it can be seen everywhere. Also occurs northwards to the northwestern tip of Sulawesi tengah province, but rare here. It has so far never been recorded on Java. However, the species also showed up in a recording made north of Balikpapan (east-Kalimantan, Borneo), which is only 270 km west of west-Sulawesi where the species occurs as well. More observations from Borneo are urgently required to understand its distribution. Hunting behaviour identical to P javanicus. Some species of Miniopterus may overlap in echolocation with this species.

Pipistrellus stenopterus
Distribution: Malaysia and Singapore, Sumatra needs to checked with detector for presence. I only had the opportunity to see the species well in Kuala Lumpur where it is common. I recorded typical sounds of the species in Singapore, although it is believed to have disappeared there. In flight, the species reminds rather of a Molossid (or a small Nyctalus) than a pipistrelle with its narrow wings. Its behaviour is also more like Nyctalus or another open space flyer. In the evening, the bats quickly gain height and pass the observer on a straight course to the hunting grounds. Foraging height is probably well above 15 m, but further observations are required. It is probably very common within its distribution limits.

Myotis muricola
By using a detector may be falsely identified as a Pipistrellus-species. Distribution: May be second commonest bat species of Indonesia. More widespread than P javanicus. As common on Flores and Sulawesi as in Malaysia. Possibly heard once in west-Papua, but eastern limit probably in Moluccans. The species can be found in gardens of large cities, villages, rainforests and may even fly into half-open houses. Large groups often gather above small rivers to hunt. The bat often flies very close to the observer. The echolocation then reacts to the observer. It may be that the bat sometimes deliberately inspects humans, as is known for Plecotus and gleaning bats such as Myotis nattereri. Emerges later than pipistrelles and Scotophilus, mostly stays below 4 m from the ground (typical height 1.80m) or close to structures or trees. The bat is very manoeverable and can even continue hunting below roofs of terraces during heavy downpours. Similar species: Miniopterus overlaps in frequency but M muricola always uses pulses durations below 5 ms. Behaviour is also very different.

Scotophilus kuhlii
Distribution: There are 2 echolocation types: QCF: above 38 kHz and the other below 40 kHz. All Scotophilus in Kuala Lumpur and Singapore are above 38 kHz, whereas most animals in west-Java use the below 40 kHz type. In fact, each type uses an alternating frequency. In Malaysia mostly 42 and 39 kHz, on Java mostly 39 and 37 kHz, but occasionally as low as 34 kHz. However, QCF frequency also depends on pulse duration which should be taken into account when comparing the two types. The high (Malaysian-) type is also found on Java, but is rarer. The same situation is present on Bali. I have only few recordings of Scotophilus kuhlii from Sulawesi, which were all the low type. The low type was also recorded on Lombok. In addition to Sc celebensis there also appears to be yet another Scotophilus type in Sulawesi, similar to Sc collinus, but this requires further study. Sc kuhlii (38 kHz) is very common and may locally be the commonest species (e.g. on Bali). It emerges early and can be seen practically anywhere in Indonesia in the evening sky, including motorways, industrial areas, remote islands, up to the edges of the rainforest. The appearance of the species in flight is reminiscent of Eptesicus. However, Scotophilus tends to fly faster, often on a straight course and it flies in much wider circles than Eptesicus, but generally at the same height. Bats may skim over small trees, but don't dive as much into dense corners as Eptesicus does and rarely at low altitudes. It may also be seen flying relatively high up in the sky (15-25m), hunting together with Pipistrellus javanicus, Saccolaimus saccolaimus and swifts, but the species clearly lacks the shape and speed of true open-air foragers. The repertoire of social calls (always used at colony) of this species is impressive. It probably is a very sociable species. Bats also roost under roofs in groups of only 2-5 individuals. Rain delays its emergence, but bats are able to hunt in light rain (as many other species). However, bats have never been observed to continue hunting in heavy rain, whereas swifts are able to do so (also at low altitudes).

Saccolaimus saccolaimus
Distribution: By far the commonest emballonurid of Indonesia and extremely widespread. It occurs in Malaysia, all over Java and Bali (but not yet heard on Flores) and also on Sulawesi and west-Papua (only heard once). It is commonly heard above cities, rice fields, forest-edges, cultivated land, mountain landscapes (heard up to 1600m) and also close to, and above sea. The species seems to be quite hardy: it was heard hunting in wind and rain at a temperature of only 10C in the mountains. It may be absent from large rainforests. This species has a very particular body shape in flight, having a big body and narrow wings that never appear to be stretched completely, giving it a plover-like flight-behaviour. The bats emerge early and can be seen flying 15-30 m up in the air, making circles of over 100 m in diameter. The bats can often be seen first initiating a dive by flapping the wings rapidly and probably flying up a little bit, followed by a diagonal dive to the prey, often over several metres. This behaviour implies that the bat feeds on large insects that can be detected from long distances. However, the bat has also been seen feeding on a swarm of small insects together with other bat species. In this case, Saccolaimus often took a rapid turn to the side to ultimately catch the prey in a U-turn motion. The bats are rarely seen flying below 15m. Social calls have only been recorded once at the north coast of Bali. It consists of a modification of the sonar sounds and can be heard with the unaided ear and sounds as if the bat is emitting double or triple pulses.

Taphozous melanopogon
Distribution: Although this species is likely to be picked up easily with a bat-detector from a long distance it has so far only been recorded in Kuala Lumpur, Flores (large colony), Sulawesi and Bali. Except for Flores and south Bali, all observations were just occasional single individuals. Habitat preference may be related to limestone areas and most observations came from dry areas. In Bali, animals probably roost in sea cliffs, as has been observed in Lombok (Kitchener et al., 2002). The species may be common locally, but on the whole, it can even be considered rare, as it seems to be absent from large areas. So far, I have never been able to see bats hunting. The species seems to emerge later than Saccolaimus saccolaimus. A study by Wei et al. (2008) in China showed that the species feeds strongly on moths, Coleoptera and Hemiptera and relatively few Diptera compared to many Vespertilionidae. Taphozous may therefore be a specialist for large prey.

Taphozous longimanus / Taphozous theobaldi (echolocation not yet described)
It is possible that T longimanus overlaps greatly with T melanopogon and T theobaldi with S saccolaimus in echolocation so they are simply not recognised when using a bat-detector. However, if there is a difference, these bat species have never been detected anywhere in Indonesia so far, despite their presumed status of being common bats. Both bat species are presumed to be easily detected with a bat-detector.

Mosia nigrescens
Distribution: Very common in west-Papua, reasonably common in Sulawesi and probably also common in Halmahera and other parts of the Moluccans. The species only occurs in the vicinity or inside forest of some age (probably >80 years). At the edge of its distribution (Sulawesi) this requirement seems to be stricter as the species was only found near very old and tall forest. In such areas the species may be fairly common and even large groups may be found hunting (sometimes low over the ground). The species may also hunt somewhat outside its preferred forest in other habitats, but it seems not much further than 1 km. In Papua, Mosia nigrescens is the earliest bat to appear and during these bright conditions it flies like a swift alongside forest edges, low over the ground, but also under tree crowns or overhanging branches in dark spots. Later, in complete darkness, open spots are visited as well. The species may be as agile as Myotis muricola, but its flight seems faster and can be more hectic, especially when hunting in a group, where it reminds of a swarm of bees. The species probably hunts on small insects. It can enter dense space and may also be able to detect flying prey there, but this needs further confirmation.

Emballonura monticola
Distribution: Little can be said from my own observations since I have so far only found 8 roosting individuals in a small cave in south-Sulawesi. I also failed to follow the bats to their hunting grounds to observe hunting behaviour. So far, the species appears to be rare in large parts of Indonesia.

Emballonura alecto (not 100% sure)
Distribution: I have only recorded this bat on Flores hunting around the summit of Mt Mbeliling and near Ruteng. The bat is easily picked up with a bat-detector and unlikely to be missed if the observer nears its hunting grounds. The bats on Mt Mbeliling could be observed well during hunting. They were flying in circles around the summit, only about 2-4 m from the ground, sometimes quite near to the tree crowns. During this behaviour they constantly changed their pulse design radically and produced an abnormal amount of buzzes, without any clear behavioural changes as seen in Vespertilionidae. Many small moths were present, but it could not be verified whether the bats were actively hunting on these moths.

Chaerephon plicata
Distribution: Heard all over Java and also on Bali. Although this species uses extremely loud echolocation pulses, it may be missed by the observer who is too far away from a colony-site. The animals probably hunt regularly well above 100 m height from where they can no longer be detected from the ground. The species also lives in colonies in big cities, such as Jakarta. In west-Papua, Mormopterus is the commonest small Molossid-species. Identifying high flying Molossidae with a detector is a tricky business as their calls become fairly featureless at these altitudes and also tend to vary in frequency. Hunting behaviour is hard to observe as bats quickly climb as high as the eye can just follow them in the evening sky. Bats have been seen hunting as low as 10 m above a small lake, flying at high speed. One emerging bat was clocked at 60 km/h by car. When flying back to the colony, a stream of bats tumbles down from far above. The social calls used in the roost are quite distinctive and roosts can be found easily during daytime. Roosts are known to attract predators. Near the temple of Tanah Lot on Bali, barn owls make use of flood lights to hunt on these bats. The bats mob the owls by chasing them, a behaviour also observed in Myotis dasycneme and long-eared owls. The species is known to roost in cracks and buildings, but I found one roost in east-Java in a tree.

Hesperoptenus gaskelli (not 100% sure)
Distribution: This species was heard in only two locations around Lore Lindu in the south and south-western edge of this national park in central Sulawesi. Both locations were near a river with old forest with very large trees nearby. One individual could be observed hunting. It looked like a small, robust version of Eptesicus and was flying in circles of only 8 metres in diameter under a giant tree. The frequency-alternation was 100% in the recording, which has also been observed in Hesperoptenus blanfordi. It may be that this species is one of the few half-open space bats (similar to Scotophilus), but then within tropical rainforests. If this is true, many secondary rainforests will not provide a sufficient amount of open space for this species to hunt as present in primary rainforests. More research is needed on this topic, but Hesperoptenus bats may be one of the best indicator species of forest quality of the insect eating bats of Indonesia. The species is picked up easily with a bat-detector and is unlikely to be missed, if present.

Last updated 24.3.2010