Prepared by Martin Schulz and Linda F. Lumsden
Department of the Environment and Heritage, 2004
ISBN 0 642 55012 3
Part B: Distribution and location
- Habitat critical to the survival of the species
- Mapping of habitat critical to the survival of the species
- Important populations
- Current known national distribution
- Historical distribution
- Extent and geographic location(s) of populations
- Evidence for decline in the distribution and abundance
Endemic to Christmas Island. Wood Jones (1910) reported that small bats "which are said to be the Pipistrellus murrayi from Christmas Island" had been sighted on Cocos and Keeling Islands as "waifs and strays" although they had never become established residents there. There have been no subsequent records and no specimens were collected to substantiate this report. Therefore it is considered that the Christmas Island Pipistrelle is confined to Christmas Island (Lumsden & Tidemann 1999).
Little information was recorded in the early literature about the historical distribution of this species. Lister (1888) observed a small bat on the island but no specimens were collected. Andrews (1900) did not comment on its distribution or abundance when he described the species. However, he stated that "all species of mammals are extremely common" which may be inferred to include the Christmas Island Pipistrelle. In the following seventy years there were only passing references to the species. For example, Gibson-Hill (1947) commented "both bats, of which Mr Tweedie took examples in 1932 were flourishing during the period of my stay on the island". In 1976, Bell (1976) recorded that "both bats are in good numbers".
Due to the lack of information no historical distribution map could be prepared. It is likely that the species was widespread throughout the entire island. Due to the size of the island and the former continuous primary rainforest cover, it is likely that the species comprised a single population with no distinct geographical barriers to prevent genetic mixing between different locations on the island.
There have been a number of studies in the last two decades that have examined the distribution, abundance and status of the Christmas Island Pipistrelle. In 1984, Tidemann (1985) undertook the first targeted study, with a small amount of follow up work in 1988. In 1994, Lumsden & Cherry (1997) conducted a preliminary re-assessment of the status of the species. This study was followed by a comprehensive investigation of the distribution, abundance and ecology in 1998 (Lumsden et al. 1999). Since then several consultancies for environmental impact assessments have incorporated investigations of the pipistrelle (M. Bamford and G. Richards, pers. comm.). However, only one of these studies (Bamford & Bamford 2002) could be incorporated into the Plan, as the others have not yet been released into the public domain (as at November 2003). Lumsden et al. (1999) recommended that a monitoring program be undertaken by Parks Australia North (PAN) staff on Christmas Island. However, since this recommended monitoring program was not adopted the data from the 1998 study is the most recent comprehensive data available. Consequently, it is used to represent the 'current' situation, however, there is an urgent need to reassess the situation given recent changes.
A number of techniques were used to determine the distribution and abundance of the Christmas Island Pipistrelle in 1998:
- Ultrasonic bat detectors (which record the high frequency echolocation calls produced by bats) were set at 84 sites located throughout the island (Figure 1). These sites were primarily situated along tracks, since roads and tracks are used extensively by insectivorous bats as foraging habitat. The pipistrelle was recorded at 41 of the 84 sites sampled (49%). In the western section of the island the species was recorded at most of the sites sampled (90% of the 31 sites), while less than half the sites in the southern section recorded bats (44% of the 16 sites), and few of the sites in the north-eastern section recorded bats (16% of the 37 sites). In addition to providing distributional data, detectors also provide relative levels of activity. Most of the sites with high (defined as > 1 pass per minute) or moderate (1 pass per 1-10 minutes) levels of activity were located in the western section of the island (Figure 1). In contrast, all sites in the southern and north-eastern sections had only low levels of activity (i.e. < 1 pass per 10 minutes), with the exception of a single site in the centre of the island (classified as within the southern section, Figure 1).
- Driving searches: additional distributional data was collected by driving roads at night searching for bats using the following techniques:
- Extensive driving was undertaken at night while checking detector and trap sites (approximately 2,500 km over the 6 week study). Every individual seen in the headlights was recorded. Virtually all accessible roads were driven at night. A number of tracks in the western and southern sections of the island were not sampled due to extensive treefalls.
- Driving detection: an additional 242 km of driving was undertaken with a bat detector aimed out the window of a slowly-moving vehicle, so that bats could be recorded by sound as well as sight. Most of the major roads on the island were sampled using this technique (Lumsden et al. 1999).
Figure 2 indicates all roads sampled (both driving techniques combined) and the locations where bats were recorded. These results support the stationary detector site data (Figure 1), with the majority of records from the western section of the island, despite extensive driving in all three island sections.
- Harp traps were set at 16 sites to capture individuals for the purpose of collecting morphometric and demographic data.
The known distribution of the Christmas Island Pipistrelle (as at 1998) is shown in Figure 3, with all records combined, incorporating stationary detector sites, the driving searches, harp trapping and a limited number of roost sites that were located by tracking radio-tagged individuals.
While no pipistrelles were recorded from most of the north-eastern section of the island, it is possible that low densities of individuals occur in parts of this area. For example, in October 2001, Bamford & Bamford (2002) observed a single bat on two consecutive nights (possibly the same individual), foraging in the proposed southern extension to the airport runway. No other individuals were observed in this area or along the roads between this location and the Settlement.
Figure 2. Roads driven at night searching for the Christmas Island Pipistrelle and the locations where pipistrelles were seen during the 1998 study (adapted from Lumsden et al. 1999). Approximately 2,500 km were driven at night during this study, 242 km of which incorporated the use of a bat detector aimed out of the vehicle window, in addition to visual observations.
Figure 3. Known distribution of the Christmas Island Pipistrelle on Christmas Island in 1998 and the sections of the island referred to in the text (adapted from Lumsden et al. 1999). Records shown in black are from stationary detector sites, driving searches and harp trapping. Roosts sites located during the 1998 study are shown in red.
- 1. Comparison of studies undertaken in 1984 and 1998
- 2. Comparison of studies undertaken in 1994 and 1998
- 3. Anecdotal evidence
The Christmas Island Pipistrelle appears to have undergone a significant population decline and range contraction since the mid-1980s when Tidemann (1985) found the species to be common and widely distributed over the island. Population decline in a species is determined by repeatable techniques, demonstrating range contraction and/or loss in numbers. Tree-dwelling insectivorous bats have a unique set of characteristics that make it difficult to document population decline:
- The Christmas Island Pipistrelle does not roost in caves or other situations where individuals can be readily observed and population trends assessed. Instead the species roosts in small numbers in cryptic locations and regularly shifts between a number of roost sites.
- The species is nocturnal making it more difficult and time consuming to obtain distributional and abundance data than for other groups (e.g. insectivorous forest-dwelling birds).
- It is not possible to obtain density measures, such as is routinely undertaken for forest birds using standardised census sampling techniques. Instead relative abundance is assessed in terms of the number of bat detector passes over a period of time. This approach provides useful comparative data on the relative amount of bat activity. However, it cannot be used to represent the number of individuals present in an area since the technique does not distinguish between a small number of individuals making regular passes and a larger number of individuals making single passes.
- In many bird census techniques the behaviour of individual birds is recorded e.g. feeding, resting and flying. However, using any sampling technique to detect tree-dwelling bats (e.g. ultrasonic detector, visual observations or trapping) it is difficult to attribute how individuals are utilising a particular site. An exception is that with ultrasonic detectors actual prey capture can be identified by characteristic feeding buzzes. However, for individuals not emitting feeding buzzes it cannot be ascertained if they are utilising a sampling area searching for food, are in transit between roosting and foraging sites or are present in the area for some other reason.
- Little is known of temporal usage of sites by tree-dwelling bats.
A complicating factor is the rapid change in technology that makes it difficult to compare current to past tree-dwelling bat studies (compared, for example, to forest-dwelling birds where essentially over the last couple of decades techniques to determine distribution and abundance has remained unchanged):
- Ultrasonic Detectors: The primary technique used in recent studies to assess the distribution and relative abundance of the pipistrelle was ultrasonic bat detectors. Detector technology has advanced considerably in recent years, from basic units that required constant monitoring to advanced units using timers and storage facilities that allow remote detection throughout the night.
- Trapping: Harp traps started being used in Australia in the late 1970s. Current designs of harp traps are more efficient than the earlier designs. Some species of tree-dwelling bats were rarely recorded prior to the widespread use of harp traps.
- Transmitters: The only reliable method to detect the roosts of most tree-dwelling bats is by radio-tracking. It is only in recent years that transmitters have become sufficiently lightweight to use on small bats. The technology of batteries have also resulted in units now lasting for considerably longer providing the opportunity for increased likelihood of roost detection and better understanding of roost usage patterns.
Given these constraints, the evidence for a decline and range contraction in the Christmas Island Pipistrelle is as follows (taken from Lumsden et al. 1999):
There appears to have been a dramatic change in the distribution and abundance of the Christmas Island Pipistrelle since the mid-1980s when Tidemann (1985) undertook the original ecological study of the species. However, quantifying these changes are difficult as different techniques were used in that study, compared to the more recent studies (Lumsden & Cherry 1997, Lumsden et al. 1999).
Tidemann (1985) provided a map showing all the locations where the pipistrelle was recorded during his study (reproduced in Figure 4). These records were mainly from sightings while driving along roads, with some additional locations from harp trap captures. For the purpose of comparison, Figure 4 shows all sightings of pipistrelles recorded while driving during the 1998 study (this does not include the 242 km of driving detection as this technique was not used by Tidemann), combined with harp trap captures. Although the distribution and intensity of sampling may not be identical, this comparison provides an indication of distributional trends. The exact routes driven during the 1984 study are not known, however it is likely that the majority of the accessible tracks were driven at night, as was the case in 1998 (refer to Figure 2). By comparing the two maps in Figure 4 it is apparent that the species has contracted westwards and that there were less recorded sightings in 1998 in contrast to 1984. In 1984 pipistrelles were observed in the Settlement area on several occasions, and in areas in the north-east section where they now appear to be absent or in very low numbers. Extensive amounts of driving were conducted in the central plateau area during 1998 and no pipistrelles were seen. In contrast, the apparent disappearance from the Circuit Track, east of Winifred Beach Track, in the southern part of the western section, is probably due to a sampling artefact, as it was sampled frequently during 1984, but was largely inaccessible in 1998 due to numerous treefalls, with only limited sampling undertaken along the western section of this track (see Figure 2).
The studies in 1994 (Lumsden & Cherry 1997) and 1998 (Lumsden et al. 1999) employed identical sampling methods at stationary detector sites using Anabat detectors. It is therefore possible to directly compare results from these two studies to investigate changes in population status. In both studies pipistrelles were recorded at less than 50% of the sites sampled (Figure 5). The westward contraction appeared to be already well advanced in 1994, with most records concentrated in the western end of the island and pipistrelles recorded at only one site in the north-eastern section. No pipistrelles were recorded at this site in 1998.
To assess changes in relative activity levels at individual sites, 22 of the 27 sites sampled using detectors in 1994 were resampled in 1998. This revealed an overall mean reduction in the amount of bat activity of 33% from 1994 to 1998 (Lumsden et al. 1999). The main area of difference between the two years was in the centre of the island, where four sites revealed a decrease in the category of activity level, from either high to moderate, or moderate to low (Figure 5). This area was on the edge of the distribution of the pipistrelle in 1998, and therefore may have been reflecting the westward contraction of the species at that time.
Figure 4. Range contraction of the Christmas Island Pipistrelle on Christmas Island, between studies in undertaken in 1984 (Tidemann 1985) and 1998 (Lumsden et al. 1999). So that the data are comparable, only the bats observed while driving and the trapping records are included from the 1998 survey which were the techniques used in 1984 (refer text for more detail).
Anecdotal evidence also suggests a decline in the Christmas Island Pipistrelle. For example, the species was regularly seen in the grounds of the Parks Australia North (PAN) office at Drumsite in the Settlement until the mid-1990s, but not seen subsequently (M. Orchard, PAN, pers. comm., cited in Lumsden et al. 1999). Pipistrelles were regularly seen foraging in the clearing at the Christmas Island Research and Education Station in the centre of the island in the 1980s (H. Rumpff, PAN, pers. comm., cited in Lumsden et al. 1999), but in 1994 and 1998 were only occasionally recorded. In 1993 and 1994, R. Hill (pers. comm., cited in Lumsden et al. 1999) recorded very few visual observations in primary rainforest while conducting ecological studies on the Christmas Island Hawk-Owl Ninox natalis.
The Christmas Island Pipistrelle has been recorded in a range of habitats on the island, including plateau and terrace rainforest, secondary rainforest regrowth (of all ages), mine regeneration areas and formerly around the Settlement area (Tidemann 1985, Lumsden & Cherry 1997, Lumsden & Tidemann 1999, Lumsden et al. 1999). However, when identifying habitat critical to the survival of the species, it is important to identify components of vegetation types critical to different life cycle requirements:
The foraging habitat is the best-understood requirement in terms of identification of habitats critical to survival. Bats that are seen or heard in flight at night may be using an area as a foraging location, or for commuting between a roost site and foraging area (which can also be considered as habitat critical to survival). To identify sites that are specifically being used as foraging areas, the recordings made using ultrasonic detectors are examined for characteristic feeding buzzes.
The Christmas Island Pipistrelle is an edge specialist where it forages on a variety of flying insects, in particular moths and beetles (Lumsden & Cherry 1997, Lumsden et al. 1999). Evidence suggests it favours vegetation ecotones, tracks and other small gaps within primary rainforest. Tidemann (1985) recorded it foraging on the ecotone of primary rainforest and rehabilitation areas or secondary regrowth, and along tracks and drill lines within primary rainforest. Individuals were also encountered foraging over the High School and inside the open-air Christmas Island Club. In October 2001 Bamford & Bamford (2002) observed an individual foraging along the ecotone of secondary forest and a fernfield in an old mine site, near the southern end of the airport runway. Lumsden et al. (1999) found the highest levels of foraging activity occurred in areas of primary rainforest (feeding buzzes were recorded at 73% of the 15 sites where bats were recorded), secondary rainforest regrowth (50% of the eight sites where bats were recorded), and the ecotone of primary rainforest and secondary rainforest regrowth (43% of seven sites where bats were recorded). An example of a site where high levels of bat activity were recorded is shown in Figure 6 . Low levels of foraging activity were recorded in rehabilitation areas (25% out of the four sites with bats). No foraging activity was recorded at mined sites (n = 6 sites) and no bat activity was recorded around the Settlement (n = 5 sites) or along the coastline (n = 3 sites).
Within primary rainforest, Lumsden & Cherry (1997) suggested that the main foraging activity was concentrated along edges within small clearings, such as tracks, regenerating drill lines and clearings caused by treefalls. Lumsden et al. (1999) tested this at 16 paired sites where bat activity levels were sampled on tracks and in the adjacent rainforest, and found higher foraging activity levels along tracks compared to adjacent rainforest away from distinct edges.
Three environmental variables influenced the observed patterns of foraging distribution (from Lumsden et al. 1999):
- areas with high levels of flying insect availability.
- 'section of the island', with 86% of sites utilised for foraging in the far west, compared to 26% of sites in the remainder of the island.
- proximity to free water, which may be a reflection of the majority of bats recorded in the western section of the island, such as in the vicinity of The Dales.
Within foraging areas, bats have been recorded feeding from just above the ground level (approximately 0.1 m) to 20 m above primary rainforest canopy (Tidemann 1985, Lumsden & Cherry 1997, Lumsden et al. 1999).
Information on foraging habitat has primarily been collected in the dry season. It is currently not known whether foraging habitat preferences alter during the wet season.
All roosts of the Christmas Island Pipistrelle have been located within primary plateau rainforest. The species is also likely to roost in similar situations in terrace rainforest. It is not known whether secondary rainforest regrowth currently provides roosting habitat for this species, however, it is likely to provide potential roosting habitat in the future. No roosts have been found in caves, rock overhangs or buildings (Lumsden et al. 1999, Lumsden & Tidemann 1999).
Tidemann (1985) located a single radio-tagged individual roosting in a mass of epiphytic vegetation on a canopy tree Syzygium nervosum, approximately 15m above the ground. Lumsden et al. (1999) tracked seven radio-tagged bats and found them roosting singly or in clusters of up to 47 individuals, in a variety of situations in primary plateau rainforest within the Christmas Island National Park (see Figure 3):
- Under exfoliating bark of dead canopy trees, predominantly Tristiropsis acutangula, 6 to 20 m above the ground (n = 7) (Figure 7 ).
- Under flaking fibrous matter on the trunk of live Arenga Palms Arenga listeri, 15 m above the ground (n = 1).
- Under dead fronds of live A. listeri (n = 1) or Pandan Pandanus sp. (n = 1), 15 and 5 m above ground respectively (Figure 8).
- Under a Strangler Fig against the trunk of a canopy tree 5 m above the ground (n = 1) (Figure 9).
- In the hollow of a Syzygium nervosum 26 m above the ground level (n = 1) (Figure 10).
Available information suggests that roost fidelity is variable with some individuals shifting between roosts daily while others utilised the same site for at least seven consecutive days. As with many other small insectivorous bats, this species displayed roost area fidelity, shifting roost site regularly between a number of nearby roosts (distance between consecutive roosts: 14 to 186 m, n = 9).
All information on roost site selection has been collected in the dry season. It is currently not known whether roost selection dynamics alter during the wet season.
The Christmas Island Pipistrelle is likely to form maternity roosts (where females give birth to their young) during the wet season. All individuals examined by Tidemann (1985) appeared to be in reproductive synchrony, and he concluded that birthing was likely to occur towards the end of December with lactation expected to last for about four weeks into mid or late January. Insectivorous bats often utilise a variety of situations as non-breeding roosts but are highly specific in selecting maternity roosts in the breeding season (Kunz & Lumsden 2003). In tree-roosting bats, these maternity roosts frequently occur in specific types of trees, which are present in low numbers in the landscape (e.g. Lumsden et al. 2002). There is no information currently available on maternity roost characteristics selected by the Christmas Island Pipistrelle. These roosts are likely to be situated within primary rainforest, possibly in tree hollows.
No information is currently available on the habitat favoured by this species as commuting routes between roost and foraging areas. Limited radio-tracking data suggests individuals can travel distances greater than what may be expected for such a small species. For example, a radio-tagged male was caught at a foraging site only 20 minutes after it had departed a roost, covering a straight-line distance of 2 km during this time (Lumsden et al. 1999).
It is not known if this species will cross extensive areas of open modified landscapes, such as mined areas, to reach isolated or disjunct patches of primary and/or secondary rainforest.
Little information is available on the relative importance of various habitat types for roosting, foraging, commuting and maternity sites during all seasons of the year. Until such information is available, habitat critical to survival of the Christmas Island Pipistrelle, based on the requirements established by Regulation 7.09 of the EPBC Act, is defined as:
- All areas of primary rainforest, since this habitat is known to support foraging, roosting and commuting habitat; and
- All areas of secondary rainforest regrowth (of all ages), since this habitat is known to provide important foraging habitat, provides commuting habitat, may currently provide roosting habitat, and is likely to support roosting and maternity sites in the future.
The majority of recent records of this species are from the western section of the island and therefore this area is the most critical for the immediate conservation of the species. However, due to the species' rarity, it is important that all areas on the island that fit the criteria for habitat critical to the survival of the species be identified as such in this plan. Habitat critical to the survival situated in the south and north-east sections may provide refuge for relict populations due to the unknown impacts of the Yellow Crazy Ant in areas of important foraging and roosting habitat in the western section of the island. Furthermore, habitat critical to the survival in the south and north-east sections of the island support areas of vegetation that, with appropriate management, will present opportunities for bat re-colonisation to ensure the long-term future of the species. This approach follows Regulation 7.09 (1f) of the EPBC Act, which states that habitat critical to the survival of the species includes areas necessary to ensure the long-term future of the species through reintroduction or re-colonisation.
The map of habitat critical to the survival of the species (Figure 11 ) is based on the habitat identified above.
The vegetation map of the island is based on vegetation communities, and no maps are available to distinguish areas of primary and secondary rainforest. Therefore to map habitat critical for the survival of the Christmas Island Pipistrelle the following vegetation communities have been incorporated (which will include areas of both primary growth and secondary regrowth of each community): Tall Closed Forest, Deep Soil Phase; Closed Forest Freshwater Seepage; Closed Forest Scree/Pinnacle Phase; and Closed Forest, Shallow Soil Phase.
Prior to human settlement, it is considered highly likely that the species would have occurred as a single population across the island. This is due to the island's small size, the continuous primary rainforest cover, and the absence of any distinct geographical/vegetation barriers to prevent genetic mixing between different locations on the island. Since the pipistrelle is endemic to Christmas Island and is currently listed as endangered, it is considered that all remaining components of this population, and all areas identified as habitat critical to the survival, are important for the long-term conservation of the species. Small colonies situated in the south and north-east sections of the island may form important relicts due to the unknown impacts of the Yellow Crazy Ant in areas of high pipistrelle foraging activity and important roosting habitat in the western section of the island.
Figure 11. Habitat critical to the survival of the Christmas Island Pipistrelle based on closed forest and tall closed forest vegetation communities, including both primary forest and secondary rainforest regrowth. The shaded area shows the habitat critical to the survival of the pipistrelle, and thick grey line indicates the outline of the Christmas Island National Park.