Roost-Boxes As a Tool in the Conservation of Tree Roosting Microbats

Roost‐boxes as a tool in the conservation of tree roosting microbats (Microchiroptera) in a highly‐modified agricultural landscape

Quarry Life Award Research Project, Australia

Project Topic: Biodiversity and Rehabilitation

Stephen Griffiths

July 2012

Department of Zoology The University of Melbourne Victoria 3010 Australia Telephone: +61 3 8344 6244 Fax: +61 3 8344 7909

Roost-boxes as a tool in the conservation of tree roosting microbats

Abstract The loss, modification and fragmentation of natural habitats constitute a major threat to bat populations worldwide. This is particularly relevant in Australia where extensive loss of native habitat since European settlement has resulted in significant negative pressure on microbats (Microchiroptera), the majority of which rely on tree hollows for roosting. However, because microbats are small, nocturnal and remain hidden in roosts during the day, few people are aware of the diversity or abundance of bats that roost in trees in both urban and rural areas. I used bat detectors to examine activity of microbats at two sites in a highly-modified agricultural matrix. The species assemblage recorded comprised the majority of microbat species known to occur in the Western Volcanic Plains region of Victoria. A total of 6,214 echolocation call sequences were recorded over 39 consecutive nights at the two sites. Considerable variation in activity was documented both within and between nights. The echolocation data revealed minimal levels of foraging activity. At one site, social calls were recorded in the hour prior to civil twilight (i.e. prior to nightfall) on 17 nights, providing indirect evidence of bats roosting diurnally in tree hollows within an isolated stand of mature Eucalyptus cladocalyx. Artificial roosting boxes (bat-boxes) were installed to provide supplementary roosting habitat as an initial step toward investigating the efficacy of bat-boxes as a targeted conservation tool within the framework of a long- term ecological management and restoration plan. The presence and activity of microbats recorded in this study, and specifically the detection of social calls produced by diurnally roosting bats, has implications for the management and rehabilitation of isolated patches of land within highly-modified agricultural landscapes. Increasing the awareness of land managers and decision makers to the benefits of these species (e.g. regulation of herbivorous insect abundance), will enhance knowledge of this faunal group in the community and provide further reasons for prioritising the management and conservation of scattered trees within urban and rural environments.

Roost-boxes as a tool in the conservation of tree roosting microbats

Introduction A wide variety of vertebrate taxa use tree hollows (also referred to as tree holes or cavities) for shelter and as breeding sites (Goldingay 2009). Worldwide there are approximately 260 species of bird and 360 species of non-flying mammals that use tree cavities (Newton 1994; Novak 1999), while in Australia, as many as 300 native vertebrate species (birds, bats, arboreal marsupials, reptiles and frogs) use tree hollows (Gibbons and Lindenmayer 2002; Kunz and Lumsden 2003; Goldingay and Stevens 2009).

Bats are among the most threatened fauna in Australia, with 36 species listed under The Action Plan For Australian Bats (Duncan et al. 1999). Day-roost sites have been identified as a key limiting resource for microbat conservation, but we know almost nothing about the causes and consequences of roosting in different types of tree hollows or artificial nesting boxes (Turbill 2006; Goldingay 2011). The dramatic decline of Australian native habitats since European settlement has led to a growing awareness of the impact of habitat loss on native fauna, and revegetation efforts, both in farmland (Kavanagh et al. 2007) and in suburbia (Harper et al. 2005a,b), are increasingly common. However, trees planted now may take up to 100 years to develop hollows suitable for use by wildlife (Lindenmayer et al. 1993; Weinberg et al. 2011). Therefore, while revegetated areas can provide foraging habitat for bats soon after planting, the lack of hollows may limit colonisation of these areas as roosting habitat.

One short to medium term method of compensating for limited roosting sites is to install nesting boxes (bat-boxes) as substitutes for natural hollows (Arnett and Hayes 2000; Brittingham and Williams 2000; Flaquer et al. 2005; Lesinski et al. 2009). There have been few studies of bat-box use in Australia, particularly in agricultural regions, and consequently relatively little is known of the use and preferred designs of bat-boxes by Australian tree roosting microbats (Irvine and Bender 1995; Smith and Agnew 2002; Goldingay and Stevens 2009). My objective in the present study was to examine microbat activity in a highly-modified agricultural landscape and conducted a preliminary assessment of the efficacy of bat-boxes as a targeted conservation tool within the framework of a long-term ecological management and restoration plan. Specifically, I investigated: (1) temporal patterns (hourly and nightly) in bat activity; (2) the diversity of

Roost-boxes as a tool in the conservation of tree roosting microbats species present; (3) the level of foraging activity; and (4) the potential value of deploying bat-boxes as a short to medium term conservation tool.

Methods Study sites I conducted fieldwork at two former sheep grazing properties located in the Western Volcanic Plains of Victoria, Australia. The region is characterised by temperate grassland and grassy eucalypt woodland, now dominated by introduced grassland species, with sparsely scattered paddock trees and occasional trees planted along fence lines as windbreaks (DEWHA 2008). In 2008, the Australian government upgraded the listing of the natural temperate grassland and the grassy eucalypt woodland of the Volcanic Plains of Victoria to critically endangered, the most protected conservation status under the Federal Environment Protection and Biodiversity Conservation Act 1999 (DSEWPC 2011). The climate of the Western Volcanic Plains is temperate with warm to hot summers (average summer maximum 24.6°C) and cool to cold winters (average winter maximum 12.6°C). Rainfall on the plains ranges from 600 to 800 mm per annum and occurs mostly between April and November. Annual average rainfall at the Australian Bureau of Meteorology Hamilton Airport monitoring station (37°38'39.04'' S, 142°00'47.74'' E) is 685.7 mm (Australian Bureau of Meteorology 2012).

The Warrayure Conservation Offset Site (37°44'05.65'' S, 142°12'47.93'' E) is located 230 km west of Melbourne, 14 km south-west of Dunkeld and 17 km east of Hamilton. The Warrayure site has an area of 58 hectares, comprised predominantly of degraded grassland with small patches of mature Eucalyptus cladocalyx. The site is on the north shore of Lake Linlithgow, and it adjoins the Lake Linlithgow Nature Reserve. The Strathkellar Conservation Offset Site (37°43'24.48'' S, 142°07'50.02'' E) is located 10 km west of the Warrayure site, 20 km south-west of Dunkeld and 12 km east of Hamilton. The Strathkellar site has an area of 80 hectares, comprised of highly degraded grassland and creek line tussock grassland. Native tree species are limited to a small patch of Acacia melanoxylon along the southeast boundary. The property is bordered by the Glenelg Highway to the south and Rhooks Road to the northeast. Both the Warrayure and Strathkellar Conservation

Roost-boxes as a tool in the conservation of tree roosting microbats

Offset Sites are covered by a conservation covenant and have management plans requiring the improvement of native grasslands, plus restoration of degraded areas.

Acoustic sampling of bat calls I used echolocation calls as an index of bat activity at the Warrayure and Strathkellar Conservation Offset Sites. I surveyed bat activity at both sites concurrently using ultrasonic bat detectors (AnaBat II bat detector connected to an AnaBat ZCAIM storage unit, Titley Electronics, Lawnton, Queensland). Detectors were calibrated by adjusting their sensitivity levels against an ultrasound frequency generator (AnaBat Chirper 2, Titley Electronics). Detectors were placed inside weatherproof plastic boxes secured to the trunk of a tree at a height of approximately 1.5 m, with the microphone facing upward at an angle of 45º (Figure 1). Recordings began 60 minutes before suunset and ended at sunrise, during which time the detectors were triggered automatically by ultrasonic noise.

Figure 1. AnaBat II bat detector and AnaBat ZCAIM storage units secured to trees at a) the Warrayure Conservation Offset Site and b) the Strathkellar Conservation Offset Site.

I downloaded echolocation call data to a computer using CFCread version 4.3s then manually analysed calls using AnalookW version 3.8s (C. Corben 2011, www.hoarybat.com). A single call sequence was ddefined as a file containing at least three echolocation pulses (frequency sweeps) identified as bat echolocation calls (Hourigan et al. 2008). Each call sequence, separated by more than 5 seconds, was designated as a unique file (Hayes 2000). Files that passed these criteria were then processed using AnaScheme software (Gibson and Lumsden 2003). AnaScheme uses regional identification keys to identify call sequences to taxa by extracting a range of call parameters (Lumsden and

Roost-boxes as a tool in the conservation of tree roosting microbats

Bennett 2005; Adams et al. 2010). I used an existing identification key developed to identify the species in the Grampians region of Victoria (Arthur Rylah Institute for Environmental Research 2012). Using the Grampians key, AnaScheme identifies call sequences to species, except for Nyctophilus and Mormopterus, which are grouped by genus. A list of microbat species known to occur in the Western Volcanic Plains of Victoria is provided in Appendix 1.

Call sequences for all taxa recorded were grouped to investigate activity patterns of the entire microbat community. Hourly activity patterns were recorded as the mean number of call sequences recorded per hour after civil twilight for all species during the survey period. Civil twilight times were accessed from Geoscience Australia (2012). Call sequences were screened manually for buzz calls associated with pursuit and capture of prey. Foraging buzz calls are characterised by a rapid increase in pulse repetition rate, slope, frequency and speed (Griffin et al. 1960; Schnitzler et al. 1987). Call sequences were also examined for social calls: distinctive audible contact calls made by bats from within roost sites before leaving for the night to forage (Aldridge et al. 1990; Pfalzer and Kusch 2003; Arnold and Wilkinson 2011).

Results Bat activity Over 39 consecutive nights from 20 April to 28 May 2012 (78 detector-nights) I identified 6,214 bat call sequences from 11,531 files (53.9%). A total of 5,474 and 740 call sequences were recorded at the Warrayure and Strathkellar sites respectively. Bat activity was recorded on every night at Warrayure, and on the majority of nights at Strathkellar (zero call sequences recorded on 4 nights (10.3%)). Considerable variation in the nightly number of bat call sequences was documented at both sites. An average (± standard error) of 140.4±26.7 call sequences per night was recorded at Warrayure, with a nightly maximum of 775 calls (20 April 2012) and minimum of 15 (21 May 2012). At Strathkellar an average of 19±5.2 call sequences per night was recorded, with a nightly maximum of 163 calls (20 April 2012) (Figure 2).

Roost-boxes as a tool in the conservation of tree roosting microbats

Figure 2. Number of echolocation call ssequences recorded each night at the Warrayuure and Strathkellar Conservation Offset Sites.

Hourly activity Hourly activity patterns were similar at both sites with greatest activity recorded in the first hour after civil twilight (Warrayure 18.9% and Strathkellar 41.6% of call sequences), while more than 60% of all calls were recorded in the first four hours after civil twilight at both sites. A total of 45 call sequences (0.8% of total calls) were recorded at Warrayure in the hour prior to civiil twilight, i.e. prior to nightfall (Figure 3).

Figure 3. Mean (±s.e.) number of bat call sequences per night detected each hour after civil twilight at the Warrayure and Strathkellar Conservation Offset Sites. The -1 category refers to the hour prior to civil twilight.

Roost-boxes as a tool in the conservation of tree roosting microbats

Species diversity Using the AnaScheme program, 2828 (45.5%) call sequences were ideentified to species level (or to genus for Nyctophilus sp., and Mormopterus sp.). The remainder could not be identified either as a result of being a short sequence with insufficient good quality pulses to meet the minimum criteria, or having the majority of pulses with parameters that could not be distinguished between two species (Gibson and Lumsden 2003). The following taxa were identified: Vespertilionidae: Chalinolobus gouldii, C. morio, Falsistrellus tasmaniensis, Minopteurs schreibersii bassanii, Nyctophilus geoffroyi/N. gouldi/N. timoriensis, Vespadelus darlingtoni, V. regulus, and V. vulturnus; Molossidae: Tadarida australis, and Mormopterus species 4/M. species 2; Emballonuridae: Saccolaimus flaviventris. Vespadelus darlingtoni was the most commonly recorded species at Warrayure (16.2%), while V. vulturnus dominated calls at Strathkellar (43.9%) (Figure 4).

Figure 4. Echolocation call sequences identified to species or genus bby AnaScheme; 25.8% and 58.4% of call sequences were not identified at Strathkellar and Warrayure respectively. Cg, Chalinolobus gouldiii; Cm, C. morio; Ft, Falsistrellus tasmaniensis; Msb, Miniopterus schreibersii oceanensis; N, Nyctophilus geoffrooyi/N. gouldi/N. timoriensis; Sb, Scotorepens balstonni; Vd, Vespadelus darlingttoni; Vr, V. regulus; Vv, V. vulturnus; Ta, Tadarida australis; M, Mormopterus species2/M. species 4; Sf, Saccolaimus flaviventris.

Foraging activity One hundred and fifteen feeding buzzes were recorded during this study, 112 at Warrayure (2% of total calls) and 13 at Strathkellar (1.8% of total calls) (Figure 5).

Roost-boxes as a tool in the conservation of tree roosting microbats

Figure 5. Number of echolocation foraginng buzz calls recorded each night at the Warrayure and Strathkellar Conservation Offset Sites.

Social calls Social calls were recorded in the hour prior to civil twilight on 17 nights at Warrayure, providing indirect evidence of bats roosting diurnally in tree hollows within the stand of maturre E. cladocalyx at this site. A maximum of 16 social calls was recorded on two separate occasions at Warrayure (Figure 6). No social calls were recorded at the Strathkellar site. It was not possible to identify the social calls recorded during this study to species level, as reference social calls produced by species in the Western Volcanic Plains region are not available. Examples of two social calls recorded on 20 April 2012 at Warrayure are presented in Appendix 2.

Figure 6. Number of microbat social calls recorded each night in the hour prior to civil twilighht at the Warrayure Conservation Offset Site.

Roost-boxes as a tool in the conservation of tree roosting microbats

Discussion Considerable variation in activity was documented both within and between nights during this study, however bats were present (as detected via echolocation calls) on every night at Warrayure, and on the majority of nights at Strathkellar, albeit at lower levels (Figure 2). The overall hourly pattern of bat activity featured a peak immediately after dusk, followed by a steady decrease throughout the night and only minimal activity in the second half of the night (Figure 3). Studies by Law et al. (1998) and Milne et al. (2005b) examining bat activity in southeastern and northern Australia respectively have reported similar patterns. In both studies, the majority of activity occurred in the first half of the night, with considerably less activity from midnight to sunrise. Several lines of evidence suggest this pattern is driven primarily by activity of nocturnal insects which also exhibit the greatest peak of activity at twilight, with activity dropping off during the remainder of the night until dawn (Rautenbach et al. 1988; Vaughaun et al. 1996; Jetz et al. 2003; Wickramasinghe et al. 2003a,b; Weinbeer et al. 2006).

High levels of variation in bat activity between nights has also been identified in previous studies (Hayes 1997; Milne et al. 2005b). A range of factors have been shown to influence variation in nightly bat activity, including climate variables (Bullen and McKenzie 2005; Turbill 2008; Brooks 2009), insect availability (Bell 1980; Avila-Flores et al. 2005; Akasaka et al. 2009), and lunar phase (Fenton et al. 1977; Milne et al. 2005a). While specific factors influencing activity patterns were not examined here, the findings clearly show bats were consistently present in this highly-modified agricultural landscape. The assemblage recorded comprised the majority of species known to occur in the Western Volcanic Plains region of Victoria (Figure 4, Appendix 1). However, a conservative approach should be taken when drawing inferences from a survey based solely on passively collected echolocation data, as detection rates can differ significantly between species (Hayes 2000; Sherwin et al. 2000). To provide greater confidence in recording an accurate species inventory, capture techniques (e.g. harp trapping or mist netting) and physical identification of animals should be employed in conjunction with bat detector sampling (Australasian Bat Society 2006).

Roost-boxes as a tool in the conservation of tree roosting microbats

Minimal levels of foraging activity were recording during this study, predominantly at the Warrayure site (Figure 5). Microbats are known to forage in a range of forested and rural landscapes of southeastern Australia (Law et al. 1998; Lumsden and Bennett 1995), as well as in highly-modified urban landscapes (Threlfall et al. 2012). Lumsden and Bennett (2000) suggested bats are likely to play an important role in regulating populations of herbivorous invertebrates around sparsely scattered trees, because insectivorous birds dependent on good quality forest cover are often scarce in agricultural landscapes. Many land managers are familiar with the beneficial role of birds as insectivores or pollinators (Reid and Landsberg 1999; Lindemayer et al. 2011; Schirmer et al. 2012). However, because insectivorous bats are small, nocturnal and remain hidden in roosts during the day, few people are aware of the ecosystem services they provide by eating insects in rural landscapes (Lumsden and Bennet 2005).

The presence and activity of microbats recorded in this study, and specifically the detection of social calls produced by diurnally roosting bats (Figure 6), has implications for the management and rehabilitation of isolated patches of land within highly-modified agricultural landscapes. Across much of southeastern Australia, the amount of land dedicated to conservation of biodiversity is generally small in size compared with the extensive areas transformed for urbanisation, industrialisation and agricultural development (Gobbons and Lindenmayer 2002; Lumsden and Bennett 2005; Rhodes et al. 2006). Consequently, relatively small sites dedicated to conservation and restoration often exist within a matrix of natural, semi-natural and highly modified habitats (Lindemayer et al. 2011). The mobility of bats means they can traverse the rural landscape to exploit multiple, isolated habitat patches (Lumsden and Bennett 2000). Therefore, the management of sparsely scattered and even single trees in the agricultural landscape can provide significant conservation outcomes for bats (Lumsden and Bennett 1995; Law et al. 1998).

In areas with limited roosting sites, bat-boxes can be installed as substitutes for natural hollows. In Australia, relatively little is known of the use and preferred designs of bat- boxes (Goldingay and Stevens 2009), however studies in the Northern Hemisphere provide evidence that internal microclimate, height off the ground, construction material and design can affect the attractiveness and suitability of a bat-box for the target species (Arnett and

Roost-boxes as a tool in the conservation of tree roosting microbats

Hayes 2000; Brittingham and Williams 2000; Kerth et al. 2001; Flaquer et al. 2005; Bartonicka and Rehak 2007; Lesinski et al. 2009). Therefore, the design and placement of roost boxes is likely to influence their usefulness to bats, and other wildlife, and their effectiveness in allowing the maintenance of sustainable populations of native wildlife in lower-quality, fragmented habitats.

Conclusions The loss, modification and fragmentation of natural habitats constitute a major threat to bat populations worldwide (Racey and Entwistle 2003). This is particularly relevant in Australia where the majority of microbats rely on tree hollows to roost in during the day (Churchill 2008). Echolocation data collected in this study provide indirect evidence of bats roosting diurnally in a small, isolated patch of trees located within a highly-modified agricultural matrix. Bat-boxes were installed at the Warrayure Conservation Offset Site as part of an ongoing ecological management and restoration plan, with the intention of providing supplementary microbat roosting sites (Appendix 3). Further work is planned to incorporate 6-monthly manual checks of bat-box occupancy at Warrayure, paired with additional bat detector surveys to examine seasonal patterns of activity at both the Warrayure and Strathkellar Conservation Offset Sites. This research will provide insight into the efficacy of bat-boxes as a management tool for the conservation of tree-hollow roosting microbats in highly-fragmented rural landscapes.

Roost-boxes as a tool in the conservation of tree roosting microbats

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Roost-boxes as a tool in the conservation of tree roosting microbats

Appendix 1

Table A1. Microbat species known to occur in the Western Volcanic Plains region of Victoria*, with level of taxonomic identification achieved by the AnaScheme program. Scientific name Common name AnaScheme identification Vespertilionidae Chalinolobus gouldii Gould’s wattled bat Species level Chalinolobus morio chocolate wattled bat Species level Falsistrellus tasmaniensis eastern false pipistrelle Species level Miniopterus schreibersii oceanensis southern bent-winged bat Species level Nyctophilus geoffroyi lesser long-eared bat Genus: Nyctophilus sp. Nyctophilus gouldi Gould’s long-eared bat Genus: Nyctophilus sp. Nyctophilus timoriensis greater long-eared bat Genus: Nyctophilus sp. Scotorepens balstoni inland broad-nosed bat Species level Vespadelus darlingtoni large forest bat Species level Vespadelus regulus southern forest bat Species level Vespadelus vulturnus little forest bat Species level Molossidae Tadarida australis white-striped free-tailed bat Species level Mormopterus species 2 eastern free-tailed bat Genus: Mormopterus sp. Mormopterus species 4 southern free-tailed bat Genus: Mormopterus sp. Emballonuridae Saccolaimus flaviventris yellow-bellied sheath-tailed bat Species level *Species distributions from Churchill (2008) and on advice from L. Lumsden (Department of Sustainability and Environment, Victoria).

Roost-boxes as a tool in the conservation of tree roosting microbats

Appendix 2

Figure A1. Sonograms of social call sequences produced by microbats roosting diurnally in mature E. cladocalyx at the Warrayure Conservation Offset Site. Call frequency (kHz) is presented on the y-axis, with time in seconds on the x-axis (call a) 15 second duration; call b) 12 second duration). Both call sequences are comprised of short pulses of sound within the range 7-10 kHz.

Roost-boxes as a tool in the conservation of tree roosting microbats

Appendix 3

Figure A2. a) Stand of mature E. cladocalyx at the Warraayure Conservation Offset Site. b,c,d) Purpose- built bat-boxes installed on the trunks of E. cladocalyx at Warrayure on 29 May 2012.