Bradley Law

Bat communities in a fragmented forest landscape on the south-west slopes of New South Wales, Australia

Abstract Ultrasonic detectors were used to compare bat activity and species richness at replicated continuous and isolated forests, large and small remnants, corridors and open areas on the south-west slopes of New South Wales, Australia. The habitat matrix in this area consists primarily of agricultural land interspersed with indigenous forest remnants and pine plantations. Ten taxa of bat were recorded, with the fewest in corridors. A multivariate analysis revealed that a gradient in forest area, habitat diversity and structural complexity was the most consistent predictor of activity for four taxa (C. morio, Nyctophilus spp., V. regulus and F. tasmaniensis), suggesting that these are sensitive to the effects of forest fragmentation. Six species (N. australis, M. planiceps l.p., C. gouldii, M. schreibersii, V. darlingtoni, V. vulturnus) appeared tolerant of fragmentation and were not sensitive to isolation effects. Most tolerant species were active over open areas and probably used resources in the agricultural mosaic. Typically they were fast flying, low manoeuvrability species which are predicted to forage in uncluttered habitats. Although total activity in small remnants and corridors was as great as that in large forests continuous with a 690u2008000 ha national park, feeding activity was greatest in continuous forests, suggesting that larger forests with high habitat diversity offered more foraging opportunities. Despite providing fewer feeding opportunities, remnants represent an important conservation resource for bats because activity is concentrated here and they provide potential roost sites. Activity of each species in open areas was not significantly lower than that in corridors (non-riparian), suggesting that corridors were not used regularly by bats to move through the landscape. More detailed studies of the movements of species identified as sensitive to fragmentation would help to explain how fragmentation affects these species and thus what measures are required to improve their conservation.

Tree decline and the future of Australian farmland biodiversity

Farmland biodiversity is greatly enhanced by the presence of trees. However, farmland trees are declining worldwide, including in North America, Central America, and parts of southern Europe. We show that tree decline and its likely consequences are particularly severe in Australias temperate agricultural zone, which is a threatened ecoregion. Using field data on trees, remotely sensed imagery, and a demographic model for trees, we predict that by 2100, the number of trees on an average farm will contract to two-thirds of its present level. Statistical habitat models suggest that this tree decline will negatively affect many currently common animal species, with predicted declines in birds and bats of up to 50% by 2100. Declines were predicted for 24 of 32 bird species modeled and for all of six bat species modeled. Widespread declines in trees, birds, and bats may lead to a reduction in economically important ecosystem services such as shade provision for livestock and pest control. Moreover, many other species for which we have no empirical data also depend on trees, suggesting that fundamental changes in ecosystem functioning are likely. We conclude that Australias temperate agricultural zone has crossed a threshold and no longer functions as a self-sustaining woodland ecosystem. A regime shift is occurring, with a woodland system deteriorating into a treeless pasture system. Management options exist to reverse tree decline, but new policy settings are required to encourage their widespread adoption.

The use by wildlife of paddock trees in farmland

Morning and dusk watches at live and dead trees were used to systematically investigate which species of vertebrates use paddock trees within farmland proposed for the establishment of Eucalyptus plantations in northern New South Wales. Tree-watches at 108 trees were stratified on farmland as isolated, in small patches, remnant vegetation and riparian strips plus in adjacent forest. Arboreal marsupials and bats emerged from hollows in 11% and 8% of trees, respectively. Only one colonial bat roost was observed, although the marsupials Trichosurus vulpecula and Petaurus breviceps were widespread in the landscape. Two threatened species of marsupials (Petaurus norfolcensis and Phascogale tapoatafa) were observed using paddock trees on flats or slopes outside of riparian strips. Among owls, only the Southern Boobook Ninox novaeseelandiae and Barn Owl Tyto alba were observed using tree hollows on farmland. For all hollow-dependent nocturnal fauna (marsupials, bats and owls), very large tree diameter best predicted occupation of a tree-hollow (especially if <800 m from the nearest forest). In addition to providing hollows, paddock trees were used for foraging. Morning surveys revealed 35 diurnal bird species on isolated trees, although most were generalists (e.g., Eastern Rosella Platycercus eximius, Noisy Miner Manorina melanocephala) that were also regular visitors to non-isolated trees in remnant vegetation. More forest-dependent and forest-associated bird species were recorded in forests and riparian strips than other tree categories, reinforcing the high conservation value of riparian strips in farmland. After dark, ultrasonic detectors recorded 21 species of bat (seven threatened species) flying in close proximity to paddock trees. Relatively high levels of activity were recorded at one study location for species rarely recorded in forests (e.g., Scoteanax rueppellii). Remnant Eucalyptus tereticornis and E. amplifolia were a significant source of blossom for nectarivores and they were also associated with high bat activity, possibly because they grow on fertile soil. Recommendations on tree retention guidelines are discussed.

Reliable Automation of Bat Call Identification for Eastern New South Wales, Australia, Using Classification Trees and AnaScheme Software

Accurate and efficient identification of bat (Microchiroptera) echolocation calls has been hampered by poor knowledge of the intraspecific variability in calls (including regional variation), a lack of call parameters for use in separating species and the amount of time required to manually identify individual calls or call sequences. We constructed and tested automated bat call identification keys for three regions in New South Wales, Australia, using over 4,000 reference calls in ≈300 call sequences per region. We used the program AnaScheme to extract time, frequency and shape parameters from calls recorded with the Anabat system. Classification trees were built to separate species using these parameters and provided the decision rules for construction of the keys. An ‘Unknown’ category was included in the keys for sequences that could not be confidently identified to species. The reliability of the keys was tested automatically with AnaScheme, using independent sets of reference call sequences, and keys were refined before further testing on additional test sequences. Regional keys contained 18–19 species or included species groups. We report rates of sequence misidentification (accuracy) and correct identification (detection) relative to all sequences (including ‘unknowns’) used to test each version of a key. Refined versions of the keys were accurate, with total misidentification rates of 0.5–5.3% for the three regions. Additionally, total correct identifications for regions were 56–75% (> 50% for most species), an overall high rate of detection. When ‘unknowns’ were ignored, as is common in many published studies, correct identification for regions increased to 91–99%, rates which compare favourably to the most successful classifiers tested to date. The future use of AnaScheme for automated bat call identification is promising, especially for the large-scale temporal and spatial acoustic sampling to which Anabat is particularly suited.

Designing Effective Habitat Studies: Quantifying Multiple Sources of Variability in Bat Activity

Common aims of habitat studies are to differentiate between (i) suitable and unsuitable sites for a given species, and (ii) sites used by different communities of species. To quantify differences between sites, field data of site use must be precise enough that true underlying between-site variability is not masked by within-site measurement error. We designed a pilot study to guide the development of a survey protocol for a habitat study on bats in an agricultural landscape in southeastern Australia. Three woodland sites and two scattered tree sites of 2 ha each were surveyed for nine consecutive nights. At three locations within each site (spaced > 50 m apart) one or two Anabat detectors were mounted 1 m above ground or in a tree (2 m above ground). We used mixed regression models to quantify multiple sources of variability in bat calling activity, and graphical data analysis to visualise how increases in survey effort were likely to affect inference. For the five most active species, we found that typically over 40% of variability in nightly detections occurred at the between-site level; approximately 10% occurred between locations within sites; approximately 20% was explained by night-to-night differences; and approximately 30% of variability was not attributable to systematic variation within experimental units. Differences in community composition between sites were clearly evident when two or more detectors per site were used for four or more nights. We conclude with six general considerations for the design of effective habitat studies. These are to (i) consider key contrasts of interest; (ii) use data from mild, calm, dry nights only; (iii) calibrate detectors; (iv) use multiple detectors where possible, or move a single detector within a site; (v) survey for multiple nights; and (vi) where vertical differentiation in habitat use is likely, mount detectors at different heights. These considerations need to be balanced within the context of financial and logistical constraints.

A bat survey in State Forests on the south-west slopes region of New South Wales with suggestions of improvements for future surveys

Ten State Forests on the south-west slops 01 New South Wales were surveyed for bats at 39 forest sites and 24 water-bodies using ultra-sonic bat detectors, harp-traps, mist-nets and trip-lines. Thirteen species of bats were recorded for the region. Many species were widespread. with six of the 13 species recorded at more than 50% of sites; however four occurred at less than 20% of sites. Each State Forest sampled supported at least eight species. The species of bats present were representative of the biogeographical region of the study area, lying in the transitional zone between moist climates of the east and arid environments to the west. Within the range of elevations sampled (390-1 419 m). Chalinolobus gouldii, Vespadelus vulturnus, Mormopterus planiceps lp and Scotorepens balstoni were either absent or maintained lower activity levels above 1000 m. Bat activity and species richness was also low in forests typical of the most extreme climate (Snow Gum/Black Sallee), however no differences were found b...

Geographic variation in the echolocation calls of Vespadelus spp. (Vespertilionidae) from New South Wales and Queensland, Australia

We investigated the extent of geographic variation in the echolocation calls of five species of microchiropteran Vespadelus in eastern Australia. Bat calls were recorded with Anabat II detectors and computers, and analysed using Analook software. A single call parameter, characteristic frequency (the frequency at the end of the flattest part of the call), was used to document changes in echolocation calls over geographic distance. For V. vulturnus and V. regulus, changes in call frequency were abrupt and sizeable (up to 14 kHz), with two or three frequency groups present within each species. In V. darlingtoni, the changes in frequency were gradual across their range, with an isolated island population resembling the closest region on the mainland. One species examined here, V. troughtoni, had calls that were consistent throughout its range. Calls of V. pumilus were also consistent across geographic regions except for at one site (Chichester State Forest). At this site calls occupied only the upper end of the species frequency range. Body size, measured as forearm length for each species, was significantly smaller at inland sites, but did not vary with latitude or consistently with intraspecific call variation. Broad patterns and possible causes of geographic variation in call frequency are discussed. We conclude that confident identifications of Vespadelus calls from the geographic regions outlined in this paper will only be made with reference calls collected from the relevant regions.

Influence of Landscape Structure and Human Modifications on Insect Biomass and Bat Foraging Activity in an Urban Landscape

Urban landscapes are often located in biologically diverse, productive regions. As such, urbanization may have dramatic consequences for this diversity, largely due to changes in the structure and function of urban communities. We examined the influence of landscape productivity (indexed by geology), housing density and vegetation clearing on the spatial distribution of nocturnal insect biomass and the foraging activity of insectivorous bats in the urban landscape of Sydney, Australia. Nocturnal insect biomass (g) and bat foraging activity were sampled from 113 sites representing backyard, open space, bushland and riparian landscape elements, across urban, suburban and vegetated landscapes within 60 km of Sydneys Central Business District. We found that insect biomass was at least an order of magnitude greater within suburban landscapes in bushland and backyard elements located on the most fertile shale influenced geologies (both p<0.001) compared to nutrient poor sandstone landscapes. Similarly, the feeding activity of bats was greatest in bushland, and riparian elements within suburbs on fertile geologies (pu200a=u200a0.039). Regression tree analysis indicated that the same three variables explained the major proportion of the variation in insect biomass and bat foraging activity. These were ambient temperature (positive), housing density (negative) and the percent of fertile shale geologies (positive) in the landscape; however variation in insect biomass did not directly explain bat foraging activity. We suggest that prey may be unavailable to bats in highly urbanized areas if these areas are avoided by many species, suggesting that reduced feeding activity may reflect under-use of urban habitats by bats. Restoration activities to improve ecological function and maintain the activity of a diversity of bat species should focus on maintaining and restoring bushland and riparian habitat, particularly in areas with fertile geology as these were key bat foraging habitats.

Effect of lights on activity levels of forest bats: increasing the efficiency of surveys and species identification

We investigated the effects of insect-attracting ultraviolet lights on activity of forest bats (Microchiroptera) with the prediction that lights would increase our indices of bat activity and improve species identification of recorded echolocation calls. Insect aggregations were created on forest tracks (n = 9) near Kioloa, New South Wales, using three vertically stratified insect light traps. Bat echolocation calls were recorded using a ground-based vertically oriented Anabat II detection system. Bat activity and foraging rates were higher at lit points than at unlit points, particularly when the lights were operated in full darkness. More species were identified at lit points and the sampling time required to identify the second to the fifth new species was 3.3–4.6 times shorter with lights. The presence of lights resulted in a greater number of bat passes more than five pulses in length, which was associated with an increased ability to identify passes to species level. Our study demonstrates that the use of lights in forest-based echolocation surveys can improve bat species inventories, particularly in communities where overlap in call characteristics among species is common.

Patterns in bat functional guilds across multiple urban centres in south-eastern Australia

Understanding the impacts of landscape change on species behaviour is a major challenge in landscape ecology. A focus on the functional traits of species may improve this understanding if species with similar traits (functional guilds) are impacted by landscape change in similar ways, but this idea has not been widely tested on bat communities in urban landscapes. We examined changes in bat species richness and the activity level of species in different functional guilds within 72 residential neighbourhoods across 18 towns and cities spanning over 250,000xa0square km in south-eastern Australia. Species richness increased close to native vegetation, declined with increasing urbanization, and had a hump-shaped relationship with neighbourhood vegetation cover. Also, the activity level of all bat species combined peaked at mid-range values of neighbourhood vegetation cover. The activity of species in the open-adapted guild was not strongly related to any urban characteristic, but our results concur with previous findings that the activity of most open-adapted species does not appear to be negatively impacted by urbanization. Conversely, clutter-adapted species appear more sensitive to urbanization and their activity level was negatively related to urban intensity and increased closer to native vegetation, consistent with previous studies. The functional-trait approach may improve the capacity to make generalisations across different landscape contexts for clutter-adapted and open-adapted guilds, but is currently hampered for other bat species owing to variation in the behaviour of different species assigned to the same functional guild, and a lack of ecological knowledge regarding the impacts of different types of landscape change on particular species.