Leroy Gonsalves

Mosquito Consumption by Insectivorous Bats: Does Size Matter?

Insectivorous bats have often been touted as biological control for mosquito populations. However, mosquitoes generally represent only a small proportion of bat diet. Given the small size of mosquitoes, restrictions imposed on prey detectability by low frequency echolocation, and variable field metabolic rates (FMR), mosquitoes may not be available to or profitable for all bats. This study investigated whether consumption of mosquitoes was influenced by bat size, which is negatively correlated with echolocation frequency but positively correlated with bat FMR. To assess this, we investigated diets of five eastern Australian bat species (Vespadelus vulturnus Thomas, V. pumilus Gray, Miniopterus australis Tomes, Nyctophilus gouldi Tomes and Chalinolobus gouldii Gray) ranging in size from 4-14 g in coastal forest, using molecular analysis of fecal DNA. Abundances of potential mosquito and non-mosquito prey were concurrently measured to provide data on relative prey abundance. Aedes vigilax was locally the most abundant mosquito species, while Lepidoptera the most abundant insect order. A diverse range of prey was detected in bat feces, although members of Lepidoptera dominated, reflecting relative abundance at trap sites. Consumption of mosquitoes was restricted to V. vulturnus and V. pumilus, two smaller sized bats (4 and 4.5 g). Although mosquitoes were not commonly detected in feces of V. pumilus, they were present in feces of 55 % of V. vulturnus individuals. To meet nightly FMR requirements, Vespadelus spp. would need to consume ~600-660 mosquitoes on a mosquito-only diet, or ~160-180 similar sized moths on a moth-only diet. Lower relative profitability of mosquitoes may provide an explanation for the low level of mosquito consumption among these bats and the absence of mosquitoes in feces of larger bats. Smaller sized bats, especially V. vulturnus, are likely to be those most sensitive to reductions in mosquito abundance and should be monitored during mosquito control activities.

Do mosquitoes influence bat activity in coastal habitats

Abstract Context. Conservation of insectivorous bat populations requires appropriate management of foraging habitats and the prey resources they sustain. Endangered coastal saltmarsh communities support a diverse range of aquatic and terrestrial arthropods, including the saltmarsh mosquito (Aedes vigilax Skuse), an important vector of mosquito-borne viruses and a potentially important prey resource for insectivorous bats. Prey detectability by bats is considered to be limited with low-frequency echolocation, particularly in cluttered habitats, that may render abundant Ae. vigilax populations unavailable to some bat species. Aims. To investigate relationships between availability of Ae. vigilax and non-mosquito prey, and the activity of foraging insectivorous bats in a range of coastal habitats. Methods. We measured nightly bat activity and the abundance of prey (mosquito and non-mosquito) concurrently during neap and spring tides in saltmarsh, urban and forest habitats. Comparisons were made between tidal cycle and habitats, and relationships between bat activity and the abundance of prey were examined. Key results. Whereas prey abundances were generally greatest in saltmarsh and forest habitats, bat activity was greatest in the forest habitat. However, proportional feeding activity was greatest in saltmarsh. Prey abundance was positively correlated with total bat activity only in the open saltmarsh, where an absence of clutter would maximise prey detectability and thus availability. Positive correlations between Ae. vigilax abundance and bat activity, across all habitats, were restricted to bats of the Vespadelus genus, which are small-sized bats that employ high-frequency echolocation suitable for detection of small prey along edges. Conclusions. These findings suggest that Ae. vigilax may be an important prey resource for small, high-frequency echolocating bats capable of discerning small prey within cluttered forest as well as exploiting abundant prey in the open saltmarsh. Implications. Small, high-frequency echolocating bats should be the focus of future studies investigating the importance of small prey, such as Ae. vigilax, to the diets of foraging bats.

Subtle use of a disturbance mosaic by the south-eastern long-eared bat (Nyctophilus corbeni): an extinction-prone, narrow-space bat

Abstract Context. Studies of habitat suitability in disturbed landscapes based on species traits can improve predictions about how alternative management strategies are likely to affect threatened species. Aims. We studied the south-eastern long-eared bat (Nyctophilus corbeni), which represents a group of bats prone to extinction due to attributes that adapt it to flight within cluttered forest vegetation, typically making them forest-dependent. To support decisions about management of the species in timber production forests, we investigated roost selection and characterised diet in a mosaic of disturbance histories in the Pilliga forests of north-western New South Wales. Methods. We caught 54 N. corbeni, radio-tracked 39 individuals and located 41 unique maternity roost trees. Attributes of roost trees were compared with the local neighbourhood and the landscape mosaic of habitat types and logging treatments (recently logged, recently thinned and old regrowth). Preliminary observations were collected on foraging movements. Diet was characterised for maternity and non-maternity seasons using faecal DNA techniques. Key Results. Small maternity colonies (<10 bats) were found in hollows and fissures often in exposed locations of trees with a small diameter (means range 23–39 cm) that were usually dead (82.5% of roosts). Buloke Allocasuarina luehmannii was most commonly used for roosting (49%), yet has been overlooked previously as a source of hollows for fauna. Landscape-scale habitat use was subtle: bats avoided roosting in commercially thinned stands and selected old regrowth. Logged and mechanically thinned stands were used in proportion to availability. Nyctophilus corbeni consumed a diverse range of prey in spring (November) and autumn (March), dominated by moths. Conclusions. Areas of high stem density, especially those containing dead trees, provide key roosting habitat for N. corbeni and this is likely to be a significant factor explaining the species rarity. Implications. Roosting ecology as well as foraging ecology contributes to a species’ sensitivity to disturbance consistent with trait-based predictions. Heterogeneity in the landscape should be maintained when the habitat of N. corbeni is manipulated (e.g. thinned) by retaining a diversity of stem densities, including dense patches (especially with dead A. luehmannii).

Development and field validation of a regional, management‐scale habitat model: A koala Phascolarctos cinereus case study

Abstract Species distribution models have great potential to efficiently guide management for threatened species, especially for those that are rare or cryptic. We used MaxEnt to develop a regional‐scale model for the koala Phascolarctos cinereus at a resolution (250 m) that could be used to guide management. To ensure the model was fit for purpose, we placed emphasis on validating the model using independently‐collected field data. We reduced substantial spatial clustering of records in coastal urban areas using a 2‐km spatial filter and by modeling separately two subregions separated by the 500‐m elevational contour. A bias file was prepared that accounted for variable survey effort. Frequency of wildfire, soil type, floristics and elevation had the highest relative contribution to the model, while a number of other variables made minor contributions. The model was effective in discriminating different habitat suitability classes when compared with koala records not used in modeling. We validated the MaxEnt model at 65 ground‐truth sites using independent data on koala occupancy (acoustic sampling) and habitat quality (browse tree availability). Koala bellows (n = 276) were analyzed in an occupancy modeling framework, while site habitat quality was indexed based on browse trees. Field validation demonstrated a linear increase in koala occupancy with higher modeled habitat suitability at ground‐truth sites. Similarly, a site habitat quality index at ground‐truth sites was correlated positively with modeled habitat suitability. The MaxEnt model provided a better fit to estimated koala occupancy than the site‐based habitat quality index, probably because many variables were considered simultaneously by the model rather than just browse species. The positive relationship of the model with both site occupancy and habitat quality indicates that the model is fit for application at relevant management scales. Field‐validated models of similar resolution would assist in guiding management of conservation‐dependent species.

Bassian bats in the Eyrean sub-region? Preliminary acoustic data from the Bogan and Macquarie Rivers in semi-arid NSW

We conducted acoustic surveys of insectivorous bat fauna in riparian areas along the Macquarie and Bogan River systems in the wheatbelt of semi-arid central-western New South Wales, Australia. In surveys of 10 sites we detected 11 species and two species groups of bats in eight genera. Four species, Chocolate Wattled Bat Chalinolobus morio, Large-footed Myotis Myotis macropus, Large Forest Bat Vespadelus darlingtoni and Southern Forest Bat V. regulus, are predominantly Bassian (chiefly coastal) in their recorded distributions but were detected in the semi-arid Eyrean sub-region on two rivers in vegetation dominated by River Red Gum Eucalyptus camaldulensis. The findings of this study highlight the need for further research to assess the importance of riparian corridors as habitat for insectivorous bats in semi-arid New South Wales.

Seasonal activity patterns of bats in North Sydney, New South Wales: implications for urban bat monitoring programs

Behavioural and physiological traits of bats may influence seasonal bat activity in urban areas. To examine this, we used acoustic surveys to monitor insectivorous bat activity in urban bushland and at two day-roosts of Miniopterus orianae oceanensis between September 2013 and August 2014. Day-roosts were also assessed for potential as swarming sites and monthly estimates of colony size were made at one of these, while radio-tracking was used to identify additional roosts. Acoustic surveys identified seven species, with Mi. o. oceanensis and Chalinolobus gouldii most commonly recorded. Nightly species richness was lower in winter than in other seasons, while total bat activity was greatest in autumn, reflecting increased activity by C. gouldii and Mi. o. oceanensis in this season. One Mi. o. oceanensis day-roost was used from autumn to early spring, with numbers of bats increasing from ~50 to 300 and high fidelity shown to this site by radio-tagged bats in autumn, while nightly activity at another day-roost was suggestive of swarming. Seasonal differences in bat activity were species-specific and, for Mi. o. oceanensis, corresponded to changes in population size as bats migrated to and from Sydney to meet reproductive and overwintering requirements. We recommend urban bat monitoring programs sample multiple seasons to adequately document trends in activity for all bat species.

Recent decline of an endangered, endemic rodent: does exclusion of disturbance play a role for Hastings River mouse (Pseudomys oralis)?

Abstract Context. The role of disturbance and its exclusion is fundamental to the conservation of threatened species. Aims. We used the habitat accommodation model as a framework to investigate the importance of forest disturbance for the endangered Hastings River mouse, Pseudomys oralis, focusing on timber harvesting. Methods. Our study comprised two separate surveys. We resurveyed old survey sites (n = 24) where the species was originally recorded as either present (logging excluded) or absent (subsequently logged). A second survey targeted trapping in high-quality habitat stratified by different times since logging. Finally, we analysed a 15-year trapping dataset targeting P. oralis to assess associations with co-occurring species. Key results. The resurvey of old sites resulted in 12 P. oralis individuals being trapped, compared with 46 individuals in original surveys. Substantial declines were observed over time in transects where logging was excluded (60–82% decline), whereas there was little change at transects where P. oralis was not previously trapped and that were subsequently logged. The second survey yielded 27 P. oralis captures at post-logging sites assessed as high quality. Occupancy was very high (ψ = 0.93 ± 0.21) in transects logged 7–15 years ago and was 60% less in transects where logging was excluded for 35–45 years (ψ = 0.37 ± 0.22), whereas occupancy in transects logged 2–6 years ago was intermediate. This pattern of higher occupancy in logged areas was mirrored for the mean number of P. oralis trapped per transect. Ordination of habitat data showed an association of P. oralis with heath, mat-rushes and logs, whereas rats (Rattus and Melomys) were associated with ferns and shrubs. Camera traps revealed low background levels of predator presence. A negative exponential relationship was found between probability of occupancy of P. oralis and rat abundance from a 15-year trapping dataset (44 275 trap-nights), suggesting that rats may compete with P. oralis. Conclusions. Our results supported the habitat accommodation model and suggested that disturbance is likely to influence the persistence of P. oralis. However, an interaction between predation and loss of cover from high-frequency disturbance (fire or intense grazing) cannot be excluded as a key threat. Implications. Disturbance should be incorporated into the management of some species. Adaptive monitoring is recommended to assess alternative management regimes.