Habitat relationships, activity patterns and feeding ecology of insectivorous bats of the Top End of Australia

Milne, Damian John (2006) Habitat relationships, activity patterns and feeding ecology of insectivorous bats of the Top End of Australia. PhD thesis, James Cook University.

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The wet-dry tropics of the Northern Territory (the Top End) has a diverse microbat fauna. It supports 28 of Australia’s 65 species, including one endemic species (Taphozous kapalgensis), both of Australia’s monotypic genera (Rhinonicteris and Macroderma) and two species considered to be rare or endangered (Saccolaimus saccolaimus and Hipposideros diadema). However, most aspects of the ecology of this fauna are poorly known. The aim of this study was to investigate the composition of microbat assemblages; describe the habitat relationships of the microbat fauna at both the community and species levels; assess microbat activity patterns at several temporal scales; and to conduct a dietary analysis of the microbats of the Top End. Robust methods for sampling bats are still being developed and tested. Based on recordings derived from the Anabat II detector, I compared the results of surveys where I changed the orientation of the detector, the type of recording media, and static versus active hand-held recording. Detector orientation did not significantly affect any survey results, more call passes were identified from digital recordings and more species were detected using hand-held recordings. I also derived species-accumulation curves for the Top End microbats and provide guidelines for minimum sampling effort in future studies.

Patterns in the composition of assemblages of microbat species sampled during the late dry season (the ‘build-up’) in the Top End were assessed against a range of environmental factors as well as four a priori defined habitat types (riparian, escarpments, coastal and woodlands). In general, species assemblages were not clearly defined and the number of significant environmental associations was relatively few. The most distinct species assemblages were strongly associated with topographic and climatic variables. There were also limited associations with vegetation structure, fire and local roost potential but no associations with insects or water availability. Total species diversity at sample sites was associated with distance to rivers and rainfall. Generalised linear modelling (GLM) was used to develop habitat models for 25 of the 28 microbat species of the Top End. Based on these models, a geographic information system (GIS) was used to derive probability of occurrence maps for each species. Almost all of the models identified a unique combination of environmental variables, and the resulting probability of occurrence maps revealed a variety of patterns of predicted distribution. Annual rainfall and habitat complexity were identified as significant variables in the majority of the models. All of the spatial models were combined to derive a probability map of species richness of microchiropteran bats in the Top End. This map shows greatest species richness in the north-west and north-central parts of the study area.

Temporal patterns of microbat activity and species richness were assessed at four scales: hourly, nightly, monthly and yearly, in relation to biotic (insect availability) and abiotic features in the environment. At the hourly scale, bat activity was highest in the first hour after dusk and declined throughout the night. Hourly bat activity was most closely associated with temperature. At the nightly scale there were significant associations between bat activity, moon light and temperature as well as a complex association with both moon phase and time of night. At the monthly scale bat activity increased dramatically in October which was possibly triggered by a combination of changing climatic factors that occur at this time of year in the Top End. At the yearly scale there was no overall difference in bat activity between years (n = 4) and no associations with climatic variables.

The dietary composition for 23 of the 28 Top End microbat species was described by identifying the prey remains collected from stomachs and faecal pellets to the lowest possible taxonomic level (usually order or lower). Dietary analysis revealed that most species consumed a variety of orders indicating that Top End microbats have generalist dietary requirements and/or opportunistic foraging habits. However, the dietary compositions for H. diadema, H. stenotis, Mormopterus loriae, Nyctophilus geoffroyi, N. bifax and T. kapalgensis contained only one or two insect orders suggesting these species may have more specialised diets. Microbats in the ‘Uncluttered’ foraging guild consumed proportionally more insects belonging to the orders Orthoptera and Coleoptera whereas the ‘Background clutter’ and ‘Highly cluttered’ foraging guilds consumed proportionally more Lepidoptera.

This study has greatly increased our understanding of some aspects of the ecology of microbats in the Australian wet-dry tropics. I make a number of recommendations for the conservation management and future research of Top End microbat fauna, most notably to investigate the association between microbat diversity and riparian areas, conduct further microbat surveys throughout the region to redress the still meagre number of records, and initiate targeted monitoring programs for microbats.

Item ID: 2019
Item Type: Thesis (PhD)
Keywords: microbats, microchiroptera, insectivorous bats, northern Australia, Northern Territory, Top End, wet-dry tropics, savannas, feeding, ecology, habitat relationships, temporal patterns, AnaBat, sampling, echolocation, species assemblages, distribution, diversity, environmental variables, dietary analysis, conservation, management
Additional Information:

The definitive version of Chapter 2 is available at http://www.publish.csiro.au/nid/145/issue/849.htm

The definitive version of Chapter 3 is available at http://www.wileyinterscience.com

Chapter 4 is reprinted from Biological Conservation, 130/3, D.J. Milne, A. Fisher, and C.R. Pavey, Models of the habitat associations and distributions of insectivorous bats of the Top End of the Northern Territory, Australia, pp. 370-385, Copyright 2006, with permission from Elsevier.

Chapter 5 is reprinted from Journal of Mammalogy, 86, D.J. Milne, A. Fisher, I. Rainey and C.R. Pavey, Temporal patterns of bats in the Top End of the Northern Territory, Australia, pp. 909-920, Copyright 2005, with permission from American Society of Mammalogists, Allen Press Inc.

Appendix 2 is reprinted from Australian Zoologist, 32, D.J. Milne, T.B. Reardon and F.Watt, New records for the Arnhem sheathtail bat Taphozous kapalgensis (Chiroptera: Emballonuridae) from voucher specimens and Anabat recordings, pp.439-445, Copyright 2002, with permission from the Royal Zoological Society of New South Wales.

The definitive version of Appendix 3 is available at http://pubs.nrc-cnrc.gc.ca/rp-ps/journalDetail.jsp?jcode=cjz&lang=eng

Date Deposited: 07 Dec 2008 23:53
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 0%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060208 Terrestrial Ecology @ 0%
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