Report – ZL3205 – Bat Adaptation

Bat’s Adaptation to Urbanization

Group Project in Zl3205 – Wildlife Ecology and Management, 2000-10-30

Group members: Imelda Noli, Jessica Gautherot, Roger Uusitalo and Stefan Martensson.

Introduction

While Australia is thought of as being the ‘land of the marsupials’, the native , terrestrial mammal fauna includes a remarkable diversity of eutherian mammals. This large number of endemic genera and species belong to only two orders: rodents (Rodentia) and bats (Chiroptera) (Knox et al. 1999). Bats’ long history in Australia is know through fossil records to starts as early as the late Oligocene (about 23 million years ago). Because they are flying mammals, water is less of a barrier to dispersal and the perhaps it is no surprise that the early arrival of bats came from Asia.

The impact of humans on bat populations is mixed. The increase in agriculture and the clearing of wide forest areas in Europe during the Middle Ages might have increased the species diversity and population sizes of bats in the same way it did for songbirds (Neuweiler, 2000).

Human settlements and mining activities have supplemented natural roost facilities for bats and some urban man-made structures such as church attics and barns have become favorite roosts for maternity colonies due to the fact that they are heated quickly by the sun (Neuweiler, 2000).

Bat species in the urban (Douglas, Townsville, tropical North Queensland) and natural areas were studied to see which bat species were better adapted to a broader range of areas i.e. best adaptations to urbanization.

Methods

A total of six sites were placed in the Woodland habitat and six in an urban area of Townsville, tropical North Queensland, called Douglas. Within each site a transect line was placed. Along each an ANABAT system was equally placed at three sites (site: A, site: B and site: C). The ANABAT system is designed to facilitate the identification of free flying bats by producing frequency-time graphs of audio-frequency sound using Zero Crossing Analysis. This provides a real time display of the frequency-time characteristics of incoming bat calls.

The ANABAT system was turned on every evening at sun set at a sensitivity level of 8 and turned off before 8:30am each morning. All systems were placed on a 40-70º angle facing the sky and covered with a white folder to protect it against the rain.

To view and analyse the ANABAT’s sequence files recorded each night ANALOOK was used. This program displays sequence files on a logarithmic frequency scale, providing a standardised view of complete calls, regardless of their frequency range. Steps on how this was done can be seen on pages 9-11 under List of Functions in the Zl3205 Wildlife Ecology and

Management Practical handout on Echolocation of Bats in urban landscapes, 2000.

Results

There was no significant difference between the average total bat calls recorded between each habitat over the study period [Douglas: 425; average: 20calls/species; Woodland: 399; average: 19calls/species (Fig 1)]. Two dominant species were found in the Woodland habitat. They were Chalinolobus nigrogriseus and Mormopterus norfolkensis. Whilst a total of three bat calls belonging to Mormopterus loriae, Saccolaimus flav and Miniopterus schreibersii were more frequently recorded in Douglas (Table 1). Making a quarter of the total bat calls received in Douglas was M. loriae [105 calls (Fig 1)], though only 5 calls were recorded in the Woodland habitat.

Though the total call frequency recorded in the Woodland habitat was lower than in Douglas, it holds a higher diversity of species. Many of the species not found in Douglas, were present in the Woodland habitat, though occurring in very low densities, except for M. norfolkensis one of the areas most dominant species (Table 1).

Discussion

It has been found that the species in the urban (Douglas) areas are those species that are easily adapted to a broad range of areas (Churchill, 1998).

According to Schober (1984), certain bat species will adapt to unnatural areas that can offer places of refuge that are suited to their requirements. This has been seen to be true for species that have a high tolerance to disturbed areas. Examples of disturbed area where bats have been found includes mines, tunnels, bridges and old quarries.

This can be used to explain why there is often a greater number of bats found in urban areas then in woodland and natural areas (Schober, 1984). In some cases colonisation of urban areas is only a substitute for natural areas (Schober, 1984). Quite a number of bat species all over the world have become synantrophic animals, now preferring to live near or with humans (Neuweiler 2000).

Chalinolobus nigrogriseus

Chalinolobus nigrogriseus (Hoary wattled bat) have been recorded in tree hollows and in eucalypti trees (Churchill, 1998). This may explain why they have been recorded as more predominant in the wooded areas than in the urban area.

Mormopterus loriae

Mormopterus loriae (Little northern freetail bat)is the most commonly occurring species within the urban area. It has been found to inhabit cracks in posts and in buildings (Churchill, 1998). According to Churchill, (1998) M. loriae is also found in wooded areas which is not consistent with the results (Fig 1).

Mormopterus norfolkensis

Mormopterus norfolkensis (Eastern freetail bat), although residing in the wooded habitat, has not been recorded in the urban areas (Fig 1). This may be explained by the limited ability of this species to inhabit these areas. Most recordings have been from tree hollows (Churchill, 1998) therefore offering the explanation that this species prefers natural areas. M. norfolkensis has not been recorded in the Townsville region (Churchill, 1998). The result may add to the existing data record for this species.

Mimiopterus schreibersii

Mimiopterus schreibersii (Large bentwing bat) have been found in a broad range of habitats, including man-made habitats such as mines and road culverts. Because M. schreibersii have been recorded to have moved 1300 kilometres could explain the broad range of habitats of the species

(Churchill 1998). The results indicate that this species prefer urban habitat against woodland habitat (Fig 1).

Saccolaimus flaviventris

Saccolaimus flaviventris (Yellow-bellied sheath tailed bat) is reported to occur in a wide range of habitats including abandoned nest of sugar gliders and also found outside of buildings hanging off the walls. The habitat ranges from wet and dry forests to open woodland. Their diet consists of insects and their foraging heights vary within canopies (Churchill 1998).

The results have indicated that for this species the variation between the numbers recorded from both sites is small. However, the results are in favour of the urban area (Fig 1). Due to the ability of colonizing a broad range of habitats will allow for the occurrence in both areas.

Vespadelus troughtoni

Vespadelus troughtoni (Eastern cave bat) has been found to occasionally reside in building and near well lit areas. It naturally occurs in overhang caves and boulder piles. Habitats also include mixed woodlands and coastal dividing ranges and into the drier forests of the western slopes (Churchill 1998). The results indicate a higher frequency of this species in the urban areas and it could be explained by the adaptation to illuminated areas (Fig 1).

Sources of error in techniques

When recording the calls of the bat along each individual transect it would be difficult to tell whether or not it is the same individual calling several that once. In this paper it has been assumed that one call represent one individual.

Some bat species have louder calls than others (Allen McIlwee, School of Tropical Biology, J.C.U. 2000 pers. comm.). This may have lead to the louder, more frequently occurring species to dominate the recordings of the other quieter calling species. This could explain the high frequency of recordings of S. flaviventris and M. loriae in the urban area.

Due to the similarities of frequency range of calls between certain species it was sometimes difficult to distinguish between some bat species (Allen McIlwee, School of Tropical Biology, J.C.U. 2000 pers. comm.).

References

Churchill, Sue (1998) Australian Bats. New Holland Publishers Australia.

Knox, B., Ladiges, P. and Evans, B. (1999) Biology. McGraw-Hill Book Company Australia Pty Limited, Roseville.

Neuweiler, G. (2000) The biology of bats. Oxford University Press, NY

Schober, W. (1984) The Lives of Bats. British Library Catalogue in publication Data, Leipzig, Germany

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