TRAUMA FOUND TO BE A SIGNIFICANT CAUSE OF DEATH IN A PATHOLOGICAL INVESTIGATION OF BENT-WINGED BATS ( MINIOPTERUS ORIANAE )

Determining the causes of mortality in endangered species is essential to understanding the possible reasons behind their decline and to facilitating the implementation of mitigating steps. The southern bent-winged bat (Miniopterus orianae bassanii) is a critically endangered Australian bat whose population numbers have decreased over the past 50 years. As part of a larger investigation to determine if disease could be a contributing factor to the decline, 27 southern bent-winged bats and one closely related eastern bent-winged bat (Miniopterus orianae oceanensis) that died during the study were necropsied and examined histologically. Trauma was the most common cause of death in the southern bent-winged bats, which mostly occurred at one site where fencing and other infrastructure was positioned around a key breeding cave. In response to these findings, management actions have been implemented to reduce this infrastructure-associated mortality of southern bent-winged bats. The single eastern bent-winged bat examined had a severe dermatitis caused by the mite Notoedres muris.

Polychromophilus melanipherus and haemoplasma infections not associated with clinical signs in southern bent-winged bats (Miniopterus orianae bassanii) and eastern bent-winged bats (Miniopterus orianae oceanensis)

While bats are often viewed as carriers of infectious disease agents, little research has been conducted on the effects these pathogens may have on the bat populations themselves. The southern bent-winged bat (Miniopterus orianae bassanii) is a critically endangered subspecies endemic to south-eastern Australia. Population numbers of this bat have declined over the past 50 years, but the reasons for this are unclear. As part of a larger study to determine if disease could be a contributing factor to this decline, southern bent-winged bats from several locations in Victoria and South Australia were captured and examined for the presence of the blood parasite, Polychromophilus melanipherus, and haemoplasmas (Mycoplasma sp.). Results were compared with those obtained from populations of the more common, partially sympatric, eastern bent-winged bat (Miniopterus orianae oceanensis) from three different locations in Victoria. Both organisms were found in both subspecies (prevalence of P. melanipherus 60% by PCR for southern bent-winged bats compared with 46% for eastern bent-winged bats; prevalence of haemoplasmas 10% for southern bent-winged bats compared with 8% for eastern bent-winged bats), with no association between the probability of infection, body weight, abnormal blood parameters or any other indicators of ill health. However, Victorian southern bent-winged bats had heavier burdens of P. melanipherus than both the South Australian southern bent-winged bats and eastern bent-winged bats. Further investigations are required to determine if these differences are impacting population health.

Ectoparasites are unlikely to be a primary cause of population declines of bent-winged bats in south-eastern Australia

While bats carry a diverse range of ectoparasites, little research has been conducted on the effects these organisms may have on bat populations. The southern bent-winged bat (Miniopterus orianae bassanii) is a critically endangered subspecies endemic to south-eastern Australia, whose numbers have declined over the past 50 years for unknown reasons. As part of a larger study to investigate the potential role of disease in these declines, southern bent-winged bats from four locations were captured and examined for the presence of bat flies, mites, ticks and the nematode Riouxgolvania beveridgei (previously associated with skin nodules in bent-winged bats). Results were compared with those obtained from the more common eastern bent-winged bat (Miniopterus orianae oceanensis), sampling animals from three different locations. All four types of parasite were found on both subspecies. There was no correlation between the presence of ectoparasites, body weight or any signs of disease. However, prevalence of tick and R. beveridgei infections were greater in Victorian southern bent-winged bats than South Australian southern bent-winged bats and eastern bent-winged bats, possibly indicative of some type of chronic stress impacting the immune system of this subspecies.

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Ectoparasites not associated with ill health in bent-winged bats.

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Greater prevalence of ticks and R. beveridgei infections on Victorian southern bent-winged bats.

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Bat flies and mites more common in summer. Ticks more common in spring. R. beveridgei more common in winter and spring.

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Mites more common on juvenile bats.