Nest boxes are often promoted as substitute structures for hollow-dependent fauna, but are they generally effective? In a long-term bat-box monitoring project in south-eastern Australia, box occupancy was dominated by one common and widespread urban-adapted species, Gould's wattled bat Chalinolobus gouldii. In contrast, the 13 other bat species in the area made little or no use of the boxes. Policymakers, land managers and conservation professionals working in the field of biodiversity offsets should be aware that bat boxes are unlikely to compensate adequately for the broad-scale loss of tree hollows caused by various forms of human disturbance.Mammal Review ISSN 0305-1838 bs_bs_banner SUPPORTING INFORMATIONAdditional supporting information may be found in the online version of this article at the publisher's web-site.Appendix S1. Description of the four field sites. Appendix S2. Examples of the nine different bat-box designs.Appendix S3. Summary of bat-box survey effort.

Bat boxes are often used to provide supplementary roosting habitats; however, little is known of their impacts on community composition. Data collected from a 25-year box-monitoring and 31-year harp trapping case study provides preliminary evidence that the installation of boxes may have contributed to one species, Gould’s wattled bat (Chalinolobus gouldii), dominating the bat community of a periurban park in Melbourne. This highlights the need for systematic monitoring and empirical assessment of conservation-focused bat box programs.

Organ Pipes NP in NW Melbourne is a replanted eucalypt woodland where timber bat boxes of Stebbings' English design were installed in 1992 and first used late in1994. The bats found have been over 90% Gould's and 7% Large Forest Bats. Boxes of 6 different designs were tried over 15 years, differing in internal dimensions and entrance slit size, ranging from 0.002m 3 to 0.009m 3. The first ten boxes are used only in warm months, September to February. Three fallen boxes were replaced with smaller pinus boxes, which are used over more of the year. In 1996 some boxes, conforming more to Stebbings' design, were added, which are used for a yet wider seasonal range. Another set of smaller boxes have been used mainly in cooler months, and are avoided in summer. A set of boxes made of 45mm timber are also used in colder months. Annual patterns of box usage are examined for the different box designs-some show slow build-up, usage of others fluctuate up and down in cycles of several years, or are well used but avoided for some whole years, or are little used but come briefly into favour for one year. Box orientation affects usage patterns, those facing west or east being used much more than those facing north or south, and in different seasonal patterns. Where two boxes share a tree, complementary patterns may appear, one favoured in warm months, the other in colder months. An unexpected increase in usage in 2007-8 involved two bouts of breeding. Implications for study of natural hollows are discussed.

The rate of loss of tags used to mark individuals is an important consideration in wildlife research and monitoring. Passive integrated transponder (PIT) tags (or microchips) generally have high retention rates; however, tag loss rates for small mammals such as insectivorous bats are poorly understood. We double-marked a population of Gould's wattled bats (Chalinolobus gouldii) with forearm bands and PIT tags (with the injection site sealed with surgical adhesive) in January and February 2020 to determine rates of subsequent tag loss over the short-(1-2 months) and medium-(13-14 months) term. Loss of PIT tags occurred in 4 (2.7%) of 146 recaptured individuals, all within 2 months of microchipping. We also recorded 1 occurrence of band loss 11 months after banding. Our study supports assertions that PIT-tag retention rates in small mammals are high, and suggests that rates of tag loss in small bat species are low when surgical adhesive is applied. Quantifying the rate of tag loss enables this variable to be incorporated into mark-recapture models.

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