Tracks and riparian zones facilitate the use of Australian regrowth forest by insectivorous bats.
Abstract
Documentation of habitat use by individual bat species is a key issue when assessing impacts after forests are disturbed, for example by logging. We used bat detectors to compare bat activity in unlogged forest and regrowth forest 15 years after logging in northern New South Wales, Australia. Sites of contrasting management history were replicated at the scale of small catchments, with detectors positioned on tracks, off tracks and in riparian zones in either unlogged or regrowth forest. The highest bat activity was recorded on forest tracks, with no significant difference between detectors in regrowth (mean=183 passes night-1) and unlogged forest (196 passes night-1). Activity in riparian zones was intermediate (regrowth=55 passes night-1; unlogged=26 passes night-1), while off-track sites in forest regrowth had the lowest activity levels (5 passes night-1). Species richness was lowest in the off-track samples in regrowth and highest in the on-track samples of regrowth. An index of clutter for different vegetation layers was recorded at each site. Bat activity decreased significantly with increasing clutter formed by the layer of regrowth eucalypts and/or understorey rain forest. This result strongly suggested that low bat activity off tracks was related to vegetation clutter. Specific identification of calls revealed that the suite of species associated with tracks included both those predicted by ecomorphology to be clutter-sensitive (Falsistrellus tasmaniensis, Vespadelus darlingtoni, V. pumilus and Chalinolobus morio) and clutter-tolerant (Rhinolophus megaphyllus). Elevation and temperature were also significant covariates of activity for a number of species. As part of sustainable management of regrowth forests, we advocate maintaining flyways for bats in the form of tracks and riparian zones, in addition to the widely recognized need for the retention of hollow-bearing trees as roost sites. Research on the effects of silvicultural thinning, which will reduce clutter with possible benefits to some bat species, should also be a priority in forest characterized by secondary regrowth.