Microbat responses to forest decline

Abstract

Tree declines have been recorded across forests and woodlands on most continents, causing tree mortality over thousands of square kilometres, yet the impact of tree declines upon mammals have only rarely been quantified. Once the dominant tree over the western parts of the Swan Coastal Plain in Western Australia, tuart (Eucalyptus gomphocephala) forest has been reduced to less than a third of its former range through clearing for agriculture and urban development. Additionally, over the last 30 years, the remnant population has been heavily impacted by a decline that has an unknown cause, but is likely related to a root pathogen coupled with abiotic factors (reduced rainfall, increased salinity and elevated temperatures). Tuart decline is evident as marked canopy dieback, replacement with epicormic growth and increasing bare branches, while leaf litter is lost from the tree surrounds. We examined the effect of tuart decline and other vegetation measures upon bat activity using auditory monitoring. Vegetation structure was correlated with Vespertilionidae bat activity. Falsistrellus mackenziei were more likely to forage around healthy canopies (activity positively correlated with tuart crown density and negatively correlated with tuart crown dieback). By contrast, the other three taxa were more often encountered in declining rather than healthy tuart sites. Chalinolobus gouldii was positively associated with tuart crown dieback. Activity of Vespadelus regulus and Nyctophilus spp. (species not distinguishable from their calls) were significantly positively correlated with an open tall canopy (positively with cover of plants >10 m tall and negatively with overall canopy cover density). There were no vegetation measurements that were strong predictors of activity of two Molossidae species (Ozimops kitcheneri and Austronomus australis), which intercept insects above the forest canopy. This study clearly reveals different factors influencing the activity of bat taxa, which are likely related to where they feed and their manoeuvrability around tree canopies.

Global meta‐analysis of tree decline impacts on fauna

“…Ground‐ and understorey‐foraging birds also benefit from tree declines. Some bat species also apparently benefit from a thinning canopy, likely due to increased manoeuvrability (Wentzel et al ., 2019). Other mammals may benefit from the flush of new leaves as trees attempt to recover (Anderson et al ., 2020).…”

A new bat species from southwestern Western Australia, previously assigned to Gould’s Long-eared Bat Nyctophilus gouldi Tomes, 1858

“…Investigations of the biology and conservation management of this species should be a priority. Given that the species cannot be reliably identified from other Nyctophilus species based on call characteristics (Wentzel et al, 2019), surveys should be based on live capture using mist nets or harp traps. This would also provide an opportunity to take wing biopsies from the captured individuals to genetically confirm their identification and facilitate investigation of the presence of genetic structuring within their fragmented habitat in southwest WA.…”