Landscape monitoring reveals initial trends in occupancy and activity of bats in multiple‐use forests

Abstract

Biodiversity monitoring is recognised as a key action for ecologically sustainable land use, but there are few examples of landscape programmes. We outline the first five years of biodiversity monitoring focusing on insectivorous bats in low rainfall, multiple-use forests and woodlands of the Pilliga, Australia. Using ultrasonic sampling over multiple nights, both on-and off-tracks, we identify annual trends in bat activity and occupancy and environmental covariates. Trends differed depending on whether occupancy or bat activity was the response variable. Site occupancy was almost 100% and remained stable and/or did not decline for most species nor diversity over the monitoring period, suggesting little variation in bat populations. In comparison, total activity was initially very high (567 passes night À1 on-track) and then declined by up to 40% in the following three years, but then fully recovered in the fifth year. This general pattern was evident both on-and off-tracks for most taxa, though activity was three times greater on-than off-track, highlighting the importance of these distinct habitat features for bats. Multivariate state-space (MARSS) models predicted, unexpectedly, that high winter rainfall prior to our surveys was negatively related to activity for many taxa. In contrast, disturbance from timber harvesting or fire had weak or no identifiable effects on trends in activity for most taxa. One exception was Chalinolobus picatus (threatened), whose occupancy off-tracks was negatively related to the extent of recent (<5 years) fire and to harvesting, though at the landscape scale, occupancy remained stable. This result, together with patterns for other bat taxa, suggests that disturbance effects were short-lived/dispersed and/or environmental mitigations were effective at maintaining bat populations at a landscape level. Annual monitoring highlighted annual variation in activity and its implications when setting a baseline for monitoring. We also discuss modifications to future monitoring effort, based on the existing five years of data.

Estimating density of forest bats and their long‐term trends in a climate refuge

“…Unfortunately, there are few long‐term datasets available for bats to test these ideas (Law & Blakey, 2021). Recent analysis of trends in ultrasonic activity over 5 years in dry forests and woodlands of Australia have revealed that large variations in activity were negatively related to preceding wet winters rather than drought (Law et al, 2021). We suspect recruitment rather than adult survival to be the more sensitive population attribute affected by climate conditions in south‐eastern Australia, as was found for the trawling large‐footed myotis Myotis macropus (Law et al, 2020).…”

Bats and fire: a global review

“…Only one species, Chalinolobus picatus (Gould), an edge-space forager, showed a negative response to the extent of recent burns (< 5 years); however, this species did not have a negative response to the extent of older burns. Further, the presence of C. picatus at the landscape scale was relatively stable over the 5 years (Law et al 2020) and its distribution across the Murray Mallee Region of southeastern Australia is not affected by burn extent (Senior et al 2021), suggesting that the negative effects of recent wildfire extent are local for this species. However, the distributions of several other species of bats in the Murray Mallee Region are negatively associated with burn extent (Additional file 4).…”

“…The vagility of bats suggests that we should not make direct inferences or comparisons between the results of stand and landscape-scale studies. For example, while C. picatus activity is negatively related to the extent of recent burns at the stand scale, its presence across the landscape is relatively stable over time suggesting that the effects of fire are localized (Law et al 2020). Nonetheless, at the community scale, relationships between bat richness and wildfire extent, configuration, and pyrodiversity are relatively consistent across scales from ~3-30,000 ha .…”

“…In contrast, the wildfires ranged from 3 to 85 years old and wildfire burn extents ranged from 20 to 9322 ha The authors suggested that the time since fire for many sites was so long that the structural changes to the forest were no longer biologically relevant (Austin et al 2020). In contrast, Law et al (2020) found a positive relationship between burn extent and activity of several edge-and open-space foragers for wildfire burns < 5 years old as well as burns that were 5-15 years old. Only one species, Chalinolobus picatus (Gould), an edge-space forager, showed a negative response to the extent of recent burns (< 5 years); however, this species did not have a negative response to the extent of older burns.…”

“…3). For example, many of the studies that have tested the effects of prescribed fire have been conducted at the stand scale (10-20 ha, Loeb and Waldrop 2008;Cox et al 2016;Smith et al 2020), whereas those examining wildfire are often conducted at the landscape scale (8000-> 463,000 ha, Jemison et al 2012;Steel et al 2019;Ancillotto et al 2020;Austin et al 2020;Law et al 2020;. Although some bats have relatively restricted foraging ranges (~0.5 km from the roost, Waldien and Hayes 2001), others such as Brazilian free-tailed bats (Tadarida brasiliensis [I. Geoffrey Saint-Hilaire]) or spotted bats (Euderma maculatum [J.…”