Vertical stratification of insectivorous bats (Microchiroptera) in harvested forests: assessing the role of structural clutter in shaping patterns of flight activity
Creators: name: Adams, Maria Dawn
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Mammalia
Chiroptera
Chordata
Animalia
bats
bat

description: (Uploaded by Plazi for the Bat Literature Project) In harvested forests, stand structure varies widely with logging history, yet little is  known about how differences in forest structure affect flight activity in insectivorous  bats (Microchiroptera). In this project, conducted in harvested eucalypt regrowth forests  on the south coast of New South Wales, Australia, I assessed the vertical distribution of  insectivorous bats and their potential aerial prey in relation to structural clutter. I also  assessed various methodological issues relevant to forest-bat research.  Bat echolocation activity and insect abundance were each compared in three vertical  strata (understorey, subcanopy and canopy), two locations (forest and track) and three  time periods (evening, night and dawn), in old and young regrowth sites. Mean bat  activity in the subcanopy and canopy was up to 11 times that in the understorey of  forests, a pattern opposite to that of insect abundance. However, vegetation was more  cluttered and bat activity lower in the upper strata of young, than old, regrowth. Mean  activity on the track was 2-5 times higher than in the forest, particularly at understorey  level where clutter levels differed most. Time of night had little effect on bat activity.  The negative response of bat guilds to increased clutter was strongest in the open-space  guild and weakest in the edge-space guild with the highest frequency calls, as predicted  from echolocation call design.  Although half of the young regrowth sites I used had been silviculturally thinned or  selectively harvested 4-9 years previously, there was no significant effect of thinning,  stratum or their interaction, on the activity of any bat group examined. Thinned  regrowth was less cluttered for some vegetation components, but more for others.  Therefore, thinning may not have been sufficient to remove clutter-induced restrictions  on bat activity.  Predator evasion by insects may influence their spatial distribution in forests and, thus,  their potential availability to bats. For example, atympanate (earless) moths may escape  aerial predation passively using cryptic flight behaviour in proximity to clutter, while  tympanate (eared) moths can detect approaching bats and employ evasive flight Abstract  xvi  behaviours. In my insect samples, both eared and earless macromoths (moths with  single wingspan ≥4.5 mm) were significantly more abundant and taxonomically rich in  the cluttered understorey than the upper strata of old and young regrowth forests.  Earless macromoths had greater relative abundance, and were more diverse, in both the  understorey and the foliage-rich canopy than the subcanopy, supporting the possibility  of passive predator avoidance. However, there was little evidence that frequent activity  by echolocating bats in the upper strata of old regrowth forest altered the vertical  stratification of eared moths, via evasive flight responses. Combined, macromoths were  less abundant, in both absolute and relative terms, where bats were most active. This  should confer anti-predation benefits, whether macromoths are hunted preferentially or  opportunistically. The potential availability of flying prey for forest bats clearly varies  with prey group and vertical stratum.  There are likely to be levels of clutter at which even small edge-space bats using highfrequency echolocation are restricted in flight. I assessed the flight patterns of  Vespadelus vulturnus in large circular field arenas at forest sites with different logging  histories. Light-tagged individuals used similar, direct, patterns of flight in the two  oldest classes of regrowth, selecting both subcanopy and understorey strata over the  canopy. On average, they flew in two strata and changed flight stratum every three or  four observations. However, flight patterns differed in the youngest regrowth age class,  which was either unthinned and very densely cluttered, or recently thinned and very  open in structure. In both unthinned and thinned regrowth, only the understorey was  selected and many bats returned to lower strata after an initial ascent. However, in  unthinned regrowth, bats also differed by using three strata and changing flight stratum  every two observations. Here, control of flight height may have been difficult whilst  negotiating the densely spaced stems. The tendency for bats to fly close to the ground in  thinned regrowth suggests that these sites did not provide equivalent flight conditions or  habitat for V. vulturnus as older regrowth.  I recommend that forest with tall open structure and forest tracks should be preserved in  timber production landscapes to facilitate flight and aerial foraging by bats. More  research is required to determine whether thinning practices can be refined to attract