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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
An assessment of the risk to the Large
Forest Bat Vespadelus darlingtoni from
proposed wind turbines on Lord Howe Island,
New South Wales.
A report to Lord Howe Island Board
G.A. Hoye
Fly By Night Bat Surveys Pty Ltd
ABN 48 068 562 005
PO Box 271
BELMONT NSW 2280
Tel 4947 7794
Fax 4947 7537
January 2016
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
1
INTRODUCTION
Fly By Night Bat Surveys PL was requested by the Lord Howe Island Board to assess
potential impacts to the Large Forest Bat from two proposed wind turbines to be sited in
pasture on the southern flank of Transit Hill. This species is currently the only native mammal
known to breed on the island. Previous survey has confirmed the presence of this species in
the lower elevated parts of the island including the area where the two turbines are proposed
(Fly By Night Bat Surveys 2010). A population of approximately 500 breeding females exists
north of the airstrip, with a second smaller population centred around Mount Gower and
Mount Lidgebird (Fly By Night Bat Surveys 2010-2014).
Significant mortality of microchiropteran bats has occurred at utility wind farms in North
America and Europe (eg Kunz 2007b). In eastern North America mortality from turbine strike
along forested ridge tops varies from 15.3 to 41.1 bats per megawatt (MW) of installed
capacity per year Kunz (2007b). Lower rates have been reported from other parts of the US
varying from 0.8 to 8.6 bats per MW per year. Higher mortality is associated with periods of
migration of particular tree roosting bat species and may involve bats approaching turbines for
inspection as potential roosts. (Kunz 2007a).
Two Vergnet GEV MP R 275 kW wind turbines are proposed for an area of pasture on the
northern flank of Transit Hill, southwest of the current Powerhouse site. The turbines have two
blades of 32 metres diameter set at a hub height of 55 metres (Jacobs Group 2015) and are
able to be tilted for maintenance or other equirements. They will be guyed with cables to
supporting masts. The turbines are rated for wind speeds of 12 metres per second and cut in
at wind speeds of 3.5 metres per second and cut out at wind speeds in excess of 25 metres
per second. Maximum rotor speed of 31 rpm would be achieved. The swept rotor area will
occur between 39 metres and 71 metres above ground level at the turbine locations.
To assess the activity of the Large Forest Bat, echolocation calls were recorded at a wind
monitoring mast sited immediately south of where the turbines will be located. Calls were
recorded each night over a twelve month period at three heights to assess the relative activity
of bats. Additional echolocation call detection was undertaken at locations within pasture,
forest edge and within forest habitats adjacent to the proposed turbine locations during visits
to the island in November 2014, and February, May, July and November of 2015 to assess
the relative activity of the Large Forest Bat in pasture compared with forest habitats. Capture
and banding of the Large Forest Bats was also undertaken during visits to the island to assist
in providing population estimates and provide additional information on natural movements of
individuals. It also provided information on the activity of the bats during the autumn and
winter months, as previous survey had been restricted to spring and summer (Fly By Night
Bat Surveys 2010-2014).
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
2
SURVEY METHODOLOGY
To assess the risk to resident populations of the Large Forest Bat from blade strike and
impact with guy wires and supporting masts, echolocation call detection was undertaken to
quantify the activity of this species in the vicinity of the swept rotor range.
Effect of Habitat on Bat Activity
The degree to which bats utilise pasture in the vicinity of the turbines was assessed through
the placement of Anabat SD1 and SD2 detectors within the adjacent forest, at the forest edge
and in open pasture (refer to Figure 1 and Plates 1-3). Sampling was undertaken in
November 2014, February 2015, May 2015, July 2015 and November 2015 (Table 1) to
provide information of the use of these habitats throughout the year. The sensitivity of
detectors was calibrated using a Bat Chirp Board (Nevada Bat Technology, Los Vegas USA)
to ensure units were comparable. The detectors sampled throughout the entire night with files
downloaded for subsequent analysis.
Figure 1
Sites sampled for echolocation calls to assess the effect of habitat on the
activity of the Large Forest Bat.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Plate 1
Plate 2
A detector placed in forest to the east of the turbines sites.
A detector placed at the forest edge to the east of the turbines sites.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Plate 3
A detector placed in pasture near the wind monitoring mast.
Effect of Height on Bat Activity
The second area of investigation was the activity of the Large Forest Bat at three heights
within pasture at the wind monitoring mast. Microphones were located at 2 metres, 20 metres
and 40
turbines
base of
sunrise.
metres height on a wind monitoring mast located in the clearing where the two
will be situated, and connected via cables to Anabat Express detectors near the
the mast. The detectors were programmed to come on at dusk and record until
Sensitivity of the detectors was adjusted until all three were recording the same
number of bat passes at ground level prior to placement of the microphones at the three
heights. These ensured results were comparable between the detectors. The detectors were
downloaded on visits to the island in February, May, July and November 2015.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
3 SURVEY RESULTS
Effect of habitat on Large Forest Bat activity
Activity of the Large Forest Bat was substantially higher within forest when compared to that
in pasture for all of the surveys (refer to Graph 1). Activity levels within the forest were
significantly higher than that in pasture during all four surveys (Kuskall Wallis non parametric
test, H=6.60-15.98, 2 d.f., P<0.05). Activity levels in the forest were approximately an order of
magnitude higher than that at the forest edge. There was generally an equivalent decrease in
activity from the forest edge to that in pasture despite the detector being sited less than 30
metres into the pasture from the forest edge. This pattern was repeated during surveys
undertaken in November 2014, February 2015 and May 2015. Activity between the three
habitat types was not significantly different during the July 2015 survey, with low activity at
forest, edge and pasture sites.
Graph 1
Activity of the Large Forest Bat within forest, at the forest edge and in open
pasture.
These results indicate that the Large Forest Bat does not currently forage in or commute
through the area of pasture to a substantial extent where the turbines are proposed to be
sited.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Effect of height on bat activity
Graph 2
The effect of detection height on activity levels of the Large Forest Bat at the mast.
Graph 2 displays the activity of the Large Forest Bat at the mast at 2 metres, 20metres and
40 metres height. While activity was low even at 2 metres, activity at 20 metres height was
negligible. This suggests that the small number of bats passing over the pasture do so close
to ground level. No activity was present at 40 metres height, indicating that the likelihood of
the Large Forest Bat passing through the swept rotor area of the proposed turbines is low.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Temporal variation in Large Forest Bat activity in the vicinity of the mast
Graph 3
Nightly variation in activity of the Large Forest Bat at ground level at the mast.
As seen in Graph 3, activity of the Large Forest Bat at ground level at the mast varied from no
or little activity on some nights to over 50 passes per night on a few occasions. While activity
fluctuated from November until April, activity declined dramatically from the end of March with
little to no activity in winter. Activity is presumed to have increased again sometime between
September and November 2015, but faults with the microphones of the detectors in late
September resulted in no data being recorded for this period
Activity of the Large Forest Bat at 20 metres height at the mast was substantially less than
that at ground level (refer to Graph 4). Activity was recorded on far fewer nights than at
ground level and echolocation call passes rarely peaked over 10 passes per night. Most
activity was recorded during December 2014 with no call passes being recorded at this height
after early January. No echolocation call passes were recorded at 40 metres height at the
mast.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Graph 4
Nightly variation in activity of the Large Forest Bat at 20 metres height at the mast.
Mean nightly activity levels at the three detector heights at the mast are shown in Graph 5.
While activity of the Large Forest Bat was low, even at ground level in the vicinity of the mast
during the summer months from November to March, even lower activity was recorded from
April until September. This indicates that the probability of blade strike is even lower during
the winter. It should be noted that the detector at ground level ceased functioning in
September 2015 and activity from then until early November was not recorded. It is likely
however that activity of the Large Forest Bat begins to increase from winter lows sometime in
late September or early October.
Graph 5
Activity levels of the Large Forest Bat at the mast at the three heights sampled.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Graph 6
Mean nightly activity of the Large Forest Bat at ground level at the mast site.
The pattern of activity of nightly activity of the Large forest Bat at ground level at the mast for
the period between November 2014 and February 2015 is displayed in Graph 6. While some
variation in activity was present throughout the night from dusk, a distinct peak was present at
dawn. Mean activity was however very low with this peak representing just over one
echolocation call pass per 15 minute period.
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DISCUSSION & RECOMMENDATIONS
While significant mortality of microbats from blade strike of wind turbines has been recorded
in both Europe and North America (Erickson et al, 2004, Hayes 2013), the position in
Australia is less clear. By the end of 2014, 1866 turbines had been installed across 71 sites
across southern Australia (Clean Energy Council 2015). Few reports are publicly available on
mortality of microbats at these sites. At two wind farms in Tasmania, Gould’s Wattled Bats
Chalinolobus gouldii accounted for the majority of carcasses found during searches, with
almost all adult males or females in approximately equal proportions (Hull & Cawthen 2014).
Most of the fatalities at these sites occurred during autumn. Two of the carcasses however
were Vespadelus species with one at least most likely Vespadelus darlingtoni, the microbat
currently extant on Lord Howe Island.
It is currently uncertain whether mortality occurs chiefly as a result of direct blade strike or is
the result of barotrauma due to increased pressure close to blades (Ellison 2012). Earlier
investigations suggested barotrauma to the lungs and possibly other organs accounted for
46% of bats killed at turbines with 92% of bats having haemorrhaging in the thoracic and/or
abdominal cavities (Baerwald 2008). Later studies cast some doubt on the level of deaths
from barotrauma and the degree to which this contributes to turbine related deaths is
currently uncertain (Grodsky et al 2011; Rollins et al 2012). The majority of bat fatalities in
North America are believed to be of migrating bats in autumn (Ellison 2012). The main
species involved are tree roosting, relatively large species that are known to forage widely in
open spaces. It is possible that they are examining turbines as potential roost sites or for
social interactions with other individuals (Horn et al 2012; Jameson & Willis 2014). Bats have
been found to be more active around turbines at lower wind speeds and often approach
turbines from downwind (Cryan et al 2014). Barclay et al (2007) found that the number
fatalities of bats increased exponentially with tower height in contrast to nocturnal birds. This
may be due to bats migrating at lower elevations than nocturnal birds. In a survey at two wind
farms in northwest Portugal, Amorim et al (2012) found that most mortality occurred during
autumn. Both bat activity and mortality were significantly correlated with wind speed,
temperature and relative humidity.
The Large Forest Bat appears to form two largely separate sub populations on Lord Howe
Island, one centred around the settled area of the northern part of the island and the other
around the southern mountains. No movement of banded bats between the two areas has
been recorded since banding commenced in 2010. In the more studied ―northern‖
population, considerable movement of individuals has been recorded between trapping sites
(Hoye, unpublished). In females, the maximum movement between capture sites recorded is
1332 metres with over 75% of movements less than 500 metres (Hoye 2012). Movements of
males was even less.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Targeted survey was undertaken over twelve months from November 2014 until November
2015 to assess use of the proposed turbine sites. Activity levels in the pasture in the vicinity
of where the turbines are proposed were very low when compared with that within adjacent
forest. Within pasture activity of the Large Forest Bat was highest near ground level and was
an order of magnitude lower at 20 metres height. No activity was recorded at 40 metres
height which equates with the bottom of the swept rotor area of the proposed turbines.
Activity was also highly seasonal with peak activity between October and March. These
results suggest that the turbines pose a low probability of blade strike to the Large Forest Bat
from random interactions. The support masts and guy wires will be situated closer to the
forest edge where activity of the Large Forest Bat is higher. The risk of collision with these
structures may be higher. No evidence of mortality form collision with the guy wires and wind
wind monitoring mast was gathered during visits to the island from November 2014 until
November 2015. The small size of the Large Forest Bat (~4-7 grams) and the relatively high
pasture present in the vicinity of the wind monitoring mast would have resulted in a l ow
probability of seeing carcases during these visits.
While there would appear to be a low probability of blade strike due to random collisions, this
may not be the case if Large Forest bats are attracted to the turbines for roost inspection or
other reasons. Jameson & Willis (2014) found that microbats were attracted to large
structures. While there has been low activity recorded in the vicinity of the wind monitoring
mast installed in November 2014, this may or may not be the case for the turbines. Some
monitoring is justified when the turbines are first commissioned. Some echolocation call
detection around the turbines when they are first installed would indicate if they attract bats. A
search of the ground below the turbines and associated guy wires ans support masts for
carcasses should also be carried out seasonally for the first year following their commission.
The small size of microbats can result in removal of carcasses by predators. Introduced Black
Rats (Rattus rattus) as well as two native birds, the Lord Howe Currawong (Strepera
graculina crissalis) and Australian Kestrel (Falco cenchroides) are likely predators of bat
carcasses around the proposed turbines. The long grass where the turbines are proposed to
be sited may hamper carcass searches. The use of a sniffer dog may assist in finding dead
bats in this area. The use of trained dogs has been found to at least double the number of
carcasses found during searches around turbines (Ellison 2012). The feasibility of using
sniffer dogs should be evaluated. Keeping the grass cropped low in thevicinity of the turbines
would also assist in finding carcasses. Currently, the Large Forest Bat is monitored partly
through capture and marking (Fly By Night Bat Surveys PL (2011-2014). This would appear
to be the most efficient method for monitoring the persistence of the Large Forest Bat in the
northern section of the island against a range of possible impacts including rat predation,
proposed rat control and climate change. Mortality from the wind turbines is unlikely to be
sufficient to be detected from the marking program. The installation of permanent monitoring
site on the island whereby echolocation calls are constantly recorded and analysed would
provide an additional method of assessing the relative abundance of the Large Forest Bat on
an ongoing basis. This is feasible using similar equipment as that used to monitor call activity
at the mast. It would provide a cost effective means of monitoring the presence of the Large
Forest Bat and would also indicate if vagrant microbat species reach the island.
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Assessment of risk to Large Forest Bat on Lord Howe Isand from proposed wind turbines .
Glenn Hoye
January 2016
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