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Impacts of artificial lighting on bats: A review of challenges and solutions

Authors:
  • University of the West of England/Conservation Research Africa

Abstract and Figures

Light pollution is a major emerging issue in biodiversity conservation, and has important implications for policy development and strategic planning. Although research is now addressing the negative impacts of anthropogenic noise on biota, less attention has been paid to the effects of light pollution. Changes in lighting technology have led to a diverse range of emerging low energy light types and a trend towards the increased use of white light. Light pollution affects ecological interactions across a range of taxa and has adverse effects on behaviours such as foraging, reproduction and communication. Almost a quarter of bat species globally are threatened and the key underlying threat to populations is pressure on resources from increasing human populations. Being nocturnal, bats are among the taxa most likely to be affected by light pollution. In this paper we provide an overview of the current trends in artificial lighting followed by a review of the current evidence of the impacts of lighting on bat behaviour, particularly foraging, commuting, emergence, roosting and hibernation. We discuss taxon-specific effects and potential cumulative ecosystem level impacts. We conclude by summarising some potential strategies to minimise the impacts of lighting on bats and identify key gaps in knowledge and priority areas for future research.
Content may be subject to copyright.
Mammalian
Biology
80
(2015)
213–219
Contents
lists
available
at
ScienceDirect
Mammalian
Biology
jou
rn
al
hom
epage:
www.elsevier.com/locate/mambio
Review
Impacts
of
artificial
lighting
on
bats:
a
review
of
challenges
and
solutions
Emma
Louise
Stone,
Stephen
Harris,
Gareth
Jones
School
of
Biological
Sciences,
University
of
Bristol,
Life
Sciences
Building,
24
Tyndall
Avenue,
Bristol
BS8
1TQ,
UK
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
18
September
2014
Accepted
17
February
2015
Handled
by
Danilo
Russo
Available
online
24
February
2015
Keywords:
Artificial
lighting
Light
pollution
Bats
Ecosystem
services
Bio-indicators
a
b
s
t
r
a
c
t
Light
pollution
is
a
major
emerging
issue
in
biodiversity
conservation,
and
has
important
implications
for
policy
development
and
strategic
planning.
Although
research
is
now
addressing
the
negative
impacts
of
anthropogenic
noise
on
biota,
less
attention
has
been
paid
to
the
effects
of
light
pollution.
Changes
in
lighting
technology
have
led
to
a
diverse
range
of
emerging
low
energy
light
types
and
a
trend
towards
the
increased
use
of
white
light.
Light
pollution
affects
ecological
interactions
across
a
range
of
taxa
and
has
adverse
effects
on
behaviours
such
as
foraging,
reproduction
and
communication.
Almost
a
quar-
ter
of
bat
species
globally
are
threatened
and
the
key
underlying
threat
to
populations
is
pressure
on
resources
from
increasing
human
populations.
Being
nocturnal,
bats
are
among
the
taxa
most
likely
to
be
affected
by
light
pollution.
In
this
paper
we
provide
an
overview
of
the
current
trends
in
artificial
lighting
followed
by
a
review
of
the
current
evidence
of
the
impacts
of
lighting
on
bat
behaviour,
partic-
ularly
foraging,
commuting,
emergence,
roosting
and
hibernation.
We
discuss
taxon-specific
effects
and
potential
cumulative
ecosystem
level
impacts.
We
conclude
by
summarising
some
potential
strategies
to
minimise
the
impacts
of
lighting
on
bats
and
identify
key
gaps
in
knowledge
and
priority
areas
for
future
research.
©
2015
Deutsche
Gesellschaft
für
Säugetierkunde.
Published
by
Elsevier
GmbH.
All
rights
reserved.
Shedding
light
on
the
challenges
how
important
is
light
pollution?
Global
increases
in
urbanisation
(Grimm
et
al.,
2008)
and
human
development
have
led
to
a
dramatic
rise
in
both
the
extent
and
intensity
of
artificial
lighting
throughout
the
20th
and
21st
cen-
turies
(Cinzano,
2000,
2003;
Cinzano
et
al.,
2001;
Hölker
et
al.,
2010a).
Light
pollution
affects
every
inhabited
continent;
electric
lighting
has
increased
nocturnal
sky
brightness
by
20%
(Hendry,
1984).
Worldwide,
artificial
lighting
is
increasing
by
around
6%
per
annum
(Hölker
et
al.,
2010b),
and
there
was
a
24%
increase
in
light
pollution
in
the
UK
between
1993
and
2000
(CPRE,
2003).
Tradi-
tionally
street
lights
consisted
of
sodium
discharge
lamps
which
generate
light
via
electric
discharges
through
a
gas
or
vapour.
The
most
common
lights
used
were
Low
Pressure
Sodium
(LPS)
and
High
Pressure
Sodium
(HPS).
LPS
lights
are
narrow
spectrum,
emit-
ting
an
orange-based
light
with
a
correlated
colour
temperature
(CCT)
of
1807
Kelvin
(K),
and
an
absence
of
ultraviolet
(UV)
light.
HPS
are
broad
spectrum
generating
a
pinkish
light
with
a
CCT
of
2005–2108
K,
with
some
light
emitted
in
the
UV
spectrum.
Trends
Corresponding
author.
Tel.:
+00
265(0)
993367832.
E-mail
address:
emma.stone@bristol.ac.uk
(E.L.
Stone).
in
lighting
technology
have
led
to
changes
in
the
spectral
content
of
artificial
lighting
(Davies
et
al.,
2013a;
Frank,
1988;
Massey
and
Foltz,
2000)
from
predominantly
orange
sodium-based
lighting
in
the
1960s
and
1970s
(Gaston
et
al.,
2013)
to
broader
wavelength
lights
such
as
high-brightness
light-emitting
diodes
(LEDs).
Today
a
variety
of
light
types
are
used
globally
each
with
differing
CCT
and
wavelengths
(Table
1,
Fig.
1).
LEDs
produce
monochromatic
radia-
tion
and
their
colour
tone
is
defined
by
the
dominant
wavelength
(Fig.
2),
so
LEDs
can
be
a
variety
of
CCTs
from
“warm
white”
simi-
lar
to
LPS
to
“blue
white”
similar
to
metal
halogen.
LEDs
had
a
31%
growth
in
market
share
in
2010
(Steele,
2010)
and
are
expected
to
represent
60%
of
the
market
share
by
2020
(Peters,
2011).
Ecological
impacts
of
lighting
Global
levels
of
light
pollution
are
set
to
increase
as
human
populations
rise
and
become
more
urbanised.
There
has
been
increasing
awareness
of
the
ecological
impacts
of
light
pollution
associated
with
urbanisation
(Davies
et
al.,
2013b;
Gaston
et
al.,
2012,
2013;
Harder,
2002;
Hölker
et
al.,
2010a,
2010b;
Longcore
and
Rich,
2004;
Navara
and
Nelson,
2007;
Smith,
2009).
Light
pollution
affects
ecological
interactions
across
a
range
of
taxa
and
negatively
affects
critical
animal
behaviours
including
foraging,
reproduction
and
communication
(for
reviews
see
Gaston
et
al.,
2013;
Longcore
http://dx.doi.org/10.1016/j.mambio.2015.02.004
1616-5047/©
2015
Deutsche
Gesellschaft
für
Säugetierkunde.
Published
by
Elsevier
GmbH.
All
rights
reserved.
214
E.L.
Stone
et
al.
/
Mammalian
Biology
80
(2015)
213–219
Fig.
1.
Spectral
composition
of
common
street
light
types.
Source:
Gaston
et
al.
(2013).
and
Rich,
2004;
Rich
and
Longcore,
2006).
Light
pollution
is
now
recognised
as
a
key
biodiversity
threat
and
is
an
emerging
issue
in
biodiversity
conservation,
with
important
implications
for
policy
development
and
strategic
planning
(Hölker
et
al.,
2010b).
Being
nocturnal
bats
are
among
those
species
most
likely
to
be
affected
Fig.
2.
Spectra
of
coloured
and
white
LEDs.
Source:
Anon
(2005).
Table
1
Common
light
types
and
colour
temperatures.
Light
type Colour
Correlated
colour
temperature
(K)
Low
pressure
sodium
(LPS/SOX)
Yellow/orange
1807
High
pressure
sodium
(HPS/SON)
Pinkish/off
white
2005–2108
Compact
fluorescent Warm
white 2766–5193
Metal
halide
(MH)
Blue-white
2720–4160
Light
emitting
diode
(LED)
White/warm-white
2800–7000
Source:
Gaston
et
al.
(2012).
by
lighting,
although
artificial
light
can
have
an
impact
on
a
wide
range
of
taxa
and
behaviours.
Impacts
of
artificial
lighting
on
bats
As
the
second
most
species-rich
mammalian
order
in
the
world
(Wilson
and
Reeder
2005)
bats
represent
a
significant
contribu-
tion
to
global
biodiversity
(Altringham,
1996;
Racey
and
Entwistle,
2003).
Bats
make
effective
bio-indicators,
capturing
the
responses
of
a
range
of
taxa
and
reflecting
components
of
biological
diver-
sity
such
as
species
richness
and
biodiversity
(Jones
et
al.,
2009).
Due
to
their
high
niche
diversity
bats
are
also
effective
ecologi-
cal
indicators
reflecting
responses
over
a
range
of
trophic
levels
and
highlighting
effects
of
environmental
degradation
on
specific
ecological
processes
that
are
key
to
ecosystem
functioning.
Bats
are
potentially
effective
bio-indicators
for
conservation
biologists
measuring
the
human
impact
on
the
environment,
including
the
impacts
of
light
pollution
as
their
relative
abundance,
species
rich-
ness,
and
vulnerability
to
disturbance
can
be
relatively
easy
to
monitor
over
successive
years
(Fenton
et
al.,
1992).
Bats
are
therefore
critical
to
ecosystem
functioning
and
should
be
included
in
conservation
plans
aimed
at
preserving
the
integrity
of
ecosystems
(Kalka
et
al.,
2008).
Declining
bat
populations
may
compromise
important
ecosystem
services,
so
understanding
their
conservation
needs
is
vital
(Williams-Guillén
et
al.,
2008).
Urbani-
sation
and
development
affect
bat
habitats,
either
through
direct
loss
or
disturbance
from
light
and
noise
pollution
or
human
activities.
Connectivity
of
habitat
and
foraging
areas
to
roosts
is
fundamental
to
the
survival
of
many
bat
populations
(Verboom
and
Huitema,
1997).
Linear
landscape
features
such
as
hedgerows,
river
banks
and
canals
are
important
for
bats,
often
being
used
for
forag-
ing
and
commuting
(Limpens
and
Kapteyn,
1991;
Verboom
et
al.,
1999;
Park,
2015).
Changes
in
habitat
affect
the
quantity,
qual-
ity
and
connectivity
of
foraging,
drinking
and
roosting
resources
available
to
bats.
E.L.
Stone
et
al.
/
Mammalian
Biology
80
(2015)
213–219
215
Fig.
3.
Commuting
route
of
Rhinolophus
hipposideros
in
England
illuminated
with
experimental
HPS
street
lamps.
Source:
Stone
et
al.
(2009).
The
natural
light
dark
cycle
(LDC)
is
a
critical
factor
entrain-
ing
the
biological
“circadian”
rhythms
of
those
organisms
exposed
to
the
daily
fluctuation
of
sunlight
(Aschoff,
1960,
1965,
1981).
Daily
patterns
of
activity
and
behaviour
in
bats
are
influenced
by
the
LDC
(Haeussler
and
Erkert,
1978).
The
timing
of
nightly
emer-
gence
from
roosts
is
influenced
by
the
timing
of
sunset
(Erkert,
1982),
and
foraging
activity
and
behaviour
is
affected
by
moonlight
(Morrison,
1978;
Salda˜
na-Vázquez
and
Munguía-Rosas,
2013)
and
night
length
(Frafjord,
2013).
Artificial
lighting
can
have
an
impact
upon
a
range
of
bat
behaviours
including
foraging
and
commuting,
emergence,
roosting,
breeding
and
hibernation.
Artificial
lighting
can
damage
bat
foraging
habitat
directly
making
an
area
unsuit-
able
for
foraging,
or
indirectly
by
severing
commuting
routes
from
roosts,
through
light
spillage
onto
hedgerows
and
watercourses
(Rasey,
2006).
Impacts
on
foraging
and
commuting
behaviour
Spatial
avoidance
and
habitat
fragmentation
Light
that
spills
onto
bat
commuting
routes
or
flyways
can
cause
avoidance
behaviour
for
some
species
and
fragment
the
network
of
commuting
routes.
Activity
of
Rhinolophus
hipposideros
and
Myotis
spp.
was
significantly
reduced
along
commuting
routes
illuminated
with
HPS
and
LED
street
lights
(Stone,
2011;
Stone
et
al.,
2009,
2012)
(Fig.
3).
Rhinolophus
hipposideros
and
Myotis
spp.
avoided
commuting
routes
illuminated
with
LEDs
at
light
levels
of
3.7
lux
(Stone
et
al.,
2012).
In
Canada
and
Sweden
Myotis
spp.
were
only
recorded
away
from
street
lights
(Furlonger
et
al.,
1987;
Rydell,
1992).
Despite
the
presence
of
street
lit
areas
within
their
home
range,
lit
areas
were
never
used
by
Rhinolophus
ferrumequinum
(Jones
and
Morton,
1992;
Jones
et
al.,
1995).
Disruption
of
com-
muting
routes
can
force
bats
to
use
alternative
routes
to
reach
their
foraging
grounds.
The
quantity
and
quality
of
alternative
routes
will
vary
on
a
site-by-site
basis.
Bats
may
be
forced
to
use
sub-
optimal
routes
that
may
cause
them
to
fly
further
to
reach
their
foraging
grounds,
resulting
in
increased
energetic
costs
due
to
increased
flight
time.
Alternative
commuting
routes
may
be
subop-
timal
in
terms
of
vegetation
cover,
resulting
in
increased
predation
risk
or
exposure
to
the
elements
(wind
and
rain)
with
the
asso-
ciated
increased
energetic
costs.
Where
alternative
routes
are
not
available,
bat
colonies
may
be
isolated
from
their
foraging
areas,
potentially
forcing
them
to
abandon
their
roost.
Such
disturbance
disrupts
the
ecological
functionality
of
the
landscape
by
creating
barriers
to
effective
animal
movement.
Increased
foraging
opportunities
Some
bat
species
are
attracted
to
lights
because
of
the
higher
numbers
of
insects
(particularly
moths)
attracted
to
street
lights,
especially
lights
emitting
short
wavelengths
(Eisenbeis,
2006;
van
Langevelde
et
al.,
2011).
For
such
light-tolerant
bat
species
artificial
lights
create
an
illuminated
night
niche
that
acts
as
an
artifi-
cial
feeding
resource.
Bats
of
the
genera
Chalinolobus,
Cormura,
Cynomops,
Diclidurus,
Eumops,
Eptesicus,
Lasiurus,
Mormopterus,
Molossus,
Myotis,
Nyctalus,
Nyctinomops,
Pipistrellus,
Tadarida,
Sac-
copteryx
and
Vespertilio
have
been
recorded
foraging
at
street
lights
(Avila-Flores
and
Fenton,
2005;
Barak
and
Yom-Tov,
1989;
Bartoniˇ
cka
et
al.,
2008;
Bell,
1980;
Belwood
and
Fullard,
1984;
Blake
et
al.,
1994;
Catto,
1993;
de
Jong
and
Ahlén,
1991;
Fenton
and
Morris,
1976;
Fullard,
2001;
Furlonger
et
al.,
1987;
Geggie
and
Fenton,
1985;
Haffner
and
Stutz,
1985/86;
Hickey
et
al.,
1996;
Hickey
and
Fenton,
1990;
Jung
and
Kalko,
2010;
Kronwitter,
1988;
Rydell,
1991,
1992,
2006;
Rydell
and
Racey,
1995;
Scanlon
and
Petit,
2008;
Schnitzler
et
al.,
1987;
Shields
and
Bildstein,
1979).
Higher
densities
of
bats
have
been
recorded
in
areas
illuminated
with
Mercury
Vapour
Lamps
(MVL)
compared
to
unlit
areas
e.g.
densities
of
Pipistrellus
spp.
were
10
times
higher
in
lit
versus
dark
areas
in
England
(Rydell
and
Racey,
1995),
and
densities
of
Eptesi-
cus
nilssoni
were
5–20
times
higher
in
areas
lit
with
MVL
compared
to
dark
areas
in
Sweden
(Rydell,
1991).
Activity
levels
of
Pipistrel-
lus
pipistrellus,
P.
pygmaeus
and
Nyctalus/Eptesicus
spp.
were
higher
at
white
ceramic
metal
halide
(MH)
compared
to
LPS
street
lights
(Stone
et
al.,
2015).
The
highest
levels
of
bat
activity
in
lit
areas
have
been
recorded
at
white
lights
(Avila-Flores
and
Fenton,
2005;
Blake
et
al.,
1994;
Rydell
and
Racey,
1995).
This
is
reflected
in
the
higher
numbers
of
insects
attracted
to
white
MVL
than
HPS
(Rydell,
1992).
LPS
(orange)
lights
do
not
appear
to
attract
insects,
with
insect
numbers
as
low
as
those
recorded
on
unlit
streets
(Rydell,
1992).
HPS
lights
attracted
57%
fewer
insects
than
white
MVL
in
Germany
(Eisenbeis,
2010).
MVL
lights
are
energy-inefficient
and
are
now
being
phased
out.
Fast-flying
species
adapted
to
forage
in
open
areas,
particularly
bats
of
the
genera
Eptesicus,
Nyctalus
and
Pipistrellus,
may
benefit
from
the
increased
foraging
opportunities
provided
at
lamps,
which
attract
high
densities
of
insects.
However,
while
providing
a
feeding
resource
for
some
bats,
artificial
lights
can
potentially
increase
mor-
tality
risk
due
to
collision
with
vehicles:
juveniles
may
be
at
higher
risk
of
predation
due
to
their
slower
and
less
agile
flight
(Racey
and
Swift,
1985).
Whether
mortality
risk
increases
in
lit
situations
deserves
further
research.
Reduced
foraging
opportunities
Illumination
of
foraging
areas
can
potentially
prevent
or
reduce
foraging
activity,
causing
bats
to
pass
quickly
through
the
lit
area
or
avoid
it
completely
(Polak
et
al.,
2011).
Lighting
can
disrupt
the
composition
and
abundance
of
insect
prey
(Davies
et
al.,
2012).
Acoustic
tracking
demonstrated
that
Eptesicus
bottae
failed
to
for-
age
under
lit
conditions
(Polak
et
al.,
2011).
Artificial
illumination
in
foraging
habitats
can
effectively
cause
a
loss
of
foraging
areas
for
some
bat
species.
Experiments
with
both
captive
and
free-flying
bats
showed
reduced
foraging
success
of
frugivorous
bats
(Carollia
sowelli)
under
lit
conditions.
Bats
harvested
fewer
fruits,
which
could
have
negative
impacts
on
seed
dispersal
(Lewanzik
and
Voigt,
2014).
Currently
there
is
a
lack
of
empirical
evidence
on
the
impact
of
lighting
on
foraging
success
of
insectivorous
bat
species.
Impacts
on
emergence,
roosting
and
breeding
Delayed
emergence
Disturbance
by
external
lights
during
emergence
can
delay
the
timing
and
prolong
the
duration
of
emergence
for
some
species.
216
E.L.
Stone
et
al.
/
Mammalian
Biology
80
(2015)
213–219
Extending
twilight
caused
delayed
emergence
in
Rhinolophus
hip-
posideros
(McAney
and
Fairley,
1988)
and
light
intensity
was
an
important
factor
determining
the
onset
of
emergence.
This
species
leaves
exposed
roost
exits
later
than
exits
close
to
extensive
vege-
tation
(Duvergé
et
al.,
2000).
External
lighting
reduced
the
number
of
Pipistrellus
pygmaeus
emerging
from
roosts
(Downs
et
al.,
2003),
and
delayed
emergence
in
R.
ferrumequinum,
Myotis
emargina-
tus
and
M.
oxygnathus
(Boldogh
et
al.,
2007).
Myotis
myotis
failed
to
emerge
from
their
roost
under
experimental
illumination
of
their
flight
path
(Decoursey
and
Decoursey,
1964).
Lighting
and
noise
during
a
music
festival
caused
delayed
emergence
of
Myotis
daubentonii
in
England
(Shirley
et
al.,
2001).
Delayed
emergence
caused
by
light
disturbance
will
result
in
reduced
foraging
time
and
bats
may
be
forced
to
compensate.
Delayed
emergence
also
increases
the
risk
that
bats
will
miss
the
peak
in
abundance
of
insects
that
occurs
at
dusk,
thereby
reducing
the
quality
of
forag-
ing
time
(Rydell
et
al.,
1996).
Delayed
emergence
could
therefore
negatively
affect
the
fitness
of
individuals
and
the
roost
as
whole.
Spatial
avoidance
or
roost
abandonment
Long-term
exposure
to
light
during
emergence
may
cause
bats
to
use
alternative
exit/entrances
if
available
and
in
the
worst
case
scenario
may
cause
bats
to
abandon
the
roost
or
become
entombed.
A
maternity
roost
of
1000–1200
female
Myotis
emarginatus
was
abandoned
after
lighting
spilled
directly
onto
the
entrance
(Boldogh
et
al.,
2007).
Full
illumination
of
roosts
has
been
shown
to
cause
sudden
declines
in
bat
numbers.
Numbers
of
Myotis
lucifugus
and
Eptesicus
fuscus
declined
by
between
53–89%
and
41–96%
respectively
upon
installation
of
incandescent
lamps
(40
and
60
watts),
cool
fluorescent
lamps
(40
watts)
and
spotlights
(150
watts)
inside
nursery
roosts
(n
=
3
Myotis
lucifugus
roosts;
n
=
6
Eptesicus
fuscus
roosts)
(Laidlaw
and
Fenton,
1971).
Lighting
that
spills
directly
into
a
roost
can
cause
roost
aban-
donment
or
death
and
can
have
consequences
for
predation
and
connectivity.
Bats
may
be
forced
to
use
alternative
exits
that
may
be
suboptimal
in
terms
of
predation
risk.
Alternative
exits
may
increase
mortality
risk
due
to
their
location
in
relation
to
the
sur-
rounding
landscape
e.g.
bats
may
be
forced
to
fly
across
roads
once
leaving
the
exit,
or
due
to
their
situation
e.g.
located
low
to
the
ground
or
near
a
window
sill
enabling
easy
access
for
predators
such
as
domestic
cats
(Ancillotto
et
al.,
2013).
Reduced
reproductive
success
Internal
and
external
lighting
around
a
bat
roost
can
have
an
impact
on
the
fitness
of
the
colony
through
reduced
juvenile
growth
rates.
Colonies
of
Myotis
emarginatus
and
Myotis
oxygnathus
in
buildings
which
were
illuminated
from
the
outside
had
lower
juvenile
growth
rates
than
colonies
in
non-illuminated
buildings
(Boldogh
et
al.,
2007).
Reduced
individual
fitness
can
have
impli-
cations
for
the
long-term
survival
of
a
colony,
making
them
more
susceptible
to
other
threats
such
as
predation.
Bats
are
long-lived
and
slow
to
reproduce,
meaning
they
take
time
to
recover
from
population
declines.
Impacts
on
hibernating
bats
Hibernation
is
an
extended
form
of
torpor
(a
period
when
a
bat
allows
it
body
temperature
to
fall
below
its
active
homoeother-
mic
level
to
conserve
energy),
and
can
occur
on
a
seasonal
basis
in
response
to
changes
in
temperature
and
food
supply
(Altringham,
1996).
Hibernation
is
an
integral
component
of
the
life
history
of
both
temperate
and
even
some
tropical
bats
(Altringham,
1996).
The
nature
and
extent
of
the
impacts
of
lighting
on
hibernation
will
depend
on
many
factors,
including
the
thermoregulatory
flex-
ibility
of
the
species
in
question,
with
more
flexible
species
able
to
adapt
to
artificial
stressors
such
as
lighting,
and
therefore
less
likely
to
be
affected
negatively
(Boyles
et
al.,
2011).
Overwinter
survival
of
bats
is
largely
dependent
on
their
ability
to
find
a
hiber-
nation
site
with
suitable
microclimatic
conditions
to
allow
efficient
energy
budgeting.
Increased
arousal
from
torpor
caused
by
disturb-
ance
such
as
lighting
can
potentially
cause
energy
losses,
and
may
disrupt
circadian
rhythms,
which
may
reduce
overwinter
survival.
Spatial
avoidance
or
roost
abandonment
The
illumination
of
hibernation
sites
may
cause
spatial
avoid-
ance
so
that
bats
have
to
find
alternative
hibernation
sites.
There
is
currently
no
published
evidence
of
the
impacts
of
lighting
on
hibernating
bats,
but
evidence
from
summer
roosts
(see
above)
suggests
that
bats
would
avoid
roosting
at
illuminated
hibernation
sites.
Further
research
is
required
to
understand
the
conservation
and
energetic
consequences
of
illuminating
hibernation
sites.
If
bats
were
deterred
from
using
preferred
hibernacula,
this
could
have
significant
conservation
consequences,
potentially
affecting
overwinter
survival.
Increased
arousal
from
hibernation
It
is
possible
that
light
disturbance
within
a
hibernation
site
would
cause
bats
to
arouse
from
torpor.
At
present
there
is
no
empirical
evidence
that
light
stimulates
arousal
in
hibernating
bats.
Laboratory
studies
found
that
bats
do
not
arouse
when
exposed
to
slight
variations
in
light
(Speakman
et
al.,
1991),
although
this
study
only
tested
the
effect
of
the
light
emitted
from
a
14
watt
head
torch
for
a
very
brief
time.
This
may
not
therefore
be
representative
of
the
impacts
of
other
light
types
on
bat
hibernation.
If
hibernat-
ing
bats
were
disturbed
regularly,
this
would
result
in
significant
energetic
costs,
perhaps
reducing
their
overall
fitness
and
ability
to
survive
the
winter
and
subsequent
spring.
In
addition,
artificial
lighting
may
disrupt
circadian
rhythms
during
hibernation.
In
mar-
itime
Britain,
hibernating
bats
are
most
likely
to
arouse
close
to
dusk
so
they
can
exploit
the
peak
in
insect
abundance
(Hope
and
Jones,
2013;
Park
et
al.,
2000).
As
light
can
act
as
a
zeitgeber
to
entrain
circadian
rhythms,
it
has
the
potential
to
disrupt
them
also.
Species-specific
effects
Responses
to
light
pollution
are
species-specific
(Rydell,
1991),
and
so
care
must
be
taken
in
making
generalizations
about
poten-
tial
impacts
across
bat
species.
Species-specific
responses
to
light
may
be
a
function
of
flight
morphology
and
echolocation:
rela-
tively
fast-flying
bats
which
typically
forage
in
the
open
using
long
range
echolocation
pulses
such
as
Eptesicus,
Nyctalus
and
Pipistrel-
lus
species
are
attracted
to
street
lights
(Blake
et
al.,
1994;
Rydell,
1991,
1992),
whereas
slow-flying
bats
with
echolocation
adapted
for
cluttered
environments
appear
to
avoid
street
lights
due
to
light-dependent
predation
risk
(Furlonger
et
al.,
1987;
Rydell,
1992;
Stone
et
al.,
2009,
2012).
Species
that
are
light-averse
often
possess
wing
morphologies
associated
with
higher
extinction
risk
(Jones
et
al.,
2003)
and
so
may
be
of
conservation
priority.
In
addition
there
have
been
very
few
studies
assessing
the
impacts
of
lighting
on
frugivorous
and
nectarivorous
bats
(although
see
Lewanzik
and
Voigt
(2014))
and
a
diversity
of
responses
are
likely
to
occur.
How
big
are
the
impacts:
community
and
ecosystem
effects?
To
date
there
is
no
specific
evidence
of
community
or
ecosys-
tem
level
effects
of
artificial
lighting
on
bats.
However,
evidence
suggests
that
the
effects
of
lighting
on
bats
are
likely
to
cascade
to
the
community
level.
Lighting
may
alter
the
balance
of
com-
munities
through
competitive
exclusion
of
less
tolerant
species,
as
more
light-tolerant
species
may
out-compete
them
for
aerial
insect
prey.
A
possible
cause
of
the
population
decline
in
Rhinolophus
E.L.
Stone
et
al.
/
Mammalian
Biology
80
(2015)
213–219
217
hipposideros
in
Switzerland
was
competitive
exclusion
by
Pipistrel-
lus
pipistrellus,
which
was
able
to
take
advantage
of
the
increased
foraging
opportunities
provided
by
street
lights
(Arlettaz
et
al.,
2000).
However
as
R.
hipposideros
avoids
lit
areas,
this
conclusion
is
perhaps
unlikely.
Insects
may
be
attracted
away
from
dark
areas
creating
a
“vac-
uum
effect”
(Eisenbeis,
2006).
This
is
supported
by
experiments
with
aquatic
insects
in
Germany
in
which
higher
numbers
of
insects
were
recorded
under
HPS
lamps
away
from
waterways
than
at
unlit
waterways
(Perkin
et
al.,
2014).
The
“vacuum
effect”
may
nega-
tively
affect
bats
by
reducing
prey
availability
for
species
that
do
not
forage
in
lit
areas.
Artificial
lighting
may
also
act
as
a
barrier
for
dispersing
insects,
disrupting
movement
and
gene
flow
among
populations,
which
could
contribute
to
insect
population
declines
(Fox,
2013).
Lighting
also
alters
the
community
composition
of
the
insect
prey
of
bats.
Higher
abundances
of
predatory
and
scavenging
ground-dwelling
arthropods
occur
under
HPS
lights
than
at
sites
between
lamps
(Davies
et
al.,
2012),
including
carabid
beetles,
which
are
eaten
by
gleaning
bats
such
as
Myotis
myotis
(Arlettaz,
1996).
Macromoths
exhibit
species-specific
differences
in
attrac-
tion
to
MH
and
HPS
lamps
(Somers-Yeates
et
al.,
2013).
As
insects
are
important
in
ecosystem
functioning
(Fox,
2013),
such
changes
in
community
composition
can
have
cascading
effects
at
higher
tropic
levels
and
consequential
effects
for
ecosystem
service
pro-
vision.
The
increased
densities
of
insects
at
street
lights
may
have
ecosystem-level
impacts.
Moths
attracted
to
street
lights
have
increased
mortality
rates
(Frank,
1988;
Longcore
and
Rich,
2004)
and
larger
moths
are
more
attracted
to
lights
than
smaller
moths
(van
Langevelde
et
al.,
2011).
This
size-dependent
mortality
risk
can
have
cascading
effects
for
trophic
interactions
and
ecosystem
services.
There
is
some
evidence
that
artificial
lighting
may
affect
ecosystem
service
provision
by
reducing
bat-mediated
seed
dis-
persal.
Experiments
with
fruit
bats
(Carollia
sowelli)
in
Costa
Rica,
recorded
reduced
harvesting
success
of
wild
Piper
infructescences
when
plants
were
illuminated
with
HPS
lights,
suggesting
a
reduc-
tion
in
seed
dispersal
(Lewanzik
and
Voigt,
2014).
Solutions
and
future
challenges
Strategies
to
minimise
effects
Avoidance
The
simplest
and
most
effective
way
to
minimise
the
effects
of
lighting
on
bats
is
to
avoid
illuminating
the
areas
being
used
by
bats.
Where
the
area
used
by
bats,
such
as
foraging
or
commuting
habi-
tat,
is
already
illuminated,
lights
can
be
switched
off
or
removed,
or
light
can
be
excluded
using
physical
barriers
such
as
hedgerows
and
walls.
In
many
cases
existing
lamps
are
outdated,
poorly
installed
and/or
maintained,
resulting
in
light
trespass
into
unwanted
areas.
For
example,
31%
of
UK
street
light
columns
had
exceeded
their
lifespan
by
2010
and
were
due
for
replacement
(Anon.,
2009).
Tres-
pass
from
existing
lights
can
be
reduced
by
simple
maintenance
such
as
altering
the
beam
angle
of
the
lamp,
installation
of
hoods
and
reflectors
to
direct/restrict
light
to
where
it
is
needed,
com-
plete
replacement
with
new
directional
lamps,
or
the
construction
of
physical
barriers
(Gaston
et
al.,
2012).
Where
new
developments
are
planned,
it
is
possible
to
avoid
illuminating
areas
used
by
light-averse
bats
through
careful
planning.
Where
possible,
light
exclusion
zones
(dark
areas)
should
be
created
which
are
interconnected
to
allow
such
bats
to
move
freely
from
their
roosts
along
commuting
routes
to
their
foraging
grounds
without
being
subject
to
artificial
illumination.
In
many
cases
however,
it
is
not
feasible
to
have
light
exclusion
zones
in
all
the
parts
of
a
site
occupied
by
bats
and
removal
of
lights
may
not
be
practical
or
desirable
from
the
human
perspective.
Variable
lighting
regimes
In
some
cases
the
impacts
of
lighting
on
bats
may
be
minimised
by
changing
the
duration
and
timing
of
lighting
regimes,
to
suit
both
human
and
wildlife
use
of
the
site.
Such
strategies
are
termed
vari-
able
lighting
regimes
(VLRs)
and
involve
switching
off
or
dimming
lights
for
part
or
all
of
the
night
and
could
be
an
effective
strategy
to
minimise
effects
on
bats.
The
majority
of
UK
local
authorities
and
councils
have
commenced
lighting
reduction
strategies
and
are
adopting
VLRs
with
Central
Monitoring
Systems
(CMS)
which
allow
for
remote
switching
off/dimming
lights
when
human
activity
is
low
e.g.
between
00.30
and
05.30
am.
Lights
are
being
switched
off
between
midnight
and
05.00
am,
using
remote
dimming
tech-
nology,
on
several
sections
of
the
motorway
network
in
England,
resulting
in
30%
reductions
of
carbon
and
electricity
consumption
in
each
section
and
lower
numbers
of
road
traffic
accidents
after
VLRs
were
installed
(Highways
Agency,
2011).
CMS
technology
can
be
used
to
switch
lights
off
during
periods
of
high
bat
activity,
such
as
commuting
or
emergence
to
minimise
impacts,
though
the
peak
times
of
bat
activity
may
occur
in
the
early
evening
when
lighting
is
necessary
because
traffic
and
human
activity
levels
are
also
high
then.
Lights
can
also
be
dimmed
e.g.
to
30%
power,
for
periods
of
the
night
to
reduce
illumination
and
spill.
CMS
LED
lamps
have
been
installed
along
a
canal
used
by
bats
in
London
as
part
of
the
Arcadia
Project.
The
CMS
allow
bespoke
dimming
regimes
to
reduce
the
light
levels
to
1
lux
at
times
of
low
human
activity
(Fure,
2012).
The
appropriate
lighting
regime
for
an
area
will
be
site-specific
and
dependent
on
the
nature
of
public
use
and
type
and
amount
of
bat
activity.
Lights
can
also
be
fitted
with
movement
sensors
that
switch
lights
on
as
people
approach
and
switch
them
off
after
people
pass.
Movement
sensors
can
reduce
the
overall
lit
time
for
the
environ-
ment,
allowing
for
longer
periods
of
darkness
than
lamps
that
are
lit
all
night,
potentially
reducing
the
impact
on
bats
and
insects.
However,
the
effectiveness
of
VLRs
is
reliant
upon
a
good
under-
standing
of
the
timing
and
nature
of
bat
activity
in
an
area.
Currently
the
impacts
of
VLRs
on
bats,
both
in
terms
of
dimming
and
timing
of
lighting,
are
not
known
and
further
research
is
required.
Reducing
the
intensity
of
light
Reducing
light
intensity
will
reduce
the
overall
amount
and
spread
of
illumination
(Gaston
et
al.,
2012).
For
some
bat
and
insect
species
this
may
be
sufficient
to
minimise
disturbance
or
the
mag-
nitude
of
any
negative
impacts
and
disruption
to
circadian
rhythms.
However,
some
species
may
require
very
low
light
levels
to
have
little/no
impact
on
behaviour
and
circadian
rhythms.
Stone
et
al.
(2012)
tested
the
effect
of
LED
lights
on
bats
along
commuting
routes
at
three
light
intensities:
mean
3.6
lux,
mean
6.6
lux,
and
mean
49.8
lux.
Activity
of
Rhinolophus
hipposideros
and
Myotis
spp.
was
reduced
at
all
light
intensities,
even
at
3.6
lux.
Average
light
levels
recorded
along
preferred
commuting
routes
of
Rhinolophus
hipposideros
under
natural
unlit
conditions
were
0.04
lux
across
eight
sites
(Stone,
2011).
When
mitigating
the
impacts
of
lighting
for
such
species,
very
low
lux
levels
may
not
be
suitable
for
human
requirements.
In
such
cases
reducing
intensity
may
not
be
appro-
priate
and
alternative
strategies,
such
as
dark
corridors
or
physical
barriers,
may
be
preferable.
Currently
there
is
a
lack
of
evidence
regarding
the
light
intensities
below
which
there
are
no/reduced
impacts
on
bats,
and
responses
are
likely
to
vary
between
species
and
behaviours.
A
“light
threshold”
below
which
there
is
little
impact
on
bats
may
not
exist
for
those
species
that
may
be
light
averse
regardless
of
light
intensity
e.g.
possibly
Rhinolophus
hip-
posideros.
218
E.L.
Stone
et
al.
/
Mammalian
Biology
80
(2015)
213–219
Light
intensity
can
be
reduced
by
dimming
lights
(e.g.
using
CMS
technology),
changing
the
light
source
(e.g.
new
technologies
such
as
ceramic
MH
often
have
a
lower
wattage
compared
to
old
lamp
types
such
as
HPS)
or
creating
physical
barriers
such
as
walls,
or
hedgerows
to
reduce
the
total
amount
of
light
reaching
an
area.
HPS
lights
have
been
fitted
with
louvres
to
reduce
light
spill
on
the
Grand
Canal
in
Dublin,
reducing
light
intensity
on
the
river,
allow-
ing
bats
to
fly
in
darkness
(Fure,
2012).
However,
there
is
a
trade-off
between
reduced
intensity
and
the
pattern
of
light
distribution.
Some
older
light
types
such
as
HPS,
produce
a
heterogeneous
light
environment
whereby
light
intensity
declines
steeply
away
from
the
light
source.
However,
some
new
technologies
such
as
LEDs
pro-
duce
a
uniform
light
distribution
resulting
in
a
loss
of
dark
refuges
between
the
lamps
(Gaston
et
al.,
2012).
In
such
cases
it
may
be
preferable
to
increase
the
spacing
between
the
units
to
create
dark
refuges
to
facilitate
the
movement
of
light-averse
bats.
Changing
the
light
type
Light
technology
is
developing
rapidly
and
there
is
a
general
trend
towards
white
light
due
to
the
increased
colour
render-
ing
and
perceived
brightness
for
the
human
eye
compared
to
HPS
or
LPS
lights
(Knight,
2010;
Lockwood,
2011).
Emerging
light
types
increasing
in
popularity
include
white
LED,
warm-white
LED,
and
MH.
Warm
white
(600
nm)
LED
street
lights
are
being
tested
in
the
Netherlands
for
their
potential
to
reduce
nega-
tive
impacts
on
bats
(Fure,
2012).
There
is
increasing
concern
that
the
shift
to
broad
spectrum
lighting
could
alter
the
bal-
ance
of
species
interactions
(Davies
et
al.,
2013a).
Few
studies
have
compared
the
effects
of
impacts
of
different
light
types
on
bats
across
species
and
behaviours,
although
there
was
no
dif-
ference
in
the
nature
and
magnitude
of
the
effect
of
LED
and
HPS
lights
on
commuting
Rhinolophus
hipposideros
(Stone
et
al.,
2012).
Lights
emitting
blue,
green
or
UV
wavelengths,
such
as
MH
or
mercury
light
sources,
attract
large
numbers
of
insects
and
increase
insect
mortality
(Bruce-White
and
Shardlow,
2011;
Frank,
2006;
Somers-Yeates
et
al.,
2013).
Some
LED
lamps
attract
fewer
insects
than
MH
and
MV
(Eisenbeis
and
Eick,
2011).
Dif-
ferent
light
types
are
likely
to
have
different
effects
on
bats,
and
these
effects
will
be
species-
and
behaviour-specific.
Choice
of
light
type,
and
hence
its
spectral
distribution
will
inevitably
be
a
compromise
between
wildlife
and
public
requirements.
However,
potential
negative
impacts
on
light-averse
bats
and
insects
can
be
minimised
by
avoiding
short
wavelength
“blue”
lights
(Falchi
et
al.,
2011).
Are
we
in
the
dark:
setting
priorities
and
key
questions?
The
effects
of
lighting
on
bat
hibernation
are
currently
not
known.
Given
the
importance
of
hibernation
for
the
survival
of
many
temperate
species,
this
is
an
area
that
requires
urgent
atten-
tion.
Key
questions
include
the
impacts
of
lighting
on
arousal
and
overwinter
survival.
A
key
topic
requiring
further