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105
Herpetological Conservation and Biology 14(1):105–110.
Submitted: 12 September 2018; Accepted: 25 January 2019; Published: 30 April 2019.
NocturNal activity of aNtiguaN lizards
uNder artificial light
Andrew S. MAurer1,2,6, ChriStopher J. thAwley3, AlexAndrA l. FireMAn2,
SeAn t. Giery4, And JAMeS t. Stroud5
1Department of Applied Ecology, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695, USA
2Jumby Bay Hawksbill Project, Antigua, West Indies
3Department of Biological Sciences, University of Rhode Island, 120 Flagg Road, Kingston, Rhode Island 02881, USA
4Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269, USA
5Department of Biology, Washington University in St. Louis, St. Louis, Missouri 63130, USA
6Corresponding author, email: asmaurer@ncsu.edu
Abstract.—Widespread human development has led to the proliferation of articial light at night, an increasingly
recognized but poorly understood component of anthropogenic global change. Animals specialized to diurnal
activity are presented opportunities to use this night-light niche, but the ecological consequences are largely
unknown. While published records make note of nocturnal activity in a diversity of diurnal taxa, few case studies
have gone beyond isolated observations to quantify patterns of nocturnal activity, document animal behavior, and
describe new species interactions. From 13 June to 15 July 2017, we conducted hourly nocturnal surveys to assess
how two species of diurnal Anolis lizards (Leach’s Anole, Anolis leachii, and Watt’s Anole, A. wattsi) use articial
light on Long Island, Antigua. Our data show that both anole species foraged in articially illuminated habitats
and were more active prior to sunrise compared to the early night. Mark-resight data for a focal species, A.
leachii, suggest that patterns of nocturnal activity were not signicantly different between individuals. Finally,
our behavioral observations for the two anoles and a third lizard species, the nocturnal Thick-tailed Gecko
(Thecadactylus rapicauda), reveal a lack of agonistic interactions. Our study reveals an altered temporal niche
for two diurnal Antiguan lizards and adds to a growing body of evidence documenting the broad inuences of
anthropogenic change on biodiversity.
Key Words.—Anoles; Anolis leachii; Anolis wattsi; ALAN; articial light at night; light pollution; night light niche
iNtroductioN
As global anthropogenic change accelerates, the
occurrence of articial light at night is increasing in
extent and density (Hölker et al. 2010; Gaston et al.
2015). Articial lighting during dark hours alters
natural light regimes under which animal behaviors
have evolved. This ecological light pollution has
important biological consequences, including changing
animal activity patterns (Longcore and Rich 2004).
Indeed, as a result of urbanization and articial lighting,
many diurnal species have been recorded extending or
switching typical daytime behaviors into the night (e.g.,
Perry et al. 2008).
Plasticity in activity pattern can allow organisms
to exploit the evolutionarily novel night-light niche
(Garber 1978; Gaston et al. 2014), which may come
with a variety of benets and costs. For example, use
of articially lighted habitats can allow individuals to
acquire additional energy by extending foraging times.
Insectivores may forage on arthropods attracted to
lights (Verheijen 1960), a behavior commonly observed
in lizards (Perry and Fisher 2006; Martín et al. 2018).
Activity at night may also allow for maintenance of
territories, additional opportunities for courtship and
reproduction, and avoidance of competition (Rich and
Longcore 2006). Use of the night-light niche may also
entail costs, including increased energy expenditure,
non-optimal thermal conditions, disruption of
endocrine function, increased competition, or increased
susceptibility to some predators (Petren et al. 1993;
Perry and Lazell 2000; Perry and Fisher 2006; Ouyang
et al. 2018).
Despite a growing interest in the ecological effects
of articial light at night, its effects on animal behavior
remain relatively underexplored. The availability of
articial light is especially relevant for animals whose
dominant sense is sight, such as diurnal lizards of the
genus Anolis (hereafter, anoles). Seventeen species
of anole have been documented using articial lights
(Perry et al. 2008). Most anecdotal observations of
nocturnally active anoles document foraging behaviors
(Perry and Fisher 2006). Reports of displaying males
(Robert Trivers, pers. comm.), courtship (Bowersox et
al. 1994), and reproduction, however, suggest that a
wider range of behaviors regularly occur around articial
Copyright © 2019. Andrew S. Maurer
All Rights Reserved.
106
Maurer et al.—Nocturnal activity in Antiguan anoles.
lights (Wilson and Porras 1983). Yet, the diversity and
prevalence of such behaviors used at articial lights has
not been systematically studied.
Other relevant questions about the use of the night-
light niche remain unaddressed. For instance, detailed
observations of activity patterns at articial lights across
the entire night have not been made in any anole species.
Moreover, anecdotal reports that typify current literature
do not follow specic individuals. Consequently,
we lack basic information about whether individuals
vary in their use of articially lighted habitats. The
demographics of individuals using lights at night are
also unclear. While anoles of both sexes have been
reported using lights at night, some observations
(e.g., Powell and Henderson 1992) have suggested a
bias towards young males. In sum, moving beyond
an anecdotal listing of species using articial lights is
needed. Determining the behaviors, demographics, and
individual variation associated with use of articial lights
at night is necessary for understanding the ecological
and evolutionary impacts for diurnal organisms.
In summer 2017, we documented the nocturnal
behavior and activity patterns of two species of diurnal
anole, Leach’s Anole (Anolis leachii) and Watts’ Anole
(A. wattsi), at an articial light source in Antigua, West
Indies. During normal diurnal activity, these species
occur alongside various other lizards, most notably
Griswold’s Ameiva, Ameiva griswoldi (Kolbe et al.
2008), and occupy the same habitats used by nocturnal
geckos (e.g., native Thick-tailed Geckos, Thecadactylus
rapicauda, and non-native tropical House Geckos,
Hemidactylus mabouia). We assessed the types and
timing of anole behaviors shown through the night
and monitored marked individuals to assess whether
individuals consistently used the novel niche and how
this behavior varied between individual anoles.
Materials aNd Methods
From 13 June to 15 July 2017, we performed nightly
lizard surveys on Long Island, Antigua (17.156235°N,
61.751053°W) from approximately 2000 to 0600. Over
this period, sunset ranged from 1841 to 1844 and sunrise
from 0533 to 0541. We surveyed an approximately 28
m2 porch featuring a single articial light source that
pointed straight down from the ceiling (height: 3 m). We
conducted visual surveys every hour per night except
during occasional periods in the middle of the night
(e.g., 2200–0100) when we were only able to survey
opportunistically. For every individual lizard observed,
we recorded the time, perch location, and height. At the
start of the study, and when new individuals appeared
thereafter, we captured and marked each A. leachii.
For each individual, we determined its sex, measured
its snout-vent length (SVL), and gave each a unique
alphanumeric dorsolateral mark allowing for future
identication.
To assess whether individual A. leachii varied in
their use of the night-light niche, we calculated the
mean proportional similarity (mean PSi; an index of
inter-individual variation, also known as individual
specialization) between individual and cumulative
(population) distributions of activity (following
methods in Kamath and Losos 2017). This procedure
tests whether patterns of nocturnal activity observed
in each individual diverged from those observed for
the entire population. We calculated individual and
population level indices of individual specialization
(PSi) using the PSicalc function in the RInSp R package
(Zaccarelli et al. 2013). The P value was calculated by
comparing observed distributions to randomly sampled
distributions from the population distribution. Values
of PSi range from one (low inter-individual variation)
to zero (high inter-individual variation). We performed
all analyses in R v. 3.2.2 (R Core Team 2015) using
RStudio (version 1.0.136, R Team 2015) with α = 0.05.
results
We made 99 observations of A. leachii, A. wattsi, and
T. rapicauda. No other lizard species were observed.
We frequently detected all three species during the same
survey, and on several occasions detected multiple A.
leachii individuals on the same survey. We did not
observe any intra- or interspecic agonistic interactions
or visual displays (e.g., headbobbing, push-ups, or
dewlap extensions) during surveys.
The three lizard species exhibited distinct perch
heights: A. leachii typically perched high on walls,
between 2.4 and 3.0 m, A. wattsi was only observed on the
porch oor, and T. rapicauda displayed a variable perch
height, ranging from behind shutters at approximately
1.2 m to using the ceiling at 3.0 m. We observed the
lizards feeding on a variety of nocturnal invertebrates,
particularly small insects and Lepidoptera; foraging
appeared to be the primary behavioral mode. We also
made isolated observations of A. leachii catching and
eating arthropods including a cockroach (Blattodea) and a
tarantula (Cyrtopholis sp., likely C. bartholomaei; Fig. 1).
Our mark-resighting approach resulted in 78 A.
leachii detections with eight conrmed individuals (ve
sightings were attributed to unmarked individuals), 12
A. wattsi sightings of one conrmed individual, and
nine sightings of T. rapicauda (individuals not marked).
We were able to denitively determine the sex of six A.
leachii males based on scales at the base of the tail by the
cloaca, and we expect that the remaining two A. leachii
individuals were also male based on size and behavior.
Anolis wattsi is sexually dimorphic in color (Lynn 1957),
and the single individual we observed was male.
107
Herpetological Conservation and Biology
Our surveys starting roughly one hour after sunset
revealed activity patterns for A. leachii and A. wattsi
that were both right-shifted (relative to midnight as
the center of the x-axis; Fig. 2). The detections for A.
wattsi, however, were densely distributed around 0500
resulting in a pronounced unimodal peak, whereas A.
leachii detections were more evenly distributed through
the night (Fig. 2). There was no signicant difference
between individual nocturnal activity patterns for A.
leachii (mean PSi = 0.41 ± [SD] 0.30, P = 0.732; Fig.
3). SVL measurements from four A. leachii individuals
indicated a mean body size of 9.5 ± (SE) 0.13 cm; all of
the individuals detected were of similar size.
discussioN
Our results illuminate several important aspects of
the contemporary natural history of Antiguan lizards.
First, we describe previously undocumented nocturnal
behaviors in A. wattsi alongside the extensive use of
a nocturnal light source by A. leachii. Second, our
observations suggest the primary driver of nocturnal
activity in anoles is foraging opportunity. Third, the
observed nocturnal activity was skewed toward early
morning hours. Fourth, use of the night-light niche was
restricted to male anoles. Fifth, individual variation
in A. leachii nocturnal activity appears to be limited,
suggesting that all individuals are taking advantage of
this novel resource in a similar way.
Our observations suggest that the primary driver of
nocturnal activity in both species of Antiguan anole was
the novel foraging opportunity presented by arthropods
drawn to articial lighting. We did not detect any
behaviors associated with territorial maintenance or
reproduction. Further, we did not observe intra- or
interspecic agonistic interactions during our surveys
(e.g., dewlapping). Because effective communication
via the dewlap is specialized to specic photic conditions
in anoles (Leal and Fleishman 2004), it is possible
figure 1. An adult male Leach’s Anole (Anolis leachii) forages
on a tarantula (Cyrtopholis sp.) under an articial light source
on Long Island, Antigua, in summer 2016. (Photographed by
Alexandra L. Fireman).
figure 2. Overlapping density plots compare the temporal
distributions of nocturnal detections for Leach’s Anole, Anolis
leachii (n = 78 observations), and Watts’ Anole, A. wattsi (n =
12 observations). Sunset (1842) and sunrise (0535) are shown
with dashed gray lines. Hourly surveys typically started at
approximately 2000; the A. leachii curve extends earlier due to
kernel density smoothing.
figure 3. Indices of individual specialization (IS) in nocturnal
activity for eight Leach’s Anole (Anolis leachii) individuals (n =
78 observations). Points represent the mean pairwise similarity of
that individual to all other individuals (PSi); error bars represent
one estimated standard deviation. The mean population level of
individual specialization is represented by a bold blue line and
lighter dotted lines represent one standard deviation (mean PSi =
0.408 ± [SD] 0.30). Nightly surveys were conducted at an articial
light source on Long Island, Antigua, from 13 June to 15 July
2017, resulting in 73 detections of marked individuals.
108
Maurer et al.—Nocturnal activity in Antiguan anoles.
that the evolutionarily novel photic conditions around
articial lights may disrupt normal communicative
behaviors.
The use of the night-light niche by Antiguan anoles
has interesting implications for interactions with
coexisting nocturnal lizards. At our study location in
Antigua, T. rapicauda were also present around the
focal light source, with typically only a single individual
observed. This species could represent an interspecic
competitor for both A. wattsi and A. leachii or a potential
prey source for large A. leachii; however, we did not
observe any interactions between anoles and geckos, and
nocturnally active A. leachii did not appear to be large
enough to prey on observed T. rapicauda individuals.
We also did not observe any other syntopic lizard
species using articial lights (e.g., Ameiva griswoldi).
Future work should explore if use of the night-light
niche confers physiological or demographic benets (or
costs) to anoles, potentially through competitive release,
protection from predators, or subsidized predation on
aggregated prey.
The observed nocturnal activity patterns for A.
leachii and A. wattsi were right-skewed relative to a
center of midnight, with 48% of observations occurring
within 2 h prior to sunrise. Previous observations
of anole nocturnal activity (including in A. leachii)
were concentrated in the hours following sunset (e.g.,
Schwartz and Henderson 1991; Stroud and Giery 2013),
though A. carolinensis activity has been documented
roughly 2 h prior to sunrise (McCoid and Hensley
1993). With our observed activity concentrated closer to
sunrise, this could provide evidence that the exploitation
of the night-light niche by Antiguan anoles occurred
because of an earlier start to diurnal activity, rather than
an extension of diurnal activity past sunset. Because
our rst survey was typically 45–60 min after sunset,
our inferences here are limited and we do not have data
to rule out a post-sunrise activity period. Our anecdotal
observations, however, support our nding of increased
activity later in the night; we never observed A. wattsi
during the hours around sunset, and several A. leachii
exhibited behavior where they would appear for the rst
time in a survey night after midnight. Irrespective of
specic nocturnal patterns, our daytime observations as
well as those documented in previous studies in Antigua
(e.g., Kolbe et al. 2008) suggest that activity remains
much higher during the day than night for both species.
Kolbe et al. (2008) present diel patterns in abundance
that suggest a crepuscular schedule for A. wattsi and less
pronounced peaks closer to midday for A. leachii. In
sum, it is unclear if we will continue to see a gradual
shift toward more nocturnal use of articial lights, or if
we are observing the rare behavior of a few opportunists
or subset of the population.
Our analysis of inter-individual variation in A.
leachii nocturnal activity showed no difference in the
patterns of the eight marked individuals. This lack
of variation suggests that individuals at our study site
are adapting to the novel night-light niche similarly;
however, three individuals were only detected once
each, and our inferences into inter-individual trends
are limited in general by sample size. We were able
to conclusively determine the sex of six of eight A.
leachii; cloacal scales are pronounced in mature males
and ambiguous in females and subadult males (Lovern
et al. 2004). We made no conrmed sightings of female
anole activity in a set of 90 total observations, and it
seems likely that nocturnal behavior in female A. wattsi
and A. leachii is either nonexistent or very rare at this
site. Therefore, this study suggests a possible sexual
bias in the exploitation of the night-light niche. This
is consistent with previous observations of nocturnal
activity in the Anguilla Bank Anole (A. gingivinus;
Powell and Henderson 1992). Further research would
benet from exploring this sexual bias in activity and
should investigate what factors might drive sex-based
differences in use of the night light niche.
To develop a more comprehensive understanding
of the effects of light pollution, it will be important to
consider how prevalent exploitation of the night-light
niche is across species and contexts, and why individual
species may vary in their use of this evolutionarily novel
opportunity. Though A. wattsi is more abundant than
A. leachii in Antigua (Kolbe et al. 2008), our study
suggests that nocturnal activity is more common in
A. leachii. Moreover, the limited available evidence
suggests that A. leachii has been using articial light
sources for some time (Schwartz and Henderson 1991).
The reasons for this are unclear, but the disparity may
shed light on the traits valuable for taking advantage of
nocturnal opportunities. Anolis leachii is larger than A.
wattsi and thus could be a stronger competitor in any
agonistic interactions with nocturnal species. Further,
A. leachii typically occupies higher perches than does
A. wattsi (Kolbe et al. 2008), a trait that coincides with
a closer proximity to light sources that are most often
located high on walls and ceilings. Perhaps A. leachii
started to use the night-light niche when arthropod
prey aggregated in front of them at light sources at the
beginning of their natural diurnal activity.
Our observations of a single male A. wattsi
exhibiting nocturnal foraging activity may be the result
of idiosyncratic individual behavior. More nocturnal
surveys are needed to better establish how prevalent
this behavioral shift is for the species; however, with
78 A. leachii detections, our inferences are more robust
for this species. Additionally, our observations of A.
leachii using articially lighted habitats are not isolated.
109
Individuals of the species shifted into the night-light
niche at least as early as 1991 and likely before (Schwartz
and Henderson 1991). We have also incidentally
observed A. leachii nocturnal foraging behavior around
articial lights in other areas of Antigua away from
the focal study area (e.g., Hodge’s Bay and Piccadilly,
Antigua). In each situation A. leachii were foraging on
ying insects by articial light sources, suggesting that
the use of the night light niche by A. leachii could be
widespread on Antigua.
The body of research documenting use of articially
lighted habitats by a variety of taxa continues to grow
(Rich and Longcore 2006). Evidence is mounting
that suggests humans are contributing to increasing
nocturnality in wildlife (e.g., in mammals; Gaynor et
al. 2018). As more ecological impacts become apparent
(Gaston et al. 2014; Dominoni et al. 2016), investigating
the tness consequences of light at night will become
increasingly important. Despite this, light at night
remains understudied as a topic of regional conservation
concern in the Caribbean. We suggest that future
research should examine whether Caribbean species
show an ability to exploit the night-light niche and how
the use of this niche may result in downstream effects on
species persistence and ecosystem function.
Acknowledgments.—This project occurred during
eld work funded by the Jumby Bay Island Company.
We thank them for continual funding for the Jumby Bay
Hawksbill Project. Christopher J. Thawley was sup-
ported by a National Science Foundation Postdoctoral
Research Fellowship in Biology (#1711564).
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aNdrew s. Maurer is a National Science Foundation Graduate Research Fellow at North Carolina State
University, Raleigh, USA, a Fulbright Student Fellow, and a Research Associate with the Jumby Bay
Hawksbill Project in Antigua, West Indies. Andrew received his B.A. (2012) in Environmental Studies
and Spanish from Eckerd College, St. Petersburg, Florida, USA, and went on to pursue a graduate
research program in Hawksbill Sea Turtle (Eretmochelys imbricata) nesting ecology. (Photographed
by Kyle Pagel).
christopher J. thawley is a National Science Foundation Postdoctoral Fellow at the University
of Rhode Island, Kingston, USA, where he studies impacts of urbanization with a focus on articial
light at night (ALAN). Chris received his Ph.D. from Penn State University, University Park, USA,
where he studied adaptation of fence lizards to pressures imposed by invasive re ants. He received
his B.S. (2004) from Davidson College, Davidson, North Carolina, USA, and his M.S. (2011) from the
University of Alabama, Tuscaloosa, USA. Chris is broadly interested in how species adapt to rapid
environmental changes and is a strong proponent of scientic outreach. (Photographed by Fern Graves).
alexaNdra l. fireMaN is an M.S. student at the University of Maryland, Solomons, USA, Chesapeake
Biological Laboratory, and a Field Director for the Jumby Bay Hawksbill Project in Antigua, West
Indies. Alex received her B.A. (2016) in Biology and Earth and Environmental Science from Wesleyan
University, Middletown, Connecticut, USA, and is now pursuing an M.S. degree in Marine Estuarine
Environmental Science. Her research focuses on the foraging ecology and strategy of the Caribbean
Hawksbill Sea Turtle (Eretmochelys imbricata) over time. (Photographed by Alexandra L. Fireman).
seaN t. giery is a Postdoctoral Fellow at the University of Connecticut, Storrs, USA. His research
program examines the evolutionary origins and ecological consequences of phenotypic variation. He
uses natural and human-disturbed ecosystems to identify eco-evolutionary processes and their effects on
population persistence and ecological function. He received his B.S. from the College of Environmental
Science and Forestry of the State University of New York, Syracuse, USA, in 2002, his M.S. from The
University of Hawaii at Manoa, USA (2009), and Ph.D. From North Carolina State University, Raleigh,
USA (2016). (Photographed by Market Zimova).
JaMes t. stroud is a Postdoctoral Research Associate at Washington University in St. Louis, Missouri,
USA. In general, James is interested in understanding how species, particularly Anolis lizards, react
to novel abiotic and biotic conditions, such as behavioral changes with urbanization or patterns of
coexistence with distantly related congenerics. James received his B.Sc. in Zoology with Conservation
from the University of Wales, Bangor, UK (2008), his M.Sc. from the University of Hull, UK (2011),
and his Ph.D. from Florida International University, Miami, USA (2018). (Photographed by James T.
Stroud).