Journal of Threatened Taxa | www.threatenedtaxa.org | 26
September 2019 | 11(12): 14503–14510
Brief
insight into the behavior, activity, and
interspecific interactions of urban Trimeresurus
(Cryptelytrops) albolabris
(Reptilia: Squamata: Viperidae) vipers in
Bangkok, Thailand
Curt Hrad
Barnes 1 & Tyler Keith Knierim 2
1,2 Suranaree University of Technology, School of Biology,
Institute of Science, 111 Suranaree Subdistrict, Muang
District, Nakhon-Ratchasima, 30000, Thailand.
1 chradbarnes@gmail.com
(corresponding author), 2 tyler.k.knierim@gmail.com
Abstract: Green Pit Vipers are a widely distributed, diverse
group of snakes which occur across a variety of habitats. Little is known about their natural history
in anthropogenically modified environments, and no ecological work has
investigated their persistence in cities.
We non-invasively photo-monitored White-lipped Green Pit Vipers Trimeresurus (Cryptelytrops)
albolabris in the metropolis of Bangkok,
Thailand (n = 4 individuals, mean = 2,658 minutes per individual). Subsequently, we preliminarily characterize
urban green pit vipers as nocturnal predators, displaying ambush-foraging at
night, sheltering during the day, and having limited movement in between
temporal periods. We recorded two
predation events of vipers capturing and ingesting anuran prey. Vipers infrequently displayed tail
undulations (239 minutes total), with one event occurring immediately before a
predation event. We also document
chemosensory, probing, and mouth-gaping behaviors
having occurred exclusively at night.
Other vertebrates including birds, frogs, geckos, small mammals, and a
cobra were photographed interacting with focal vipers or their immediate
surroundings (315 minutes total).
Knowledge of organisms in tropical urban environments is scarce, and the
persistence of venomous snakes in these unique and challenging habitats
requires further study.
Keywords: Activity, behavior,
conservation, White-lipped Green Pit Viper.
doi: https://doi.org/10.11609/jott.5116.11.12.14503-14510
Editor: Gernot Vogel, Heidelberg, Germany. Date
of publication: 26 September 2019 (online & print)
Manuscript details: #5116 | Received 24 May 2019 |
Final received 11 July 2019 | Finally accepted 06 September 2019
Citation: Barnes, C.H. & T.K. Knierim (2019). Brief insight into the behavior, activity, and interspecific interactions of urban
Trimeresurus (Cryptelytrops)
albolabris (Reptilia:
Squamata: Viperidae) vipers in Bangkok, Thailand. Journal of Threatened Taxa 11(12): 14503–14510. https://doi.org/10.11609/jott.5116.11.12.14503-14510
Copyright: © Barnes & Knierim.
2019. Creative
Commons Attribution 4.0 International License.
JoTT allows unrestricted use, reproduction,
and distribution of this article in any medium by adequate credit to the
author(s) and the source of publication.
Funding: The materials
used in the study and production
of the subsequent
manuscript were completed voluntarily by the authors without support from a funding agency.
Competing interests: The authors declare no competing
interests.
Author details: Curt Hrad Barnes is a PhD student in the
Department of Biology at Suranaree University of
Technology. His research and professional interests span a diverse range of
topics and taxa, but his current focus is primarily venomous snake ecology and
conservation. Tyler Keith Knierim is completing
his master’s degree at Suranaree University of
Technology in Thailand. Additionally, he instructs middle school science
courses and has an interest in herpetofauna of Indochina and urban ecology.
Author contribution: Both CHB and TKK conceived and designed the study concept, while TKK
designed and implemented monitoring and data collection in the field. CHB lead
the writing of the manuscript with significant guidance and contribution from
TKK.
Acknowledgements:
We thank Suranaree
University of Technology for supporting our ongoing research investigating the
ecology of venomous snakes living in human-dominated landscapes.
Introduction
White-lipped Green Pit Vipers (Trimeresurus
(Cryptelytrops) albolabris)
are a widely distributed arboreal pit viper belonging to the genus Trimeresurus, which is comprised of over 40
species inhabiting various regions in Asia (Uetz
& Hallermann 2015). At least eight species are currently known to
occur in Thailand (Cox et al. 2012), with some species, like the Phuket Pit
Viper (Trimerersurus (Popeia) phuketensis)
becoming described as recently as 2011 (Sumontha et
al. 2011). While the taxonomy and
phylogeny of the genus Trimeresurus has
largely been resolved (Malhotra & Thorpe 2004), genera and nomenclature
designation remains unclear (David et al. 2011). Two species of green pit vipers, the Big-eyed
Green Pit Viper (T. macrops) and White-lipped
Green Pit Viper, inhabit Thailand’s large metropolitan capital Bangkok (Cox et
al. 2012).
Both, White-lipped and Big-eyed Green Pit Vipers have
been previously reported to be responsible for
95% of the envenomating snake bites in the Bangkok metropolitan area (Meemano et al. 1987; Mahasandana
& Jintakune 1990) and 30–40 % throughout Thailand
(Viravan et al. 1992; WHO 2010). Despite being widely distributed throughout
southern and southeastern Asia, little research has
investigated the in situ ecology of green pit vipers. Work has largely focused on the habitat use,
basic biology, and spatial ecology of radio telemetered Big-eyed and
White-lipped Green Pit Vipers in rural or forested habitats (Devan-Song
et al. 2016, 2017; Barnes et al. 2017; Strine et al.
2018). These studies, however, did not
report data on the predatory behavior or
interspecific interactions of White-lipped Green Pit Vipers in highly urbanized
study sites. To address this knowledge
gap, we utilized a time lapse camera to investigate and provide preliminary
study of White-lipped Green Pit Viper behavior and
activity patterns in Bangkok, Thailand.
We also provide observations of syntopic
organisms that were accidently photographed while vipers were present (or
within 12 hours of abandoning sites) within this highly disturbed landscape.
Methods
We surveyed for green pit vipers from a public roadway
(Bangna Trad 19, Yaek 12),
visually scanning vegetation where the road bordered a densely vegetated 0.20ha
vacant lot (Image 1A). The property is
located at (676494 E / 1512069 N; 47 P) in the Bangna
District of Bangkok, Thailand. Dominant
vegetation cover along the roadside and adjacent vacant lot predominantly
consisted of non-native trees (Leucaena leucocephala), and vines (Antigonon
leptopus). We opportunistically surveyed for
vipers after dark, beginning our searches at 21.00h between 30 October–16
November 2018. When a viper was located,
we positioned a Bushnell field camera (Trophy Cam HD Essential E3, Model:
119837) with infrared night capability on a tripod spaced 1–2 m from each focal
viper. We programmed the camera using a
combined setting, including field scan, which continuously captured one photo
every minute, along with motion sensor, which took photos upon movement trigger
outside of the regular 1-minute intervals.
Only photos taken at the 1-minute intervals were
utilized in our activity pattern analysis.
The remaining pictures taken by the motion trigger were intended to be
used as supplements (for identification and context) in the case of
interactions and observations of or with other organisms. Care was taken when placing cameras to
minimize our disturbance to the vipers.
Herein we report observations from four individual
adult White-lipped Green Pit Vipers that had not abandoned their position in
their photo frames within an hour of us setting the cameras. We left cameras stationed at the viper
locations from their initial spotting at approximately 21.00h on the first
night to 21.00h on the third night of monitoring, allowing two days and one
full night (with one partial night after setting and one partial night before
retrieving the camera) of photo observation without a visit from us to the
site. We did not handle vipers and
attempted to limit our disturbance to the habitat during camera setting by avoiding
contact with connective vegetation. Upon
camera removal on the third night, we also attempted to capture close-up images
of each viper using Nikon D7000 camera to determine their sex (larger body and
head size for females, and presence of a postocular
stripe for males; Devan-Song et al. 2017) later (Image 1B). We monitored one viper per each two-day photo
monitoring period because we were limited to one trail camera for field
use. We determined that each individual
we monitored was unique through general visual appearance, size,
coloration/markings, and presumed sex.
We classified each time-lapse image with a green pit
viper from our trail camera into one of four primary behavior
states, defined as: ambushing, moving, resting, and sheltering following
classification used by Strine et al. (2018). States are behaviors
of relatively long duration (2 or more frames in our study (Martin &
Bateson 2007). Ambush behavior was defined as maintaining a stationary foraging
position, having a semi-coiled body with the head set in a bent neck,
ready-to-strike position. Moving behavior was defined as a complete transference of the body
of a viper from one site to another on camera frame or from a site on frame to
off frame (or off camera to on camera).
Resting was defined as having un-raised head settled on the body or
habitat feature in what could best be described as a relaxed position. We classified a viper as being in a
sheltering state only when it was not visible and other primary behaviors were not observable due to obstruction by
vegetation or other habitat features.
Additionally, we only defined behavior as
sheltering if we could confirm both entrance and departure from the visually
obstructing microhabitat feature on camera frame.
Other behavior states we
observed, although infrequently, include feeding and tail undulation. Feeding was the behavior
state used to collectively describe restraint and ingestion (until prey not
visible and fully inside focal viper) processes of predation. We defined tail undulation similarly to Clark
et al. (2016) as continuous, clear movement of the tail without pause for two
or more consecutive time-lapse image scans (2 minutes).
Behavioral events (instantaneous behaviors,
only observed for 1 frame in our study; Martin & Bateson 2007) irregularly
observed in our study include mouth gaping and probing, which we defined
similarly to Barbour & Clark (2012).
A chemosensory probe (“probe”) was a clear (not blurred on camera, which
could suggest a predatory strike towards prey) extension of the head beyond the
body coil with a closed mouth towards a habitat feature. A mouth gape (“gape”) occurred when a viper
opened its mouth at a ≥ 45˚ angle.
Behavioral events (probe and gape) and infrequently observed behavioral states (feeding and tail undulation) were
recorded, but not included in our activity pattern analyses. We also attempt to document (but not analyse)
all vertebrates observed on the cameras when vipers were present at or recently
(within 12 hours) abandoned sites, so as to provide context for behaviors observed, potential prey and predators of green
pit vipers, and general diversity in urban Bangkok; all of which have been
scarcely studied prior.
We utilized the methodology developed by Ridout & Linkie (2009) to determine
the daily activity patterns of vipers and quantify the amount of temporal
overlap between active (ambush and movement) and inactive behaviors
(resting and sheltering) using the ‘overlap’ package (Meredith & Ridout 2016) in program R (version 3.5.1; R Development
Team 2018). First, a non-parametric
circular kernel-density function was employed to assess comprehensively
(summarized, since behaviors were discrete, i.e.,
only one behavior recorded at any given minute
interval) daily activity patterns. Then
a coefficient of overlap (Δ) was used to measure the extent of overlap between
two kernel-density estimates, taking the minimum of the density functions from
two sets of samples being compared at each point in time. Overlap was determined to be the area under
both the density curves. The coefficient
of overlap ranged from 0 (no overlap) to 1 (complete overlap) (Ridout & Linkie 2009; Linkie & Ridout 2011). We calculated the 95% confidence intervals of
each overlap index using smoothed bootstrap with 999 resamples (Meredith & Ridout 2016).
Results
In total, we set cameras for 10,628 minutes over the
course of 11 days between 30 October and 16 November 2018 (mean 2,658 minutes
per individual, n = 4, Table 1), which corresponds to the end of the rainy
season in central Thailand (Singhrattna et al. 2005)
and the end of the mating season for the species in Thailand (Chanhome et al. 2011).
Vipers were positioned 10–50 cm above ground when recorded and generally
moved out of frame when having left that height range.
We observed vipers ambushing for 2,872 minutes,
sheltering for 467 minutes, and moving for 89 minutes. Ambush behavior was most frequently observed at night (18.00–06.00
h), sheltering during the day (under concrete buildings facing south and west,
with about a 10cm opening with chunks of concrete wedged in), and movement
occurring irregularly during both times (Fig. 1). Activity pattern overlap was minimal for
active (ambush and movement) and inactive (sheltering) behaviors
(Fig. 1, Δ = 0.05, CI = 0.08–0.10).
Males were most frequently observed ambushing (77.0% of observations),
then sheltering (20.3%), and moving least frequently (2.7%). Female vipers were most frequently observed
ambushing (97.6%) and least frequently moving (2.4%), and never sheltering in
frame (i.e., in immediate proximity to their camera location).
Tail undulation was observed concurrently with ambush
foraging behavior for 239 minutes by both females
(176 minutes) and one male (V4, 63 minutes).
It was observed in the presence of frogs (family: Microhylidae,
likely genus Microhyla) for 17 minutes and in
the presence of a single gecko (Hemidactylus
sp.) for four minutes. One of
the males (V4) was observed undulating for nine minutes (23.49–23.57 h)
immediately preceding predation of one of the small frogs (at 23.58 h). The same male was also observed depredating a
frog the following night (18.36–18.41 h, Fig. 2, 18 h 38 min between predation
observations), although undulation was not observed immediately preceding the
second predation event.
We observed 11 probing events by a single male (V4,
4min) and a single female (V2, 8min) viper, all of which were during the night
time. Four mouth-gaping events were
observed for a single male (V4, 3min) and a single female (V2, 1min), also all during
the nocturnal hours.
Large rats (Rattus spp.) were visible on
cameras for 10 minutes in the presence of two ambushing vipers (V1 & V3),
both vipers appeared to react in response to the rat’s activity. The rats were observed with refuse or food
(indistinguishable on camera) in their mouths for seven minutes. Both vipers pulled their heads back towards
their body coil in response to all rats passing within approximately 30cm of
their location. The male (V3) temporarily
abandoned his ambush site during one interaction when a rat ran in front of his
ambush target location. An adult Tokay
Gecko Gekko gecko was visible within
50cm of viper for five minutes, which did not elicit a response from the focal
viper (V3). The adult rats and Tokays
were likely too large prey for the vipers in our observations, however,
White-lipped Green Vipers have been recorded previously to eat small mammals
and geckos (including other Gekko spp.; Chanhome et al. 2011; Devan- Song et al. 2017). Small (prey-sized) geckos (likely genus Hemidactylus or Gehyra,
6min) and frogs (family Microhylidae, likely genus Microhyla, 38min) were observed in the frame while
vipers were ambushing.
One type of small frog (family Microhylidae,
likely genus Microhyla, 181min) and another
type (likely genus Hylarana, 2min) were visible
on camera during which vipers were not present at ambush or shelter sites.
Small (prey-sized) geckos (likely genus Hemidactylus
or Gehyra) were observed for nine
minutes. Large skinks (genus Eutropis) were visible on camera for 10 minutes
during the daytime. Small passerine
birds were observed for 15 minutes during the daytime (Oriental Magpie-Robin Copsychus saularis,
1min; Streak-eared Bulbul Pycnonotus blanfordi, 12min; unidentifiable species, 2min), and of
these observations one minute featured two birds which perhaps suggested a
mated pair (P. blanfordi). Large rats were visible for 38 minutes when
vipers were not visible, of which one minute featured a rat with food or
refuse. A Monocled
Cobra Naja kaouthia
was observed crawling directly past a viper’s previous ambush site (11.33h)
five hours and 30 minutes after a viper (V4) was observed ambushing; the same
viper returned and resumed ambushing at the same site after nightfall, six
hours and 27 minutes following the cobra observation. Knowledge of N. kaouthia
diet is largely unpublished, however, they have been documented as preying
primarily on snakes (but not green pit vipers, 21.7% of total diet
composition), bird eggs (11.3%), and rodents (65.7%) in central Thailand (Chaitae 2000; summarized in Chanhome
et al. 2011).
Discussion
Our observations revealed novel and interesting
insight into the persistence of an ambush-foraging snake species in highly
degraded and disturbed habitat. During
11 days of camera monitoring, we witnessed multiple interactions (including
predation events) and gained insight into behaviors
and activity periods of green pit vipers in a previously unstudied habitat type
(urban). We were able to confirm similar
general behavioral trends between our city vipers and
radio-telemetered White-lipped and Big-eyed Green Pit Vipers in rural and
forested habitats in another region of Thailand (Strine
et al. 2018; Barnes et al. in preparation).
These behaviors are characterized by nocturnal
active foraging (ambushing), diurnal inactive (sheltering), and infrequent
short distance (within camera frame, < 0.5 m) movement primarily between
ambush and shelter sites. Overlap of
active (ambush and movement) and inactive (sheltering) behaviors
was minimal, primarily limited to early evening and mornings (Fig. 1). Infrequently observed behaviors
of suspected chemosensory function (probing and mouth gaping; Clark et al.
2016) were only observed nocturnally.
Similar observation of active and chemosensory behaviors
primarily during the night and inactive behaviors
during the day by rural, natural forest, and urban vipers may suggest limited
plasticity of White-lipped Green Pit Viper activity patterns, although
retention of similar habitat (functionally, with the non-native trees and vines
in Bangkok) and prey may partially explain similar behavior
observed between habitat types. Urban
White-lipped Green Pit Viper resting and sheltering behavior
expression differed from previous observation of green pit vipers in natural
forest and rural habitat, however.
Interestingly, we did not observe resting behavior by the city vipers; however, resting behavior has been frequently documented from green pit
vipers in rural and forested habitats (Strine et al.
2018; Barnes et al. in preparation). We
postulate that the vipers at our highly urbanized study site may prefer to rest
in hidden shelters, rather than in the open as was observed from the vipers in
the forested and rural studies.
Additionally, vipers in our study only utilized terrestrial shelter
sites (beneath cover objects) which may be unusual for what is usually
characterized as an arboreal species.
Phenotypic plasticity of organisms in natural habitats and urban environments
has been documented for many groups of organisms with regards to shelter sites,
foraging, and reproduction within the context of behavior
(summarized in Lowry et al. 2012).
The vertebrate abundance that we observed on camera
appears surprisingly high for such a disturbed habitat. We were able to observe multiple species of
birds, geckos, lizards, frogs, and even a cobra, all of which may serve as
potential prey (geckos, lizards, and frogs), predators (cobra), or antagonists
(birds) to green pit vipers. Remote
time-lapse cameras may thus provide an additional tool for sampling diversity
in urban habitats. While none of the
vertebrates photographed in our study are classified as threatened by the IUCN
Red List, our cobra observation was significant as common cobras (monocle and
spitting, N. kaouthia and N. siamensis, respectively) inflict approximately 23% of
all venomous snakebites in Thailand (Warrell 2010).
We did not observe human-viper interactions during our
short study. While large and charismatic
snake species are frequently killed in Thailand (Marshall et al. 2018), a
previous radio telemetric study suggests people in rural areas are tolerant of
green pit vipers so long as they do not come into direct interaction (Barnes et
al. 2017). Similarly, both in this work
and a previous study (Barnes et al. 2017), vipers appear tolerant to the
presence of people so long as they do not make physical contact (i.e., touch)
with the snakes. Green pit vipers are
responsible for inflicting the majority of venomous snake bites in Bangkok (approximately
95% of all bites; Meemano et al. 1987; Mahasandana & Jintakune
1990).
We strongly discourage long distance mitigation
translocation (moving a snake from a site of conflict with people, to a
different site outside of their home range) (Sullivan et al. 2014) due to
limited activity and movement we observed in our work. A previous study of White-lipped Green Pit
Viper in Hong Kong suggests non-natural (increased and erratic) movement,
decreased fecundity, and significantly increased mortality of individuals
resulted from being translocated outside of their home ranges (Devan-Song et
al. 2017). Short distance mitigation
translocation (within home range (Brown et al. 2009); previously suggested to
be < 0.5ha area for White-lipped Green Pit Vipers (Barnes et al. 2017;
Devan-Song et al. 2017)) or soft releases (gradual release with a limited
acclimation period (Tuberville et al. 2005; Kingsbury & Attum
2009)) may suffice as less detrimental alternatives.
Although observations of large rats were infrequent on
our cameras (only 48min total), all interactions (10min when vipers were
present) elicited visible reactions from focal vipers. Both vipers (one male and one female) which
interacted with rats clearly pulled their heads out of ambush position, while
the male focal viper even temporarily moved away from his ambush site. We were unable to definitively discern the
rat species observed on camera, although three Rattus species are known
to be abundant in Bangkok, Rattus norvegicus, R. exulans,
and R. rattus (Chotelersak
et al. 2015); the Brown Rat R. norvegicus is an introduced species (Ruedas 2016).
Interestingly, rat species in Bangkok have been suggested to utilize
different habitats and different habitat features (R. norvegicus being
primarily terrestrial and R. exulans usually
confined to smaller villages, for example; Chotelersak
et al. 2015), suggesting niche partitioning which could subsequently interact
with and influence the behavior of White-lipped Green
Pit Vipers (generally considered habitat generalists) differently depending on
habitat type. While small mammals have
previously been recorded as prey for White-lipped Green Pit Vipers (Chanhome et al. 2011), our study also suggests the direct
disturbance by rats may play an important role in ambush site selection of
green pit vipers in urban habitats.
Additionally, we observed rats on camera (8min) carrying what appeared
to be refuse or food, which may have been anthropogenic in nature and
subsequently suggested human support of local rat populations. The abundance and influence of these various
rat species, both native and introduced, on green pit viper foraging and
activity patterns in the urban interface requires further attention.
Many green pit viper species possess orange or red colored tails.
While, the function has not been widely discussed but defense and caudal luring may certainly be speculated. We categorized the behavior
as tail undulation so as to be conservative in our assessment; however, we
suspect the behavior to be a form of caudal
luring. Although primarily observed when
potential prey was not visible (218min), we also observed tail undulation in
the presence of prey species (geckos and frogs, 21min) and immediately preceded
one of the two predation events (9min, followed immediately by predation in the
next scan/minute). Our observations
support the functionality of tail colorations in luring prey, while Greene
& Campbell (1972) and Greene (1973) proposed tail colorations to function
as defensive warnings when used by T. gramineus. One of us (C. Barnes) has observed both
functions for Big-eyed Green Pit Vipers (Barnes & Tipprapatkul
2019), which is sympatric in Bangkok and thought to be closely related to the
White-lipped Green Pit Viper.
Interestingly, vipers (White-lipped, Big-eyed, and Vogels
Green Pit Viper T. vogeli) were rarely
observed displaying tail undulation behavior (only
one Big-eyed Green Pit Viper out of 21 individuals of several species studied
on camera) in rural and forested habitats in a previous study (Barnes et al. in
preparation), contrasting to most urban (3 out of 4 individuals) White-lipped
Green Pit Vipers in this current report.
Tail undulation and chemosensory behaviors
could be investigated further in ex situ (under controlled laboratory conditions)
vipers, using prey type and viper age as variables (refer to Reiserer 2002 for example with multiple other species of
viper).
Snake behavior in urban
environments remains poorly understood, particularly within the overall context
of ecology. Future research into the behavior of green pit vipers in urban areas would benefit
from investigation of the effects of non-natural lighting (i.e., streetlights)
and vibration (from vehicle traffic or construction). Concurrent habitat assessment (characterization)
and use, both natural and anthropogenic would prove invaluable. Whether or not the green spaces we observed
White-lipped Green Pit Vipers to persist in serve as islands, bottlenecks, or
ecological traps for the species could be revealed by population and genetic
analysis. Previous camera study has
suggested increased interactions and change in species occurrence of mesocarnivores with increased urbanization intensity
(Parsons et al. 2019); more intensive (larger sample size during multiple
seasons) work should be conducted to understand interactions among conspecifics
(between and within sexes, age classes of White-lipped Green Pit Vipers),
co-occurring green pit vipers (Big-eyed Green Pit Vipers, in Bangkok), and
other native and non-native animals in tropical urban environments.
While our current work revealed brief but valuable
insight into green pit viper ecology in tropical urban habitat, much work
remains to properly characterize persistence and natural history in this unique
and challenging environment. Further
time-lapse camera studies would provide novel conservation and ecological
information on green pit vipers and syntopic
organisms in urban areas in tropical southeastern
Asia. We strongly caution extrapolation
from our preliminary observations and encourage more intensive (larger sample
size over multiple seasons) investigation.
Table 1. Basic summary of our four focal White-lipped Green
Pit Vipers Trimeresurus albolabris
observed for 2,156–2,856 minutes each with proportion of active (ambush and
movement behavior states) and inactive (resting and
sheltering).
|
Viper ID |
Sex |
Time observed (in minutes) |
Proportion active/inactive |
|
V1 |
Female |
2,156 |
1:0 |
|
V2 |
Female |
2,803 |
1:0 |
|
V3 |
Male |
2,817 |
0.67:0.33 |
|
V4 |
Male |
2,856 |
1:0 |
For
figures & image – click here
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