Tokay geckos (Fig. 1) are a noisy fixture in Southeast
Asian rainforests, issuing their onomatopoetic calls
from dusk to dawn (and sometimes even during the
day) from diverse perches throughout a wide range of
microhabitats, ranging from pristine to disturbed areas
(e.g., Manthey and Grossmann, 1997; Chan et al., 2006;
Grismer, 2011). Unfortunately, these geckos (especially
their tongues!) have become threatened in their native
habitats by international trade, and their conservation
is becoming an international priority (Bauer, 2009;
Subramanean and Reddy, 2012). Given how well this
species advertises itself in its habitats and how high of
an interest it commands in the field of herpetoculture
(e.g., McKeown and Zaworski, 1997; Toth, 2020)
and traditional medicine, it may be surprising that
very few studies, as opposed to faunal surveys, deal
directly with the ecology and behaviour of the species.
Outside of the many notes on G. gecko, in which single
dietary observations and aspects of natural history in
introduced populations are reported, we found exactly
two studies detailing the natural history of G. gecko
more broadly and in what is presumed to be its native
habitat, namely Stanner et al. (1998) and Aowphol et
al. (2006). Furthermore, even though there is ample
mention in the literature, as well as in online reports, of
the aggressive behaviour shown by the species towards
humans and other geckos (e.g., Grismer, 2011; Kaiser
et al., 2013) this behaviour appears to be a matter of
general knowledge, yet there are no formal studies or
scientific reports documenting this##. Our report fills
a gap in our understanding to show the extent of this
Ataúro Island is a small (area 105 km2) Inner Banda
Arc island of volcanic origin and lies ca. 25 km off
the coast of Dili, the capital city of Timor-Leste. It
has a fairly diverse reptile fauna, of which G. gecko
is an audible, integral part (see Kaiser et al., 2013).
On 31 January 2010, during our first survey to assess
the island’s herpetofauna, we witnessed an unusual
behavioural episode involving G. gecko. While eight
of us were walking along the island’s main road in the
evening (19:30 h) from Tua Ko’in Lodge (8.2531°S,
125.6072°E) southwards to the town of Vila, we heard
G. gecko calls along the road. At one point, in a grove
of tall trees that formed a canopy over the road, we
heard a brief (< 1 min duration) noisy squabble above
us, which culminated when a tokay gecko landed on the
road right at our feet. This male individual displayed
Herpetology Notes, volume 13: 969-971 (2020) (published online on 26 November 2020)
: an extreme case of male-male aggression in
Tokay Geckos (Gekkonidae: Gekko gecko) on Ataúro
Hinrich Kaiser1,* and Mark O’Shea2
1 Department of Biology, Victor Valley College, 18422
Bear Valley Road, Victorville, California 92395, USA;
and Department of Vertebrate Zoology, Zoologisches
Forschungsmuseum Alexander Koenig, Adenauerallee 160,
53113 Bonn, Germany.
2 Faculty of Science and Engineering, University of
Wolverhampton, Wulfruna Street, Wolverhampton WV1 1LY,
* Corresponding author. E-mail: firstname.lastname@example.org
# Our title is a reference to the highly acclaimed 2012 James
Bond film with the same name. Bond films are filled with
male-male aggression, and in this case the topic of our paper
literally fell from the sky. The title of the film actually ref-
erences Skyfall, Commander Bond’s childhood home in the
## Of course, as a popular terrarium animal, there exist reports
about male-male aggression of G. gecko in captivity. For ex-
ample, Borg and Borg (1981) observed how three wild-caught
tokays from Bali fought and injured each other after having
been placed into a terrarium, which led Borg (2004) to issue
a “main rule” for keeping this species: do not keep males to-
Hinrich Kaiser & Mark O’Shea
no righting response or other movement and appeared
dead. Shining our flashlights immediately up into the
trees (approximate height 6 m above the road) allowed
us to see an especially large G. gecko retreating along
the length of a large overhanging branch. Closer
investigation of the deceased individual (deposited in
the collection of the United States National Museum,
Smithsonian Institution, accession number USNM
579056) revealed a definite set of bloody toothmarks
on both sides of its body and across its ribcage (more
visible on the lighter-coloured venter), a match to the
dimensions and dentition of G. gecko.
We reconstruct the episode as follows. Two adult male
geckos with territories in trees on either side of the road
forage along the edges of their respective territories and
encounter each other on a branch over the road, which
acts as a connector between established territories.
In the ensuing agonistic encounter, both individuals
vocalise and proceed to square off, including attempts to
bite. During this vicious engagement, one gecko gains
a firm hold on the other via a strong bite, inadvertently
killing it in the process. Facing no further resistance and
sensing no movement, the victor ends his struggle and
releases the loser, who unceremoniously drops down to
Our reconstruction of this tokay gecko aggression
event, which was heard but only partially observed,
is not merely based on assumptions but on solid
circumstantial evidence. During our walk that evening,
as on all night walks during survey periods, we looked
into the surrounding vegetation with flashlights. Based
on the absence of rats, snakes, or birds in general
during our walk and specifically along the branch and
trees where the observation took place (and absent any
rustling caused by other animals in the vicinity) and our
knowledge of the different vocalisations produced by G.
gecko (Yu et al., 2011), we discount the interpretation
that our auditory observation was related to something
other than intraspecific aggression. We had heard the
characteristic territorial calls of the species numerous
times from the bushes and trees lining the road and
beyond. The overheard squabble involved clear
intimidation „barks“ (sensu Brillet and Payette, 1991),
to the exclusion of other types of vocalisation (i.e., this is
inconsistent with a failed mating or predation attempt).
The bite force of G. gecko (Montuelle and Williams,
2015; Ross et al., 2018) is strong enough to break
through the carapaces of large insects and the bones
of small vertebrates, and it may well be forceful
enough to squeeze the ribcage of a conspecific to exert
sufficiently strong and sudden pressure on the heart and
internal organs to cause death. We do not believe that
the fall from the branch and the impact with the road
had any causation in the demise of the individual we
examined, given that tokays may jump some distance
and there was absolutely no post-fall movement. While
vocalisations are commonly used by these geckos in
territorial displays and agonistic encounters, the type of
intraspecific aggression we report here has never been
documented in detail. Doubtlessly, many people have
seen agonistic encounters, on account of G. gecko being
firmly established in disturbed areas and even cities
(Grismer, 2011), but only Chan et al. (2006) mentioned
any intraspecific aggression among males. One probable
reason for this is that most agonistic conflicts between
G. gecko males do not lead to the fairly spectacular
death of one of the combatants. We do not wish to imply
that fighting to the death is anything other than a very
rare and unintended consequence of regular territorial
conflicts between conspecifics that are ordinarily
relatively well-matched, but this encounter serves to
illustrate the extreme vigor with which male G. gecko
defend their territories from their rivals.
Acknowledgments. We thank our incredible fieldwork team,
including Venancio Lopes Carvalho, Laca Agivedo Varela, Zito
Afranio Soares, Luis Lemos de Araujo, Jester Ceballos, Scott
Heacox, Eric Leatham, Caitlin Sanchez, Dan Suzio, Marianna
Tucci, and “MJ” Weil for their eyes, ears, and nimble feet and
fingers to allow us an assessment of the Ataúro herpetofauna.
We very much appreciate the help of Aaron Bauer, who once
Figure 1. Aggressive pose of a male Gekko gecko from Ataúro
Island, Timor-Leste. While this is not one of the individuals
involved in the altercation we describe herein, the photo serves
to illustrate the fierce disposition and sharp dentition of these
sizable lizards. Photo by Mark O’Shea.
again came through with a key reference. We also gratefully
acknowledge the support and interest of Manuel Mendes, Director
of National Parks, who issued our research and export permits.
Our visits to Ataúro were supported by stipends to HK from a
Title V Grant to Victor Valley College and by financial assistance
to our U.S.-based students from the Associate Student Body at
Victor Valley College and the Victor Valley College Foundation.
This paper is Contribution No. 23 from the Tropical Research
Initiative at Victor Valley College.
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An extreme case of male-male aggression in Tokay Geckos, Timor-Leste 971
Accepted by Maximilian Dehling