Threats faced by hepertofauna (amphibians and reptiles)
Anslem de Silva
Herpetologist, Amphibia and Reptile
Research Organization of Sri Lanka
15/1 Dolosbage road, Gampola, Sri Lanka
Articles by Anslem de Silva focus on the present (2005) status of reptiles
of Sri Lanka on five headings taxonomy,
ecological status, threats, distribution
and conservation and management.
Population growth and human settlement
rapid increase in human population has occurred in Sri Lanka over the past
century with much land being cleared for agriculture, plantations, and human
settlements. Erdelen (1988) has shown that the area of natural forest cover
is inversely proportional to population growth, thereby disturbing, fragmenting,
and reducing the natural habitats of animals. Furthermore, the human consumption
rate of the flesh and eggs of some reptiles such as sea and fresh water turtles,
Crocodylus palustris, C. porosus
, and Varanus bengalensis
has also increased. Also a high rate in killing and excessive collecting of
reptiles (de Silva, 1982, 1984, 1990a & 1990b; Gans, 1973; Crusz, 1973;
1984; Erdelen 1988; Richardson, 1994; Senanayake et al,1977; Whitaker and
The Accelerated Mahaweli Project was the biggest single human settlement scheme
in recent years and resulted in the replacement of about 200,000 hectares
of natural wildlife habitats with agriculture (Baldwin, 1991). It is one of
the largest irrigation projects to be carried out in Asia and many reptiles
were killed and considerable extents of their nesting habitats were destroyed
in the process.
Over a thousand hectares of forests and grasslands are set on fire annually.
These fires may be a serious threat to the herpetofauna, including their eggs
that are laid in leaf litter. Daniels (1991) considers this a threat faced
by amphibians in India.
Secondary effects of deforestation
Increasing temperatures and decreasing annual rainfall is a trend seen in
Sri Lanka in the recent past (Fernando & Chandrapala, 1991).This may have
adverse effects on reptiles that require moist cool habitats (discussed above).
In the first quarter of 1992 a catastrophic mortality of Cophotis ceylanica
was observed around Hakgala (1,500 m) and Nuwara Eliya (1,800 m) where hundreds
of dead specimens were found within a few days (de Silva, 1996, Palihawadana,
1998). Although post mortem and other pathological examinations were not conducted
to ascertain the cause of death, an extended drought with high temperatures
reported during this period is believed to have been a major contributory
factor (de Silva, 1996). According to Fernando and Chandrapala (1991) there
has been an increase in temperature and a decrease in the annual rain-fall
in these areas during the past century.
Pesticides were first used in Sri Lanka to control malaria in 1946. Since
then there has been a gradual increase in the use of pesticides. Presently
some 100 active ingredients are used in both agriculture and in public health.
Sri Lanka imports about 2000 metric tons of pesticides per year, 70 % being
used in paddy cultivation. (Mubarak, 1986). Although there is no data regarding
the direct effects of pesticides on reptiles, a considerable number of human
deaths occur in Sri Lanka annually due to toxic effects of pesticides. According
to the Ministry of Health (1999) it is the 5th leading cause of human death
in Sri Lanka: often due to self ingestion while accidental poisoning is
caused while spraying pesticides on paddy and vegetable fields. Frogs that
were common in paddy fields in the past are now less common. It is reasonable
to assume that use of pesticides and herbicides in paddy cultivation could
be a factor responsible for reducing the frog populations. The author took
part in a survey around Naula and Dambulla in 1970-80 to investigate the
effects of spraying malathion for malaria mosquitoes. During this survey,
all householders informed the author that since spraying they have not observed
a single house gecko in their houses, which had been common earlier. High
application rates of nitrogen fertilizer may be another contributory factor.
Nearly one third of Sri Lanka's land is cropped, and its farmers use 77-124
Kg of nitrogen fertilizer per hectare which is 2 to 8 times more fertilizer
than is used in any other country in the region (Baldwin, 1991).
In Sri Lanka an appreciable number of reptiles and amphibians are run over
daily and killed by road traffic (Bambaradeniya et al., 2001; de Silva, 1999,
2001, 2003). One of the first reports on this aspect was documented by the
author in a study of the herpetofauna of the Horton Plains National Park (de
Silva. 1999). In a subsequent study along the Dolosbage road, Gampola was
that used by the author daily to travel from his residence to Gampola town.
This stretch of road is approximately 2.25 long. The authors’ house
was built in the early 1970’s. Up to 1997 there was less traffic on
this road, thus there was virtually no road deaths of reptiles and amphibians
along this stretch of road. However, this increased to approximately six road
kills per year since 1997. Forty-four reptiles comprising of 15 species and
4 amphibians comprising of 2 species were run over and killed by vehicles.
The common (8) reptile that was run over and killed was Calotes calotes. All
were males. One Coeloganthus helena with a rat in its mouth was observed run
over and killed. The present study, though observed twice a day by the author
has shown 44 road deaths. However, several checks daily will show more as
it was observed that during the day crows feed on road kills. However, these
random observations made in 2.25 km stretch reflect the magnitude of road
kills of reptiles and amphibians in Sri Lanka annually. Furthermore, many
colleagues from different parts of the island too have informed the author
of several road kills they observe regularly, including juvenile crocodiles.
Under the Fauna and Flora Protection Ordinance (Amendment-Schedule 1) all
reptiles are protected except Naja naja, Bungarus caeruleus, Bungarus
ceylonicus, Daboia russelii,
and Echis carinata
. Only occasional
permission is given by the Department of Wildlife to zoos and researchers
to study or export reptiles under the provisions of CITES. Nevertheless, there
is evidence that reptiles are smuggled out of the Island quite often.
Killing of snakes
Snakes, both venomous and non-venomous, are widely killed in Sri Lanka through
fear and ignorance, as a precautionary measure against snakebite. The high
incidence of snakebite morbidity and mortality in Sri Lanka is the major contributory
factor for this attitude (de Silva, 1981 & 1982. In the Accelerated Mahaweli
areas the settlers are constantly exposed to snake bite (de Silva, 1981; de
Silva & Ranasinghe, 1983; de Silva & Hewage, 1987; Deniyage &
de Silva 1989). Field observations conducted in all the Mahaweli settlements
indicated that many snakes are 'over killed', especially the Russell's viper
(Daboia russelii) and the common krait (Bungarus caeruleus).
Furthermore, a host of other non-venomous and venomous snakes such as the
Trinket snake (Coeloganthus helena), common kukri snake (Oligodon
arnensis) the Gamma cat snake and Forsten's cat snake (Boiga trigonata
trigonata and Boiga forsteni) and the green pit viper (Trimeresurus trigonocephalus)
were also killed usually while clearing forests during preparation of land.
Studies indicated that an average of five snakes was killed each day in the
Mahaweli settlement areas alone (de Silva, 1982, de Silva & Ranasinghe
Species specific threats
Ongoing studies on geckos and skinks show that despite the fact that Calodactylodes
is both widespread in the savannah and locally abundant
where it occurs, it remains vulnerable to a variety of threats. Perhaps most
importantly, the boulder outcrops with which it is associated are naturally
discrete from one another, promoting the isolation of individual populations.
Prior to human modification of the landscape, the surrounding monsoon forest
would have provided corridors connecting boulder retreats. These forests,
however, are now highly fragmented, in part due to extensive logging and clearing
for agriculture over the past several centuries. As a result much of the region
is covered by extensive grasslands and fire resistant trees such as Terminalia
chebula, Terminalia bellirica, Phyllanthus emblica
and Careya arborea
which are unsuitable for Calodactylodes
. On a smaller scale, other
possible threats are those associated with direct disturbance of rocky retreat
sites and the immediately adjacent vegetation. Thus interesting scenarios
of possible population “isolation” within the same locality of
was observed. This may lead to eventual
extinction of the species.
More articles on reptiles........
Taxonomy and ecological status
Distribution, conservation and management.