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Anslem de Silva
Herpetologist, Amphibia and Reptile
Research Organization of Sri Lanka
(ARROS)
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
A
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
Whitaker, 1978).Mahaweli Project
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.
Forest fires
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
Climatological changes
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.
Agrochemical use
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).
Road kills
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.
Smuggling
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 1983).
Species specific threats
Ongoing studies on geckos and skinks show that despite the fact that Calodactylodes illingworthorum 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 Calodactylodes illingworthorum was observed. This may lead to eventual extinction of the species.
More articles on reptiles........
Taxonomy and ecological status
Distribution, conservation and management.