الفهرس 
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Abstract
. The snake species of the present study have slow reproductive cycles since they reproduce once every year. It thus takes long time to restore their original numbers after any decline in their population sizes.
2. The two snake species of the present study proved to be good indicators for heavy metal pollution.
3. The environment in which the two snake species live is contaminated with considerable levels of heavy metals.
4. The levels of heavy metal concentrations in snake tissues differ with the snake species, sex, organ type, and season of the year. All these factors must be taken into consideration when comparing the heavy metal load between different areas.
5. The results of the present study are of special interest to wildlife conservationists and agricultural authorities since they help manage the natural populations of snake species and identify hazardous materials in the environment.
Recommendations
1. More studies on the population ecology and reproductive cycles of different Egyptian snake species are needed.
2. To evaluate the efficacy of different snake species as bioindicators of environmental pollutants and to include more tissue types, such as the gonads, in future studies.
3. Snake species must enjoy more protection measures.
4. Survey of the level of pollutants in different environments must be regularly carried out for identifying hazardous materials and help control environmental pollution.
The present work aims to study some aspects of the population ecology of two snake species present in agricultural areas of Egypt; namely, the African beauty snake, Psammophis sibilans, and the flowered racer, Platyceps florulentus. It also aims to study the efficiency of such snakes as bioindicators of heavy metals in the habitats in which they live. Snakes were collected from Al-Sahayra area, Al Sharqiya Governorate, which is a rural area located to the East of Nile Delta, some 108 km to the northeast of Cairo. Sampling of snakes was carried out along a period of 19 months extending from December 2019 to June 2021, inclusive. Field trips were stopped for several months due to the Governmental lockdown regulations connected with COVID-19 pandemic. The actual sampling months were thus 12 months representing all months of the year.
Ecological studies included the determination of age, age structure, sex ratio, dietary habits, and reproductive cycles. The efficacy of the liver and kidney tissues of these two snake species to accumulate heavy metals was also examined.
The total number of specimens of both snake species collected throughout the study period (79 individuals) was generally low. The numbers of Psammophis sibilans (51 individuals) noticeably exceeded those of Platyceps florulentus (28 individuals). The largest numbers of individuals of both snake species were collected in winter and spring.
Age was determined on the basis of the snout-vent length (SVL). Individuals of Psammophis sibilans and Platyceps florulentus having SVLs of 420 mm and 505 mm and more, respectively, were considered as adult individuals. The results showed that adults greatly outnumbered sub-adults in both snake species. Middle-aged and young adult individuals formed the majority of the populations of the two snake species followed by old adults.
Males of both snake species outnumbered females in the total sample collected throughout the study period. The results of the study also indicated that the body weight of both sexes of the two snake species clearly increased with the increase in age.
The dietary habits were determined by examining the contents of the alimentary canals of collected snakes. Prey items in the form of fur, legs, and long bones of rodents as well legs of toads were recovered from the alimentary canals of snake specimens collected in autumn, spring and summer seasons. No prey items were recovered from snakes collected in winter.
The study of the reproductive cycles of both sexes depended on the gross as well as the histological examination of gonads. Sperm count was also useful in studying the reproductive cycles of males. The results indicated that the male reproductive cycles of the two snake species were of the vernal type, and the female reproductive cycles were of the prenuptial type. The reproductive cycles of both sexes of the two snake species were synchronous.
The concentrations of heavy metals in snake tissues were determined by using Inductively Coupled Argon Plasma spectrometry. The two snake species proved to be good ecological indicators of heavy metals present in the environment. Eight heavy metals were detected in the liver and kidney tissues of snakes; namely, iron, zinc, copper, lead, manganese, nickel, chromium, and cadmium. Differences in the concentrations of these heavy metals were correlated with each of snake species, body organs, sex, and seasons of the year. The highest concentration levels of investigated heavy metals were in autumn and summer, while the lowest concentration levels were in winter season. The results indicated that the total mean concentrations of heavy metals in liver and kidney tissues of male individuals exceeded that of female individuals in the two snake species during the four seasons of the study period. It was clearly evident that the total concentrations of metals in the liver and kidney tissues of Psammophis sibilans were higher than those in Platyceps florulentus in all seasons of the year. The results also indicated that the mean concentrations of zinc, iron, copper, and manganese were higher in the liver than in the kidney, while the concentrations of nickel, chromium, cadmium, and lead were higher in the kidney than in the liver of the two snake species.
The study area proved to be a polluted area in terms of the metal pollution index.
The same heavy metals were detected in the soil of the present study area. The highest concentrations of all detected metals were in summer, while the lowest concentrations were in winter. In all seasons, the mean concentrations of Zn, Cu, Mn, Cd, Cr and Pb in the study area exceed their ̋soil background values̏, inferring the influences of anthropogenic activities. The mean concentrations of Fe and Ni, on the other hand, were below their background values. According to the ̋degree of contamination̏, the present results indicated that the soil of the study area exhibited very high contamination in summer, and considerable contamination in the other seasons. The calculated values of the ̋pollution load index̏ showed that the soil was moderately polluted in all seasons.
When comparing the concentrations of metals in the soil with the metal concentrations in the snake tissues, we observed that the concentrations of nonessential heavy metals; i.e., Pb and Cd in snake tissues were higher than soil concentrations. The highest concentrations of Pb and Cd in snake tissues exceeded their highest concentrations in soil by 2.4 and 8.6 folds, respectively. Therefore snakes are good indicators for environmental contamination.
The use of fluctuating asymmetry of head scales of the two snake species proved to be an easy measure of environmental pollution. Results of the study of fluctuating asymmetry supported the conclusion that the study area was a polluted one.
The results of the present study are of special interest to wildlife conservationists since they help manage the natural populations of these snake species. The determination of the heavy metal load of snakes is useful for identifying the hazardous materials in their environment and help control environmental p