ON THE BIOLOGY OF THE VENOMOUS SNAKES OF ISRAEL. II

ABSTRACT

Two species of venomous snakes are dealt with in the present, second part of this work: Echis colorata Günther, 1878 and Pseudocerastes fieldi Schmidt, 1930.

Colour and pattern of Echis colorata in Israel are very variable and match to a certain degree the colours of the environment. The species inhabits rocky and broken ground, contrary to other side winding desert viperids that live on sandy soils. In Israel, sandy desert biotopes are inhabited by desert viperids other than Echis colorata. Side winding is not an efficient means of locomotion in the typical biotope of Echis colorata and is not regularly used by this species. The employment of sidewinding depends to a certain degree on the substrate on which the snake is moving, and on its state of stimulation. It is predominantly a desert snake, adapted to extremely arid surroundings, but along with several other desert species it has succeeded in penetrating northwards as far as Mt. Gilboa, which has Mediterranean climate. Food may be a factor regulating population density by affecting the breeding of females and the survival of young. The species takes well to irrigated agriculture, as seen from the recent development of a high population density in the Ein Gedi oasis, where it feeds mainly on frogs. Echis colorata is oviparous and has a rather low reproductive capacity, as the average number of eggs is only 7.6 per clutch and females generally do not breed every year. Resorption of eggs occurs under certain conditions. The eggs are relatively large and the young hatch with a large yolk reserve. Males are on the average larger than females and there is overlapping in body-tail relation as well as in the number of ventrals and caudals. Echis colorata is compared with Echis carinata as to biotope, distribution, and reproduction.

Pseudocerastes fieldi displays little variability in colour and pattern. It lives in partly sandy areas and, although a side-winder, makes also much use of rectilinear and serpentine movements. As with Echis colorata, the use made of sidewinding by this species depends also to a certain degree on the substrate and on stimulation. Difference in speed according to size is more pronounced in the rectilinear than in the side-winding progression. The species is often found in bushes. It prefers to feed on birds, but accepts also carcasses. Migrating birds probably form a considerable part of the diet of this species. It is oviparous and has a relatively high reproductive rate. The eggs are laid in an advanced stage of development.