Ecology and vagility of the grass snake Natrix natrix helvetica Lacépède

Brown, Peter Ronald (1991) Ecology and vagility of the grass snake Natrix natrix helvetica Lacépède. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The movement ecology of free-ranging grass snakes (Natrix natrix) was examined at a site in Hampshire, England. Miniature radio transmitters were surgically implanted into 18 adult snakes for periods ranging between 7-313 days and the behaviour of the snakes observed. Several of the transmitters contained built-in thermistors which enabled the body temperatures of snakes to be remotely measured and logged. The use of space was examined using two methods of home range analysis. Minimum Convex Polygon analysis showed that intraspecific variation in the size of home ranges was high (0.54-33.49 ha), but Multi-nuclear Polygon analysis showed that only a small percentage of each range was used intensely. Monthly range sizes were greatest in May and July and the ranges for all months overlapped considerably. The monthly ranges of individual snakes also overlapped and this is discussed. Most daily distances moved were small and snakes did not move at all on 65% of daily observations. However, 1.5% of observations recorded daily movements over 300m. Seasonal migration was observed in both sexes but not in all cases. Movement was much reduced in the periods before ecdysis and after feeding. The preferred body temperature of the snakes was approximately 31^oC. Snakes warmed rapidly on emergence and cooled more slowly on submergence. Emergence appeared to be initiated by increased substrate temperature and submergence by decreased insolation. Body temperatures less than the preferred maximum were attained by snakes which could do so without emerging and this is discussed. Body temperatures fluctuated considerably while snakes were moving and activity was possible under a wide range of body temperatures. The preferred habitats of snakes were deciduous woodland and grassland, and snakes showed a marked preference for linear habitats, in particular woodland edges. Snakes selected microhabitats which provided both cover and basking opportunities. Laboratory investigation using time-lapse video showed that grass snakes exhibited a behavioral response to areas previously used by the adder Vipera berus, though no such response to areas using by conspecifics. The use of scent trailing and chemical cuing are discussed.

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