Comparative thermal ecology of the British snakes

Gaywood, Martin John (1990) Comparative thermal ecology of the British snakes. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A comparative study was made of the thermal ecology of the smooth snake Coronella austriaca, the grass snake Natrix natrix and the adder Vipera berus. Particular emphasis was placed on strategies employed in behavioural thermoregulation. Snakes were captured from several sites in Hampshire, England, and kept in landscaped outdoor vivaria. Operative temperatures available to the snakes in the outdoor vivaria were estimated using snake models. Body temperatures were measured and recorded using biotelemetric equipment, and their behaviour was observed. Snakes were also studied in a laboratory arena using time-lapse video equipment. Adders attained the highest body temperatures with a mean selected body temperature (calculated from `plateau phase' body temperatures attained after an initial heating phase and before a cooling phase) of 33.2^oC ± 1.86 (n = 491) outdoors and 35.5^oC ± 2.27 (n = 159) in the laboratory. The respective values for smooth snakes were 30.3^oC ± 1.64 (n = 377) and 30.8^oC ± 1.25 (n = 241) and for grass snakes 29.3^oC ± 2.63 (n = 291) and 31.0^oC ± 2.10 (n = 189). When conditions were thermally unlimiting, the snakes attained higher body temperatures than during periods of thermally limiting conditions. Outdoor conditions were found to be thermally unlimiting for all 3 species for only a relatively small proportion of the time during their `active' season. Adders displayed a greater ability to temporally utilise thermally unlimiting conditions. They basked in the open for relatively long periods. A sit-and-wait predatory strategy may be used in conjunction with basking. Adders emerged earlier and submerged later, emerged on a greater number of occasions and had a wide repertoire of thermoregulatory behaviour (e.g. dorso-ventral flattening, alteration of body aspect, body coiling, adjustment of body area exposure, basking site selection, thigmothermy). Smooth snakes were also heliothermic and were capable of very precise thermoregulation. Mosaic basking was observed far more than basking in the open and movement was observed less than in the adders or grass snakes. This related to the smooth snake's cryptic lifestyle. Mosaic basking was considered to be an extreme (and energy-efficient) form of shuttling heliothermy, utilising sunny and shaded areas simultaneously. Grass snakes engaged in movement more than the other species in the outdoor vivaria, especially during thermally unlimiting conditions. This was related to their widely foraging predatory strategy. Details of behavioural thermoregulatory strategies and other aspects of general thermal ecology are discussed.