[Stefan-A]

http://links.jstor.org/sici?sici=002...rigin=crossref

Abstract

Western terrestrial garter snakes (Thamnophis elegans) are the only Thamnophis known to constrict prey, and previous studies suggest that they are relatively inefficient constrictors. To quantitatively evaluate that perception, we compared the constricting behavior of T. elegans to that of a more typical constrictor, the gopher snake, Pituophis catenifer. We recorded the behavior of snakes preying upon mice under controlled laboratory conditions, focusing on behavioral measures related to the function of efficiently subduing and ingesting prey. Compared to gopher snakes, western terrestrial garter snakes showed the following characteristics indicating they are relatively inefficient constrictors: (1) greater variability in the method of applying constricting coils; (2) a weaker tendency to constrict prey; (3) longer times to subdue prey; (4) a lower frequency of trials in which coils were parallel; and (5) absence of the behavior of releasing the initial bite on the prey prior to the initiation of swallowing. These differences between the two species might be a result of differences in recent selective regimes, because western terrestrial garter snakes rely less heavily than gopher snakes on prey for which constriction is likely to reduce a snake's feeding costs. Another, not mutually exclusive, explanation for the behavioral differences is that they reflect the more recent evolutionary origin of constriction in T. elegans than in P. catenifer. Despite their relative inefficiency, the Colorado T. elegans used in this study nearly always killed the mice they constricted prior to ingesting them. In contrast, previous studies have indicated that T. elegans from the Pacific Northwest rarely kill mice they constrict. This difference may represent intraspecific geographic variation in constricting behavior. However, a recent molecular systematic study suggests that Colorado and Pacific Northwest T. elegans may represent distinct species in which constriction has independently evolved.

Bolded some parts that I found especially interesting.