Observation of aberrant growth in a Timber rattlesnake (Crotalus horridus)

Abstract

In Crotalus horridus, a species in need of conservation in Kansas (Brown 1993), growth is generally positively correlated with the number of rattle segments, in accordance with the frequency of ecdysis. In compiling 17 years (1990-2006) of timber rattlesnake morphologic data from a population in northeastern Kansas, Fitch and Pisani (2006) noted that, among males, snakes whose snoutvent length (SVL) fell within the range of 628-720mm (mean = 675.2mm) typically exhibited a button and 3 additional rattle segments. An overlap in this range is seen with individuals bearing a button plus 2, 4, 5 or, at most, 6 segments in a rattle that normally would show appreciable distal taper. Therefore, the collection of an anomalous male snake (Fig. 1) from northeastern KS weighing 199.5g, with a SVL of 668mm and an incomplete string of 18 rattle segments in May of 2007 was unexpected. Predictably, aside from the terminal segments, the rattle was not markedly tapered (see Table 1 below), an indication that growth did not accompany the addition of new segments beyond the fourth or fifth shed. This period is typically when the most significant (p=0.95) gains are made in the growth of northeast Kansas timber rattlesnakes (Fitch and Pisani 2006). The high correlation between segment width and incremental growth of rattlesnakes is well-documented (Fitch and Pisani 1993; Klauber 1956).