Biology and status of timber rattlesnake ( Crotalus horridus) populations in Pennsylvania

Abstract

The purpose of this study was to examine certain aspects of the life history and ecology of the timber rattlesnake ( Crotalus h. horridus) in Pennsylvania, and to evaluate the reported decline in numbers of this species. The influence of commercial hunting has been considered and suggestions are made for conservation of this unpopular but intriguing snake. The previous and present abundance of rattlesnakes was first considered by a programme of interviews with commercial hunters. Visits were also made to many supposed den sites in central Pennsylvania, and to four rattlesnake hunts held in the summer of 1976. There were consistent reports of a large recent decline in the number of rattlesnakes seen and captured. These opinions of the scarcity of rattlesnakes were personally confirmed by visits to known dens. One rattlesnake den was chosen for a study on dates of first capture in the spring, on transplantation of snakes from other localities, on movements of newly released and long-term den residents, and on rodent populations. During three consecutive springs the dates of first capture of rattlesnakes varied only between April 23 and 30, despite marked differences in the pattern of air and ground temperature variation. Many snakes transplanted to a new den site apparently left the area almost immediately. Six out of 33 adults released were recaptured at the new den; three of these hibernated there. Only one of the 48 newborn rattlesnakes released soon after birth in the autumn was recaptured in the subsequent spring. On emergence from hibernation two rattlesnakes were tracked by radiotelemetry. They remained at the den until June, and left soon after shedding. One snake was followed to a distance 1055 m from the den over a period of 69 days. Considerable rodent food was available on the talus slopes of this den. Mice ( Peromyscuc leucopus) were abundant; in a 0·7 ha grid trapped for one week the population was estimated at 61/ha. Nine gravid rattlesnakes were held in the laboratory to obtain information on litter size. The average litter was seven (range 5–9) and females lost an average of 41% of their body weight during parturition. The metabolic demands of pregnancy are high and females only reproduce every two, or possibly every three, years. The smallest female to produce a litter had a snout-vent length of 770 mm, and it is estimated that this animal was five years old. Positive correlations between head length and snout-vent length, and body weight and snoutvent length were found. No significant differences in these relationships between the sexes or between snakes freshly caught in different areas were noted. There was a decline in relative body weight and head length after prolonged starvation in captivity. Male rattlesnakes have significantly longer tails than females. The timber rattlesnake in Pennsylvania is rapidly approaching extinction. Prohibition of bounties, snake hunts, and commercial sale of snakes, and protection of rattlesnakes in remote areas of state and national forests would significantly enhance the prospects for survival of viable populations of Crotalus horridus.