ECOLOGY AND BEHAVIOR OF THE TIMBER RATTLESNAKE ( CROTALUS HORRIDUS ) IN THE UPPER PIEDMONT OF NORTH CAROLINA : IDENTIFIED THREATS AND CONSERVATION RECOMMENDATIONS

A disjunct population of the Timber Rattlesnake (Crotalus horridus) was studied in the Sauratown Mountains, an upper Piedmont monadnock in north-central North Carolina. Anecdotal evidence suggests that this population is declining. A field study was thus initiated to examine the reproductive ecology, spatial requirements, and possible causes of the population decline in state parks that represent habitat islands surrounded by a fragmented landscape intersected with roads. Of snakes examined (N = 96), ten were implanted with radiotransmitters and radiotracked, five for multiple seasons. Mass of pregnant females (N = 11) suggests that a minimum of 500 g is necessary for reproduction. Snakes hibernated as singles or small groups at elevations from 466 to 655 m. Non-random movements, stable home ranges, and site fidelity were observed in telemetered snakes. Males had larger home ranges and on average moved greater distances and more often than females. Disproportionate male mortality is a significant cause of population decline, causing a skew in the sex ratio (Male:Female, 1:3.7). Our observations show that humans may negatively impact pregnant females and their habitat. Management response to nuisance snakes was examined, and subsequently changed at Hanging Rock State Park. Short-distance translocation (N = 31), for example, was determined to be 100% effective in managing nuisance rattlesnakes. Management recommendations include public education as to the presence and protected status of C. horridus in North Carolina state parks, termination of long-distance translocation as a conservation management practice, and restriction of access to sites occupied by pregnant females. 313 Tyler Lane, Boone, North Carolina 28607, USA E-mail: jsealy@boone.net Data collection primarily occurred within the boundaries of Hanging Rock State Park, which constitutes the largest section of the Sauratown range (Fig. 2). The park encompasses 2,517 ha and has an elevational range of 298 to 785 m including six peaks: Hanging Rock Bluff, Moores Knob, Cooks Wall, Wolf Rock, Devils Chimney, and Reuben Mountain. Hanging Rock Bluff is the west-facing terminus of Hanging Rock Ridge that stretches generally east from the bluff and includes three lesser peaks (the “Three Sisters”) referred to herein as the Hanging Rock Mountains. Sauratown Mountain and Pilot Mountain (including Pilot Mountain State Park) lie 4.5 and 13 km to the west, respectively (Fig. 2). Hanging Rock State Park experiences heavy public use, receiving more than 400,000 visitors (100,000 562 J. Sealy Fig. 1. Location of the Sauratown Mountains in the northern Piedmont of North Carolina. Data Source: U.S.G.S. Prepared by Art Rex, 2001 Fig. 2. Fragmented and road intersected landscape surrounding the Sauratown Mountains in Stokes and Surry Counties, NC. Data Source: NC CGIA. Prepared by Art Rex, 2001 vehicles) annually with the majority of visitors from April through October. The park contains 8 km of paved roads and 30 km of hiking trails. Public facilities include a visitor center, a campground containing 81 campsites, six rental cabins, a lake for swimming and boating, a bathhouse, four open-air shelters for large day-groups, and 65 picnic tables. Two parking lots can accommodate 682 vehicles and are often filled to capacity during the summer months, especially on weekends. Facilities for staff include a maintenance area, barracks for seasonal workers, and four full-time residences for permanent staff. Study Procedures Timber Rattlesnakes were captured from May 1990 to October 1997. Regular searches of exposed rock outcrops allowed individuals to be located at their hibernacula. As summer progressed and they dispersed, my searches focused on rock formation types used by pregnant females (Martin, 1993). Park personnel captured many “nuisance” rattlesnakes on park roads, in campgrounds, and in other public areas, and several residents living adjacent to the park provided captured or dead snakes for the study. I collected road kills, canvassed park roads at night for snakes, and in one instance, purchased a snake captured outside the park boundary from a commercial snake collector. An enclosure of 1.2 m high, 2 cm mesh hardware cloth fencing was constructed around a hibernaculum entrance to capture emerging snakes (J. Sealy, unpublished). Sex was determined by tail length and/or subcaudal counts (Gloyd, 1940; Klauber, 1972; Palmer and Braswell, 1995). Where necessary I examined the interior of the cloaca for reddish to purplish vascularized tissue of the hemipenis, revealed by gently expressing the superficial exterior of the cloaca (this method has been used by W. Brown, pers. comm.). Snakes listed as “sex unknown” were individuals that escaped without physical examination or were severely damaged or decomposed road kills. Two females obtained dead were necropsied to examine reproductive condition. Females were considered reproductive for the year they produced a litter. Pregnant females, therefore, were considered reproductive in their year of capture, and were identified by their distended lower body (Fitch, 1987; Martin, 1993) or (rarely) females were palped to detect enlarged follicles and/or embryos. Females diagnosed as post-partum and found in spring and early summer were considered reproductive the previous year (Martin, 1993). Postpartum females were identified by their collapsed abdomens and loose, longitudinal, posterior skin folds (Macartney and Gregory, 1988). Following capture, individuals were stretched along an incrementally marked snake hook and measured for total length (rounded to the nearest centimeter), from tip-of-snout to base-of-rattle (Klauber, 1972). Nuisance snakes captured by park personnel were measured in a portable squeeze box by marking a continuous line on a plastic sheet and measuring its length with a rolling map measurer (Brown, 1991). Snakes receiving radiotransmitters were measured while anesthetized. All snakes were weighed with 1-kg Pesola scales to the nearest 5 g while secured in bags. Age estimates were made from rattle-segment counts using data and methods described by Martin (1993). Rattle segment counts included the basal segment and, where present, the post-natal button. In the Appalachian Mountains, which are similar in climate and habitat to the Sauratowns, Martin (1993) found that shedding rates in C. horridus are predictable based on active season length. Thus, age estimates can be made from complete rattle strings representing all of the snake’s sheds since birth when the shedding rate is known. The shedding rate varies with age and must be considered when calculating the total age for adults. Shedding rates for juveniles are higher than those for adults. Juveniles typically shed twice per season every year, whereas adults shed twice per season every third or fourth year. Further, adults shed once per season during intervening years. Based on knownage snakes sampled by Martin (1993), Aldridge and Brown (1995), and data on a longer active season in the Sauratowns, I estimate an 11-shed (10 + button) snake to be at least 6 years old. When broken rattle strings were tapered, the number of missing segments was determined by comparison with photocopies of complete ones (Martin, this volume), thus facilitating an accurate estimate of age. Martin (1993) reported that the first 10 rattle segments taper, allowing the inference that broken untapered strings are missing at least 10 segments. When estimating ages of individual snakes with such rattles (typical of older adults), those with untapered rattle strings having seven or more segments were assigned to the 10-year-old or older age class. Individuals with broken untapered rattle strings having fewer than seven segments were placed in age classes of knownage snakes of corresponding total length. Subjects were uniquely marked with indelible ink by writing a number on both sides of the basal rattle Biology of the Vipers 563