Observations of Courtship in the Rattlesnake, Crotalus viridis oreganus

Abstract

According to Fitch and Glading (1947) and Fitch (1949), the northern Pacific rattlesnake (Crotalus viridis oreganus) generally mates during a twomonth period following spring emergence, usually in well concealed situations such as burrow entrances, rock crevices, or under the edges of brush or logs. The mating snakes were sensitive to disturbance and quick to separate. Unfortunately, the secretive nature of most snakes renders field analysis of courtship behavior difficult or impossible. The few other accounts of courting rattlesnakes in the field (e.g., Wood, 1933; Bogert, 1942; Lowe, 1942; Klauber, 1956; Duvall et al., 1985) provide little quantitative data. Laboratory studies have elucidated the courtship behavior of the western massasauga, Sistrurus catenatus tergeminus (Chiszar et al., 1976), and the western diamondback rattlesnake, C. atrox (Gillingham et al., 1983). The courtship of C. atrox appears to follow the triphasic scheme described for colubrids (Gillingham, 1979): tactile-chase (phase I), tactile-alignment (phase II) and intromission and coitus (phase III). I here report laboratory observations on the courtship of C. v. oreganus. Seven adult rattlesnakes were housed together in a 165 x 87 x 86 cm wooden pen with a paper floor covering, rocks and a glass vessel containing water. Mice were accepted as prey on a regular basis. Temperature was 26-31?C during the light cycle (0600-2000). Six snakes (4 6) were collected in April 1983 (Walla Walla County, Washington); the seventh, a female (65.1 cm SVL; 174 g), was collected in March 1984. After refusing food during a regular feeding session, this female was isolated in a smaller wooden cage where ecdysis occurred four days later (10 July 1984). When reintroduced to the pen on 27 July, and again on several occasions through 13 August, the largest male (77.2 cm SVL; 332 g) actively courted her. Courtship intensity decreased during this period. Several times other males briefly (c 11 min) courted her as well. Most observations, which lasted 70-120 min between 1900 and 2200 (while lights remained on), were terminated when the male lost interest in the coiled female. Several of the later observations, which lacked the intensity and consistency of earlier male courting efforts, were recorded on videotape. The following analysis retains terminology developed by Gillingham (1979). However, phase II events clearly consisted of three distinct behaviors, for which new terminology is introduced. A verbal description of repetitions of the entire three-part phase II sequence was recorded by a second observer, who timed each clearly demarcated cycle with a stopwatch. In addition, forward-jerks during the flexion-cycle (described below) were incremented on a hand-held counter. Fifty complete sequences from the first two obervations were evaluated for phase II events. The tongue-flick rate (TFR) and additional motor pattern details were determined from videotape. Selected behavioral events were scored using a microcomputer (Radio Shack TRS-80) timing subroutine, then loaded onto a VAX 11/750 for subsequent analysis and graphic display. In most courting snakes phase I consists of chases (female flees, male pursues) or chasemounts (male maintains contact during pursuit). Phase II begins when the male exhibits tail-search copulatory attempts (TSCA), which are tactile attempts by the male's tail to locate the female's cloaca. In the present study, the female usually remained coiled and quiescent. Only occasionally did the female flee and a chase ensue. However, chases often interrupted rather than preceded phase II behavior. Phase I behavior was therefore istinct from phase II only in the initial absence (2.6, 7.4 min) of TSCA. When chases interrupted phase II behavior, TSCA was quickly resumed once contact was reestablished.