Desert Massasauga Rattlesnakes (Sistrurus catenatus edwardsii) in Southeastern Colorado: Life History, Reproduction, and Communal Hibernation
We studied Desert Massasauga Rattlesnakes (Sistrurus catenatus edwardsii) in southeastern Colorado in 1998 and 2005–2007. Mark–recapture data for 770 snakes indicated a population size of >3,500 snakes in an area of approximately 4,800 ha. Field growth rates and size class frequency distributions showed that average snake age was 3 yr; 4 yr old snakes were frequently encountered, but less than 4% were 5 yr or older, suggesting low survivorship beyond this age. Conversely, initial growth was rapid; snakes grew an average of 0.57 mm/day in their first full year. Desert Massasaugas mated in fall and spring, producing 2–7 (mean 3.3) young in late August to early September, and reproduction appeared to be biennial. Desert Massasaugas showed maternal attendance for at least 5 days postparturition, and neonate dispersal corresponded with the first shed. Radioed Desert Massasaugas (N = 15) used rodent burrows as hibernacula, and within 50 m of Desert Massasauga hibernacula, eight snake, five anuran, and two turtle species use the same area for hibernation. Low prey density at the hibernaculum indicates that stable hibernation conditions are the primary resource attracting a diverse assemblage of species to this area. The hibernaculum area serves as a critically important winter refuge for numerous species and supports the largest known population of Desert Massasaugas. This population is considered stable at present; however, because of rapidly changing climatic conditions, habitat loss and degradation, anthropogenic disturbance, and shifts in prey abundance, it may become threatened in the near future, and continued monitoring is warranted.Abstract
Range of Massasauga Rattlesnakes (Sistrurus catenatus) in North America. The study site in Colorado (*) is at the northern limit of the distribution of Desert Massasaugas. Adapted from Mackessy (2005).
Photographs (left) and aerial image of study site. The hibernaculum is in the foreground of both photographs, and at the tips of the arrows in the aerial image, and the drainage of the area is indicated in the lower left photograph by a solid black line. Symbols on the aerial image are individual snake locations from the telemetry study (Wastell and Mackessy, 2011); all snakes move from the hardpan shortgrass habitat (left side of image) to forage during summer months in the sandhills habitat (right side; primarily east of road).
Size distribution of Desert Massasaugas captured at the study site, 1998 and 2005–2007 (N = 770). Bars and numbers above histograms indicate age class as defined in Results. YOY, young of year.
Approximate age class frequency of Desert Massasaugas captured at the study site, 1998 and 2005–2007 (N = 770). Snakes older than four years were rarely encountered.
Average daily growth rates of three size classes of Desert Massasaugas (±1 SE, N = 49). Although juvenile and adult male snakes tend to show higher growth rates than females, these differences are not statistically different.
Field growth rate estimates for female and male Desert Massasaugas in Colorado. (A) Percent increase in length of females as a function of initial capture length (N = 26). (B) Growth rate of females as a function of initial capture length (N = 26). (C) Percent increase in length of males as a function of initial capture length (N = 23). (D) Growth rate of males as a function of initial capture length (N = 23). All plots are based upon recapture data obtained for snakes in 2005–2007. SVL, snout–vent length.
Number of Desert Massasaugas encounters per month for 2005–2007 (N = 770). Note that June and July are underrepresented because snakes are in summer foraging areas in the sand hills, are highly cryptic, and are rarely encountered.
(A) Birth site for snake 148.396; the black arrow indicates the opening to the rodent burrow used as a retreat. The opening faces west/southwest. (B) Female Desert Massasauga (snake 148.396) showing maternal attendance of neonates. Pre-ecdysis neonates were frequently observed basking on or near their mother; two are visible.
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