Sistrurus catenatus

Kubatko et al. (2011) used a multigene data set to infer two clades among the three previously recognized subspecies. One clade contained the eastern subspecies (S. c. catenatus) and the other clade contained the two western subspecies (S. c. tergeminus and S. c. edwardsii). Kubatko et al. (2011) recommended elevating S. c. catenatus. However, if the recommendation was followed at that time, it would also require elevating S. c. tergeminus and the formation of three new combinations. In addition, Holycross et al. (2008) discovered that S. c. tergeminus is actually subsumed by S. c. catenatus because the type locality of catenatus is within the range of tergeminus, and that the name Crotalus massassaugus Kirtland, 1838 would be the available and valid name for the eastern subspecies. As such, tergeminus was not currently a valid name and if the Kubatko et al. recommendation was followed, the specific epithet for the eastern form would be massassaugus. Crother et al. (2011) submitted a petition to the ICZN for conservation of the names catenatus and tergeminus. The subsequent opinion by the ICZN (2013) retained the names S. catenatus and S. tergeminus by designation of neotypes for both species. In this database we follow SSAR and the recommendation of Kubatko et al. (2011) and elevate tergeminus, leaving no recognized subspecies of catenatus.

Occurs in the southern Great Lakes region and Midwest; much habitat has been lost as a result of human activities and natural succession, resulting in population reduction and fragmentation.

Range extends from southern Ontario and western New York west across Michigan and southern Wisconsin to southeastern Minnesota, eastern Iowa, and eastern Missouri, south to southern Illinois, central Indiana, southern Ohio, and western Pennsylvania; a disjunct population exists at the eastern end of Michigan's Upper Peninsula (Conant and Collins 1991). Subspecies catenatus may intergrade with subspecies tergeminus in north-central Missouri (Beltz, in Johnson and Menzies 1993, which see for further details). The historical range in Canada extended throughout the mesic prairie and wetlands that formerly were common in southwestern and west-central Ontario (Johnson and Menzies 1993).

Recent evidence (see Szymanski 1998) indicates that massasaugas in all of Missouri and Iowa likely represent subspecies catenatus (eastern massasauga), so all populations north and east of the Missouri River probably should be regarded as S. c. catenatus. This is the circumscription used by the USFWS (2009) for the eastern distinct population segment of Sistrurus catenatus.

Szymanski (1998) determined that this snake is extant in 236 "sites," which represent an unknown but much smaller number of distinct occurrences.

Loss, destruction, or modification of habitat (the primary threat factor ranked here) is affecting at least 50 populations rangewide. A few examples (from USFWS 2009) are as follows. In Illinois, the Des Plaines River Valley population continues to be fragmented into smaller subpopulations isolated by development or otherwise unsuitable habitat (Mierzwa 1993). In Michigan, a major residential development, at the Green/Union Lakes site in Oakland County, Michigan, recently eliminated much of and severely degraded the remaining habitat (Legge 1996). At Wixom, Michigan, both wetland and upland habitat were recently degraded by agricultural practices and highway construction (Legge 1996). Similarly, in Bremer County, Iowa, a golf course is encroaching upon massasauga habitat (Christiansen 1993). In Wisconsin, cranberry operations are potential threats to massasauga populations (Cathy Carnes, U.S. Fish and Wildlife Service, in litt., 1997). In Pennsylvania, four companies applied for sand and gravel mining permits in areas supporting massasauga populations (Andrew Shiels, Pennsylvania Fish & Boat Commission, in litt., 1997). More recently, a sizeable area that included hibernation and gestation habitat in Pennsylvania was converted from grassland to row-crop agriculture (Benjamin Jellen, St. Louis University, pers. comm., 2008, cited by USFWS 2009). One of Ohio's largest populations (Killdeer Plains) was bulldozed and plowed under in 1994. In addition, urban encroachment has disrupted the natural disturbance processes (such as hydrological cycles and fire frequency), and subsequently, changes in habitat structure and vegetative composition have occurred. For example, in Pennsylvania, woody vegetation was cited as a threat at 75 percent of the massasauga sites surveyed (Reinert and Bushar 1993). Furthermore, loss of suitable habitat area may be occurring where invasive woody vegetation is altering the vegetative structure of massasauga habitat, even at some protected sites (USFWS 2009).

The over-harvesting of massasaugas is well documented, and the pernicious effects of past anti-rattlesnake campaigns are still visible today. Several populations have been harvested beyond a recoverable threshold and are functionally extinct. Intentional killing and illegal collection continue. Recent law enforcement actions involving individuals from several states revealed the immediacy and magnitude of this threat. An Indiana Department of Natural Resources law enforcement investigation in 1998 uncovered a well-organized, multi-state effort to launder state-protected reptile species (including eastern massasauga). The investigation concluded with the indictment of 40 defendants.

Predation under natural conditions is not a notable threat. However, with habitat loss, many populations have become small and isolated and so are more sensitive to predation (and to losses from road mortality or direct persecution). Further, the biology of the species makes females most susceptible, which exacerbates the impacts of predation. The thermoregulatory needs of the gravid females render them most vulnerable to collection and predation. This implies that populations occurring at low densities are particularly sensitive to collection or predation (i.e., predation/collection of just a few individuals could greatly diminish the population's reproductive potential). Similarly, a Population Viability Analysis (PVA) indicated that populations are most sensitive to adult mortality. Given the species' low biological replacement rate, even small increases in adult mortality can precipitate irreversible declines. These biological traits and the threat factors synergistically interact, which exacerbates the effects of individual factors and can lead to an extinction vortex for those populations affected by one or more factors.