Crotalus horridus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Reptilia Squamata Viperidae

Scientific Name: Crotalus horridus
Species Authority: Linnaeus, 1758
Common Name(s):
English Timber Rattlesnake

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2007
Date Assessed: 2007-03-01
Assessor(s): Hammerson, G.A.
Reviewer(s): Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)
Listed as Least Concern in view of its very wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

Geographic Range [top]

Range Description:This species ranges widely in the United States, ranging marginally into southern Canada (where it is extinct). Its range extends from central New England to northern Florida, and west to eastern Texas, central Oklahoma, eastern Kansas, southeastern Nebraska, southern and eastern Iowa, and southeastern Minnesota (Martin, in Tyning 1992; Ernst and Ernst 2003; Campbell and Lamar 2004). The distribution is spotty along the western and northern edges of the range. Sizeable populations still occur in the Appalachian Mountains from Pennsylvania though the Virginias, across eastern Kentucky and Tennessee to northeastern Alabama, in the Ouachita and Boston mountains of Arkansas and extreme eastern Oklahoma, in heavily wooded sections of the southeastern Coastal Plain from North Carolina to northeastern Florida and west to Louisiana and southern Arkansas, and in the Piedmont in the Uwharrie National Forest of central North Carolina and Pine Mountain of west-central Georgia (Martin in Tyning 1992). See Martin (in Tyning 1992) for a detailed range map and further details on current known distribution. Dens occur at elevations of up to about 5,000 feet in the southern Appalachians, 2,200 feet in southern New England, and about 1,300 ft in northeastern New York, Wisconsin, and Minnesota; individuals may range to higher elevations in summer (Martin in Tyning 1992).
Countries occurrence:
United States
Regionally extinct:
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:This species is represented by a large number of occurrences (see Martin in Tyning 1992), though most may not represent populations that are viable in the long term. The adult population size is unknown but presumably exceeds 100,000. This snake is still fairly common in some parts of its range. The Canadian population in southern Ontario is extinct, having been last recorded in 1941. It is declining or extirpated in all northeastern states. In New York, it is extirpated at 26% of historically known dens, nearly extirpated at another 5% (Stechert in Tyning 1992). The population in central Connecticut is declining slowly (Fritsch, in Tyning 1992). It survives in at least five population clusters in Massachusetts (French, in Tyning 1992) and just a few in Connecticut (Klemens 1993). One population is known to be extant in New Hampshire (Taylor and Soha, in Tyning 1992), two in Vermont (DesMeules, in Tyning 1992). It is extirpated in Rhode Island (Raithel, in Tyning 1992) and apparently also in Maine (Hutchinson and Hunter, in Tyning 1992). There has been a 50 to 66% loss of known populations in southern New Jersey (Zappalorti and Reinert, in Tyning 1992). It is extirpated in about half of the counties in which it was recorded in Ohio (Wynn, in Tyning 1992). It has declined substantially in Minnesota (Keyler and Oldfield, in Tyning 1992). No careful mark-recapture population estimates have yet been published. One long-term study (W.S. Brown, northeastern New York) will provide such estimates after several more years of field work. What has been clear to date is the difficulty of recapturing individuals other than gravid females regularly. This problem may cause violation of an important sampling assumption of equal catchability of all sizes and age classes, an assumption necessary for population estimates to be valid. Brown (unpubl. data) has recaptured many snakes after long lapses (up to nine years) and it remains to be seen how the problem of inconsistent recaptures will affect calculations. From earliest settlement of the North American continent, hunting rattlesnakes at their dens became a regular habit of many pioneers. Babcock (1929) commented: "It is probably only a matter of time when the timber rattlesnake in New England will share the fate of the passenger pigeon." Recognizing the scarcity of objective data to show trends in numbers, an overall consensus among virtually all scientists and field observers is that the timber rattlesnake indeed is declining over most parts of its range. The first major recent warning was published by Galligan and Dunson (1979) who, on the basis of counts of snakes turned in by snake hunters and on interviews with them at a number of local community-sponsored rattlesnake hunts in Pennsylvania, documented severe declines in timber rattlesnake numbers. Stechert (1982) summarized factors in the historical decline in New York. Brown (1984, 1988) suggested denning populations in New York have been reduced by 50 to 75% of their historical numbers. Martin (1982) stated that most long-term observers feel that most dens are at 15% to 20% levels compared to 40 years ago. Its area of occupancy, number of subpopulations, and especially population size are probably still declining, possibly at a rate of more than 10% over three generations (roughly 20 to 30 years).
Current Population Trend:Decreasing
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:In the northeast, this species inhabits mountainous or hilly deciduous or mixed deciduous-coniferous forest, often with rocky outcroppings, steep ledges, and rock slides (Petersen and Fritsch 1986, Brown 1993). In the upper midwest, this snake occurs on steep rocky bluffs and bluff prairies with oaks (Breckenridge 1944, Oldfield and Keyler 1989, Vogt 1981). In the central midwest, optimum habitat is a high, dry ridge with oak-hickory forest interspersed with open areas (Minton 1972), and "deciduous forest, especially along hilltop rock outcrops in thick woods" (Fitch 1958). In the south, preferred habitat is "hardwood forests of the type found in Loess Bluff and in many river bottoms" (Cook 1943), swampy areas and floodplains (Mount 1975), wet pine flatwoods, river bottoms and hydric hammocks (Ashton and Ashton 1981), and hardwood forests and cane fields of alluvial plain and hill country (Dundee and Rossman 1989). Fogell et al. (2002) documented a relatively high level of agricultural field use at the western edge of the range in Nebraska. Activity is primarily terrestrial, but timber rattlesnakes sometimes climb into vegetation (see Fogell et al. (2002). Hibernacula are typically located in a rocky area where underground crevices provide retreats for overwintering, such as a fissure in a ledge, a crevice between ledge and ground, talus (rock slide) below a cliff, open skree slope (fallen rocks not associated with a cliff), or fallen rock (talus or skree) partly covered by soil (Martin 1989). At least in the northeastern part of the range (Reinert 1984, Reinert and Zappalorti 1988, Hammerson and Lemieux 2001), males and non-gravid females are primarily forest dwellers and gravid females use open, sparsely forested sites. Similarly, in Wisconsin Keenlyne (1972) reported gravid females using flat slab rocks and grassy, open slopes. This open habitat was not used by males or nongravid females. "Transient habitat" a somewhat arbitrary category, generally is within 200 m of a den. It tends to be broken by the rough topography and rocky terrain near the den site and supports more open woodland with exposed clearings and shelter rocks. This habitat occurs on outcrop knolls (Brown 1989) used as "stop-over" basking locations by rattlesnakes migrating away from a den in spring. This habitat also is used by gravid females during their reproductive year.

Threats [top]

Major Threat(s): Summary of primary threats: loss of habitat; habitat fragmentation and isolation of populations, which may become small and nonviable; and direct mortality caused by humans (including illegal snake hunters) and vehicles as habitat is encroached upon by urban/residential development (Brown in Tyning 1992, Brown 1993).

1. HABITAT DESTRUCTION: In states where the snake is legally protected, housing developments near rattlesnake dens are causing the most serious problem. Current laws generally do not mandate habitat protection for endangered or threatened species. In some areas, persons encountering rattlesnakes in new developments have cooperated with protection efforts by calling persons authorized to catch and transport live rattlesnakes. This is an important factor in successfully protecting rattlesnake populations near developments.

2. MARKET HUNTING: Bounty systems have caused a high level of deleterious exploitation and significant reduction or extirpation of populations by a mere handful of people (W.S. Brown unpubl. data). In some areas (e.g., Pennsylvania) bounty hunting led to rattlesnake hunting among the general population and became a major outdoor activity promoted by sports and civic groups. Commercial collecting for the pet trade is an ever-present current threat, despite some decline in recent years. Single individuals have been responsible for removal of several thousand snakes (Stechert 1980). Today, a growing number of persons maintain reptiles in private collections. Timber rattlesnakes, beautiful and easily kept in captivity, are much sought-after. Private collectors are supplied by an often illicit network of collectors, dealers, and buyers.

3. SNAKE HUNTING FOR "SPORT," ORGANIZED SNAKE HUNTS OR "ROUND-UPS." In Pennsylvania, organized snake hunts caused injury and cruelty to captured snakes, displacement from familiar range, removal of gravid females from already-depleted populations, and habitat destruction by snake hunters (Galligan and Dunson 1979, Reinert 1988). Despite regulations, timber rattlesnake populations in Pennsylvania were legally "harvested" at a nonsustainable level, leading to the collapse of most den populations (Martin et al. 1990). In response, Pennsylvania regulations were amended such that the open season extends from the second Saturday in June through July 31, with daily bag limit of one snake. These regulations should protect snakes at den sites, prevent stockpiling of snakes, and discourage rattlesnake hunting altogether.

4. SHADING-OVER: In some regions, several investigators believe that "shading over" by the growth of large trees on and near a den may be causing conditions that are incompatible with long-term viability for timber rattlesnakes. According to this view, there is a need for an open, lightly wooded or brushy early successional plant association to provide an optimal denning environment. In contrast, Martin (pers. comm. 1990) says: "Shading over of the den site does not present a problem for snakes at emergence time when the trees are bare or just starting to leaf. The problem is shading over of the rocks that are used as gestating and birthing rookeries." Similarly, in Connecticut, G. Hammerson (pers. obs.) found that heavy shading (in summer) did not discourage den use, but he observed reduced use of a gestation/birthing site after it was shaded by growing vegetation. The possible threat of shading-over deserves further study, but it seems likely that shading has temporary, localized effects that are insignificant over the long term on a landscape scale.

5. LOGGING: Commercial tree removal may not necessarily cause long-term harm to a timber rattlesnake population's habitat, but can pose a direct threat to the snakes if conducted during the active season (mainly April-October).

6. ROAD MORTALITY: New Jersey Pine Barrens populations suffer from excessive mortality of gravid females due to vehicular traffic on roads and trails (Zappalorti and Reinert in Tyning 1992). Ill-placed developments and associated new roads and increased traffic can lead to increased mortality of rattlesnakes even in areas several miles from the development.

Conservation Actions [top]

Conservation Actions: At least several occurrences are protected. Protection needs: 1) protect all known denning areas and adequate surrounding foraging habitat (generally a radius of about 1.5 to 2.5 miles from the den site) (see Brown 1993); 2) foster protection through public education; and 3) do not reveal den locations to the general public or unknown persons.

Citation: Hammerson, G.A. 2007. Crotalus horridus. The IUCN Red List of Threatened Species 2007: e.T64318A12765920. . Downloaded on 17 January 2017.
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