- Linnaeus, 1758
Other English Common Names: timber rattlesnake
Taxonomic Status: Accepted
Related ITIS Name(s):
Crotalus horridus Linnaeus, 1758 (TSN 174306)
French Common Names: crotale des bois
Unique Identifier: ELEMENT_GLOBAL.2.100455
Element Code: ARADE02040
Informal Taxonomy: Animals, Vertebrates
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference: Collins, J. T. 1990. Standard common and current scientific names for North American amphibians and reptiles. 3rd ed. Society for the Study of Amphibians and Reptiles. Herpetological Circular No. 19. 41 pp.
Concept Reference Code: B90COL01NAUS
Name Used in Concept Reference: Crotalus horridus
Taxonomic Comments: Pisani et al. (1972) examined morphological variation in primarily the midwestern portion of the range and concluded that the recognition of subspecies is not warranted. Brown and Ernst (1986) examined mostly eastern specimens and concluded that the upland and lowland forms (subspecies horridus and atricaudatus, respectively), are taxonomically distinct, at least in the portion of the range east of the Appalachians. Clark et al. (2003) examined mtDNA variation and found that distinct mtDNA lineages are evident, but the divergences are not deep and the lineages do not correspond with the traditional subspecies. No subspecies recognized by Crother et al. (2008).
Global Status: G4
Global Status Last Reviewed: 24Feb2014
Global Status Last Changed: 29Sep1997
Rounded Global Status: G4 - Apparently Secure
Reasons: Large range in the eastern United States, but occurrence is spotty in most regions; most populations have been depleted or exterminated by humans, and most are declining.
Nation: United States
National Status: N4
National Status: NX
U.S. & Canada State/Province Status
Alabama (S5), Arkansas (S4), Connecticut (S1), District of Columbia (SH), Florida (S3), Georgia (S4), Illinois (S3), Indiana (S2), Iowa (S3), Kansas (S3), Kentucky (S4), Louisiana (S3S4), Maine (SX), Maryland (S3), Massachusetts (S1), Minnesota (S2), Mississippi (S5), Missouri (S3S4), Nebraska (S1), New Hampshire (S1), New Jersey (S1), New York (S3), North Carolina (S3), Ohio (S1), Oklahoma (S3), Pennsylvania (S3S4), Rhode Island (SX), South Carolina (SNR), Tennessee (S4), Texas (S4), Vermont (S1), Virginia (S4), West Virginia (S3), Wisconsin (S2S3)
Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: XT
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Extirpated
Comments on COSEWIC: Designated Extirpated in May 2001. Status re-examined and confirmed in November 2010.
IUCN Red List Category: LC - Least concern
NatureServe Global Conservation Status Factors
Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: The 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 Lamaer 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).
Number of Occurrences: 81 to >300
Number of Occurrences Comments: 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.
Population Size: 100,000 to >1,000,000 individuals
Population Size Comments: Adult population size is unknown but presumably exceeds 100,000. This snake is still fairly common in some parts of its range.
Number of Occurrences with Good Viability/Integrity: Many to very many (41 to >125)
Overall Threat Impact: High
Overall Threat Impact Comments: 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 (1990, pers. comm.) 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, 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.
Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Area of occupancy, number of subpopulations, and especially population size probably are still declining, possibly at a rate of more than 10 percent over three generations (roughly 20-30 years).
Long-term Trend: Decline of 30-50%
Long-term Trend Comments: Declining or extirpated in all northeastern states. In New York, extirpated at 26% of historically known dens, nearly extirpated at another 5% (Stechert, in Tyning 1992). Population in central Connecticut is declining slowly (Fritsch, in Tyning 1992). 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). Extirpated in Rhode Island (Raithel, in Tyning 1992) and apparently also in Maine (Hutchinson and Hunter, in Tyning 1992). There has been a 50-66% loss of known populations in southern New Jersey (Zappalorti and Reinert, in Tyning 1992). Extirpated in about half of the counties in which recorded in Ohio (Wynn, in Tyning 1992). 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 forty years ago.
Intrinsic Vulnerability: Highly vulnerable
Other NatureServe Conservation Status Information
Inventory Needs: Most population locations are relatively well known, but the current condition of many populations is uncertain and should be ascertained.
Protection Needs: Protect all known denning areas and adequate surrounding foraging habitat (generally a radius of about 1.5-2.5 miles from the den site) (see Brown 1993). Foster protection through public education. Do not reveal den locations to the general public or unknown persons.
(200,000-2,500,000 square km (about 80,000-1,000,000 square miles))
The 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 Lamaer 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).
U.S. States and Canadian Provinces
Endemism: occurs (regularly, as a native taxon) in multiple nations
U.S. & Canada State/Province Distribution
AL, AR, CT, DC, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, ME, MN, MO, MS, NC, NE, NH, NJ, NY, OH, OK, PA, RI, SC, TN, TX, VA, VT, WI, WV
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted.
Range Map Compilers: NatureServe, 2005
U.S. Distribution by County
||County Name (FIPS Code)
New Haven (09009)*,
New London (09011)
Des Moines (19057),
Van Buren (19177)
Jo Daviess (17085),
La Salle (17099)*,
New Hanover (37129),
Red River (48387),
Chesapeake (City) (51550),
Hampton (City) (51650),
Newport News (City) (51700),
Suffolk (City) (51800),
Virginia Beach (City) (51810),
La Crosse (55063),
St. Croix (55109),
* Extirpated/possibly extirpated
U.S. Distribution by Watershed
||Watershed Name (Watershed Code)
Piscataqua-Salmon Falls (01060003)+*,
Upper Connecticut-Mascoma (01080104)+*,
Middle Connecticut (01080201)+,
Lower Connecticut (01080205)+,
Middle Hudson (02020006)+,
Lower Hudson (02030101)+,
Upper Delaware (02040101)+,
East Branch Delaware (02040102)+,
Middle Delaware-Mongaup-Brodhead (02040104)+,
Middle Delaware-Musconetcong (02040105)+,
Upper Susquehanna (02050101)+,
Upper Susquehanna-Tunkhannock (02050106)+,
Upper Susquehanna-Lackawanna (02050107)+,
Upper West Branch Susquehanna (02050201)+,
Middle West Branch Susquehanna (02050203)+,
Bald Eagle (02050204)+,
Lower West Branch Susquehanna (02050206)+,
Lower Susquehanna-Penns (02050301)+,
Upper Juniata (02050302)+,
Lower Juniata (02050304)+,
Lower Susquehanna-Swatara (02050305)+,
Lower Susquehanna (02050306)+,
South Branch Potomac (02070001)+,
North Branch Potomac (02070002)+,
Upper James (02080201)+,
Lower James (02080206)+,
Hampton Roads (02080208)+
Upper Dan (03010103)+,
Pamlico Sound (03020105)+,
Upper Neuse (03020201)+,
New River (03020302)+,
Lower Cape Fear (03030005)+,
Northeast Cape Fear (03030007)+,
Upper Yadkin (03040101)+,
South Yadkin (03040102)+,
Lower Yadkin (03040103)+,
Upper Pee Dee (03040104)+,
Rocky, North Carolina, (03040105)+,
Upper Catawba (03050101)+,
South Fork Catawba (03050102)+*,
Upper Broad (03050105)+,
South Carolina Coastal (03050202)+,
St. Marys (03070204)+,
Upper Suwannee (03110201)+,
Lower Suwannee (03110205)+,
Santa Fe (03110206)+,
Upper Genesee (04130002)+,
Lower Genesee (04130003)+*,
Mettawee River (04150401)+,
Otter Creek (04150402)+*,
Lake Champlain (04150408)+
Upper Allegheny (05010001)+,
Middle Allegheny-Tionesta (05010003)+,
Middle Allegheny-Redbank (05010006)+,
Tygart Valley (05020001)+,
Lower Monongahela (05020005)+,
Upper New (05050001)+,
Middle New (05050002)+,
Upper Kanawha (05050006)+,
Lower Scioto (05060002)+,
Ohio Brush-Whiteoak (05090201)+,
Middle Ohio-Laughery (05090203)+*,
Middle Wabash-Little Vermilion (05120108)+,
Middle Wabash-Busseron (05120111)+*,
Lower Wabash (05120113)+*,
Little Wabash (05120114)+*,
Upper White (05120201)+,
Lower White (05120202)+,
Upper East Fork White (05120206)+,
Lower East Fork White (05120208)+,
Silver-Little Kentucky (05140101)+,
Lower Ohio-Bay (05140203)+,
Lower Ohio (05140206)+*
Upper French Broad (06010105)+,
Upper Little Tennessee (06010202)+,
Lower Little Tennessee (06010204)+*,
Lower St. Croix (07030005)+,
La Crosse-Pine (07040006)+,
Lower Chippewa (07050005)+,
Upper Iowa (07060002)+,
Grant-Little Maquoketa (07060003)+,
Lower Wisconsin (07070005)+,
Lake Red Rock (07100008)+,
Lower Des Moines (07100009)+,
The Sny (07110004)+*,
Lower Illinois-Senachwine Lake (07130001)+*,
Lower Illinois (07130011)+,
Upper Mississippi-Cape Girardeau (07140105)+,
Big Muddy (07140106)+,
Keg-Weeping Water (10240001)+*,
South Fork Big Nemaha (10240007)+,
Big Nemaha (10240008)+*,
Middle Big Blue (10270202)+,
Lower Big Blue (10270205)+,
Lower Little Blue (10270207)+
Lake Texoma (11130210)+,
Bois D'arc-Island (11140101)+,
Lake Fork (12010003)+,
Lower Trinity-Tehuacana (12030201)+,
Lower Trinity-Kickapoo (12030202)+,
Lower Brazos-Little Brazos (12070101)+,
Lower Colorado-Cummins (12090301)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
Basic Description: A venomous snake (rattlesnake); adults usually are about 90-152 cm long.
General Description: Horny rattle or button on end of tail; pupil of eye vertical in bright light; numerous small scales on top of head; head much broader than neck; pit on each side of face between (but lower than) eye and nostril; color pattern varies geographically but almost always has dark crossbands; background color usually yellow, black, or gray, sometimes with a reddish stripe along the middle of the back. Total length seldom exceeds 150 cm, never exceeds 200 cm.
Diagnostic Characteristics: In areas where no other rattlesnakes of the genera Crotalus (rattlesnakes proper) or Sistrurus (pygmy rattlesnakes) occur, this snake may be distinguished by its rattle. It differs from harmless snakes of similar appearance by having a pit on each side of the face infront of and below the eye. Petersen and Fritsch (1986) provided color photographs and scale diagrams of harmless species commonly mistaken for the timber rattlesnake. One of these species, the milk snake (Lampropeltis triangulum), is slender and has skin that may be described as smooth, shiny, or glossy. In contrast, the timber rattlesnake is heavy-bodied with, keeled scales; overall, a rattlesnake's skin appears coarse-textured, velvety, or dull. Two other species, the northern water snake (Nerodia sipedon), and the astern hognose snake (Heterodon platirhinos), although having keeled scales and a dull texture, lack the distinguishing characteristics of a rattlesnake.
Reproduction Comments: Mating occurs in summer, early or mid-July through late September in Virginia, New York, and Connecticut (Martin 1992, Brown 1995, Hammerson and Lemieux 2001). Young are born usually August-early October. Females reproduce at intervals of 2-5 years (but minimum interval is 3 years in northeastern New York) (Gibbons 1972; Keenlyne 1978; Galligan and Dunson 1979; Fitch 1985; Martin 1988, 1993); the interval may average 3 years in many areas). About 10-75% of the adult females are gravid in a given year (Brown 1991, Martin 1993). Age of first reproduction in females has been reported in several studies as follows: four years in Wisconsin and Kansas (Keenlyne 1978, Fitch 1985), five years in Pennsylvania (Galligan and Dunson 1979), six years in South Carolina (Gibbons 1972), 5-11 years (mean about 8) in northwestern Virginia and vicinity (Martin 1993), and 7-11 years in northeastern New York (Brown 1991, 1993). Litter size varies geographically, as summarized by Fitch (1985) (area, mean, range): northeastern (New York), 9.3, 4-14; northwestern (Wisconsin), 8.4, 3-11; west-central (Kansas), 8.5, 5-14; southeastern (South Carolina), 12.6, 10-16. A combined picture of the reproductive pattern is low-frequency birthing and delayed age of first reproduction.
It should be noted that, as in morphological characteristics and habitat, life history characteristics vary geographically. With longer active season lengths and warmer climates, southern populations of C. horridus may grow faster, mature earlier, and reproduce more frequently than do northern populations. There also is an indication that litter size is larger in southern than in northern populations.
Maximum longevity in northern New York is about 20-25 years (Brown 1991). A captive lived almost 37 years (Cavanaugh, 1994, Herpetol. Rev. 25:70).
Ecology Comments: Timber rattlesnakes in northern and upland areas commonly hibernate communally. The largest aggregations include about 200 individuals; most are much smaller, typically less than 60. Lowland populations overwinter singly or in small groups.
In areas where communal denning occurs, maximum individual range length, determined by radio-telemetry for complete or nearly complete active seasons in New Jersey and Connecticut, was as follows: 1.9-3.6 km (mean 2.4-2.7 km) in adult males, 0.5-2.6 km (mean 1.1-1.3 km) in nongravid adult females, and 0.3-2.0 (mean 0.8-1.2 km) in gravid females (Reinert and Zappalorti 1988, Hammerson and Lemieux 2001).
These snakes incur a high rate of mortality in their first year. Populations cannot withstand high rates of adult mortality.
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: Timber rattlesnakes migrate seasonally between hibernacula and summer habitat. Individuals rarely may migrate up to 7.2 km from their hibernaculum (Brown 1993), but extensive radio-telemetry data for populations in New Jersey (Reinert and Zappalorti 1988) and Connecticut (Hammerson and Lemieux 2001) indicate that males generally stay within 3.6 km of their hibernaculum and females range no farther than 2.3 km.
Neonates evidently find hibernacula by scent-trailing adults (Brown and MacLean 1983, Reinert and Zappalorti 1988, Hammerson and Lemieux 2001).
Palustrine Habitat(s): FORESTED WETLAND, Riparian, SCRUB-SHRUB WETLAND
Terrestrial Habitat(s): Bare rock/talus/scree, Cliff, Forest - Conifer, Forest - Hardwood, Forest - Mixed, Shrubland/chaparral, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Special Habitat Factors: Burrowing in or using soil, Fallen log/debris
Habitat Comments: 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 nongravid 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.
Adult Food Habits: Carnivore
Immature Food Habits: Carnivore
Food Comments: Primary food is small mammals, but in the southern part of the range the diet also commonly includes lizards. Sometimes eats birds, bird eggs, and other small animals. Individuals may ambush prey traveling on fallen logs (Reinert et al. 1984). Little or no feeding is done by gravid females (Reinert and Zappalorti 1988).
Adult Phenology: Circadian, Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Immature Phenology: Circadian, Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Phenology Comments: Seasonal cycle may be summarized follows for three areas, western Virginia (Martin 1989), northeastern New York (Brown 1989), and central Connecticut (Hammerson and Lemieux 2001): general emergence, 18 April-12 May in Virginia, 7 May-21 May in New York, mid-April to early May in Connecticut general ingress, 1 October-21 October in Virginia, 14 September-1 October in New York, mainly mid-September to late October in Connecticut.
In the south, C. horridus has a longer active season (late spring, summer, and early autumn) than a hibernating season, whereas in the north the hibernating season exceeds the active season in length. In South Carolina, few are seen before mid-May in most years, active as late as November; most often encountered in early evening and at night (Gibbons and Semlitsch 1991). In Florida and Texas, spends 2-3 months at overwintering dens but occurs on the surface during warm periods throughout the winter (Martin, in Tyning 1992).
Activity is primarily diurnal in spring and fall, more crepuscular/nocturnal in summer.
Timber rattlesnakes add a segment to the rattle each time they shed. Adults shed 1-2 times each year, juveniles more frequently.
Length: 189 centimeters
Economic Comments: Venomous but not aggressive, defensive if disturbed; human fatalities have resulted from bites (Ernst 1992).
Stewardship Overview: The timber rattlesnake is a long-lived and slow-maturing ectothermic vertebrate. It has a low reproductive rate and a relatively long mean generation time. These demographic traits are the main reasons why recovery of depleted populations will be slow. Many populations have been exterminated since colonization of the North American continent, and most remaining denning colonies have been reduced drastically in numbers through organized snake hunting and commercial collecting for the exhibit and net trades. The chief threat today is land development and habitat destruction.
The spatial and seasonal biology are centered on its den, where an entire population undergoes communal hibernation through the winter months. The snakes are seasonally migratory, moving away from their den in spring and back to it in autumn. Protecting a viable population depends on protecting the den itself as well as adequate areas of habitat around the den. Males use a home range area of approximately 500 acres, nongravid females of 100 acres. Protecting an area of 2.5 miles in radius around a den (19.6 square miles total area) is recommended as necessary to safeguard a timber rattlesnake population. A 1.5-mile radius (seven square miles total area) will protect most females, but may not be adequate for protection of the entire population. A circular area may not be strictly required in all cases, as certain migration directions and elevations may be preferred over others.
The main ways to manage and safeguard known populations of this species are: (1) Protecting the snake at its known denning colonies through vigilance; (2) Maintaining Secrecy by not revealing to anyone localities of den sites; (3) Avoiding Disturbance of the snakes by restricting or preventing humans from visiting dens and transient habitats; (4) Patrolling the area during vulnerable times, particularly the spring emergence period and the summer gestating and birthing period; and (5) Vegetation thinning to prevent shading-over at some den sites.
Restoration Potential: There have been no studies of population dynamics, and no quantitative data to document actual recovery potential. What follows is speculative, but based on sound biological intuition.
Most workers with good knowledge believe depleted populations can recover. The exact minimum viable population size and timing of this recovery are unknown. Minimum population size needed for recovery probably must consist of at least 30 to 40 adults, with at least four or five mature females. Given the late age of maturity and slow rate of reproduction, recovery probably would require many years. If such a small population were completely protected, it might gradually build up to an average den size of 60 to 100 animals with a representative age distribution within twenty to thirty years.
Martin (1990, pers. comm.) reports the following: "One den that had been depressed to about 50 to 60 snakes in 1968 by hunting pressure, had climbed to about 120 to 130 snakes in 1983 [a 15-year interval]." Martin (in Tyning 1992) believed that a minimum of 8 adult females was needed for a population to be viable.
Preserve Selection & Design Considerations: An adequate area of undisturbed summer range habitat surrounding a timber rattlesnake den is vitally important for protecting a viable population. A 1.5-mile radius of protected habitat around a den is adequate for females, but an additional protected zone of one mile beyond this is recommended to accomodate the greater dispersal distances of adult males, which not uncommonly range up to approximately 2.5 miles from their den. This zone extending from 1.5 to 2.5 miles from the den buffer zone might be habitat of lesser quality or it might contain some human incursion. This additional area, even if it consists of moderately disturbed habitat will offer additional protection to the population. Although a 2.5-mile migratory distance as a measure of radial protection from a den applies to many populations, in some areas and at some dens this distance may be less than the distances moved by many snakes in the population. Each specific area should be studied in detail to ascertain the patterns of movements of migrating rattlesnakes. In general, as a working recommendation, an area within 2.5 miles of a den seems critical for protecting most timber rattlesnake populations studied to date.
In many areas it may be impossible to obtain an unbroken circular tract of land around a den, and it also may not be biologically realistic in terms of the snakes' movement patterns. Some populations apparently use "corridors" for their migrations in certain directions, thus making some segments of habitat far more heavily used than others. Timber rattlesnakes seem to avoid difficult sheer ledges that may rim one side of a den, and, where dens are at a lower elevation than summer range, most of the snakes tend to go upslope to areas of higher elevation. Home ranges may be often non-overlapping, or may occur in separate areas of the available habitat, and rattlesnakes may shift their activity areas from one year to the next (W. S. Brown, unpubl. obs.; Hammerson and Lemieux 2001), so known data from short-term studies should not be the basis for truncating the protected zone.
Management Requirements: Specific management strategies include:
SECRECY: It is essential to never reveal the location of hibernating dens to anyone, except for valid reasons (e.g., research or protection). Local media and popular magazine writers, in particular, should not be given specific locality information. More than all other factors, it is this lapse of judgement on the part of those with this sensitive knowledge which has, over the years, led to massive exploitation.
AVOIDING DISTURBANCE: Timber rattlesnakes on their dens and in transient habitats are prone to being disturbed. Repeated visits to den sites or to specific "snake rocks" can put the normal behaviors of these snakes at risk of disruption. Repeated visits to particular rocks frequented by the snakes, and capturing or frightening them at such rocks, will cause abandonment. Thus, visits to den sites and to specific shelter rocks in transient habitats should be curtailed to avoid disturbing the snakes.
PATROLS: Rattlesnakes are especially vulnerable during spring emergence (April-May) and during gestating and birthing (July to mid-September). During these times closing off access to the den itself is an important action. Also, the researcher/manager may want to simply avoid disturbing the animals during these vulnerable periods unless these periods are being used to conduct specific counts for population estimates.
PREVENTING SHADING-OVER: One worker (A. Smith, Jr., pers. comm.) has actively managed one den area by selective removal of larger shade trees in the vicinity of a den. W. B. Allen (1990, pers. comm.) suggested an active management approach to the problem of shading-over: during winter months authorized personnel equipped only with saws could cut vegetation shading the den sites and drop shading trees downhill below the den; cut brush could be dropped at the base of the ledges and left there. However, it is important to note that not all agree that prevention of shading-over of dens is necessary or advisable in all circumstances.
LOGGING IN WINTER: In the vicinity of a den, logging should be restricted to the winter months of November through March where snake are hibernating. This will prevent the snakes' being killed by loggers.
ROAD CLOSURES AND PRUDENT LOGGING: For the New Jersey Pine Barrens, Zappalorti and Reinert (in Tyning 1992) recommended closing certain roads to vehicular traffic (to reduce kills of gravid females) and clearcutting blocks of forest between dens and roads (to provide suitable basking areas other than road sides).
FENCING: Fencing, though somewhat expensive, can be used effectivly to prevent encroachment of rattlesnakes into established vacation "camps" (Brown, in Tyning 1992). However, fencing can reduce or eliminate access to summer habitat and should not be used to facilitate new developments.
TRANSLOCATION: Translocation could be effective in restoring a viable population in historical sites that still have favorable habitat, but translocations of reptiles generally have had poor success; justification for such a project should be closely examined and any translocations should be closely monitored (Brown, in Tyning 1992). In Pennsylvania, Reinert and Rupert (1999) found that translocated snakes experienced lower survival and exhibited much greater movements than did resident individuals in the same area. The snakes did locate active hibernacula, apparently by following resident snakes. The authors did not recommend translocation as a standard conservation practice because of its immediate and long-term negative impacts. Hammerson believes that successful translocation and reestablishment of an extirpated population likely would require multi-year release of neonates at a historical den site.
Monitoring Requirements: Long-term monitoring is necessary to show population trends over time scales appropriate for long-lived species such as Crotalus horridus.
The most uniform procedures recommended for comparable monitoring between areas are: 1. Sighting Rate: for example, number of snakes detected per hour. 2. Capture Index: Trends may be shown over seasons, and between months, by calculating the number of snakes caught per capture day. A capture day is defined simply as any day on which at least one rattlesnake is caught (Brown 1989, 1991). An index of snakes seen/sighting day, or, in combination with total time spent in the field, an index of snakes seen/hr/person may be feasible.
Generally, most experienced field workers feel that under ideal weather conditions, 25% is about as large a proportion of the snakes that might be visible on the surface at any one time in any one place. Martin et al. (1990) estimated that during peak spring emergence usually only 5% to 15% of the population may be seen. In some populations, the percentage may be even smaller (G. Hammerson, pers. obs.).
Estimates of population sizes of dens have been made in several areas using a combination of the estimated proportions of the snakes visible on the surface, and repeated observations over a sampling period of several years. In their recent extensive survey of the timber rattlesnake in Pennsylvania, Martin et al. (1990) stated: "We believe that with two to four visits per year over four to five years it is possible to fairly accurately estimate the population of a den colony."
DEN ON SITE:
1. Spring Sampling: Counts of rattlesnakes seen on or near a den should be made at three-day intervals for about a three-week period during the snakes' peak emergence period (varies with latitude and elevation). A healthy den (30 to 100 individuals) should produce roughly eight to 15 individuals seen on at least several days.
2. Summer Sampling: Counts of gravid females may be made in August in transient habitat near a den. Although the frequency of females gravid varies widely from year to year (often 25%-75%), at least several females should be seen. One den of about 125 snakes (all age/size classes) consistently observed for ten years yielded 3-5 gravid females each year (W. S. Brown, unpubl. obs.), or perhaps 20 to 25% of the approximately 15 to 20 adult females believed to be present in this den population. In conducting visual sampling at such a den area, approximately four or five visits might be made, at weekly intervals or less, to achieve a reliable count of gravid females.
DEN OFF SITE:
1. Summer Sampling: Sampling summer range will not prove to be productive by standard snake-searching methods. Only occasionally will a rattlesnake turn up. But if spots occur that attract rattlesnakes, it is usually worth checking them. Sites such as rocky clearings, rock walls along roads or fields, rock piles, quarries, and cleared spots in housing developments are good candidates for locating a rattlesnake on summer range. Because of annual variation in use by rattlesnakes, these sites will require a 4-5-year period of monitoring to provide a realistic estimate of relative abundance.
2. Interviews with Local Residents: Where rattlesnake distributions are not well known, asking local people if they occasionally or regularly see (or kill) rattlesnakes is worthwhile . If their residences are within rattlesnakes' summer migratory range, at least one local resident will probably report that they do. About three residents living in proximity should be interviewed, and, if all report no sightings, very likely no rattlesnakes exist in the region.
See Sadighi et al. (1995, Herpetol. Rev. 26:189-190) for information on the use of a remotely triggered camera to monitor timber rattlesnakes.
Management Research Needs: Research is needed on the following:
(1) Quantitative data on population densities; mark-recapture estimates of population sizes of denning colonies including tests of assumptions of random sampling;
(2) Long-term comparative measures of population trends;
(3) Reproductive biology of females: age of first reproduction, reproductive frequency, litter size;
(4) Age-specific survivorship, particularly among newborn and in the first year;
(5) Factors causing mortality: Assessment of role of density-dependent and density-independent factors;
(6) Detailed seasonal movements of adults in communally denning populations;
(7) Mechanisms of den-finding in newborn; movement patterns of newborn from birth site to den;
(8) Ability of translocated or introduced rattlesnakes to "take to" and become established in a historical site or formerly extirpated den.
Use Class: Not applicable
Subtype(s): Birthing Area, Hibernaculum
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals in or near appropriate habitat where the species is presumed to be established and breeding.
MINIMUM EO CRITERIA for Feauture Label = HIBERNACULUM: These sub-occurrences are defined by any collection or reliable observation of one or more individuals in or immediately adjacent to a crevice probably used for overwintering, In the northern part of the range, individuals observed from March to early May and from late September through November generally (but not always) are at or near overwintering sites. Use of a site as a hibernaculum should be confirmed by multiple observations or ideally by information from radio-tagged individuals.
Separation Barriers: Consistently busy highway; highway with obstructions impassable to a snake; major river with strong, persistent current; urbanized area dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 7 km
Alternate Separation Procedure:
The following qualify as distinct occurrences: (1) occurrences based on hibernacula separated by more than 7 kilometers of suitable habitat from the nearest known hibernaculum (applies to northern populations that use communal hibernacula). A lesser distance can be used if radio telemetry data indicate than populations using different hibernacula less than 7 kilometers apart are separated by a distinct gap and are not likely to come into contact with one another; additionally, hibernacula more than 7 km apart are part of the same occurrence if the summer home ranges of populations from the two hibernacula are known to overlap); (2) occurrences separated by more than 7 kilometers of suitable habitat between observation sites for individuals of unknown hibernaculum origin or for populations in which communal denning does not occur; (3) occurrences separated by separated by more than 1 km of moderately unsuitable habitat (occasionally traverseable by low numbers of individuals).
Separation Justification: Brown (1993) reported that adult male C. horridus may move up to 7.2 kilometers from their hibernaculum, and females disperse up to 3.7 km, with mean maxima of 4.1 km and 2.1 km for males and females, respectively. Brown (1993) did not describe his methods, but the data evidently were based on recaptures of individuals marked by ventral scale clipping. Martin (1989) reported that rattlesnakes in Virginia were found up to 5.5-6 km from the nearest known den, with a mean of 2.5-2.8 km for large numbers of adult males, adult females, and juveniles found on roads, but these data may not accurately reflect actual migration distances because the hibernaculum was positively known for only a few individuals, and these few were not among the individuals that were farthest from a known den.
Long-distance movements of 5-7+ km from hibernacula reported by Brown (1993) and Martin (1992) have not been confirmed by radio-tracking methods. Intensive studies of radio-tagged individuals in New Jersey (Reinert and Zappalorti 1988) and Connecticut (Hammerson and Lemieux 2001) indicate that male timber rattlesnakes generally range less than 3.7 km from their hibernaculum, and females tend to disperse not more than 2.3 km. In accord with these data, maximum length of representative full-season activity areas for several radio-tracked C. horridus in Pennsylvania was less than approximately 2.6 km (Bushar et al. 1998: Figure 3). Other studies of radio-tagged C. horridus (Fitch and Shirer 1971, Galligan and Dunson 1979, Brown et al. 1982) yielded relatively small dispersal distances, but these data are not comparable to Reinert and Zappalorti (1988) and Hammerson and Lemieux (1991) because the studies encompassed less than two months of the active season or were based on translocated snakes not involved in normal behavior.
Nevertheless, radio-telemetry data for adult males and females support Martin¿s (1992) statement that individuals from hibernacula within 4 km of each other "can probably be considered as part of a breeding population as long as wooded corridors exist between them." In Connecticut, males found paired with females from different hibernacula had moved up to at least 3.6 km from their hibernaculum (Hammerson and Lemieux 2001). Existing radio-telemetry data do not support Martin¿s belief that "dens located within about 5-7 miles [8-11 km] of each other could be considered as part of a metapopulation because of occasional breeding by males and females from different dens while on distant summer range¿" Data of Reinert and Zappalorti (1988) and Hammerson and Lemieux (2001) suggest that individuals from hibernacula more than 6 km apart are unlikely to encounter one another. Evidence of genetic differentiation among populations in hibernacula within a few kilometers of each other (Bushar et al. 1998) also suggest that interbreeding between individuals from hibernacula 8-11 km apart is highly improbable. In Pennsylvania, Bushar et al. (1998) found that in general the genetic differences between hibernaculum populations reflected geographic distance between hibernacula, though gene flow between hibernacula also appeared to be influenced by structural habitat features such that relatively large genetic distances may occur between some hibernaculum populations that are within a few kilometers of each other.
SEPARATION JUSTIFICATION FOR FEATURE LABEL = HIBERNACULUM: Hibernacula separated by 300 m or more are likely to used over the short term by different groups of individuals. However, individuals in hibernacula separated by more than 300 m may use a common birthing area, suggesting that in such cases the populations should be combined as a single sub-occurrence (William H. Martin, pers. comm.). The value of 300 m is a somewhat arbitrary distance that seems to be practical for managing data for different hibernacula.
Separation distance for Birthing Area has not yet been determined.
Inferred Minimum Extent of Habitat Use (when actual extent is unknown): 3 km
Inferred Minimum Extent Justification: Inferred extent distance refers to hibernacula. In Connecticut, most individuals stayed within 3 km of their hibernaculum, but some males traveled up to 3.6 km from their wintering site (Hammerson and Lemieux 2001).
Author: Hammerson, G.
U.S. Invasive Species Impact Rank (I-Rank)
Not yet assessed
NatureServe Conservation Status Factors Edition Date: 08Sep2006
NatureServe Conservation Status Factors Author: Brown, W. S., P. Novak, and G. Hammerson
Management Information Edition Date: 06Feb2002
Management Information Edition Author: BROWN, WILLIAM S. EDITED AND REVISED BY G. HAMMERSON
Element Ecology & Life History Edition Date: 28Jan2010
Element Ecology & Life History Author(s): Brown, W. S., and G. Hammerson
Zoological data developed by NatureServe and its network of
natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).
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