COSEWIC Assessment and Status Report on the Timber Rattlesnake Crotalus horridus in Canada – 2001

Illustration of the Timber Rattlesnake (Crotalus horridus).

Extirpated – 2001

Table of Contents

Document Information

List of figures


Document Information

COSEWIC - Committee on the Status of Endangered Wildlife in Canada

COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:

Please note: Persons wishing to cite data in the report should refer to the report (and cite the author(s)); persons wishing to cite the COSEWIC status will refer to the assessment (and cite COSEWIC). A production note will be provided if additional information on the status report history is required.

COSEWIC. 2001. COSEWIC assessment and update status report on the Timber Rattlesnake Crotalus horridus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 24 pp.

Smith, Kim. 2001. COSEWIC status report on the Timber Rattlesnake Crotalus horridus in Canada, in COSEWIC assessment and status report on the Timber Rattlesnake Crotalus horridus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 1–24 pp.

For additional copies contact:

COSEWIC Secretariat
c/o Canadian Wildlife Service
Environment Canada
Ottawa, ON
K1A 0H3

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Cover illustration/photo:
Timber Rattlesnake -- ©Illustration by Marisa Bonofiglio, Woodbridge, Ontario.

© Her Majesty the Queen in Right of Canada, 2010.
Catalogue No. CW69–14/111–2002E–IN
ISBN 0–662–31880–3

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COSEWIC
Assessment Summary

Assessment Summary – May 2001

Common name
Timber Rattlesnake

Scientific name
Crotalus horridus

Status
Extirpated

Reason for designation
The Timber Rattlesnake once occupied much of the Niagara Escarpment and other regions of southern Ontario, but has not been seen in the province since 1941 despite intensive searches and its easy identification.

Occurrence
Ontario

Status history
Designated Extirpated in May 2001. Assessment based on a new status report.

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COSEWIC
Executive Summary

Timber Rattlesnake
Crotalus horridus

Description

The Timber Rattlesnake is a large venomous rattlesnake, characterized by yellow or brown coloring with dark brown or black V–shaped bands across the back. Adult sizes range from approximately one to two meters. The head is triangular with a distinct “neck”. As with all pit vipers, there is an opening visible between the eye and the nostril. Males are much longer and heavier than the females. Timber Rattlesnakes can be confused with Massasauga rattlesnakes and some non–venomous species, such as the fox snake. All non–venomous snakes lack the facial pit of the rattlesnakes. The Massasauga rattlesnake has nine large scales on its head, whereas the Timber Rattlesnake has many small scales on its head.

Distribution

This species was last sighted in Canada in 1941. Historically, the snake ranged throughout southern Ontario and southern Quebec. As there have been no recorded observations of the Timber Rattlesnake in almost 60 years, it is assumed not to exist in Canada.

Habitat

The ideal habitats for this rattlesnake are forested areas with rocky outcrops, dry ridges and second growth coniferous or deciduous forest. The winter habitat is primarily the den, which is located on a south facing rocky outcrop. In summer, the preferred habitat for males and non–pregnant females is a well–canopied forest with thick vegetation, whereas pregnant females prefer a more open forest with many fallen logs and a warmer climate. The estimated area needed for a viable population is 50 km².

General Biology

The Timber Rattlesnake is a “sit and wait” predator. The preferred prey is rodents and other small mammals; however, the snakes also eat carrion, reptiles, amphibians, and birds, and their eggs. Female snakes usually do not eat during gestation.

The snakes mate in late summer, with the birth of 5–13 snakelings occurring from late August to mid September. The females reproduce once about every three years. Male snakes mature at a mean age of 4 years, while females mature at a mean age of 6 years, depending on the location of the population. They can live up to 25 years, reaching their adult size by about 4–5 years.

Timber Rattlesnakes are heliothermic, meaning that they regulate their temperature through daytime basking. Though they are mostly active by day, during a hot summer they may also be active at night. The mean summer temperature of a Timber Rattlesnake is 26.9°C and the mean winter (hibernation) temperature is 10.0°C. In the northern part of their range, they hibernate from September to April (an average of 7.4 months) in communal dens. They are very loyal to their den site and will return year after year. They are seasonally migratory -- from the den site to the summer habitat and back again. Males migrate further than females, likely to search for mates.

The rattle is the most obvious behavior of these snakes, apparently used when the individual feels angry or threatened. In general, they are very mild–mannered and will not strike unless provoked. There is only a single recorded incident in Canada of a Timber Rattlesnake bite resulting in death -- a soldier in the Battle of Lundy’s Lane in 1814. Male snakes engage in “combat dances” with other males to determine dominance.

Population Size and Trends

There are no known populations of the Timber Rattlesnake in Canada and the last sighting was almost sixty years ago. It is therefore assumed that the size of the Canadian population of Timber Rattlesnakes is zero.

Limiting Factors and Threats

Populations of Timber Rattlesnakes are limited in the northern parts of their range by a small number of suitable nest sites. The snake is slow to mature, has few snakelings in each litter and a low juvenile survival rate. Taken together, these factors result in a small number of new individuals added to the population each year. Historically, they have been subject to human exploitation, such as bounty hunting, collection and sport hunting. Today, road accidents and human destruction of habitat (either directly or indirectly), and deliberate killing of venomous snakes all contribute to the Timber Rattlesnake’s population reduction.

Existing Protection

Each of the US states in which this snake is found affords the species some degree of protection, however, the level varies from state to state. The last state lifted the bounty on Timber Rattlesnakes in 1971. In Ontario, the Natural Heritage Information Center determined that the Timber Rattlesnake is extirpated, the chance of rediscovery being very small. In addition, it is designated as endangered by both the Ontario Ministry of Natural Resources’ Committee on the Status of Species at Risk in Ontario and the Ontario Endangered Species Act.

COSEWIC History
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.

COSEWIC Membership
COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.

Definitions (2010)

Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)
A wildlife species that no longer exists.

Extirpated (XT)
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A wildlife species facing imminent extirpation or extinction.

Threatened (T)
A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)*
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)**
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)***
A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

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COSEWIC Status Report on the Timber Rattlesnake Crotalus horridus in Canada – 2001.

Introduction

The Timber Rattlesnake, Crotalus horridus, is the only wide–ranging woodland rattlesnake of the deciduous forest biome of eastern North America (Brown, 1993) (See Fig. 1) The most common colour phases in the northern parts of its range are termed ‘yellow’ and ‘black’, because the dorsal pattern consists of dark brown or black, V‑shaped crossbands on a yellow, brown or black ground colour (Schmidt and Davis, 1941). Variations of these colour phases occur in the western and southern portions of its range (see canebrake rattlesnake, below) (Conant and Collins, 1991). Striped mutations and amelanistic partial albinos have also been recorded (Hudson and Carl, 1985; Dundee, 1994a). Although some authors believe that colour phases are sex related (Ditmars, 1907), others have suggested that the variation is a thermoregulatory adaptation, as black specimens occur with greatest frequency in mountainous regions (Schaeffer, 1969). Colour phases of newborns are readily distinguished after the first molt (Ibid.). Newborn Timber Rattlesnakes have yellow on the lateral and ventral surfaces of their tails, but are not thought to use their tails as “lures”, as do other juvenile snakes with similar colouration (Neill, 1960).

The head is roughly triangular and abruptly distinct from the neck (Anderson, 1965). The facial or loreal pit, which is present between the eye and the nostril on all pit vipers, functions in detecting the body heat of endothermic prey (Schmidt and Davis, 1941). The pupil of the eye is always vertically elliptical in the pit vipers, a feature associated with nocturnal habits (Ibid.).

Figure 1.  Distribution of the Timber Rattlesnake (Crotalus horridus) in North America. From Conant and Collins, 1991.

Map of the North American distribution of the Timber Rattlesnake.

The pit and the vertical nature of the pupil are characteristics that can be used to distinguish the Timber Rattlesnake from similarly patterned non–venomous snakes, such as the eastern fox snake (Elaphe gloydi)(Harding, 1997). To discriminate between timber and Massasauga rattlesnakes (Sistrurus catenatus), the number and size of the scales on the dorsal surface of the head can be informative. The Timber Rattlesnake has many small scales, whereas the Massasauga has nine large scales (Ibid.)

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Taxonomy

Until recently, southern populations of the Timber Rattlesnake were widely recognized as a separate subspecies, the canebrake rattlesnake (C. h. atricaudatus) (Schmidt and Davis, 1941; Anderson, 1965; Martof et al., 1980). Although the taxonomic status of the Timber Rattlesnake remains somewhat ambiguous in the eastern portion of its range (Brown and Ernst, 1986), it is generally accepted that the subspecific status of the canebrake rattlesnake is not warranted (Behler and King, 1996) and that Timber Rattlesnakes are monotypic (Collins and Knight, 1980).

Other common names include American viper, bastard rattlesnake, black rattlesnake, common (timber) rattlesnake, eastern rattlesnake, great yellow rattlesnake, mountain rattlesnake, mountain timber rattler, North American (horrid) rattlesnake, Northern banded rattlesnake, northern rattlesnake, pit viper, rock rattlesnake, velvet tail, yellowish brown rattlesnake and yellow rattlesnake (Wright and Wright, 1957). The specific Latin name horridus means “dreadful”, in reference to the venomous nature of the Timber Rattlesnake (Collins and Knight, 1980).

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History of the Timber Rattlesnake in Canada

The earliest record of Timber Rattlesnakes in what is now Ontario dates back to September 1669, where there is a reference in the journal of Rene de Brehart Galinée, who was attached to M. de La Salle’s party (Logier, 1939). The locality was near an Indian village called Otinaoustettaoua, which is near present–day Waterdown, in Halton County (Ibid.). Another early account of a Timber Rattlesnake was of one collected by Captain G. Wilkinson near the end of Point Pelee in September 1818 and reported by Patch (1919, cited in Logier, 1925). It was “an old specimen measuring 56 inches in length … as this one was such an old specimen and as no others have been taken there in recent years, Mr. Patch was of the opinion that it was the last of its race”. Another possibility was that it merely swam or drifted across Lake Erie from a neighbouring population on one of the U.S. islands or mainland (F. Cook, pers. comm.). Relict populations of Timber Rattlesnakes were known to have persisted on South Bass Island and on the Catawba peninsula of Ohio until at least 1951 (Langlois, 1951). Historical records are widely scattered and anecdotal and do not provide a clear picture of the species’ former abundance and distribution (Cook, 1999; see also Fig. 2).

Figure 2.  Distribution of the Timber Rattlesnake (Crotalus horridus) in Ontario. From Oldham and Weller, 2000.

Map of the Ontario distribution of the Timber Rattlesnake.

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Distribution

North America

At the time of European settlement, the Timber Rattlesnake was found in 30 states and was extremely abundant in areas of suitable habitat (Casper and Hay, 2001). By the early 1970’s, the Timber Rattlesnake had been nearly extirpated in all but the most remote sections of the United States (Morris, 1974). The species is still found in Alabama, Arkansas, Connecticut, District of Columbia, Delaware, Florida, Georgia, Iowa, Illinois, Kansas, Kentucky, Louisiana, Massachusetts, Maryland, Minnesota, Mississippi, Missouri, North Carolina, New Hampshire, New Jersey, New York, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, Vermont, Wisconsin and West Virginia (Casper and Hay, 2001; Harding, 1997). They have been extirpated from the states of Maine and Rhode Island, and may be close to extirpation in New Hampshire (Brown, 1993). Timber Rattlesnakes are one of only a handful of North American rattlesnakes that are found east of the Mississippi River (Schmidt and Davis, 1941; Morris, 1974). See Figure 1 for the North American range.

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Canada

The Timber Rattlesnake is no longer found anywhere in Canada. The last Timber Rattlesnake sighting was in the Niagara Gorge, Ontario in 1941 (Ontario Herpetofaunal Summary [OHS], unpubl. data; Cook, 1999). Historically, the Timber Rattlesnake has been reported from the counties of Essex, Halton, Kent, Elgin, Bruce, Peel, Niagara, Welland, Hamilton–Wentworth and the Manitoulin District in Ontario (Logier and Toner, 1961; OHS, unpubl. data). There have also been scattered reports of Timber Rattlesnake sightings in extreme southern Quebec along the U.S. border. However, none of these reports has ever been fully substantiated, and the adjacent populations in New York State (which may have acted as a source population for Quebec) have been extirpated (see Cook, 1999 and Mélançon, 1950 for more detailed summaries of Quebec reports). See Figure 2 for the Timber Rattlesnake’s range in Ontario.

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Habitat

Habitat Requirements

Timber Rattlesnakes prefer areas not frequented by people (Ditmars, 1907; Anderson, 1965), although few such sites still exist (DeGraaf and Rudis, 1983). Ideal habitats are forested areas with rocky outcroppings, dry ridges and second growth coniferous or deciduous forests (Ibid.). Favourite basking rocks are used year after year, and may attract many snakes at one time (Harwig, 1966).

The most important habitat component of northern Timber Rattlesnakes is the communal den within which hibernation takes place. A population is defined by its’ den, which is critical to the survival of the entire population (Brown, 1993). Granitic escarpments and ledges with accumulations of talus are common features of den sites (Brown, 1991), the majority of hibernacula being found on south facing slopes (Galligan and Dunson, 1979). Other habitat components are the summer habitat, where snakes move and forage, and transient habitat located in between summer habitat and the den (Brown, 1993).

Specific summer habitat requirements differ according to sex and age class. Males and non–gravid females utilize forest habitat with greater than 50% canopy closure, thick surface vegetation and few fallen logs (Reinert and Zappalorti, 1988b). In contrast, gravid females prefer less densely forested areas with 25% canopy closure, equal proportions of vegetation and leaf litter on the forest floor, frequent fallen logs and warmer climatic conditions (Ibid.). An area of approximately 50 km² of suitable habitat is required to sustain a population (Brown, 1993).

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Habitat Trends

In a letter to Francis Cook dated 15 September 1963, Frank Darroch described the changes to the habitat where he collected the last known Timber Rattlesnake in Ontario in 1941 (Cook, 1999): “The place where I found the snake has in the last ten years been entirely destroyed as a habitat, by the new road put in for the new hydro power plant.” Thus, the persistence of Timber Rattlesnakes in that area of the Niagara region seems highly unlikely.

Optimal forest composition and management strategies for Timber Rattlesnake habitat remain a subject of debate because canopy cover is a significant factor in the temperature profile of a den site. According to some researchers, the natural progression of forest succession may in fact be incompatible with the long–term survival of Timber Rattlesnake dens if the forest cover results in too much shade (Brown, 1993). Others doubt the negative impacts of increased shading, and believe that selective tree removal as a management strategy may actually do more harm than good (Reinert, pers. comm. to Brown, 1993).

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Habitat Protection

One seemingly harmless, yet potentially significant example of habitat alteration is the repositioning of basking and shelter rocks by people looking for Timber Rattlesnakes (Brown, 1993). Continuous disturbance of this sort may eventually cause snakes to abandon these sites altogether (Ibid.). It is preferable instead to check for snakes under rocks using mirrors and flashlights in order to minimize potential disturbance (Harwig, 1966).

The remote areas preferred by Timber Rattlesnakes are becoming increasingly less ideal because of enhanced access to such areas via four–wheel–drive and off–road vehicles (Galligan and Dunson, 1979; Brown, 1993). Protected public lands and privately owned nature preserves have contributed significantly to the conservation of Timber Rattlesnakes where they still exist (Ibid.), although some public lands may have been managed with the goal of eliminating Timber Rattlesnakes because of fears that their presence might deter visitors (Cook, 1999).

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General Biology

Food Habits

The foraging behaviour of Timber Rattlesnakes was studied in detail in Pennsylvania (Reinert et al., 1984). The predominant ambush position of this sit–and–wait predator involves coiling adjacent to a fallen log with the head positioned perpendicular to the long axis of the log. Small mammals are the favoured prey; different species are consumed in proportion to their prevalence at the site. White footed mice (Peromyscus leucopus) and red–backed voles (Clethrionomys gapperi) comprised the bulk of the diet of one sample, at 65% and 20% respectively (Ibid.). An eastern chipmunk (Tamias striatus), a cottontail rabbit (Sylvilagus floridanus) and an unidentified bird were also taken, each representing 5% of total prey consumed in the above study. Similarly in Virginia, the three leading foods were mice, chipmunks and cottontail rabbits (Uhler et al., 1939). Census data of white–footed mice around a Pennsylvania rattlesnake den revealed a density estimate of 61 mice/ha (Galligan and Dunson, 1979). Other studies also support the contention that the Timber Rattlesnake consumes small mammals almost exclusively (Schmidt and Davis, 1941). However, carrion, reptiles, amphibians, birds and their eggs are also eaten (Uhler et al., 1939; Myers, 1956; Anderson, 1965; Keenlyne, 1972). Ironically, the food habits of the Timber Rattlesnake make it an economically valuable species which, were it not for its venomous nature, might actually have been encouraged to set up residence in Ontario (Logier, 1939; Martof et al., 1980).

Keenlyne (1972) studied the sexual differences of feeding habits of Timber Rattlesnakes in Wisconsin. Gravid females did not contain any food items, while 30.3% and 35.0% of males and non–gravid females, respectively, contained at least one food item. During follicle development, females either ate more, or were more efficient at converting food to stored visceral fat. The cessation of feeding was apparently induced by the development of large offspring. Observations on gravid females in captivity also indicated that the snakes did not feed during gestation (Odum, 1979).

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Reproduction

Male Timber Rattlesnakes reach maturity at an average age of 5.3 years in northeastern New York (Aldridge and Brown, 1995) and 4 years in South Carolina (Gibbons, 1972). Mean age of first reproduction for females averaged 7.8 years in northwestern Virginia (Martin, 1993), 6 years in South Carolina (Gibbons, 1972), four years in Kansas (Fitch, 1985) and 9–10 years in northeastern New York (Brown, 1991).

In the northern parts of their range females reproduce on average every three years (Brown, 1993; Martin, 1993), with 10–75% of females in a population reproducing in any given year (Galligan and Dunson, 1979). Fat stores are extremely diminished in post–partum females (Gibbons, 1972), with a mean mass difference of 306 g between gravid and post–partum females in a New York population (Brown, 1991). This weight loss represents 41% of female body weight (Galligan and Dunson, 1979). Foregoing reproduction in some years is apparently necessary to allow females to gain weight and store yolk protein in the developing eggs (Galligan and Dunson, 1979; Brown, 1981). Foraging success and the ability of females to regain mass may be the main determinant of the length between successive reproductive events (Brown, 1991).

Ovulation occurs from late May to early June, while maximum spermatogenesis is reached in July, continuing through September (Aldridge and Brown, 1995; Martin, 1993). Mating takes place in late summer (Martin, 1993) and young are born from late August to mid–September (Galligan and Dunson, 1979). Opinion varies as to whether females give birth at den sites or at ‘maternity rocks’ some distance away (Galligan and Dunson, 1979). Typical litter size varies from five to thirteen young, according to geographic location (Edgren, 1948; Anderson, 1965; Galligan and Dunson, 1979; Brown, 1993) and gestation period can vary as much as four to six weeks, depending on weather (Martin, 1996). Parturition of a brood of ten took 4½ hours to complete, with the birth of each snakeling taking between five and 25 minutes (Trapido, 1939). Sex ratio in a New Jersey brood was 1:1 (Odum, 1979).

Timber Rattlesnakes produce stillborn young and abort infertile eggs at a frequency of about 20% (W.S. Brown, pers. comm. to Fitch, 1985). Of a litter of twelve born to a New York snake, one was stillborn and an infertile egg was also deposited (Stewart et al., 1960). Similarly, in a New Jersey litter of 13 born in captivity, one snakeling was born dead, and another had a birth defect that would prevent it from eating (Odum, 1979).

Male Timber Rattlesnakes may use scent trailing to locate receptive females (Reinert and Zappalorti, 1988b). During courtship, the male repeatedly strokes the neck region of the female with his chin (Anderson, 1965).

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Growth and Survivorship

Contrary to popular belief, rattlesnakes cannot be aged directly by counting the number of segments in the rattle. This is true for two reasons; first, a segment is added each time a snake sheds (not necessarily once a year) and second, segments are continually being broken off – most wild–caught individuals have between five and nine segments in their rattles (Schmidt and Davis, 1941). If the rattle becomes accidentally lost, the end of the tail remains blunt, never pointed (Ibid.). Zoos have reportedly been known to attach additional rattles on the end of broken ones to make them appear more impressive (Ditmars, 1907; Schmidt and Davis, 1941).

Average shedding rate of Timber Rattlesnakes in northern New York was 1.44 sheds per year (Brown, 1988), compared to two sheds per year in Kansas (Fitch, 1985). Sheds can be measured directly by painting the rattle and then counting unpainted segments upon recapture (Brown, 1991). Most rattle growth occurs within the first four sheddings, and the increase in diameter of successive segments is less than 5% after the seventh ecdysis (Fitch, 1985).

Timber Rattlesnake life history is characterized by delayed maturity, low reproductive potential and high longevity (Fitch, 1985). In a Kansas population, mortality was estimated at 45% in first–year young, and 25% annually thereafter (Ibid.). The dynamics of this population suggests a rapid turnover, with newly matured adults comprising a high proportion of the total population. Other studies have also indicated that juvenile mortality is probably high (Odum, 1979). The natural lifespan of the Timber Rattlesnake in the northern part of its range is approximately 25 years (Brown, 1993). A Louisiana Timber Rattlesnake lived 36 years, 7 months and 27 days in captivity, reaching a total length of 1770 mm (Cavanaugh, 1994).

In Pennsylvania, newborns ranged from 220–280 mm snout–vent length (SVL) (Galligan and Dunson, 1979). They increased in size to 400–550 mm SVL in their third year, 640–740 mm in their fourth year and 760–900 mm SVL by their fifth summer (Ibid.). Timber Rattlesnakes in South Carolina reached lengths of 650–750 mm SVL by the end of their second summer (Gibbons, 1972). Growth rates and size of newborns appears to be highly variable geographically, and Brown (1991) presents a table summarizing both growth rates and minimum age of first reproduction of Timber Rattlesnakes throughout their range. Males grow considerably longer and heavier than females, and there is no apparent reproductive advantage for females obtaining a larger body size (Gibbons, 1972). Growth rate slows after maturity (Galligan and Dunson, 1979), and adult total length ranges from 900–1890 mm (Conant and Collins, 1991).

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Physiology

The Timber Rattlesnake is a heliothermic species, with the ability to regulate its temperature by radiation absorption throughout its daytime activities (Odum, 1979). Approximately half of a Timber Rattlesnake’s daily activity cycle is spent basking, in order to maintain its preferred body temperature (Ibid.). Temperatures of free–living New York Timber Rattlesnakes ranged from 12.5°C to 33.3°C from early June to early August (Brown et al., 1982). Mean body temperature during this time was 26.9°C (Ibid.). During hibernation in the same population, mean body temperatures from September through May ranged from 4.3°C to 15.7°C, with a mean value of 10.5°C (Brown, 1982).

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Specializations for Defence

Timber Rattlesnakes are venomous. The severity of a snakebite depends on the amount of venom injected, the toxicity of the venom, and the depth and location of the bite (Minton, 1953). Fatal bites often involve small children (Guidry, 1953), who are more sensitive to venom due to their smaller size. Death from a Timber Rattlesnake bite can occur in as little as 35 minutes (Hutchinson, 1929), particularly if the individual is allergic to pit viper venom (Parrish and Thompson, 1958). Symptoms of Timber Rattlesnake poisoning include swelling, pain, respiratory difficulty, weakness, giddiness, haemorrhage, weak pulse or heart failure, nausea, vomiting, ecchymosis, heart pain, gastric disturbance, paralysis and unconsciousness or stupor (Hutchinson, 1929). Freshly decapitated rattlesnakes are still dangerous, as muscles can contract to inflict a deadly bite (Ditmars, 1907). Recently milked rattlesnakes are also capable of producing serious bites, and there is no evidence that previously exposed victims develop any sort of immunity through antibody production (Parrish and Thompson, 1958).

Bites from rattlesnakes at the time of shedding and replacement of fangs indicate that the injection apparatus may not be fully functional at this time, as some victims bitten during this period did not exhibit any symptoms of poisoning (Hutchinson, 1929). The first shedding of maxillary fangs takes place at a very early age, as evidenced by the fact that newborns have been found with fangs in the functional position (Barton, 1950). Venom is clear and watery in newborns, becoming bright yellow and concentrated as the snake matures (Johnson et al., 1968).

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Hibernation

Hibernation in the northern parts of the Timber Rattlesnake’s range occurs in the cracks of rocky ledges, usually facing south (Odum, 1979). In Ontario, hibernacula were most often located along the Niagara escarpment, following the limestone outcropping northward toward the Manitoulin District (Logier and Toner, 1961).

Timber Rattlesnakes often hibernate with copperheads (Agkistrodon spp.) and other snakes in the United States, due to the scarcity of hibernacula (Galligan and Dunson, 1979; DeGraaf and Rudis, 1983; Conant and Collins, 1991). They exhibit high fidelity to hibernacula (Odum, 1979; DeGraaf and Rudis, 1983), and some snakes follow specific routes to and from hibernacula each season (Brown et al., 1982). Hibernation is almost always communal, with only scattered reports of individuals hibernating singly (Neill, 1948; Odum, 1979). Timber Rattlesnakes near the northern extent of their range typically hibernate for 7.4 months, with the active period extending from early May through late September (Brown, 1991). Spring emergence is likely affected, but not completely determined, by temperature (Galligan and Dunson, 1979). Additionally, some snake hunters claim that Timber Rattlesnakes will not leave the den until they have shed (Ibid.).

Laboratory and field studies suggest that newborn Timber Rattlesnakes are able to follow the scent trails of adults to communal hibernacula (Brown and MacLean, 1983; Reinert and Zappalorti, 1988a). This ability could be crucial to the survival of newborns through their first winter, as they may be born a considerable distance away from any suitable hibernaculum (Reinert and Zappalorti, 1988a).

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Movement and Migration

Timber Rattlesnakes are seasonally migratory, from den to summer range and back (Brown, 1993). A variety of habitats are traversed throughout the active season, depending partly on individual age and reproductive state. Timber Rattlesnakes may swim across lakes during their seasonal migrations (Neill, 1948), and small Timber Rattlesnakes have been found as high as 9 m in trees (Saenz et al., 1996).

Timber Rattlesnakes may be active by day or night; nocturnal activity is especially common during hot summer nights (Martof et al., 1980). They tend to disperse upslope to high ridges removed from human settlement when they emerge from hibernation (Brown, 1981), and move in a looping pattern during the active season that returns them to the same hibernaculum (Reinert and Zappalorti, 1988b). Female Timber Rattlesnakes may or may not return to hibernation sites to give birth to young (Galligan and Dunson, 1979; DeGraaf and Rudis, 1983). Movements of gravid females are generally confined to thermally optimal gestation sites, such as open outcrop knolls in the vicinity of the den (Reinert and Zappalorti, 1988b; Brown, 1991).

Migration distances of males in general are greater than those of females because they actively engage in seeking mates (Reinert and Zappalorti, 1988b). The mean maximum migratory distance from the den was 4.07 km for males and 2.05 km for females in northeastern New York (Brown, 1993). The maximum single migratory movement away from a den was 7.2 km for a male in the same population. Translocated males have significantly larger activity ranges, range lengths and mean distances moved per day than native males (Rupert and Reinert, 1992). Timber Rattlesnakes collected during organized round–ups are often released far away from their point of capture, and this action most likely leads to the death of the snake, because of its unfamiliarity with its surroundings (Brown, 1993). Many translocated snakes immediately leave the area in which they are released (Galligan and Dunson, 1979).

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Behaviour

The most distinctive behaviour of rattlesnakes in general is the use of the rattle itself. Rattles are vibrated sideways at about 48 cycles per second (Schmidt and Davis, 1941). Timber Rattlesnakes generally begin to rattle when approached within 1–2 m (Barbour, 1950). Rattlesnakes are deaf to the sound of their own rattles, and are thought to use them when angry or threatened (Ditmars, 1907).

Timber Rattlesnakes are considered the most mild–mannered of any of the North American rattlesnakes, and individuals usually do well in captivity (Ditmars, 1907; Anderson, 1965; Morris, 1974). In general, they do not strike unless provoked, preferring instead to remain concealed (Ditmars, 1907). The “combat dance” of male Timber Rattlesnakes has been interpreted either as an expression of sexuality, or as a competitive interaction for food or dominance (Sutherland, 1958). This is a shy and secretive species and reports of Timber Rattlesnakes biting humans are rare (Ditmars, 1907; Brown, 1981). The only Canadian report of a possible Timber Rattlesnake bite, and subsequent fatality, was that of a soldier bitten during the Battle of Lundy’s Lane near Niagara Falls in 1814 (see Cook, 1999 for details).

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Vulnerability

Clearing of land, killing by humans and commercial exploitation have all contributed to the decline of the Timber Rattlesnake throughout its range (Weller, 1982; DeGraaf and Rudis, 1983). Habitat destruction of Timber Rattlesnake sites includes blasting and filling–in of dens with concrete, logging, mining, and gas wells (Brown, 1993). Because they are large and poisonous, Timber Rattlesnakes engender a large amount of human hostility (Plourde et al., 1989). The introduction of pigs into the countryside contributed to the demise of the Timber Rattlesnake; pigs are protected from envenomation by their thick layer of fat that prevents the venom from entering circulation, and thus are able to kill and eat rattlesnakes (Nash, 1908). The colonial nature of Timber Rattlesnakes was a factor contributing to their extirpation from Canada by humans (Plourde et al., 1989).

Timber Rattlesnakes have been the object of bounty hunting since as early as 1719 (Klauber, 1956, cited by Galligan and Dunson, 1979; Brown, 1981; Casper and Hay, 1998). In Wisconsin, bounty records showed a 70–80% decline over a seven–year period (Casper and Hay, 1998). Bounty records from one county in Minnesota declined from 4,955 in 1980 to 191 in 1987 (Ibid.). A number of populations from New York appear to have been extirpated, primarily because of over–hunting (Brown, 1981). In addition to bounty hunting, rattlesnakes have also been harvested for their oil (Ibid.) and for their rattles (Anderson, 1965). Because of their gregarious nature, hundreds were sometimes killed in a raid on a single den (Schmidt and Davis, 1941). Clearly, the potential impacts of human persecution are enormous.

As with most other reptiles, road–kill is an additional aspect of human–induced mortality (Martin et al., 1992; Dundee, 1994b; Jensen et al., 1994). In a Timber Rattlesnake population in New York, male road–kills outnumbered female road–kills 3.9:1.0, and human–caused mortality rates in general were much higher for males than for females (13:1) (Aldridge and Brown, 1995). Conversely, in a study in Georgia, gravid females constituted the majority of road–killed snakes (Neill, 1948).

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Population Sizes and Trends

Population Size

All available evidence indicates that the population size of the Timber Rattlesnake in Canada is zero. The species has not been sighted in Canada in almost 60 years.

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Population Distribution, Persistence and Trends

Frank Darroch collected the last confirmed Timber Rattlesnake in the Niagara Gorge on August 22, 1941 (Cook, 1999). Since this time, many researchers have conducted searches (including Frank Darroch, E.B.S. Logier, Frank Ross, Craig Campbell and James Kamstra), but no Timber Rattlesnakes have been found (Ibid.). It is almost a certainty that the Timber Rattlesnake has been extirpated, as demonstrated by the following quotes:

1881   Garnier: “rapidly becoming extinct [in Ontario]”
1908   Nash: “formerly common and generally distributed throughout the province now nearly extinct”
1939   Logier: “that the early distribution of this snake in Ontario was more extensive seems likely”
1982   Weller: “may very well have been extirpated in Ontario”
1984   Cook: “the last specimen taken in Ontario was from Niagara Glen in 1941”
1989   Johnson: “extirpated from Ontario”
1989   Plourde et al.: “extirpated”
1993   Brown: “probably extirpated [from Ontario]”
1999   Cook: “almost certainly extirpated in Canada”

Population declines have also been noted throughout the Timber Rattlesnake’s range in the United States, particularly in New York, Pennsylvania, Virginia, Connecticut and New Jersey (Brown, 1981, 1993; Reinert, 1990). Timber Rattlesnakes once occurred throughout the Carolinas and Virginia, but they have been eliminated from areas of extensive deforestation and human settlement (Martof et al., 1980). In Missouri, the Timber Rattlesnake population is gradually being reduced, and the species has been practically exterminated in some areas where it was formerly common (Anderson, 1965). Minor range extensions have been reported relatively recently in Virginia (Martin et al., 1992), Louisiana (Lutterschmidt, 1992; Dundee, 1994b) and Florida (Jenson et al., 1994). Of the populations that remain, many have been reduced to 15–20% of their numbers a few decades ago (Martin, 1983). The minimum viable population size for Timber Rattlesnake recovery is estimated at 30 to 40 individuals with an even age distribution and at least four or five mature females per den (Brown, 1993).

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Limiting Factors and Threats

Human exploitation, through bounty hunting, commercial collecting and sport hunting, is the leading cause of Timber Rattlesnake decline throughout the species’ range (Galligan and Dunson, 1979; Brown, 1993). Over a few decades, a single Timber Rattlesnake hunter is known to have collected 2900–5000 snakes from New York alone (Stechert, 1982; Brown et al., 1994). Snake hunters report that it is not difficult to ‘hunt out’ (i.e. extirpate) an entire den (Galligan and Dunson, 1979). Gravid females are particularly susceptible to persecution due to their preference for more open habitats and the predictability with which they occupy specific sites (Brown, 1993). Gravid individuals comprised 84% of female Timber Rattlesnakes turned in during organized snake hunts in Pennsylvania (Reinert, 1990 in Brown, 1993).

Several biological traits of the Timber Rattlesnake greatly reduce its ability to recover from large–scale losses of adults in a population. These features include slow maturation rates, low reproductive output, low juvenile survival and slow population replacement rate (Harding, 1997). Because females do not mature until about eight years old and reproduce on average only once every three years (Martin, 1993), most females will give birth to no more than five broods throughout their lifetime, assuming a lifespan of 22 years (Brown, 1991). These demographic characteristics also make the Timber Rattlesnake a species in which there is little natural “harvestable” surplus of adult individuals (Brown, 1993). One Utah rattlesnake population heavily hunted for only one year had still not recovered 12 years later (Woodbury and Hansen, 1950 cited in Galligan and Dunson, 1979).

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Special Significance of the Species

Timber Rattlesnakes are large, oviviviparous, iteroparous, long–lived and slow to mature, with a relatively long mean generation time (Brown, 1991). As such, they have the capacity to contribute significantly to our knowledge of covariation in life history traits (Ibid.).

Timber Rattlesnakes have been employed as study subjects to test a number of novel techniques. Sadighi et al. (1995) used remotely triggered cameras to monitor the occurrence of Timber Rattlesnakes in the wild. Additionally, the population genetics of Timber Rattlesnakes have been analyzed using microsatellite markers (Bricker et al., 1996; Villarreal et al., 1996; Bushar et al., 1998).

Timber Rattlesnakes in the Big Black Mountain area of Kentucky play a prominent part in certain religious rites in the area (Barbour, 1950). A local pastor is said to have captured a four–foot specimen in his bare hands after chanting the “magic words” (Ibid.).

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Existing Protection

In Ontario, the Timber Rattlesnake has been assigned a rank of ‘SX’ by the Natural Heritage Information Centre as apparently extirpated from Ontario (Oldham, 1997). The Ontario Ministry of Natural Resources’ Committee on the Status of Species at Risk in Ontario (COSSARO) has designated the Timber Rattlesnake an endangered species under the following criteria: “any native species that, on the basis of the best available scientific evidence, is at risk of extinction or extirpation throughout all or a significant proportion of its Ontario range if the limiting factors are not reversed” (Ibid.). The Timber Rattlesnake was among the first snakes to be officially designated as an endangered species under Ontario’s Endangered Species Act, 1973 (Weller, 1982).

The Timber Rattlesnake receives varying degrees of protection throughout its range in the United States. It is an endangered species in Massachusetts, where it may not be harassed, killed, collected or held in possession except under special permit (Jackson and Mirick, 1996). Penalties can range as high as a $5,000 fine and/or imprisonment for 180 days, in addition to a restitution payment of $2,000 per animal killed (Ibid.). The practice of paying bounties on Timber Rattlesnakes in New York ended in 1971 under the Fish and Wildlife Law (Brown, 1981). In 1971, Vermont became the last New England state to remove the bounty on the Timber Rattlesnake (DeGraaf and Rudis, 1983). According to Casper and Hay (2001), C. horridus is designated as extirpated in Maine and Rhode Island, endangered in Connecticut, Massachusetts, New Hampshire, New Jersey, Ohio, Vermont, and Virginia, threatened in Illinois, Indiana, Minnesota, New York, and Texas, a protected species in Maryland and Kansas, protected from take in Oklahoma and Pennsylvania and a protected wild animal in Wisconsin

Since 1996, the Nature Conservancy has ranked the Timber Rattlesnake “G5” (Oldham, 1997). However, in light of its range–wide decline, the U.S. Fish and Wildlife Service is conducting a review of the Timber Rattlesnake for possible protection under the federal Endangered Species Act (Casper and Hay, 2001). Although the Timber Rattlesnake was proposed for listing under Appendix II of the CITES Convention in 1997, the proposal was not adopted because it was argued that international trade was minimal, and that the species would benefit more by increasing protection in the United States (Ibid.).

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Evaluation and Proposed Status

The designation of status for the Timber Rattlesnake is quite straightforward: it has not been reported in this country in almost 60 years. The Timber Rattlesnake has already been designated as extirpated in Ontario by the Nature Conservancy (Oldham, 1997), and the vast majority of experts agree that the Timber Rattlesnake no longer exists in Canada. Thus the proposed status for COSEWIC is extirpated.

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Technical Summary

Crotalus horridus

Timber Rattlesnake    Crotale des bois

Extent and Area information

•  extent of occurrence (km²)0
•  specify trend (decline, stable, increasing, unknown) 
•  are there extreme fluctuations in EO (> 1 order of magnitude)? 
•  area of occupancy (km²)0
•  specify trend (decline, stable, increasing, unknown) 
• are there extreme fluctuations in area of occupancy (> 1 order magnitude)? 
•  number of extant locations0
•  specify trend in # locations (decline, stable, increasing, unknown) 
• are there extreme fluctuations in # locations (> 1 order of magnitude)? 
•  habitat trend: specify declining, stable, increasing or unknown trend in area, extent or quality of habitatunknown

Population information

•  generation time (average age of parents in the population) (indicate years, months, days, etc.)~13 years
•  number of mature individuals (capable of reproduction) in the Canadian population (or, specify a range of plausible values)0
•  total population trend: specify declining, stable, increasing or unknown trend in number of mature individuals 
•  if decline, % decline over the last/next 10 years or 3 generations, whichever is greater (or specify if for shorter time period) 
•  are there extreme fluctuations in number of mature individuals (> 1 order of magnitude)? 
•  is the total population severely fragmented (most individuals found within small and relatively isolated (geographically or otherwise) populations between which there is little exchange, i.e., ≤ 1 successful migrant/year)? 
•  list each population and the number of mature individuals in each 
•  specify trend in number of populations (decline, stable, increasing, unknown) 
•  are there extreme fluctuations in number of populations (>1 order of magnitude)? 

Threats (actual or imminent threats to populations or habitats) [add rows as needed]

  • human destruction of nesting habitat through direct action, mining, logging, drilling gas wells.
  • decimation of population through hunting, road-kills, persecution because of discrimination against venomous snakes.

Rescue Effect (immigration from an outside source)

•  does species exist elsewhere (in Canada or outside)?yes
•  status of the outside population(s)?declining
•  is immigration known or possible?no
•  would immigrants be adapted to survive here?yes
•  is there sufficient habitat for immigrants here?unknown

Quantitative Analysis (yes)

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Acknowledgements

This report could not have been completed without the assistance of a number of people. Francis Cook graciously allowed me to include information contained in his unpublished Timber Rattlesnake account in his upcoming book, “The Natural History of Amphibians and Reptiles in Canada”. Mike Oldham provided me with pertinent information from the Ontario Herpetofaunal Summary. Ron Brooks and Glenn Barrett supplied advice and technical assistance. Funding provided by the Canadian Wildlife Service, Environment Canada.

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Final edit by Ronald J. Brooks and Elinor J. Hughes.

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The Author

Kim Smith completed her Honours B.Sc. at the University of Guelph in 1996, with a specialization in wildlife biology. From 1996 to 1998, she conducted field work on a variety of taxonomic groups, including marine invertebrates and sea ducks, marine fishes, reptiles, waterfowl and mammals. She is currently working toward an M.Sc. on wood turtles with Dr. Ron Brooks at the University of Guelph. Kim has also written COSEWIC status reports on the queen snake (Regina septemvittata) and the northern ribbon snake (Thamnophis sauritus septentrionalis).

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Authorities Consulted

Canada

Francis Cook, Researcher Emeritus, Canadian Museum of Nature

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United States

Howard Reinert, Department of Biology, The College of New Jersey

William S. Brown, Associate Professor Emeritus, Department of Biology