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COSEWIC assessment and status report on the eastern ribbonsnake in Canada

Biology

 

Feeding habits

The Northern Ribbonsnake feeds in the morning or early evening, and prey is detected both by olfaction and by vision (Ernst and Barbour, 1989). Many authors have commented on the absence of earthworms in the diet of this species (Ditmars, 1907; Toner, 1935; Logier, 1958; Froom, 1972; Minton, 1972; Lazell, 1976; Harding, 1997), unlike most other members of the genus.  Carpenter (1952a) examined the food preferences of 547 Michigan ribbonsnakes, in both field and laboratory. Amphibians comprised 90% of prey items taken in the wild. Two fish and two caterpillars were also recovered from ribbonsnakes, with the remainder of food items consisting of unidentified material. In laboratory feeding trials, many of the prey items offered were not consumed, including small gartersnakes (Thamnophis spp.), hairy caterpillars, soft bodied caterpillars (which were consumed in the field), spiders, ants, grasshoppers, beetles, leeches and earthworms. Conversely, several prey items not found in wild-caught ribbonsnakes were accepted in the laboratory: these included Jefferson's Salamanders (Ambystoma jeffersonianum), American Toads (Bufo americanus), minnows and chopped fish. Carpenter (1952a) believed that the scarcity of fish as prey in the wild snakes’ diet was probably due to the difficulty the snakes have in capturing them, because fish were readily eaten in the laboratory.

Brown (1979) examined the stomach contents of 21 Northern Ribbonsnakes from Michigan and New York. All 27 food items found were amphibian and 93% were anurans. Small Leopard Frogs (Rana pipiens) comprised 18 of the 27 food items. Other species consumed in smaller numbers were Spring Peepers (Pseudacris crucifer), newts (Notophthalmus spp.), a Green Frog (R. clamitans), a very small American toad (Bufo americanus) and (probably) a Pickerel Frog (R. palustris). Only three of the 21 stomachs examined contained more than one food item.  Betz (1981) made observations on the feeding preferences of a captive Northern Ribbonsnake from the Bruce Peninsula, Ontario. The snake refused every frog offered to it, feeding instead chiefly on Redback Salamanders (Plethodon cinereus). Minnows and goldfish were also consumed occasionally.

Evans (1942) describes the fishing method used by two ribbonsnakes in Missouri. The snakes swam with mouths fully open and upon contact with a fish the mouth immediately closed, thus capturing the prey. Carpenter (1952a) watched an adult female ribbonsnake chasing frogs along the shoreline of a pool in Michigan. Over a period of 45 minutes, the snake chased and missed eight frogs.

As might be expected, there are also stray reports of atypical prey taken by ribbonsnakes. Hamilton and Pollack (1956) reported a large lycosid spider as the only prey item in the stomach of an Eastern Ribbonsnake. Young ribbonsnakes may consume insects on a more regular basis (Froom, 1972).

Reproduction

Ribbonsnakes are viviparous, with a small average litter size ranging from 5 to 12 (Froom, 1972), and a maximum of 20 (Logier, 1958; Johnson, 1989). Milnes (1946) reported a brood of 10 born in captivity on 5 September, while Gilhen (1984) reported a litter of seven, also born on 5 September, in Nova Scotia. It is believed that Northern Ribbonsnakes have reproductive strategies similar to Eastern Ribbonsnakes (Hunter et al., 1992).  In the Great Lakes region, some Northern Ribbonsnakes mature by their second year, whereas the remainder mature in their third year (Harding, 1997). Although growth slows for both sexes after maturity, females appear to continue growing at a faster rate than males (ibid.). Brood size is significantly correlated with snout-to-vent length in Western Ribbonsnakes (Thamnophis proximus) (Clark, 1974); this is likely the same in Northern Ribbonsnakes.

Burt (1928) studied the relation of size to maturity in Michigan Eastern Ribbonsnakes. She determined that females are able to reproduce at a minimum total length of 600 mm. Seven of 13 mature females in her study did not produce young, a possible indication of low reproductive output for this species. It has been previously noted that ribbonsnakes produce fewer young than the majority of other species of the same genus (Ditmars, 1907; Swanson, 1952).

Courtship and mating generally occur in early spring, soon after emergence, but fall mating may also occur (Harding, 1997).  Johnson (1989) described the aquatic courtship of a pair of Ontario ribbonsnakes in April. The male approached by circling the female repeatedly, then dipping his head and entwining the female's body as she swam. He swam away from her for brief periods, during which time the female would circle back if he strayed too far away. This behaviour continued for 10 minutes, after which time the male tongue-flicked the female and aligned his body with hers.

Physiology

Carpenter (1956) studied the relationship between cloacal and environmental temperatures in a Michigan population of Eastern Ribbonsnakes. Cloacal temperatures were correlated more strongly with ground surface temperatures than with air or soil temperatures. More than 70% of cloacal temperatures were between 20º C and 30º C, thus indicating the preferred body temperature range for these snakes. During cold weather, cloacal temperatures were above the immediate environmental temperature; conversely, during hot weather cloacal temperatures were below the immediate environmental temperature.

Snake lungs appear to be common sites for parasitic infection. Chu (1936) examined ribbonsnakes from Michigan and West Virginia, and found them all to contain the nematode worm Rhabdias fuscovenosa catanensis, with average burdens of 7.4 and 48, respectively. Goodman (1951) also noted the tendency for “practically all gartersnakes” to be heavily parasitized by trematodes when collected in nature. He did not believe that these parasites greatly affected the health of their hosts.

Growth and survivorship

Newborn Northern Ribbonsnakes range in size from 160-240 mm total length (Harding, 1997). Total adult length averages 429.2 mm for males and 498.0 mm for females in Indiana (Minton, 1972).

Carpenter (1952b) studied the growth of Michigan ribbonsnakes in some detail, using a mark-recapture method. He found that smaller snakes grew more rapidly than larger individuals. Over a period of approximately five months, small ribbonsnakes increased in length by 13-25%, compared to an increase of 0.43-2% seen in larger specimens. Carpenter also found that the growth rate of males decreased more rapidly than the growth rate of females, and thus for any group of cohorts, females were larger than males, on average. Growth rates for specific age classes could not be determined because individual variation in growth obscured distinct size classes for snakes of the same age.

Information on survivorship is limited. Willis et al. (1982) studied tail loss patterns in ribbonsnakes and found that injured snakes less than 300 mm long (snout-vent) were never recaptured. They hypothesized that although the injuries were not immediately fatal, they created enough physiological stress during hibernation to kill small individuals. In Ontario, recruitment of young individuals might be low; of 71 ribbonsnakes found during the Hamilton Herpetofaunal Atlas, only one was a juvenile (Lamond, 1994).

Hibernation

In Ontario, the extreme recorded dates of Northern Ribbonsnake activity are from 28 March to 6 December (Mike Oldham, unpubl. data, OHS). In most years, however, the period of activity is from April to October (Lamond, 1994; Harding, 1997). In Nova Scotia, the extreme dates are 23 April to 2 October (Gilhen, 1984). During mild spells in winter and early spring, gartersnakes (genus Thamnophis) are known to come out of hibernation for short periods to sun themselves (Carpenter, 1956).

Carpenter (1953) examined the hibernacula and hibernating associations of snakes and amphibians in Michigan. An ant mound, a meadow vole tunnel and a crayfish burrow were excavated in search of hibernating reptiles and amphibians. Eleven Eastern Ribbonsnakes were found in the ant mound, five in the meadow vole tunnel, and none in the crayfish burrow. The uppermost ribbonsnake in the ant mound was dead, apparently frozen. It is believed that Ontario ribbonsnakes hibernate in animal burrows or rock crevices (Lamond, 1994). Because snakes must use hibernacula created by other animals or geologic events, their abundance may be limited by shortage of suitable overwintering sites (Carpenter, 1953).

Behaviour

The adjectives most often associated with ribbonsnake behaviour are “active” (Ditmars, 1907; Morris, 1974; Lazell Jr., 1976; Martof et al., 1980; Johnson, 1989; Harding, 1997) and “timid” and/or “nervous” (Conant, 1938b; Morris, 1974; Froom, 1972; Strickland and Rutter, 1992).  Ribbonsnakes generally do not attempt to bite when handled (Ernst and Barbour, 1989; Froom, 1972; Martof et al., 1980; Lewis, 1991).  Antipredator response in ribbonsnakes has been the focus of several studies. Scribner and Weatherhead (1995) found that ribbonsnakes rely more heavily on crypsis than on locomotion for escape from predators. Conversely, Bowers et al. (1993) found that ribbonsnakes often fled in response to predatory threat, occasionally striking as they moved away.

Ribbonsnakes are also well-known for their climbing ability (Logier, 1958; Cochran and Goin, 1970; Leviton, 1971), and have been observed as high as 2 m up in bushes (Carpenter, 1952a). Climbing and retreat into shade are behaviours associated with temperature regulation (Carpenter, 1956). During very hot and dry summers, ribbonsnakes may estivate for short periods (Ernst and Barbour, 1989).

Ribbonsnakes are predominantly diurnal, but they may forage at night during the frog breeding season (Ernst and Barbour, 1989). A gregarious species, three or four individuals are often found under a single board (Milnes, 1946). John Gilhen reported an aggregation of “some 40 or more adults, juveniles and young just lying about along the shore and on the surface in the shallows” (pers. comm.). He did qualify this observation, however, with the comment that he had never before or since witnessed an aggregation of this magnitude.