Plethodon cinereus (Green, 1818)
Eastern Red-backed Salamander, Red-backed Salamander, (Northern Redback Salamander)
© 2005 Dave Blackburn (1 of 75)
Plethodon cinereus (Green, 1818)
Gary S. Casper1
1. Historical versus Current Distribution. Eastern red-backed salamanders (Plethodon cinereus) have undergone extensive taxonomic revision. For example, two southern subspecies (P. c. serratus and P. c. polycentratus) have been combined into southern red-backed salamanders (P. serratus; Highton and Larson, 1979). Range maps reflecting this taxonomic change do not imply a range retraction for eastern red-backed salamanders. A Plethodon cinereus group has been recognized by Grobman (1944) and Highton and Larson (1979).
In the United States, eastern red-backed salamanders range throughout New England, southward to western and northeastern North Carolina, and northwestward to western Minnesota, where a disjunct population is found (Petranka, 1998). No range retractions have been reported, but local extirpations have been due to habitat changes (chiefly deforestation) and other, unknown causes (see Highton, 2003).
Eastern red-backed salamanders exhibit color variants that include red-backed and lead-backed morphs co-occurring in most populations (summarized in Petranka, 1998). Proportions of red-backed and lead-backed morphs vary predicably in many areas of the United States, but this variation is not correlated with any obvious environmental factor (Petranka, 1998).
2. Historical versus Current Abundance. Highton (2003) documents recent widespread declines in most species of this complex. Jaeger's (1980a) data actually support Highton (2003) in suggesting stable populations over a 14-yr period prior to 1980. There has been no evidence of declines in Canada (Weller and Green, 1997). However, positive correlations have been made between forest age, the quantity and quality of downed woody debris, and salamander abundance (Herbeck and Larsen, 1999); it is widely believed that abundance declined following European settlement, as virgin old-growth forests were first clearcut, then burned, then subjected to modern forestry practices with stand rotations of only a few decades. The occurrence of eastern red-backed salamanders is also positively associated with forest patch area, suggesting that forest fragmentation may result in declines (Kolozsvary and Swihart, 1999). Petranka et al. (1993) estimates that 14 million salamanders are lost annually in western North Carolina as a direct result of forestry practices (but see Ash, 1988, 1997; Ash and Bruce, 1994). Studies suggest that populations may recover from clearcutting within 30–60 yr (Pough et al., 1987; deMaynadier and Hunter, 1995). Forestry impacts demonstrated in other plethodontids probably apply to eastern red-backed salamanders as well, where five times more salamanders were found in Missouri old-growth stands (> 120 yr old) than in second-growth stands (70–80 yr old); 20 times more salamanders were found in second-growth stands than in regenerating forests (< 5 yr old; Herbeck and Larsen, 1999). Indeed, Waldick (1997) concluded that habitat modifications associated with standard forestry practices resulted in a decline of all forest amphibians in eastern North America, with terrestrial salamanders, such as eastern red-backed salamanders, being most susceptible. Selective logging appears to have less impact on this species than does clearcutting, with little difference in salamander densities detected between closed-canopy plots and 1-yr-old canopy gap plots (Messere and Ducey, 1998). In Virginia, abundance was far less in 2–7-yr-old clearcuts than in > 60-yr-old forest (Blymyer and McGinnes, 1977). McAlpine (1997a) found no evidence of decline in New Brunswick, but suggests that clearcutting, conversions to conifer plantations, and shorter cutting cycles may have depleted populations. Conifer plantations are especially harmful; their drying, acidifying, and warming effects can permanently degrade salamander habitat (Waldick, 1997).
Eastern red-backed salamanders can be extremely numerous and play an important role in forest ecology, especially in energy flow and nutrient cycling, where they are 60% efficient at converting ingested energy into new tissue (Burton and Likens, 1975b). Digestive efficiencies of 83.57–90.49% and salamander tissue energy content values of 26.51 and 25.07 J/mg ash free dry weight were calculated by Crump (1979). In a New Hampshire study, the biomass of six species of salamanders (of which eastern red-backed salamanders comprised 93.5%) exceeded that for all birds during the nesting season and was similar to the biomass estimate for all small mammals (Burton and Likens, 1975a). Available density estimates are given in Table 12. These estimates usually do not take into account the portion of the population that remains under the surface, which is probably greater than the number of individuals on the surface (e.g., Highton, 2003). Surface censuses are likely to encounter only 2–32% of the total population (Taub, 1961; Burton and Likens, 1975a; Highton, 2003). Monitoring protocols are being refined, and monitoring of some populations has begun (Carfioli et al., 2000).
3. Life History Features.
A. Breeding. Reproduction is terrestrial.
i. Breeding migrations. None reported. A prolonged mating season lasts from autumn to early spring.
ii. Breeding habitat. Spermatogenesis occurs from October–December in New York (Hood, 1934; Bishop, 1941b; Feder and Pough, 1975) and in late March in Michigan (Werner, 1969). Both temperature and photoperiod regulate the spermatogenic cycle (Werner, 1969). Ovipositing typically occurs in late spring and early summer. The earliest I have observed eggs is 28 April on Stockton Island in western Lake Superior (in an atypically early and warm spring). Unusually late dates are late October in New York (Sherwood, 1895) and 2 August in northern Michigan (Davidson and Heatwole, 1960).
i. Egg deposition sites. Females deposit eggs in moist natural cavities within leaf litter, soil burrows, or rotting logs (Test and Heatwole, 1962). Eggs are susceptible to dehydration, and the rehydration rate is slower than the rate of dehydration (Heatwole, 1961b). Egg-laying behavior is described by Madison et al. (1999). Where logging activities have reduced the number of natural cavities available in downed woody debris, females may instead utilize cavities within matted leaf litter (Petranka, 1998). The grape-like clusters are usually suspended from the cavity roof by a short stalk. Eggs of this species can be confused with those of large gastropods that also nest within rotting logs. Females usually remain coiled with the eggs for about 60 d until hatching, and this behavior is thought to provide some protection for the eggs from predators and dehydration (Petranka, 1998), as well as accrue energetic and growth costs to the brooding female (Ng and Wilbur, 1995). There is no evidence that skin secretions from brooding females have antibiotic properties (however, see Vial and Preib, 1966; and Austin, 2000 [southern zigzag salamanders, P. ventralis]). Watermolen (1996) observed a female pick up an egg mass in her mouth, breaking it free from the pedicel, and carry it deeper into a log crevice when disturbed. Brooding females do not actively forage but will eat opportunistically (Ng and Wilbur, 1995).
ii. Clutch size. Average clutch sizes are 6–9 relatively large eggs (range = 1–14). Freshly laid ova are pale yellow to yellowish white, 3.0–4.0 mm in diameter, and surrounded by two jelly envelopes (Piersol, 1910; Cockran, 1911; Blanchard, 1928a; Bishop, 1941b; Lynn and Dent, 1941; Sayler, 1966; Nagel, 1977; Lotter, 1978; Petranka, 1998). The number of mature ova has been positively correlated with female length (Nagel, 1977; Lotter, 1978), as well as with female mass but not length (Fraser, 1980), suggesting that low food levels or quality may reduce clutch size. Brooding females will aggressively defend their eggs from conspecifics (Bachmann, 1984), and sometimes males are found with brooding females (Friet, 1995). In Virginia, 95% of nests were attended by brooding females (Highton and Savage, 1961).
C. Direct Development. Embryonic gills are lost just before or shortly after hatching. The incubation period is about 6–8 wk (Burger, 1935; Davidson and Heatwole, 1960; Pfingsten, 1989b), with hatching usually taking place in August–September. Hatchlings are reported as 22 mm TL (Wisconsin; Vogt, 1981) and averaging 13.5 mm SVL (Ohio; Pfingsten, 1989b).
D. Juvenile Habitat. Similar to adults. Juveniles often remain in the nest cavity with the mother for 1–3 wk after hatching before dispersing (Piersol, 1910; Burger, 1935; Test, 1955; Highton, 1959). Kin discrimination between mother and offspring may be context dependent (Gibbons et al., 2003).
E. Adult Habitat. Eastern red-backed salamanders occupy deciduous, mixed conifer-deciduous, and sometimes northern conifer forests, where they inhabit leaf litter and utilize retreats under stones, within soil cavities, and in rotting logs. Eastern red-backed salamanders have a limited ability to burrow, being effective only in soft substrates such as leaf litter or loose humus, and they prefer to use or enlarge existing retreats (Heatwole, 1960). They may also forage in bogs (Hughes et al., 1999). Soil moisture, soil pH, cover object availability, and light intensity all affect salamander distribution, with soil pH being the most influential factor (Wyman, 1988a,b; Frisbie and Wyman, 1992; Sugalski and Claussen, 1997; Grover, 1998). Eastern red-backed salamanders prefer cool, moist microhabitats and avoid temperature extremes and desiccating environments (Heatwole, 1960). A large percentage of the total population resides below the soil surface and is typically under-sampled in surface counts and mark-recapture methods (Test and Bingham, 1948; Taub, 1961). Their highest abundance occurs in mature hardwood forests, with deep soils and abundant downed woody debris in various stages of decomposition (Grover, 1998). Pfingsten (1989b) considers eastern red-backed salamanders to be an indicator organism of the beech-maple forest in Ohio, where cool, moist conditions prevail. Removal of dead and dying timber is likely to severely impact populations of terrestrial salamanders by reducing the availability of cover objects (Grover, 1998).
Eastern red-backed salamanders avoid shallow soils, rocky substrates, hydric soils, and soils with pH < 3.7 (Wyman and Hawksley-Lescault, 1987; Petranka, 1998). Vernberg (1955) reported soil pH preferences of 6.0–6.8. Temperatures below 10 ˚C inhibit locomotion (Feder and Pough, 1975). Conifer-dominated forests often have litter temperatures of 39 ˚C (Heatwole, 1962), exceeding the maximum temperature tolerances for plethodontids (32.3–34.6 ˚C; Spotila, 1972), whereas litter in deciduous forests typically stays cooler (28 ˚C maximum; Heatwole, 1962). This phenomenon may have implications for eastern red-backed salamander distribution as global warming progresses, because increased physiological stress is likely in warm summer periods (Ovaska, 1997). There is some evidence that eastern red-backed salamander black morphs can tolerate warmer temperatures than can striped morphs, and maintenance of this polymorphism may therefore increase the species' tolerance to thermal variation (Moreno, 1989). Eastern red-backed salamanders have among the highest mean rates of dehydration and rehydration (4 mg/cm2/hr) of all plethodontids (Grover, 2000). Preferred temperatures are higher in late summer and fall (maximum August mean selected temperature 21.0 ˚C) than in early summer (mean selected temperature 16.2 ˚C in early June), possibly facilitating surface activity in the summer, spermatogenesis during the fall mating season, and the selection of well-protected hibernation sites (Feder and Pough, 1975). Field body temperatures range from 6.5–22.0 ˚C during the active season (Feder et al., 1982).
Moisture requirements also influence microhabitat choice. Soils with an interstitial relative humidity < 85% are probably unsuitable for this species (Heatwole and Lim, 1961; Heatwole, 1962).
Eastern red-backed salamanders are largely nocturnal (Piersol, 1910; Cockran, 1911; Park et al., 1931; Heatwole, 1962). Stern and Mueller (1972) reported a diurnal rhythm, as measured by oxygen consumption, with activity peaking in the early morning hours, coinciding with that time of day when the lowest temperatures and highest humidity are likely to occur.
F. Home Range Size. Kleeberger and Werner (1982) estimated home ranges in Michigan average 13 m2 for males and juveniles, 24 m2 for females.
G. Territories. Eastern red-backed salamanders scent-mark territories on the forest floor with pheromones and fecal matter, which convey information concerning body size and gender. Kin recognition is suspected (Forester and Anders, 2000), and Gillette et al. (2000) provide evidence through behavioral experiments for social monogamy. Petranka (1998) gives home area (the defended territory) averages for males, females, and juveniles as 0.16–0.33 m2. Peterson et al. (2000) emphasize that males and females can cohabit territories as pairs and allow juveniles to forage within their territories. When territorial sites are limited, pairs of females may defend sites (Peterson et al., 2000). These territories are defended aggressively against conspecific adults by threat displays and biting, and both males and females defend territories (Jaeger et al., 1982; Jaeger, 1984; Horne, 1988; Horne and Jaeger, 1988; Mathis, 1989, 1991; Simons et al., 1997; Lang and Jaeger, 2000; Maerz and Madison, 2000). The intensity of the defense varies depending on the quality of food resources contained within the territory (Gabor and Jaeger, 1999). Eastern red-backed salamanders can recognize individual neighbors by odors (McGavin, 1978), and exhibit considerable site tenacity, with 91% of recaptured, displaced individuals returning to within 1 m of their capture sites in Virginia (Gergits and Jaeger, 1990). Homing behavior has also been demonstrated in Michigan, where displaced salamanders returned to their territories after displacements of 30 m (90% return) and 90 m (25% return; Kleeberger and Werner, 1982). Jaeger et al. (1993) hypothesized that homing was accomplished by forming a cognitive map of the surrounding pheromone-marked territories of other salamanders in the home area of the forest. Territories appear to function primarily as feeding areas, but may also play a role in mating success (Jaeger et al., 1982; Mathis, 1991). A large percentage of the population may be floaters (typically smaller animals that do not hold territories); up to 49% of the animals in a Virginia study may have been floaters (Mathis, 1991). Placyk et al. (2000) reported a probable breeding aggregation of five individuals in Michigan.
H. Aestivation/Avoiding Dessication. Surface activity is reduced in mid summer (late June to August; Blanchard, 1928a; Test, 1955; Taub, 1961; Highton, 1972; Nagel, 1977; Maglia, 1996). Surface moisture and temperature affect the vertical distribution of individuals in the soil (Taub, 1961). Hot, dry conditions are avoided, but true aestivation has not been recorded.
I. Seasonal Migrations. Mid summer movements occur in response to rising temperature and falling humidity, resulting in salamanders moving to cooler, moister environments (i.e., deeper into soils and from hilltops to depressions in the forest floor; Heatwole, 1962). Waldick (1997) presents evidence of mass emigration away from a clearcut in New Brunswick.
J. Torpor (Hibernation). With the advent of freezing weather, individuals move into underground retreats, beneath stones, into ant mounds, or under and within rotting logs and stumps, where they usually remain until snowmelt (Cockran, 1911; Grizzell, 1949; Vernberg, 1953; Cooper, 1956; Sayler, 1966; Highton, 1972; Caldwell and Jones, 1973; Hoff, 1977; Lotter, 1978; Buhlmann et al., 1988). In Hoff's (1977) Massachusetts study of tree stump hibernacula, a decided preference for selecting the decayed root systems of white oak (Quercus alba) over other tree species was indicated. In Maryland, Cooper (1956) reported aquatic hibernation in 7.5–25 cm (3–10 in) of water. Regular surface activity during prolonged warm spells in winter has been observed (Highton, 1972), and based on full stomachs in January in Indiana, there is some evidence that feeding continues through the winter (Caldwell, 1975), but declines from December–February (Petranka, 1998). Eastern red-backed salamanders are not freeze tolerant and must avoid freezing temperatures using behavioral mechanisms (Storey and Storey, 1986).
K. Interspecific Associations/Exclusions. Competition between eastern red-backed salamanders and other plethodontids is recognized (e.g., Adams, 2000). Microspatial segregation occurs between eastern red-backed and Shenandoah salamanders, with possible competitive exclusion, but experimental results are inconclusive (Jaeger, 1970, 1971a,b, 1972, 1974a; Kaplan, 1977; Wrobel et al., 1980; Lancaster and Jaeger, 1995). Hybridization between eastern red-backed and Shenandoah salamanders is also reported, with concern that genetic swamping may be contributing to the decline of the Endangered Shenandoah salamanders (Thurow, 1999). Eastern red-backed salamanders are aggressive toward northern slimy salamanders (P. glutinosus), defending territories against them (Lancaster and Jaeger, 1995). Mountain dusky salamanders (Desmognathus ochrophaeus) behave aggressively towards eastern red-backed salamanders and can drive them from occupied sites (Smith and Pough, 1994). Eastern red-backed salamanders are replaced by the more drought resistant southern ravine salamanders (P. richmondi) on steep slopes in Ohio (Pfingsten, 1989b). However, in Virginia, Grover (2000) showed that eastern red-backed salamanders were displaced from moist habitats near streams and seeps by northern dusky salamanders (Desmognathus fuscus) and seal salamanders (Desmognathus monticola).
Spotted salamanders (Ambystoma maculatum) preyed upon eastern red-backed salamanders in 9% of lab trials (Ducey et al., 1994), which might best be interpreted as interspecific interference. The presence of spotted salamanders therefore can affect eastern red-backed salamander distribution on the forest floor in areas of sympatry. Possible competitive interactions between eastern red-backed salamanders and valley and ridge salamanders (P. hoffmani; Fraser, 1976b), and between eastern red-backed salamanders and Wehrle's salamanders (P. wehrlei; Pauley, 1978a,b,c), have been suggested but not conclusively demonstrated. In New Hampshire, eastern red-backed salamanders predominate in salamander assemblages, comprising 93.5% of the biomass of six salamander species (Burton and Likens, 1975a).
L. Age/Size at Reproductive Maturity. Sexual maturity is reached about 2 yr after hatching (Bausmann and Whitaker, 1987). Ohio males (n = 904) averaged 40.5 mm SVL, and females (n = 632) 41.2 mm (Pfingsten, 1989b). The smallest mature males from Ohio are reported to be 32–37 mm SVL, and females 34–39 mm (Pfingsten, 1989b). Nagel (1977) reported growth rates in an eastern Tennessee population averaging 15 mm SVL during the first year and 8 mm in the second year, with growth surprisingly not slowing during the winter (females in this study reproduced annually, so growth rates may be lower in biennially reproducing populations). Females often exhibit biennial breeding cycles in the North and annual cycles in the South (Sayler, 1966; Petranka, 1998). However, both biennial (Vogt, 1981) and annual (M. Bergeson, personal communication) breeding has been reported from Wisconsin. Females first oviposit about 3.5 yr after hatching, when they measure > 34–38 mm SVL. Males breed annually throughout the range and are sexually mature upon reaching 32–37 mm SVL (Blanchard, 1928a; Sayler, 1966; Werner, 1971; Nagel, 1977; Lotter, 1978; Petranka, 1998).
M. Longevity. Unknown.
N. Feeding Behavior. Eastern red-backed salamanders are a top predator of the detritus food chain, feeding on any prey they can capture. Salamanders will climb on vegetation to forage at night (Cockran, 1911; Burton and Likens, 1975a; Jaeger, 1978). Small invertebrates are the staple of the diet. Wyman (1988b) estimated that eastern red-backed salamanders consume 1.5 million prey items/ha/yr in New York. Ants, termites, beetles, flies, earthworms, spiders, snails, slugs, mites, centipedes, millipedes, springtails, midges, pseudoscorpions, and other lepidopterans, thysanopterans, and hymenopterans are all reported as prey (Cockran, 1911; Murphy, 1918; Blanchard, 1928a; Hamilton, 1932; Jameson, 1944; Jaeger, 1972; Caldwell and Jones, 1973; Caldwell, 1975; Burton, 1976; Hoff, 1977; Pauley, 1978b; Mitchell and Woolcott, 1985; Bausmann and Whitaker, 1987; Maglia, 1996; Hughes et al., 1999). Ants and mites formed the bulk of the diet in a Canadian jack pine forest (Bellocq et al., 2000). Eastern red-backed salamanders are also reported to eat their own cast skins and occasionally will cannibalize conspecific eggs and juveniles (Surface, 1913; Piersol, 1914; Burger, 1935; Heatwole and Test, 1961; Highton and Savage, 1961; Burton, 1976). Maerz and Karuzas (2003) report an instance of an adult cannibalizing a juvenile.
O. Predators. A wide variety of animals and one plant will prey upon eastern red-backed salamanders, with ring-necked snakes (Diadophis punctatus) and short-tailed shrews (Blarina brevicauda) likely being the most common predators. Other reported predators include woodland snakes (i.e., garter snakes [Thamnophis sp.], copperheads [Agkistrodon contortix], and ring-necked snakes; Cockran, 1911; Uhler et al., 1939; Arnold, 1982; Mitchell, 1994a; Lancaster and Wise, 1996), spiders (Lotter, 1978), rove beetles (Platydracus viduatus [Staphylinidae]; Jung et al., 2000), spotted salamanders (Ducey et al., 1994), praying mantis (Mantis religiosa: Stein, 1989), mammals (shrews [Insectivora], voles and chipmunks [Rodentia], raccoons and foxes [Carnivora]; Brodie et al., 1979; Wyman, 1988b), and birds that forage in the leaf litter (Coker, 1931; Bent, 1949; Lotter and Scott, 1977; Brodie et al., 1979; Jaeger, 1981a; Fenster and Fenster, 1996). Most brooding female eastern red-backed salamanders will desert nests and flee when approached by ring-necked snakes (Petranka, 1998). Eastern red-backed salamanders have also been found dead within the insectivorous leaves of the bog-dwelling purple pitcher plant (Sarracenia purpurea; Hughes et al., 1999). Other likely predators include woodland mice (Cricetidae, Zapodidae), centipedes (Chilopoda), and ground beetles (Carabidae).
P. Anti-Predator Mechanisms. Eastern red-backed salamanders possess noxious skin secretions concentrated along the dorsum of the tail (Brodie et al., 1979; Petranka, 1998), which convey protection. When exposed, individuals may remain motionless to avoid detection, flee for protective cover, or assume a coiled position with the tail on top, presenting a dispensable body part to the predator (see below). The mean duration of immobility of disturbed salamanders is 39.4 s (range 1.0–169.5 s, n = 287; Dodd, 1989). Eastern red-backed salamanders release alarm pheromones from skin glands when attacked, which, unlike territorial pheromones, are short lived (about 2 min; Graves and Quinn, 2000; see also Hecker et al., 2003). Tail autotomy has also been reported as an anti-predator defense mechanism (Lancaster and Wise, 1996). When encountering shrews, eastern red-backed salamanders orient their tail toward the predator and arch and undulate this appendage, which contains glands thought to be distasteful to predators (Brodie et al., 1979). Shrews ate only 40% of red-backed salamanders offered in lab trials, which was attributed to distasteful glandular secretions (Brodie et al., 1979; see also Hecker et al., 2003). Mimicry has also been postulated as an anti-predator mechanism in the erythristic (all red) color morph of eastern red-backed salamanders, which are suspected of mimicking the red eft stage of eastern newts (Notophthalmus viridescens), a highly noxious species distasteful or poisonous to predators (Tilley et al., 1982).
Q. Diseases. No information is available, but eggs are susceptible to fungal infections (Pfingsten, 1989b).
R. Parasites. The following parasites and protozoans have been reported from eastern red-backed salamanders (Rankin, 1937; Ernst, 1974; Muzzall, 1990; Bursey and Schibli, 1995; Muzzall et al., 1997; Bolek and Coggins, 1998): protozoans—Cryptobia borreli, Cytamoeba bacterifera, Eutrichomastix batrachorum, Haptophyra (= Cepedietta) michiganensis, Hexamastix batrachorum, Hexamitus spp., Hexamitus batrachorum, Hexamitus intestinalis, Karatomorpha swezi, Monocercomonoides sp., Monocercomonas batrachorum, Octomitus sp., Proteromonas longifila, Prowazekella longifilis, Trimitus parvus, Tritrichomonas augusta, and Tritrichomonas batrachorum; nematodes—Angiostoma plethodontis, Batracholandros magnavulvaris, Cosmocercoides dukae, Cosmocercoides variabilis, Falcaustra sp., Oswaldocruzia pipiens, Oxyuris magnavulvaris, and Rhabdias ranae; helminths—Brachycoelium hospitale, Brachycoelium louisianai, Brachycoelium obesum, Brachycoelium salamandrae, Brachycoelium storeriae, Cylindrotaenia americana, and Cylindrotaenia idahoensis.
4. Conservation. No range retractions of eastern red-backed salamanders have been reported, but local extirpations have been due to habitat changes, chiefly deforestation, and other, unknown causes (see Highton, 2003). Positive correlations have been made between forest age, the quantity and quality of downed woody debris, and salamander abundance (Herbeck and Larsen, 1999), and it is widely believed that abundance declined following European settlement. Despite this, eastern red-backed salamanders can be extremely numerous (see Table 12).
1Gary S. Casper
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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