California Slender Salamander
© 2009 William Flaxington (1 of 104)
Batrachoseps attenuatus (Eschscholtz, 1833)
Robert W. Hansen1
1. Historical versus Current Distribution. California slender salamanders (Batrachoseps attenuatus) occur in two principal areas: along the California coast and adjacent Inner Coast Ranges from north and east of Monterey Bay (extreme western Merced, Monterey, and San Benito counties) northward to extreme southwestern Oregon (south side of the Rogue River, Curry County; Yanev, 1978, 1980; Leonard et al., 1993); and in the western foothills of the northern and central Sierra Nevada, from Calaveras County north to at least Butte County (Hayes and Cliff, 1982; Jockusch et al., 1998). Inner Coast Range populations extend as far north as Tehama County (Jennings, 1982; Boundy, 2000). Isolated records of Batrachoseps from the floor of California’s Central Valley (Stanislaus, San Joaquin, and Yolo counties) probably represent California slender salamanders, although confirmation from genetic analysis is lacking. Additionally, there are isolated populations in Shasta County (north of California’s Central Valley) in the Little Cow and Clipkapudi Creek drainages (Stebbins, 1985).
The Sierra Nevada portion of the range is poorly defined, and some of the museum specimens currently allocated to California slender salamanders on the basis of morphology may be misidentified. Two similar-looking species approach or overlap the range of California slender salamanders in the central Sierra Nevada: gregarious slender salamanders (B. gregarius) range as far north as Mariposa County, just south of the southernmost range limits for California slender salamanders; and Hell Hollow slender salamanders (B. diabolicus) may be broadly sympatric with California slender salamanders between El Dorado and Calaveras counties, although the two have been found together at only one site (north slope of the American River; Jockusch et al., 1998).
Populations of California slender salamanders and the morphologically similar Gabilan Mountains slender salamander (B. gavilanensis) narrowly (by a few hundred m to a few km) overlap in geographic distribution along the southern border of the range of California slender salamanders in Santa Cruz and San Benito counties (Yanev, 1978, 1980; Jockusch et al., 2001).
2. Historical versus Current Abundance. Early reports (e.g., Stebbins, 1954a; Anderson, 1960) and more recent fieldwork by R.W.H., D.B.W., and colleagues suggest that California slender salamander population densities in the coastal portion of the range remain high. Estimates of densities range from 4,470/ha (Contra Costa County; Anderson, 1960, citing data from Hendrickson, 1954) to 17,290/ha on Red Rock Island in San Francisco Bay (Anderson, 1960). Stebbins (1954a) reported that a Contra Costa County population of California slender salamanders (presumably the same site studied by Hendrickson, 1954) occurred at densities relative to ensatinas (Ensatina eschscholtzii) of 7:1; he estimated the latter to occur at 170–200 adults/ac. This suggests a population density of 1,190–1,400/ac (2,939–3,458/ha) for California slender salamanders.
3. Life History Features.
A. Breeding. Reproduction is terrestrial.
i. Breeding migrations. Movements associated with reproductive activity are virtually unknown for any species of Batrachoseps. However, Anderson (1960) observed 69 adult California slender salamanders surface active during a heavy rain at night on 26 October (San Francisco Bay area); nearly all were gravid females moving uphill and across a road, a minimum distance of about 9 m. Coastal populations lay eggs shortly after the onset of fall rains, generally in October–November (Stebbins, 1951). Periods of oviposition for Sierra Nevada populations are unknown, but likely later in the year (December–January).
ii. Breeding habitat. Courtship behavior probably occurs underground (Houck, 1977b), but the timing is unknown.
i. Egg deposition sites. Females deposit eggs beneath rocks, logs, or other objects, although the paucity of nests discovered in the field suggests that most females are ovipositing underground (Burke, 1911; Storer, 1925; Myers, 1930b). Females apparently abandon eggs to communal nests, although female association with eggs has been observed (Snyder, 1923; Maslin, 1939). Storer (1925) described one nesting site as consisting of 53 eggs found “under a plank in a moist, springy place near a brush pile.” Maslin (1939) described finding a female in the act of egg laying; the female “was in a small depression in damp soil beneath a strip of tin” in the shade of a tree. Three other adult females occupied this depression, along with 74 eggs. Burke (1911) reported the discovery of 35 eggs (in groups of 21, 10, and 4) under a log in a moist ravine, unattended by any adults. Sixty-eight eggs were found in a small depression (ca. 25 mm diameter) beneath a board in late December in Contra Costa County; three adult salamanders were present under the board as well, but none was in contact with the egg cluster (R.F. Hoyer, personal communication).
ii. Clutch size. Clutch size is positively correlated with female body size. Jockusch and Mahoney (1997) reported mean clutch sizes of 8.3–13.4 eggs for four coastal populations and 6.8 eggs for a Sierra Nevada population. Maiorana (1976) found clutch sizes of 4–5 eggs for females occupying a forested area, while those from an oak woodland population produced larger clutches (7–8 eggs), with 82% and 95%, respectively, breeding annually. Mean egg diameter is 4.1 mm (Jockusch, 1997a).
C. Direct Development. Mean incubation periods for lab-incubated eggs (at 13 ˚C) ranged from 72–86 d (Jockusch, 1997a; Jockusch and Mahoney, 1997). Hatchlings have been observed in late January to February (San Francisco Bay area), and in late December at Walnut Creek (Contra Costa County) and St. Helena (Napa County; R.F. Hoyer, personal communication).
D. Juvenile Habitat. Maiorana (1976) found that juvenile California slender salamanders were more likely than adults to be active under sub-optimal surface conditions. Differential use of surface cover elements is unstudied, although juveniles often occur under relatively smaller pieces of cover.
E. Adult Habitat. Along the coast of northwestern California, California slender salamanders are largely restricted to low elevation, coastal redwood forest (Bury and Martin, 1973; Bury, 1983; Welsh and Lind, 1988). In southwestern Oregon, they are closely associated with humid coastal mixed evergreen forests (Leonard et al., 1993). Farther south, populations occur in a broader range of habitats, from moist coastal forests to oak woodlands. Sierra Nevada records are principally associated with pine-oak woodland and chaparral of the foothills (Block and Morrison, 1998), although populations may extend onto the floor of the Central Valley along riparian corridors (Hayes and Cliff, 1982). Ecological and behavioral aspects of water economy are described by Wisely and Golightly (2003).
Individuals occur under logs, bark, rocks, boards, and other surface cover, and in damp leaf litter (Stebbins, 1985). Periods of surface activity correspond closely to the rainy season (November–April/May for most of the range, later in moist, coastal forests). Maiorana (1977a) observed salamanders dead and dying in the field in the San Francisco Bay region during March and April; she attributed mortality to thermal stress. Field body temperatures for salamanders found under surface cover ranged from 2.2–15.8 ˚C (mean of 7.7 ˚C, n = 82; Feder et al., 1982; R.W.H., unpublished data).
F. Home Range Size. Aside from longer movements associated with breeding activity, individuals tend to remain within a small area over most of their lives. Anderson (1960) found short-term movements averaging 1.5 m, and Maiorana (1978a) recorded movements to 2 m. There is a strong tendency for individuals to occupy the same cover objects over several seasons; Hendrickson (1954) recaptured 59% of his marked animals under their original cover.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Surface activity corresponds to moist surface conditions, which for most of the range means a period of November–March/April, with local differences related to elevation, slope exposure, and recent precipitation. Surface activity is extended in some areas, such as those receiving daily on-shore fog or in closed canopy redwood forests, where moist conditions prevail outside the rainy season. In the San Francisco Bay area, surface activity begins in October and extends to May (or June in favorable years). In the moist redwood forests of the Santa Cruz Mountains, activity may occur in all months (Brame, 1959). During the dry season, individuals apparently retreat underground, using old root channels, earthworm burrows, or deep talus.
I. Seasonal Migrations. Unknown (but see "Breeding migrations" above).
J. Torpor (Hibernation). Rarely found on the surface during periods of low winter temperatures (e.g., soil temperatures below 5 ˚C).
K. Interspecific Associations/Exclusions. Over most of their range, California slender salamanders are the only species of Batrachoseps present. Along the southern slopes of the Santa Cruz Mountains, the ranges of California slender salamanders and morphologically similar Gabilan Mountains slender salamanders (B. gavilanensis) overlap, and they are locally sympatric (e.g., Hecker Pass on the Santa Cruz-Santa Clara County line; Jockusch et al., 2001). In general, California slender salamanders are found in more mesic and upland sites than the other species. Habitat associations for California slender salamanders in the Sierra Nevada are not well understood, and only a single area of sympatry with Hell Hollow slender salamanders is known (Jockusch et al., 1998).
Maiorana (1978a) suggested that differing patterns of fine-scale distribution between sympatric arboreal salamanders (Aneides lugubris) and California slender salamanders were due to differential cover use—arboreal salamanders prefer structurally diverse microhabitats (e.g., rock piles) with larger openings and retreats relative to those preferred by California slender salamanders. Further, she suggested that competition with arboreal salamander for burrows, rather than prey availability, may limit the density of Batrachoseps in some areas.
L. Age/Size at Reproductive Maturity. Age estimates at sexual maturity range from 2–4 yr (Hendrickson, 1954) to 2.5–3.5 yr (Anderson, 1960; Maiorana, 1976). Adult females from the San Francisco Bay region were 32–52 mm SVL (mean = 41.6, n = 79); adult males are slightly smaller (Maslin, 1939). Maximum size is 59 mm SVL (Fisher, 1953). Once sexual maturity has been attained, there is little correlation between age and size (Wake and Castanet, 1995).
M. Longevity. Hendrickson (1954) estimated longevity at < 10 yr. Based on skeletochronological data, Wake and Castanet (1995) showed that individuals live to be at least 8 yr old.
N. Feeding Behavior. Prey consist of small insects (especially springtails and small beetles), snails, isopods, mites, and spiders (Schonberger, 1944; Adams, 1968; Maiorana, 1978a,b; Lynch, 1985; Bury and Martin, 1973), captured by a projectile tongue (Lombard and Wake, 1977).
O. Predators. Several workers document predation under conditions of captivity (e.g., Hubbard, 1903; Storer, 1925; Stebbins, 1954a). Stebbins (1951) and Storer (1925) state that arboreal salamanders feed on California slender salamanders, but details are not provided and it is not possible to determine the prey species involved. The only unambiguous records of predation in the wild we can locate are by sharp-tailed snakes (Contia tenuis), Santa Cruz garter snakes (Thamnophis atratus; Stebbins, 1954a; Boundy, 1999), California giant salamanders (Dicamptodon ensatus; Bury, 1972; T. Burkhardt, personal communication), and scrub jays (Aphelocoma coerulescens; Reaser, 1997b). Several authors have suggested ring-necked snakes (Diadophis punctatus) as likely predators, and captive individuals readily consume California slender salamanders as well as other species of Batrachoseps (R.W.H., personal observations). We regard screech owls (Otus kennicottii) as likely predators as well, although this remains undocumented.
P. Anti-Predator Mechanisms. The following behaviors have been documented: coiling, violent thrashing (rapid coiling/uncoiling or “flipping” behavior), immobility/crypsis, release of adhesive skin secretions, and tail autotomy (Hubbard, 1903; Storer, 1925; Brodie et al., 1974a; Garcia-Paris and Deban, 1995). Flipping behavior may propel an individual salamander 10–20 cm where it may remain motionless (Brodie et al., 1974a). Arnold (1982) reported that in a lab-staged encounter between a California slender salamander and a garter snake, the salamander prevented ingestion by looping its tail around the snake's head to form a knot. Moreover, adhesive skin secretions released by the salamander caused the snake's jaw to remain glued shut at least 48 hr later. The drab brown to reddish-brown dorsal coloration often closely matches native substrates. Maiorana (1977b) reported that tail break frequencies of adult California slender salamanders from a population near Berkeley ranged from 28–48% annually, with an equal distribution between sexes.
Q. Diseases. Unknown.
R. Parasites. Two helminths are recorded from California slender salamanders: Batracholandros salamandrae (Lehmann, 1954; Goldberg et al., 1998c) and Cylindrotaenia diana (Helfer, 1949; Lehmann, 1960).
S. Comments. Until Yanev’s work (1978, 1980), California slender salamanders included several other forms now recognized as distinct species: black-bellied slender salamanders (B. nigriventris), gregarius slender salamanders, Hell Hollow slender salamanders (B. diabolicus, in part), as well as the recently described B. gavilanensis and B. luciae from the Coast Ranges of central California. Collectively, these taxa exhibit a derived, attenuate morphology; however, recent studies of mtDNA gene sequences (Jockusch, 1997b) support Yanev’s (1978, 1980) finding that California slender salamanders are phylogenetically isolated with respect to other members of the genus. For papers published prior to Yanev (1980), it may be impossible to determine whether references to California slender salamanders actually pertain to attenuatus or to sympatric, visually indistinguishable (and as yet undescribed) species of the Pacific slender salamander (B. pacificus) complex.
4. Conservation. Large portions of the historical range have been modified by development for housing, agriculture, and other activities, although California slender salamanders are still present over most of their original range. In some places, such as the San Francisco Bay region, they continue to be locally abundant in urban or suburban edge settings (e.g., gardens, vacant lots). Habitat loss is perhaps most important in areas where the species has only a limited presence, such as the floor of California’s Central Valley. California slender salamanders live in narrow strips of riparian oak woodlands along small creeks draining into the Central Valley. As modern agriculture replaces these residual habitats with drainage ditches, the salamanders survive only by becoming symbiotic with humans (they now occur in both Sacramento and Woodland).
Acknowledgments. We are indebted to Carla Cicero and Shawn Kuchta for assistance with literature searches. Stephen Goldberg provided key references for parasites. Bruce Bury and Tim Burkhardt extracted predation data from their field notes. Richard Hoyer shared information concerning his discovery of a communal nest.
1 Robert W. Hansen
2 David B. Wake
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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