Del Norte Salamander
© 2016 William Flaxington (1 of 51)
Plethodon elongatus Van Denburgh, 1916
Hartwell H. Welsh Jr.1
1. Historical versus Current Distribution. Del Norte salamanders (Plethodon elongatus) are restricted to the Klamath Province in northwestern California and southwestern Oregon (Brodie, 1970; Nussbaum et al., 1983; Stebbins, 1985; Leonard et al., 1993, Jennings and Hayes, 1994a; Bury and Pearl, 1999). In California, they range from central Humboldt County eastward, barely into Trinity County, and then northward through Del Norte and western Siskiyou counties. In Oregon, Del Norte salamanders occur along the coast (Curry and southernmost Coos counties) and eastward in the Siskiyou Mountains (Josephine County). They have recently been found inland along West Cow Creek in the Umpqua River watershed (southwestern corner of Douglas County; R.B.B., unpublished data). Their range is about 335 km long from north to south and extends about 130 km inland.
Van Denburgh (1916) first described Del Norte salamanders from a few specimens in Del Norte County, California. Individuals in a few more sites were found in coastal California and Oregon (Wood, 1934; Fitch, 1936), and further inland in California (Stebbins and Reynolds, 1947; Stebbins, 1951). Highton (1962a) shows 11 locality records for Del Norte salamanders, and Brodie (1970) reports 42 sites range wide. Currently, there are museum records and collected specimens from 100 sites (Bury, 1998) as follows: Oregon, 21 coastal localities and 16 inland sites; California, 39 coastal or somewhat inland sites, 12 inland sites along the Trinity River, and 12 inland sites along the Klamath River. Other records are reported in Welsh (1990), Diller and Wallace (1994), and Welsh and Lind (1995), mostly within the known range. However, these were ecological studies, and locality data are not shown by site. The number of new localities continues to increase, with mandated surveys under the Northwest Forest Plan (see below), but the limits of the range have expanded only slightly in recent years.
At the southwestern terminus of the range, two divergent lineages of Del Norte salamanders, both distinct from populations to the north, occur in the lower Klamath and Trinity River basins (a major tributary of the lower Klamath River); each may represent a new species (M.J. Mahoney, unpublished data). There is marked clinal variation in populations of Del Norte salamanders from coastal sites inland up the Klamath River corridor (Bury, 1973b, 1998). Recent phylogenetic analyses (Mahoney, 2001; unpublished data; Mead et al., in review) indicate that P. elongatus, as currently recognized, is comprised of > 1 genetically distinct lineage that could be recognized as separate taxa. The relationships among these entities and P. stormi (Siskiyou Mountains salamander, which also appears to be comprised of more than a single genetically distinct lineage) is under active investigation (M. Pfrender, M.J. Mahoney, personal communication), with new molecular data indicating that the population currently recognized as P. stormi in the Scott Bar Mountains region of Siskiyou County, California, is highly distinct and ancestral to both P. elongatus and P. stormi (Mead et al., in review).
2. Historical versus Current Abundance. Del Norte salamanders may be declining due to timber harvesting, especially in interior locales (Raphael, 1988; Welsh, 1990; Jennings and Hayes, 1994a; Bury, 1998). Prior to June 2002, this was a Survey and Manage Species that was afforded some protection on federal lands under the Northwest Forest Plan, where ground‑disturbing activities are restricted on occupied sites and a surrounding 33 m buffer (Welsh and Ollivier, in press). Now, however, all protections have been removed, and we can expect downward trends in numbers of occupied sites and population numbers to resume across federal lands as resource extraction once again impacts and reduces suitable habitats in mature and late-seral forests (Welsh and Lind, 1995).
3. Life History Features.
A. Breeding. Reproduction is terrestrial.
i. Breeding migrations. Unknown.
ii. Breeding habitat. Breeding has not been observed but probably occurs in both spring and fall (L.M. Ollivier and H.H.W., unpublished data) on the forest floor of mature to late-seral forests. Lowe and Nieto (2003) report an instance of female-female aggression associated with the courtship season.
i. Egg deposition sites. Livezey (1959) reported a subterranean nest at the base of a redwood fence post. This is probably an atypical site, given the association of this species with rocky substrates. Typical sites are probably in subterranean cavities associated with unconsolidated talus and other hard substrates.
ii. Clutch size. One subterranean nest in the wild had 10 eggs in a grape‑like cluster (Livezey, 1959). Two adult females were found with 10–11 eggs (Stebbins, 1951). Nussbaum et al. (1983) report that 18 mature females had an average of 7.0 large eggs with a range of 3–11.
C. Direct Development. Parental care is undocumented, but females likely remain with eggs.
D. Juvenile Habitat. Same as adults.
E. Adult Habitat. Adults are mostly associated with talus or rocky substrates (Nussbaum et al., 1983; Diller and Wallace, 1994, Jennings and Hayes, 1994a; Bury, 1998; Ollivier and Welsh, 1999), but they also are associated with downed woody debris in areas with nearby rock substrates (Welsh and Lind, 1991). Canopy closure of 60% or greater and older stand age are required to support populations (Welsh and Lind, 1995), except in coastal areas where talus is the primary predictor of occurrence (Diller and Wallace, 1994).
F. Home Range Size. Unknown. Sedentary, rarely moving over 7.5 m2 in 3 yr (Welsh and Lind, 1992).
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Generally, this species is far underground during the hot summer.
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). Del Norte salamanders become inactive in cold weather.
K. Interspecific Associations/Exclusions. Co‑occur with ensatina salamanders (Ensatina eschscholtzii), clouded salamanders (Aneides ferreus), black salamanders (A. flavipunctatus), wandering salamanders (A. vagrans), and, in the northern portions of their range, Dunn's salamanders (Plethodon dunni; Brodie, 1970; Bury and Pearl, 1999). Earlier thought to not occur with western red-backed salamanders (P. vehiculum; Nussbaum et al., 1983), but recently both species were found together in southern Douglas County, Oregon (R.B.B., unpublished data).
L. Age/Size at Reproductive Maturity. Mature males range from 46–68 mm SVL and mature females, 57–71 mm SVL (Nussbaum et al., 1983).
M. Longevity. Unknown in wild.
N. Feeding Behavior. Sit‑and‑wait predators that dart from cover to seize small prey such as collembolans, termites, mites, and beetles (Bury and Johnson, 1965; L.M. Ollivier and H.H.W., unpublished data).
O. Predators. Likely are prey to shrews, other carnivorous mammals, and garter snakes.
P. Anti‑Predator Mechanisms. Unknown.
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. Prior to June 2002, this was a Survey and Manage Species that was afforded protection on federal lands under the Northwest Forest Plan, where ground‑disturbing activities were restricted on occupied sites and a surrounding buffer (Welsh and Ollivier, in press). Removing this salamander from Survey and Manage protection was based on the large number of new sites with detections within the known range, as a result of pre-project surveys on federal lands. However, no considerations were given to population numbers or age structure at these sites, or whether individual sites actually represented new or distinct populations. More importantly, no consideration was given to the available molecular (M.J. Mahoney, unpublished data; Mead et al., in review) and morphological (Bury, 1973; unpublished data) data that indicate high genetic diversity, and the probability that this taxon actually is more than a single species. By contrast, molecular data were instrumental during the same review process when considering the status of the related Plethodon stormi to relax protections in the northern portion of their range. New protective measures for P. elongatus populations may prove necessary if there are two or more species in the complex. There is a critical need to map this newly discovered genetic diversity and to determine the habitat use of each taxon and how these entities are distributed relative to protected lands, and how each might respond to habitat loss and fragmentation. Protective measures should probably be directed first at the inland and more southern populations where the genetic diversity is highest. Salamanders here are also more likely to be extirpated because they occur in more isolated patches than populations on the coast and northward. This fragmentation is probably related to higher summer temperatures and reduced seasonal precipitation inland and southward.
1Hartwell H. Welsh Jr.
2R. Bruce Bury
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Apr 2019.
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