Natural History of the Shasta Salamander -
Habitat Use, Seasonal Activity, and Movements of the Shasta Salamander
The Shasta salamander (Hydromantes shastae) has the smallest known range of any Pacific Northwest amphibian (Stebbins 1985). It is endemic to the Shasta Lake region of northern California. It has been found in Shasta County in three of four limestone belts, the Kennett Formation, McCloud Limestone and Hosselkus Limestone, but it is not known from the Pit Formation (Lewendal 1995). It is distributed patchily within its known range and can be locally abundant to very rare (Papenfuss and Cross 1980, Olson 1998). When this study was initiated in 1999, there were 21 known sites of occurrence for the Shasta salamander and all of these localities were within a 27 km radius of the town of O'Brien, Shasta County, California (Lewendal 1995). At present there are 61 known sites of occurrence and it is thought that these represent less than 20 populations of Shasta salamanders (Nauman and Olson, 2004). Nauman and Olson designated populations by clumping close sites centered around key habitat features. Since 1999 the known range has also extended 16 km to the northeast of its previously known boundaries.
The study was conducted immediately down slope of Samwell Cave, on the McCloud River arm of Shasta Lake, in Shasta County, California, on lands managed by the Shasta-Trinity National Forest. The study site is bordered by a ridgeline, limestone rock outcrops and cliffs, and an intermittent creek.
In order to examine the timing of seasonal surface activity, surface movements, and surface habitat use of a population of the primarily subterranean Shasta salamander, we conducted forty-eight site visits between September 2000 and May 2001 (23 visits) and between September 2001 and May 2002 (25 visits). Cover object searches were conducted on a 2,750 square meter grid near Samwell Cave, in Shasta County, California. The sample grid was systematically searched for salamanders by turning cover objects. In order to minimize disturbance, leaf litter was not searched, all cover objects were returned to their original positions, and all searching was conducted by hand. Objects that were too large to easily replace was not surveyed. We captured 306 individuals, 77 of whom were recaptured at least once, for a total of 399 captures and a 25% recapture rate. Highest surface activity occurred in the spring.
Salamander captures increased significantly in areas with greater amounts of cover, with salamanders being found slightly more often under rock than wood, even though wood was the dominant cover type. Salamanders seek refuge during the day under cover because it provides moisture and protection from predators (Keen 1982). Cover objects may also provide daytime foraging opportunities for Shasta salamanders, since many cover objects under which salamanders were captured also sheltered invertebrates.
A unique identifying set of marks was given to each animal using visual implant fluorescent elastomer (Northwest Marine Technologies, Shaw Island, Washington), which was injected subcutaneously with a hand-held syringe into the ventral surface of the animal.
Three hundred five Shasta salamanders were marked. Most salamanders were recaptured only once (72%). Second time recaptures were fewer (24%), with three animals recaptured three times (4%). The variation in number of captures per survey, as well as our observations of five salamanders escaping down retreat holes indicates that an unknown portion of the population at any given time is using underground retreat sites.
Adults and sub-adults appeared on the surface in November of each year, prior to the appearance of juveniles. During the 2000-2001 season juveniles were not found until March. During the 2001-2002 season juveniles were found beginning in late November, but they were not captured in great numbers until February.
The percents of captures in each age class for the 2000-2001 season were 10% juveniles, 40% sub-adults, and 50% adults. The percents of captures in each age class for the 2001-2002 field season were 19% juveniles, 34% sub-adults, and 47% adults; these were not significantly different from the previous year (P=0.09)
Movement distances were calculated only for recaptured Shasta salamanders with reliable marks (n=72). Movement distances between each point of capture as well as cumulative distance moved were calculated for each salamander.
The mean cumulative distance moved was 15 m. However, 60% of the cumulative distances moved by animals were less than 15 m. Nine salamanders were recaptured in the same place one to three times and had a cumulative movement distance of zero meters. Several salamanders that were recaptured in the same place had recapture dates that were separated by two weeks to over a year from the previous capture date. The longest distance moved was 104 m by an adult male, with one year and four months separating the two captures. The longest distance moved by a female was 97.5 m, with two months separating the two capture dates.
Nonparametric logistic regression was used to determine which physical environmental variables most influenced presence, and the numbers of salamanders captured. The relationships of salamander detections with significant independent variables were all nonlinear.
The shape of the response curves indicated that the number of Shasta salamanders per grid cell per site visit was highest in the spring, in cells that had a high percent of cover, with the temperature between 3 - 8 C, and the cumulative rainfall for the previous five days > 1.5 cm. Preference was demonstrated for rock cover objects. Although we studied a single population of Shasta salamanders, it is likely that this population is exemplary of other local populations due to the limited range of this species (or species complex) and the similarity in landscape characteristics where neighboring populations are found. Based on the AIC, the relative importance of the variables in explaining the location of Shasta salamanders found in each cell per survey was X,Y coordinates of cells, Julian day of survey, percent cover per cell, average temperature for survey day, cumulative rainfall for 5 days prior to survey day, dominant cover type for each cell.
Shasta salamanders have been poorly studied because they are patchily distributed, rare throughout the landscape, and have a secretive life history. Known populations are few and far between, and are difficult to access when salamanders are active at the surface because of weather conditions that make many of the 4-wheel drive access roads and steep rocky terrain impassable. Although we studied only one population of Shasta salamanders, we were able to provide detailed baseline information concerning this population. It is likely that this population is representative of other local populations due to the similarity in basic habitat characteristics where neighboring populations are found. While the information gathered has answered several key questions, it has also brought up new questions as to how the ecology of this species compares with that of other plethodontid salamanders. In the mean time we hope this research will provide useful baseline information for the sound management of Shasta salamanders.
Keen, W. H. 1982. Habitat selection and interspecific competition in two species of plethodontid salamanders. Ecology 63: 94-102.
Lewendal, P. 1995. Habitat-use by the Shasta salamander (Hydromantes shastae). Unpublished report for the California Department of Fish and Game. 32 pages.
Olson, D. H. 1998. Management recommendations for Shasta salamander (Hydromantes shastae). Unpublished report for the USDA Forest Service. 20 pages.
Nauman, R. S. and D. H. Olson. 2004. Distribution of the Shasta salamander (Hydromantes shastae), with notes on the habitat of Ensatina (Ensatina eschscholtzii) and black salamanders (Aneides flavipunctatus) in Shasta County, California. Northwestern Naturalist.
Papenfuss, T. and D. Cross. 1980. The status of the Shasta salamander (Hydromantes shastae ) in the Mountain Gate and Cedar Creek areas of Shasta county. Unpublished report for the USDA Forest Service. 9 pages.
Stebbins, R. C. 1985. Western reptiles and amphibians. Houghton Mifflin Company, Boston, Massachusetts, USA.
NOTE: Results on this page have not been peer reviewed (DO NOT CITE).
This research was conducted by Andie Herman (email) as part of her masters thesis.