California tiger salamanders are large salamanders, with adults frequently reaching 7.5 inches or more in total length. These are thick-bodied salamanders with broad heads and blunt snouts. Adults are black or dark grey, with oval to bar-shaped spots ranging in color from white to yellow. Juveniles are dark olive green in color and do not generally have any lighter markings.
Larval tiger salamanders have external gills and are olive green in color, generally with very fine dark markings (stippling).
Eggs are laid underwater singularly or in small groups, on subsurface portions of emergent vegetation or other debris. Each egg is approximately 0.5 to 0.75 of an inch in diameter, including a thick gelatinous layer.
California tiger salamanders range from the eastern foothills of the Sierra Nevada, west to the outer coast range, from Sonoma and Yolo counties in the north, to Santa Barbara County in the south. It is believed that the salamander population on the Stanford University campus represents the only population remaining on the San Francisco Peninsula. At least two other populations of tiger salamanders once existed in the Stanford area, most notably one centered in the wetlands formerly located in Portola Valley, near the intersection of Indian Crossing and Alpine roads. Recent attempts to locate salamanders in these areas indicate that it is likely that these populations are no longer in existence.
The complex life cycle of California tiger salamanders necessitates that each individual use a mixture of habitats. Seasonal wetlands are used for reproduction. These wetlands need to retain water until May or June for successful reproduction to occur. By that time of year, the aquatic larvae should have matured to the extent that they can successfully metamorphose into the terrestrial juveniles. Occasionally reservoirs (farm ponds) or the slow-moving portions of creeks are also used for reproduction. The juveniles and adults live in grasslands and oak woodlands, mainly living underground in the burrows of rodents. California tiger salamanders do occasionally inhabit landscaped areas.
Community relationships and behavior
Migrations from the uplands, where the adults live, to the seasonal wetlands, where they breed, generally start during the first runoff-causing rains of the season (usually mid-November to early December). Depending on the year and the timing of the rain, these nocturnal migrations can include a large number of salamanders, with several hundred adults migrating on a single night not being uncommon. Additionally, during years with little rain or only daytime rains, few, if any, salamanders will migrate. Migrations may consist of moves in excess of a kilometer, though most movements are less than 500 meters. Most movements occur on the surface, but it is probable that some dispersal occurs underground through rodent burrows. Movements by adults and juveniles from the breeding sites to the uplands are not well synchronized, and generally only a few at a time disperse from the seasonal ponds on rainy nights.
Most male tiger salamanders at Stanford are ready to start breeding when they are 3 years old; most females require an additional year to reach sexual maturity.
Aside from their migratory period, adult and juvenile tiger salamanders are rarely seen above ground. For most of the year, they live in the burrows of ground squirrels, gophers and other rodents in open wooded or grassy areas. Tiger salamanders are also frequently found under debris. Occasionally, tiger salamanders are found in man-made structures, including irrigation control boxes, buildings, and drainage pipes. They are found on the surface during periods of damp weather, almost exclusively at night. California tiger salamanders do occasionally aestivate (a summer dormancy period), but adult and juvenile salamanders can be observed at night, at the entrance of burrows, year-round.
Young (larvae) are aquatic and prefer the cover of vegetation to open water. Larvae are carnivorous and feed on anuran tadpoles and various aquatic invertebrates such as crustaceans, zooplankton, snails, and insect larvae. While the “cannibal morphs” found in the larvae of other species of tiger salamanders are apparently not present in California tiger salamanders, California tiger salamanders will eat smaller members of the same species. These salamanders metamorphose into land-dwelling juveniles by May or June. After metamorphosis, the juvenile salamanders eat a wide variety of insects and other invertebrates. Juveniles generally remain near the breeding site until autumn rains, at which time they disperse to upland areas. Adult salamanders also eat a wide variety of insects and other invertebrates and are also large enough to include some small vertebrates (frogs, baby mice, etc.) in their diet.
California tiger salamander populations have declined significantly in California. The main cause is fragmentation and destruction of habitat by agricultural and urban development. Introduced species, such as other species of salamanders that hybridize with native tiger salamanders, may be a problem in some locations. Natural predators of tiger salamanders include herons, terns, raccoons, skunks, and snakes. Weather is a very important determinant of salamander reproductive success. In seasons with heavy, early rain, which trigger migration and reproduction, but little or no mid- to late-season rain, many salamander larvae will not grow enough for successful metamorphosis and survival. Biocides and other environmental contaminants undoubtedly impact California tiger salamanders in some locations. Additionally, pathogens possibly pose a threat to some populations.
California tiger salamanders at Stanford
At the present time, California tiger salamanders are concentrated in the undeveloped areas around Lagunita with the density of salamanders decreasing significantly as the distance from Lagunita exceeds 1 kilometer. The distribution of salamanders is not random, and in the heavily developed area of campus very close to Lagunita, few, if any salamanders are present. Much of the main campus is a “population sink” for salamanders, which means that any individual unlucky enough to get into the main campus will find it virtually impossible to migrate back to Lagunita. Most of the main campus is downhill from Lagunita and a myriad of curbs, steps, buildings, drains and retaining walls block migrating salamanders from reaching Lagunita. Therefore, salamanders found in the main campus are essentially lost from the breeding population, because they have virtually no chance of reproducing successfully. California tiger salamanders are especially prevalent in the lower foothills.
Scientists have studied the California tiger salamander at Stanford and in its vicinity for more than 60 years. Early work focused on local distribution and factors associated with migrations. Recent work has been centered on conservation planning for the salamanders. This work, which started in the early 1990s, has involved many Stanford-affiliated workers and researchers, including undergraduates, graduate students, post-doctoral fellows, research associates, and hired consultants and experts. Work by non-Stanford scientists on the Lagunita population has also been conducted on a sporadic basis.
Much of the recent work was conducted to implement the “California Tiger Salamander Management Agreement.” This agreement is between Stanford, Santa Clara County, California Department of Fish and Game and the U.S. Fish and Wildlife Service and was signed in June 1998. One of the key elements of the California Tiger Salamander Management Agreement was the construction in the late 1990s of five small seasonal wetlands (ponds) south of Junipero Serra Boulevard. These ponds were classified as experimental and were expected to be modified as their performance was evaluated. The goal of these wetlands is to provide supplemental breeding locations for California tiger salamanders, reduce the reliance of the local population on Lagunita, and extend their effective range farther into the foothills. By 2001, Stanford determined that two of the ponds were essentially non-functional and a third lost capacity during the floods of 1998. The two remaining ponds worked as designed, but were considered too small to contribute significantly to the persistence of the local California tiger salamander population. The constructed wetlands, however, supported large numbers of Pacific treefrogs and western toads, an array of invertebrates and were used by a wide variety of mammal and bird species.
In the fall of 2003, following two years of consultation and permitting by U.S. Fish and Wildlife Service, California Department of Fish and Game, California Regional Water Quality Control Board, U.S. Army Corps of Engineers and Santa Clara County, the two remaining ponds were reconstructed and enlarged and six additional ponds were built. In 2006, California tiger salamanders reproduced in two of the ponds. In addition, Stanford installed three amphibian tunnels under Junipero Serra Boulevard, to allow migration between Lagunita and the lower foothills.
References (PDF, 36 KB)
Click here to view images of the California tiger salamander.
Click here to view a map of the California tiger salamander on Stanford lands.