Upland Distribution of California Tiger Salamanders at Jepson Prairie - Solano Land Trust
© Gerald & Buff Corsi, California Academy of Sciences
The California tiger salamander 
(Ambystoma californiense) is an important native component of the California grassland community, and an increasingly rare species statewide. In January 2000, the U.S. Fish and Wildlife Service emergency-listed the Santa Barbara County distinct population segment as endangered. On July 17, 2002, the Sonoma County populations were also emergency-listed. Over the remainder of its range, including the Jepson Prairie ecosystem, the California tiger salamander is currently a candidate for federal listing, with a final decision on its status due by May 15, 2003. With its elevation to endangered status come restrictions that will impact land use and habitat management strategies over large areas of California.
Although California tiger salamanders breed in vernal pools and ponds, they spend most of each year and their entire subadult life (four to six years) away from water, primarily in the underground burrows of gophers and ground squirrels (Trenham et al. 2000, Trenham 2001). Because they only intermittently occupy ponds, protecting populations is more complicated than for vernal pool species that are limited to the pool basins and edges, like vernal pool crustaceans and plants. My prior studies have shown that some adult California tiger salamanders occupy burrows up to 250 meters from their breeding ponds, and occasionally move between ponds separated by up to 670 meters (Trenham 2001, Trenham et al. 2001). However, due to methodological difficulties, the spatial distribution of amphibians in the uplands is not well understood for any species.
Additional work is clearly required to understand how much and what types of upland habitat around a pond are necessary to maintain a healthy population. Because essentially all data on the upland ecology of pond-breeding amphibians come from radio telemetry studies life stages in these animals. The data from this project will give the stewards of the Jepson Prairie ecosystem and other areas the information they need to plan their burning, grazing, and other management efforts so that they do not impact the California tiger salamander. In addition, we will educate the Jepson docents and prepare an educational display. Together, these actions will serve to inform the numerous visitors to Jepson Prairie about the biology of the California tiger salamander, the details of our study, and how this new information will be important for the protection of the salamanders.
Primary Management Objective: To improve habitat management efforts on lands surrounding breeding ponds by building a statistical model that predicts the upland area needed to encompass 50, 75, 90, and 95% of a population of California tiger Salamanders. Presumably, the density of salamanders declines as one moves further from the breeding pond, but understanding the exact shape of this relationship is essential to the creation of an accurate and useful model.
Methods: To create our model we first need to determine the natural density of salamanders at a range of distances from a breeding pool. Although California tiger salamanders live predominantly underground, subadults and adults are active on the surface on rainy nights. The best method for capturing salamanders moving on the surface uses drift fences with pitfall traps (Dodd and Scott 1994). Our trap systems will include 10 meter long sections of silt fencing installed parallel to the pond edge, with the bottom 10 cm of silt cloth buried. Stakes are installed every 1 m to hold up the fence materials, creating a barrier to salamander movement at least 30 cm high. One-gallon pitfalls cans will be buried at the ends of each fence section, with the lip flush with the surface, and a plywood bucket divider installed so we will know if the animal came from the pond on non-pond direction. Migrating salamanders run into the sections of silt fence, cannot go over or under, walk along the fence, and fall into the pitfall buckets from which they cannot escape (Trenham et al. 2000).
To assess how salamander density changes with the distance from the pond, drift fences will be installed a range of distances from Olcott Lake. At each distance fence sections will be sections at 10 meters from the pond, covering portions of its entire circumference to determine if there are hotspots of salamander in-and-out migration. More distant traps will only be installed east of the road bisecting Olcott Lake, with 8, 9, 13, 16, and 19 fences at 10, 50, 100, 200, and 400 m, respectively. Because CTS only move during or following rain (Trenham 2001), traps will be opened every night when measurable rain fell during the 12 hours prior, or if rain is predicted for that night. Traps are opened and closed by removing (open) or replacing (closing) the lid on the bucket; when closed nothing can get in. In the field we will take a digital photograph of each captured salamander, and immediately release them into the nearest open gopher burrow. Photographs will be used to measure the length of each salamander, and because no two salamanders have the same spots we can also use photographs to individually identify recaptured animals.
Expected Results:
- Educate the visitors to Jepson Prairie about the ecology and status of the California tiger salamanders, and what our research is contributing.
- Produce a model of salamander density that will allow us to predict the width of surround upland buffer needed to encompass the movements of 50, 75, 90, and 95% of the California tiger salamanders in the area.
- Determine whether salamanders are equally distributed around the pond, or if salamanders enter or leave from certain directions in much higher numbers.
- Perform correlation analyses to determine how salamander density is related to other local habitat variables near each trap such elevation, gopher burrow density, distance to the nearest tree or stump, soil hardness, and soil depth.
- Because little is known about this species’ upland life history, even basic observations on the frequency, timing, and distribution of movements will be of great interest to those attempting to manage lands for this species, and will publish these findings.
