Fresno Field Station Records --

The Denver Wildlife Research Center (predecessor to the National Wildlife Research Center) conducted research at the USDA Pacific SW Forest and Range Experiment Station in Fresno, California, from the early-1960s through the late-1970s. However, wildlife research at the station first began when the Bureau of Biological Survey began conducting wildlife research at the station in 1936.

The DWRC was part of the US Fish and Wildlife Service, Bureau of Sport Fisheries and Wildlife, Division of Wildlife Research under the Department of Interior at the time it maintained a presence at the Fresno station. DWRC researchers at the Fresno station worked in close cooperation with other Federal and State agencies. Funding, office space, technical assistance, supplies and equipment were supplied by the US Forest Service and the California Department of Food and Agriculture. DWRC researchers also conducted wildlife habitat studies in cooperation with the National Park Service and the University of California.

In 1969, DWRC’s Agricultural Rodent Unit switched their efforts from controlling rodent damage to sugarcane in Texas and Louisiana to evaluating the impact of native rodents on crop and rangeland production in California, including damage to vegetation and irrigation structures. In particular, studies at the Fresno station focused on finding new and safer toxicants for controlling damage caused by California ground squirrels and voles, as well as determining the hazards of these toxicants to non-target wildlife and the endangered San Joaquin kit fox.

The establishment of the EPA in 1970 and the passing of FIFRA (Federal Insecticide, Fungicide, and Rodenticide Act) in 1972 caused a shift in the orientation of DWRC’s Agricultural Rodent Unit research. Screening of new compounds ceased and emphasis shifted to safety studies on compounds considered registerable. Much effort was placed on making zinc phosphide a general purpose rodenticide to replace compound 1080 and strychnine, which were now banned for use on Federal lands under FIFRA.

Much of the Fresno station’s research was conducted on the San Joaquin Experimental Range, a 4500-acre experimental forest 25 miles north of Fresno. In 1971, it was suggested that rodenticides used in rodent control programs might be a factor in the decline of the San Joaquin kit fox, an endangered species found only in the San Joaquin Valley of California. Researchers at the Fresno station conducted studies in 1972-1974 to determine the susceptibility of the kit fox to common rodenticides such as strychnine, compound 1080, and zinc phosphide.

Also in 1972, the annual grassland site of the International Biological Program, Grassland Biome, was established at the San Joaquin Experimental Range. From 1972-1975, DWRC researchers conducted studies supported by a grant from the National Science Foundation to the Grassland Biome Program on the ecology of small mammals including diet studies on the California ground squirrel. During the same time period, researchers carried out contract studies with the US Bureau of Reclamation to determine zinc phosphide residue levels on artichokes, sugarbeets, alfalfa, range vegetation, and soils on the Tule Lake National Wildlife Refuge in northern California. At that time zinc phosphide was the only rodenticide registered for use on a food crop. Data collected during these studies were used in registration applications for the EPA.

By 1977, research efforts once again focused on compound 1080 and evaluating an operational program using 1080-treated grain bait to control California ground squirrels. The specific objectives of these studies were to determine the efficacy of 1080 for controlling ground squirrels, the primary hazards to other rodents, rabbits, and seed-eating birds, and any secondary hazards to raptors and mammalian predators. Additionally, a cooperative study with the EPA in 1976-1977 evaluated the primary and secondary hazards to wildlife associated with aerial application of 1080-treated grain baits. DWRC research at the Fresno station ended in 1979.