Endangered Species Recovery Program
California Department of Fish and Game,
Bird and Mammal Conservation Program Rep. 95-01, 38 pp., 1995
Daniel F. Williams,
Mary K. Davis,
Laurissa P. Hamilton
We inspected sites with potential habitat for giant kangaroo rats (Dipodomys ingens) in western Fresno and eastern San Benito counties between June and August 1992. In June 1993, we revisited sites to take tissue samples for genetic studies, and looked for and discovered additional giant kangaroo rat colonies. Seventy-nine giant kangaroo rat colonies were found; one colony became extinct between 1992 and 1993. Two of the six colonies previously (1980-89) located and monitored in the Panoche Hills were extirpated. Three other previously located colonies, two in the Tumey Hills and one between Arroyo Hondo and Cantua Creek, also had disappeared. Two colonies were discovered in Indian Valley in the Panoche Hills, an area that formerly had been inaccessible. The largest colonies were found on Panoche and Mugata fine sandy-loam soils, though small numbers of small colonies were found on a wide variety of soil textures. All colonies were located in annual grassland-dominated communities. The extant colonies occupied a total estimated area of 1,882.8 ha, which is almost 6.6 times greater than the 287 ha calculated from studies in the 1980's. The estimated population size for the study area in 1992-93 was 37,125, a substantial increase compared to a prior estimate of approximately 2,000 in 1980-1985. The increase resulted from a population irruption starting in summer 1991 at the end of a 5-year drought. This irruption was widespread in central California and involved many kinds of animals.