Endangered Species Recovery Program
American Society of Mammalogists, Annual Meeting, University of Washington, Seattle, June, 1999.
Daniel F. Williams1, Patrick A. Kelly2,and Suzanne N. Nelson 2, 3 . 1Dept. of Biol. Sci., California State Univ., Stanislaus, Turlock, CA 95382. 2Endangered Species Recovery Program, 1900 N. Gateway Blvd, Suite 101, Fresno, CA 93727. 3deceased.
Population growth and dispersal of giant kangaroo rats were measured in a colony of 30 (15 females,15 males) endangered giant kangaroo rats translocated to vacant habitat on the Carrizo Plain, California, in July 1989. Eighteen progeny were captured between March and December 1990, and 95 were captured in 1991. By November, 1992, 287 additional individuals had been captured in the core area of the then expansive colony, and by September 1992, 1,303 burrow systems had been located. Between September 1992 and December 1993 we trapped for 3 nights with two traps per burrow at each burrow and captured 867 individuals outside the core area. For males that were marked in the core area and later recaptured, 92.2% had not moved. Only 7.8% (15 of 192) of males and 19.0% (44 of 232) of females recaptured outside the core area had been marked before dispersing from the core area. Though a greater absolute number and higher percentage of marked females than males appeared to have dispersed, the mean and median dispersal distances were significantly greater for males (mean 122.0 m, median, 60 m) than females (mean 98.7 m, median 30 m). Maximum distances moved were 700 m for a male and 820 m for a female. Finding fewer dispersing males probably was due to higher mortality for individuals moving farther from their natal burrow. Our data suggest a nearly 60% greater survival rate for dispersing females. The spatial pattern of colonization was not random. Though the configuration of suitable habitat strongly influenced the pattern, anthropomorphic features of the landscape, especially roads and fence lines, were used as dispersal paths. These data are discussed in the context of conservation biology and compared to genetic studies of giant kangaroo rats that suggest a much longer effective dispersal distance.