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Habitat attributes and population size of Texas kangaroo rats on an intensely grazed pasture in Wichita County, Texas.

Article Excerpt
Abstract. -- An assessment of burrows was conducted at a 15-ha site in north-central Texas known to contain a population of Texas kangaroo rats (Dipodomys elator). The greatest numbers of burrows were in loose, elevated soils where 30-year-old unburned brush piles had decayed, followed by elevated, open areas. The least occupied habitats were fence rows, woody vegetation such as lotebush (Zizyphus obtusifolia) and honey mesquite (Prosopis glandulosa), and rocks. Texas kangaroo rats favored slightly elevated, well-drained, clay loam soils. Dominant vegetation at the study site was indicative of disturbances such as intense grazing by livestock. Burrows were associated with high percentages of bare ground, and herbaceous and woody vegetation of low height. Vegetation in areas immediately surrounding burrows was significantly different from that along transects leading away from burrows in percentages of bare ground and grasses. Dipodomys elator and four other mammalian species were captured during 640 trap nights. The population size of D. elator was estimated to be 33 ([+ or -] 6) individuals. Sixty-six burrows were counted and multiple burrow use by the Texas kangaroo rat is hypothesized. Counting of burrows is less expensive and time consuming than trapping, and if suitable conversion factors can be established by additional investigations, burrow counts have potential as a means of estimating size of populations that would provide information useful to conservation of this endemic, state-listed, threatened species.

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The Texas kangaroo rat (Dipodomys elator) is listed as a threatened species by the Texas Parks and Wildlife Department (Schmidly 2004). Reasons for D. elator being listed are largely based on its apparent scarcity and small geographic range. The International Union for Conservation of Nature (1986) lists habitat loss and degradation resulting from expanding agricultural and infrastructure development as the major threats to continued existence of D. elator.

An association between honey mesquite (Prosopis glandulosa) and the Texas kangaroo rat has been well documented (Bailey 1905; Blair 1954; Carter et al. 1985; Chapman 1972; Dalquest & Collier 1964; Martin & Matocha 1972, 1991; Roberts & Packard 1973; Schmidly 2004). More recently Stangl et al. (1992) noted that extensive stands of mesquite within the range of D. elator may not be as critical as once believed for survival and persistence of the Texas kangaroo rat. Also, while working at the Wichita County study site and another nearby site, Stangl et al. (1992) discussed opportunistic use of habitat affected by human disturbances. However, during that investigation, characteristics of burrows and size of populations was not quantified. Obtaining information on habitat characteristics critical to species survival and documenting demographic changes of D. elator populations must be accomplished to evaluate the conservation status of the Texas kangaroo rat (Jones et al. 1988). Therefore, the purposes of this study were to locate potential burrows of D. elator within this study site, relate associations of burrows with soils and human disturbance, quantify vegetation associated with burrows, and examine whether there is a correlation between number of burrows and size of population.

METHODS

The study site, located in Wichita County, Texas, 3 km N Lake Buffalo Creek Reservoir (location in decimal degrees; 34.02653 N, 98.75991 W), was previously described by Stangl et al. (1992) as study site 2--Goetze property. The grazing regimen of this site has remained virtually unchanged since described by Stangl et al. (1992). The 15-ha area is fenced and bordered by wheat fields on its eastern and western sides and contains constructed earthen ponds and erosion features, such as rills and gullies. There is additional habitat occupied by Texas kangaroo rats to the north and south of this study site and it probably is open to migration from these areas.

Beginning in 1975, the study site was mechanically cleared of brush and subsequently sprayed with an herbicide four times over five year intervals. This brush was piled into mounds scattered throughout this pasture (Stangl et al. 1992), but was left unburned. Over...

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