CHARACTERISTICS OF BURROWS IN FAllOW FiElDS OF THE SOUTHERN SAN JOAQUIN VAllEY

DAVID J. GERMANO, Department of Biology, State University, Bakersfield, CA 93311

WESTLEY M. RHODEHAMEL, QUAD Consultants, 5500 Ming Ave, Suite 410, Bakersfield, CA 93309

ABSTRACT The architecture ofburrow systems ofkangaroo rats (Dipodomys spp.) vary among species and knowing how these systems are constructed could be useful in the management and conservation ofkangaroo rats. We excavated burrow svstems of the two kangaroo rat species that occur on the valley floor of the southern San Joaquin Valley in California. Systems ofboth species were located in fields that had been fallow for about eight years. We excavated 15 burrow systems of Tipton kangaroo rats (D. nitratoides nitratoides) and 10 burrow systems of Heennann's kangaroo rats (D heermanni tularensis) in areas west ofBakersfield in Kern County. In general, both species constructed shallow systems that are < 25 cm under the surface. Both species also constructed systems that included multiple openings to the surface, although ofthe systems we excavated, more openings were found in Tipton kangaroo rats systems (mean =2.5) than in burrows of Heennann's kangaroo rats (mean = 2.0). Some tunnels were unbranched, but often systems included multiple interconnecting tunnels. Mean greatest length ofburrows were similar between Tipton (1.82 m) and Heennann's kangaroo rats (1.61 m) and lengths varied between 0.75 - 3.5 m and 0.5-2.8 m, respectively. .

1995 TRANSACTIONS OF THE WESTERN SECTION OF THE WILDLIFE SOCIETY 31:40-44

Burrow systems, such as those constructed by kangaroo duced grasses, mainly Bromus madritensis ssp. rubens. rats (Dipodomys spp.), provide the occupant with shelter Saltbush (Atriplex sp.) shrubs were scattered throughout from temperature extremes and inclement weather, aid in the enclosure. Excavation ofthe burrow systems occurred the conservation ofbody moisture, provide protection from 23 November 1994 and followed four nights of trapping predators, and are used to store food reserves (Meadows 11-18 November. No were trapped during this 1991). Inalmost all instances, burrowsofkangaroo rats are session (Gennano and Rhodehamel, California State Uni· occupied by a single individual and are vigorously de­ versity, Bakersfield and Quad Consultants, unpubl. re­ fended (Jones 1993), but occasionally two adults have been port), and we were asked by personnel of Region 4 of the found in burrows (Monson and Kessler 1940, Monson California Department of Fish and Game to excavate the 1943). The architecture of burrow systems vary among burrow systems to ensure that no rodents were present. species and knowing how these systems are constructed We excavated ten burrow systems of Heennann's kan­ could be useful in the management and conservation of garoo rats in the Coles Levee Ecosystem Preserve (Sec. 35, kangaroo rats. We excavated burrow systems of the two nos, R25E, approximately 20 miles southwest ofBakers­ kangaroo rat species that occur on the valley floor of the field). These burrow systems were within 20 m ofconcrete southern San Joaquin Valley. We excavated burrow sys­ pads ofactive and abandoned oil wells. This area also was tems ofTipton kangaroo rats (D. nitratoides nitratoides), relatively flat and the ground cover was dominated by non­ a federally and state~listed endangered species, and bur­ native grasses. Saltbush shrubs were also scattered through­ rows of Heermann's kangaroo rats (D. heermanni out at these sites. Traps were set 19-22 November and tularensis), a non-listed species. No other species of burrows were excavated 9 December 1994 on the preserve. kangaroo rats inhabit the valley floor in the southern end of Only Heennann's kangaroo rats were captured at these the San Joaquin Valley, however, short-nosed kangaroo sites (Gennano, California State University, Bakersfield, rats (D. n. brevinasus) and giant kangaroo rats (D. ingens) unpubl. report). occur on the sloping plains surrounding the valley floor. Both sites were in oil fields that had a low to moderate number ofoil wells. Both sites were fallow fields that had METHODS been cultivated in the past but had not been plowed for We excavated 15 burrow systems of Tipton kangaroo approximately eight years (Marcia Wolfe, M. H. Wolfe rats, which were located in the Ten Section Oil Field (Sec. and Associates, and John Shelton, California Department of Water Resources, pers. comm.). We also excavated 11 33, nos, R26E), approximately 15 miles west ofBakers­ Tipton kangaroo rat burrows in January 1995 located in field, Kern County, California. All burrow systems of Tipton kangaroo rats were within an enclosure approxi­ natural habitat surrounding the Shafter-Wasco Landfill (Sec. 8, T28S, R24E). We excavated these burrows in the mately 0.5 ha in size that was fenced with woven-plastic erosion cloth. The site was level and covered with intro· same manner as the other burrows and used these systems as a comparison to systems constructed in fallow fields. 40 TRANS.WEST.SECT.WILDL.SOC. 31:1995 Characteristics of Kangaroo Rat Burrows • Germanetal. 41

At all three sites, we excavated burrow systems using length of burrows ranged from 0.75 m to about 3.5 m shovels, hand trowels, and our hands. A set of burrow (Table I). No kangaroo rats were found during burrow openings werejudged to be part ofa burrow system before excavation. excavation based on the closeness of burrow openings to Burrows of Heerrnann's kangaroo rats were similar to one another and their distance from other burrow openings. those ofTipton kangaroo rats. Most burrows were simple Excavation involved carefully shaving successive layers of systems with few interconnecting tunnels that were rela­ earth from atop the tunnels until we could determine their tively shallow, but two (#3 and #10) had a tunnel that depth and direction. We excavated all tunnels beginning at descended to a depth of65 cm (Fig. 2). Unlike burrows of a burrow entrance until the tunnel stopped, met with Tipton kangaroo rats. nmnels in several burrows of another tunnel, or became another opening to the surface. Heermann's kangaroo rats had enlarged areas. Also, one We measured the greatest length and maximum depth of burrow (#5) contained loose dirt mixed with seed hulls of the burrow system with a meter stick. We measured burrow grass in a tunnel with a plugged opening (Fig. 2). Average openings with a 10-cm rule. We also made a drawing of depth ofburrows ofHeermann's kangaroo rats were slightly each burrow system showing the relative orientation and deeper than those ofTipton kangaroo rats, but were shorter geometry ofthe nmnels. in greatest length (Table I). Burrows of Heermann's kangaroo rats also contained slightly fewer openings (mean = 2.0) than burrows of Tipton kangaroo rats (Table I). RESULTS Although several burrow systems had fresh dirt and tracks Burrow systems ofTipton kangaroo rats in fallow fields at some entrances, no kangaroo rats were found when these were relatively simple and were either unbranched or systems were excavated. branched into several interconnecting tunnels (Fig. I). In Of II burrow systems of Tipton kangaroo rats exca­ all cases but one, burrows were oriented in a single plane vated in natural habitat, the mean depth and length of (non-overlapping). In one system (# 10), an unconnected tunnels were greater than that found for Tipton or tunnel ran deep (42 cm) under an overlaying tunnel system Heermann's kangaroo rat systems in fallow fields (Table (Fig. I). Depth of tunnels below the soil surface ranged I). In addition, there were almost twice as many burrow from 10- 42 cm and the mean depth was 20.2 cm (Table I). openings as either species in fallow fields (Table I). The mean number of openings to the surface was 2.5, and Soils at both sites are classified as Kimberlina fine the range of openings was I - 6 (Table I). The greatest sandy loam (U.S. Soil Conservation Service 1988). These

Table I. Sununary statistics (mean ± standard deviation, range in parentheses) ofcharacteristics ofTipton kangaroo rats and Heermann's kangaroo rat burrows in the southern San Joaquin Valley. Sample size (n) ofdepth, length, and number of openings of burrows of Tipton kangaroo rat in fallow fields are greater than 15 he~ ~ ."e two systems contained unconnected tunnels (see Fig. I).

Burrow Tipton Kangaroo Rat Heermann's Characteristic Fallow n Natural n Kangaroo Rat n

Depth in cm 20.2 ± 8.69 18 38.6 ± 33.1 11 24.7 ± 21.30 10 (greatest) (10 - 42) (13 - 120) (12 - 65)

Length in m 1.82±0.81 18 2.88 + 1.32 II 1.61 ±0.77 10 (greatest) (0.75 - 3.5) (1.1 - 6.0) (0.5 - 2.8)

Number 2.5 ± 1.47 18 3.9 + 1.97 11 2.0 + 0.67 10 of Openings (I - 6) (2 - 8) (I - 3)

Width of 42.1 ± 7.75 17 39.0 ± 7.29 42 54.7 ± 13.4 19 Openings (mm) (34 - 65) (20 - 55) (35 - 90)

Height of 39.5 ± 6.02 17 38.7 ± 6.39 43 56.1 ± 11.8 19 Openings (mm) (30 - 55) (22 - 55) (36 - 80) 42 Characteristics of Kangaroo Rat Burrows • Germano et al. TRANS.WEST. SECT. WILDL.SOC. 31: 1995

are deep, well drained soils derived from granitic and (1946) found that burrow systems often were only 20 - 25 sedimentary rock. This soil type has a slope of 0 to 2%. cm below the ground surface, although occasionally a The surface layer generally is composed of brown fine tunnel would be dug to a depth of 76 cm. Heermann's sandy loam about 23 cm thick. The upper 91 cm of the kangaroo rats on the northwest side of the Valley usually underlaying material is also brown fine sandy loam, but the dig tunnels 15 - 50cm belowthe surface, but one tunnel was lower part to 180 cm is composed of pale brown silt loam found to extend 104 cm below the ground (Tappe 1941 ). (U.S. Soil Conservation Service 1988). We found a similar situation with two burrow systems of Heermann's kangaroo rats, each of which had one tunnel DISCUSSION descending to a depth of65 cm. These tunnels were much . The structure of kangaroo rat burrows were relatively deeper than the rest ofthe tunnels in that system, as well as simple in fallow fields in the southern San Joaquin Valley. deeper than the mean tunnel depth. Tappe ( 1941 ) hypoth­ Burrow systems of both Tipton kangaroo rats and esized that these deep tunnels may function to drain excess Heermann's kangaroo rats had few interconnected tunnels water out of the rest ofthe system during rainy periods. and were not dug deep below the surface. The structure of No stored seeds were seen in the burrow systems that we burrows of Tipton kangaroo rats in old fallow fields is excavated. The one depositofseedhulls mixed in loose dirt similar to the structure ofburrows ofTipton kangaroo rats that we found in a burrow ofa Heermann's kangaroo rat did that we excavated in natural habitat, although, on average, not contain intact seeds. Stored seeds have been found in they were shallower and not as long. burrows of Heermann's kangaroo rats on the northwest The shallow depth ofconstruction ofburrows ofTipton side ofthe San Joaquin Valley in hilly areas (Tappe 1941). and Heermann's kangaroo rats is similar to what had been Only small pockets of stored seeds were found in some found previously. In a study of the conspecific Fresno burrows ofFresno kangaroo rats (Culbertson 1946) and no kangaroo rat (Dipodomys nitratoides exilis), Culbertson stored seeds were found in burrows ofTipton kangaroo rats

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Fig. 1. Relative geometry and orientation of burrow systems of Tipton kangaroo rats from fallow fields in the southern San Fig. 2. Relative geometry and orientation ofburrow systems of Joaquin Valley. Clear ellipses at the end oftunnels represent open Heermann's kangaroo rats from the southern San Joaquin Valley. burrow entrances. Dark ellipses at the end oftunnels represent Markings in the drawings are the same as in Fig. 1. The arrows plugged burrows. Lines drawn through a portion ofa tunnel or an in system #3 and #10 are tunnels that descended 65 cm below entrance represents a collapsed section ofthe system. ground level. TRANS.WEST.SECT. WILDL.SOC. 31: 1995 Characteristics of Kangaroo Rat Burrows • Germano et al. 43

that we excavated in natural vegetation at the landfill site. not suggesting that all livestock grazing is harmful, W1less Culbertson (1946) notes that generally Fresno kangaroo stocking rates are high and duration ofgrazing is prolonged rats do not store seeds. This is in sharp contrast to giant to the point of significantly lowering seed production of kangaroo rats (D. ingens) that store large amOW1ts ofseed grasses and forbes. Fire in these habitats could be detri­ (Shaw 1934). However. giant kangaroo rats do not inhabit mental ifthe burn is slow and hot enough to consume seeds the valley floor (Williams and Kilburn 1991). Also. the on the groW1d. PreliminaI)' data suggest. however. that di fference in storage ofseeds between Heennann's kanga­ many fires in these habitats may not have severe conse­ roo rats on the valley floor and on hillsides may relate to the quences (Gennano and Saslaw. California State Univer­ likelihood of seed spoilage in low lying valley habitats. sity, Bakersfield. Bureau of Land Management. W1publ. Conditions in burrows ofall species ofkangaroo rats on the data). valley floor are likely too wet during the winter to avert We suggest that biologists use caution when using seeds spoiling (Culbertson 1946). burrow numbers to estimate relative density ofthese kan­ We did not find any kangaroo rats in the burrows we garoo rats. No individuals were fOW1d in any ofthe burrows excavated. We are confident. however. that the burrows that we excavated. The 15 burrow systems of Tipton that we designated as belonging to each species is correct. kangaroo rats excavated in fallow fields likely were con­ The burrows we designated as being made by Tipton structed only about a month before we dug them up because kangaroo rats were in an area in which we trapped numer­ we surveyed this area about six weeks before trapping and ous Tipton kangaroo rats previously. and burrow entrances no burrows were fOW1d. These systems did not show any were similar in size to horizontal burrows measured for this activity ofkangaroo rats at burrow entrances. but rain had species (mean width =34.7 mm. mean height =42.6, n = fallen during the month and occupied burrows of Tipton 126. Daniel Williams. in litt.). The burrows we excavated kangaroo rats often don't have fresh dirt at entrances (Best and designated as belonging to Heennann's kangaroo rats 1991). In contrast. several ofthe entrances ofburrows of were in an area where only Heermann's kangaroo rats had Heermann's kangaroo rats that we excavated had fresh dirt been caught several weeks earlier. and burrow entrances and tracks. but no rats were fOW1d. Also. two ofthe eleven were similar in size to horizontal burrows measured forthis burrow systems ofTipton kangaroo rats in natural habitat species (mean width =51.3 mm. mean height = 54.6, n =70. also had fresh dirt and tracks at burrow entrances but no Daniel Williams. in litt.). Kangaroo rats may conceal individuals were fOW1d. Because of this. we believe that themselves in side turmels in which they plug the entrance one kangaroo rat may use more than one burrow system and therefore could go W1detected during excavation (Daniel during its nightly activity. At this point. we do not know Williams, California State University. Stanislaus, pers. how many systems are used. and the number may vary comm.). In one study. burrow systems ofgiant kangaroo monthly, seasonally. or yearly. In addition, the number of rats were gassed with poison and then excavated, and entrances to burrowsofboth species is variable, and it is not sometimes no kangaroo rat was fOW1d (Shaw 1934). We do obvious from an intact burrow how many entrances one not believe that concealed occupants is a likely explanation system contains. These W1certainties make estimates of for our results. In many instances, we felt the turmel sides kangaroo rat abW1dance from burrow COW1ts tenuous for throughout the system with our hands to detect all tunnels. these species. Also. the systems we excavated were very simple com­ pared to the multi-layered and multi-branched systems of ACKNOWLEDGEMENTS giant kangaroo rats. We are convinced that no kangaroo We thank the California Deparnnent ofFish and Game rats occupied the systems we excavated. even those that for providing the impetus to begin this study. We also thank showed activity at entrances. Steve Geddes ofARCO Western Energy for allowing use Our results have conservation and management impli­ to work at the Coles Levee Ecosystem Preserve. We also cations. The Tipton kangaroo rat is listed as an endangered solicited a review from Daniel Williams. and he improved species and destruction of its burrow could directly or its content although any errors or omissions are ours alone. indirectly kill individuals. Plowing, even relatively shal­ low plowing (25 cm). ofnative or fallow lands that contain LITERATURE CITED Tipton kangaroo rats will probably destroy many. ifnot all, Best, T.L. 1991. Dipodomys nitratoides. . Spe­ of the burrow systems of this species. Also. any actions cies 381:1-7. (such as livestock grazing) that destroy most of the seed Culbertson. A.E. 1946. Observations on the natural source on the groW1d surface will directly hann both history of the Fresno kangaroo rat. J. of Mammal. Tipton and Heermann' s kangaroo rats (on the valley floor) 27: 189-203. because these species do not store seeds in large quantities Jones. W.T. 1993. The social systems of heteromyid in their burrows. and may not store any in winter. We are rodents. Pp. 579-595 In: H.H. Genoways. and J. H. 44 Characteristics of Kangaroo Rat Burrows • Germano et al. TRANS.WEST.SECT.WILDL.SOC. 31: 1995

Bro\I,n. editors. Biology of the . Amer. Shaw. W. T. 1934. The ability ofthe giant kangaroo rat as Soc. Mammal.. Spec. Pub\. No. 10. a harvester and storer ofseeds. 1. ofMammaI. 15:275­ Meadows. A. 1991. Burrows and burrowing : an 286. overview. Symposia of the Zoological Society of Tappe, D.T. 1941. Natural history ofthe Tulare kangaroo London 63: 1-13. rat. 1. of Mammal. 22:117-148. Monson. G. 1943. Food habits of the banner-tailed U.S. Soil Conservation Service. 1988. Soil survey ofK-ern kangaroo rat in Arizona. 1. of Wild\. Manage. 7:98­ County. California. northwestern part. U.S. Depart­ 102. ment ofAgriculture. U.S. Soil Conservation Service. ____. and W. Kessler. 1940. Life history notes on the 304pp. + maps. banner-tailed kangaroo rat. Merriam's kangaroo rat, Williams, D. F., and K. S. Kilburn. 1991. Dipodomys and the white-throated woodrat in Arizona and New ingens. Mammal. Species 377:1-7. Mexico. 1. of WildI. Manage. 4:37-43.