Burrows of the Sagebrush Vole (Lemmiscus Curtatus) in Southeastern Idaho
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Great Basin Naturalist Volume 47 Number 2 Article 12 4-30-1987 Burrows of the sagebrush vole (Lemmiscus curtatus) in southeastern Idaho Tim R. Mullican Idaho State University, Pocatello Barry L. Keller Idaho State University, Pocatello Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Mullican, Tim R. and Keller, Barry L. (1987) "Burrows of the sagebrush vole (Lemmiscus curtatus) in southeastern Idaho," Great Basin Naturalist: Vol. 47 : No. 2 , Article 12. Available at: https://scholarsarchive.byu.edu/gbn/vol47/iss2/12 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. BURROWS OF THE SAGEBRUSH VOLE {LEMMISCUS CURTATUS] IN SOUTHEASTERN IDAHO Tim R. Mullican' and Barry L. Keller' Abstract —Burrows of the sagebrush vole (Lemmisciis cui'tatiis) were analyzed by injecting them with expanding polyurethane foam. Average mean depth ± 1 SE of four burrows was 12.5 ± 2.6 cm. Tunnels were wider than high and flat on the bottom. Three of four burrows were nearly linear, with an average of five entrances. Burrows usually contained one nest made oi Artemisia triclentata bark. No middens or communal nests were found. The burrow structure in sagebrush habitat suggests that sagebrush voles occur singly or in pairs rather than in colonies. The sagebrush vole {Leinmiscus curtatus) the site was dominated by big sagebrush frequently has been described as a colonial {Artemisia tridentata), green rabbit-brush species, and clusters of their burrows have (Chnjsothamnus viscidiflonis), and wheat- been referred to as colonies (Hall 1928, 1946, grass {Agropyron sp.), which is considered Soper I93I, James and Booth 1952, Maser et typical habitat for sagebrush voles. Tempera- al. 1974). A few investigators have described tures on the INEL range from 39 C (maxi- the structure of sagebrush vole burrows mum) in the summer to —41 C (minimum) in (Johnson et al. 1948, Dearden 1969, Maser et the winter (Groves and Keller 1983). The av- al. 1974), but a quantitative analysis of this erage annual precipitation over a 30-year pe- structure has not been published. The taiga riod prior to our study was 19.2 cm (National vole (Microtiis xanthognathus) frequently has Oceanic and Atmospheric Administration underground structures such as middens and 1984), with peak rainfall occurring in the large winter nests which reflect their social months of May and June. organization (Wolff and Lidicker 1981). In The exact location of burrows occupied by general, quantitative analyses of the burrow sagebrush voles was determined by tracking structure of voles are needed to elucidate the animals tagged with Ta'"*". Subsequently, in- social structure of individual species as well as dividuals were removed by live trapping to to determine the effects of voles on soil struc- recover the Ta'^" tags, and the animals were ture, but few investigators have done such sacrificed to assess their reproductive condi- studies. tion (Mullican and Keller 1986). Only adult In August 1984 four sagebrush vole bur- animals over 21 g existed in the burrows we rows were injected with expanding polyure- examined. thane foam that produces an exact cast of the In September four burrows were filled with burrow system. The objectives of this paper expanding polyurethane foam with an injec- are to describe the structure of sagebrush vole tion system described by Felthauser and burrows for an Idaho population in detail and Mclnroy (1983). When injected, the foam to discuss the social organization that this into an exact cast of the burrow structure suggests. hardened system. The soil surrounding the cast was ex- details of the burrow. A Methods cavated, revealing the l-m~ wire grid with 10-cm" squares was posi- Our population of sagebrush voles was on tioned over the cast of the burrow while it was the Idaho National Engineering Laboratory still in place, and depth below the surface was (INEL) on a 1-ha live-trapping plot measured at 10-cm intervals along the length (43°31'39"N, 112°59'26"W, Butte Co., Idaho) of the burrow. After the cast was removed used to analyze population trends for this spe- from the ground, the height and width of the cies (Mullican and Keller 1986). Vegetation on cast were measured at 10-cm intervals along 'Department of Biological Sciences, Idaho State University, Pocatello, Idaho 8.3209. 276 April 1987 Mulligan. Keller: Sagebrush Vole 277 Table I. Depth from ground surface, height, and width of tunnels from four liurrows oi Lemmiscus curtatiis. Number of measurements is in parentheses. Burrow Measurement 1 Depth (cm) 10.3±4.8 20.3 ±9.8 10.6±4.1 8.8±6.4 ±1S.D. (n=42) (n = 6) (n = 8) (n = 15) Width (cm) 4.8±0.6 4.5±0.6 5.2±L1 4.6±0.5 ±1S.D. (n=19) (n = 10) (n = 5) (n = 19) Height (cm) 3.2±0.9 3.1±0.3 3.2±0.4 3.4±0.6 ±1S.D. (n=19) (n = 9) (n = 5) (n = 19) SAGEBRUSH NEST Fig. 1. Diagram of a burrow of Lemmiscus curtatus as determined from a polyurethane cast. Shaded areas indicate big sagebrush (Artemisia tridentata) canopy. Entrances are numbered. its length. Some of the casts were incomplete sagebrush {Arteinisia tridentata), and often because the pressure of our injection system tunnels were found between adjacent sage- was insufficient to completely fill the tunnels. brush (Fig. 1). The mean number of entrances Because of this, we could not obtain measure- per burrow system was 5 and ranged from 2 to ments of the height and width of the tunnels 7. The burrow tunnels were wider than high along some sections of the burrows. Position (Table 1) and were usually flat on the bottom. and number of entrances, nests, and nest Three of the burrows were nearly linear, chambers were readily apparent from the but one was complicated in structure with cast. tunnels radiating outward from a central nest chamber. Maximum straight-line length of burrows from 0.7 to 4.6 with a mean Results ranged m of 1.9 m. The average mean depth ± 1 SE of the four Three of the four burrows contained nests burrows was 12.5 ± 2.6 cm. Mean depths ± 1 that averaged 12.4 cm in diameter. Two of the SD of individual burrows ranged from 8.8 ± nests were composed entirely of shredded 6.4 cm to 20.3 ± 9.8 cm (Table 1). The burrow sagebrush bark, whereas one occupied by a entrances were usually under or near big male was composed mostly of the bedding 278 Great Basin Naturalist Vol. 47, No. 2 material used in the live traps and a small ported to have up to 30 entrances (Hall 1946, amount of sagebrush bark. No young were James and Booth 1952). The four burrows that found trapped in any of the nests. we excavated contained an average of 5 en- trances (range 2-7). The higher number of burrow entrances reported in other studies Discussion could be due to other species that previously The burrows that we examined were much occupied the burrow, the fossorial work of less extensive than those reported by Maser et other species which share the burrows oiLeni- al. (1974), who described a burrow system miscus (Miller 1930), or incorrect assumptions that covered an 11 x 26 m area. However, the about the below-ground structure of burrows burrow systems described by Maser et al. that were not excavated by investigators. (1974) proved to be abandoned burrows of the Soper (1931) found that sagebrush voles in northern pocket gopher (TJwmomys tal- southern Alberta and Saskatchewan con- poides) taken over and modified by sagebrush structed extensive runways between bur- voles. Although there is no way to know if the rows. He located sagebrush vole burrows by burrows that we described were constructed capturing individuals in traps placed in run- exclusively by sagebrush voles, the size of the ways near burrow entrances. We could not tunnel precludes previous development by find evidence of runways utilized by sage- pocket gophers on our study plot. brush voles on our study plots, as most of the We found that the average depth of bur- ground surface on this area was composed of rows was 12.5 cm. Johnson et al. (1948) found bare soil where any trail would be quickly that burrows ranged from 10 to 30 cm below obliterated by frequent winds. the surface. Dearden (1969) found that sage- In areas where sagebrush (Artemisia sp.) is brush vole burrows were shallow, extending present, nests are usually made of sagebrush to an average depth of 36 cm. Maser et al. bark (Moore 1943, Johnson et al. 1948, James (1974) stated that pocket gopher burrows in- and Booth 1952). However, Maser et al. vaded by sagebrush voles were usually 5 to 8 (1974) found that sagebrush vole nests were cm below the surface. made of leaves, stems, and seed heads of grass Burrows of the taiga vole, Microtus xan- in central Oregon. thog.nathus , are limited to the upper 15 to 25 Based on the structure of burrows, we cm of the soil due to mineral soil or permafrost found nothing to suggest that sagebrush voles (Wolff and Lidicker 1980). Apparently taiga are colonial during summer. This is consistent voles must resort to group nesting to conserve with the results of our dispersion analysis re- energy during the long winter period (Wolff ported elsewhere (Mullican and Keller 1986).