Northern Prairie Wildlife Research Center
Much literature pertains to small mammal taxonomy, feeding requirements, and other characteristics; there is little information on conservation of small mammals and their response to management techniques.
In South Dakota, nongame small mammals are among the least understood of the mammals (Choate and Jones 1981), even though they are important components of the overall biota. Little to no data are available on small mammals of the James River Basin of North Dakota (Becker 1979) or for county distributions of mammals in South Dakota (Blumberg 1993).
Trapping was conducted 23 May to 17 August 1995 and 28 May to 22 July 1996 to inventory nongame small mammals in all upland and wetland-edge habitat types on SLNWR.
Since this was an inventory-specific project, an attempt was made to place traps in areas where burrows, grass clippings, and runways were present (Bogan and Ramotnik 1993). Bats and large- and medium-sized mammals were not sampled.
To sample all habitat types, trapping was conducted on islands and in wetland-edge areas. Rare small mammals often inhabit wetland areas and can only be sampled in these habitats (J. Cornely, pers comm, USFWS, Denver).
Trap types included snap traps (museum special and regular mouse traps) and pitfall traps. The two trap types increased the likelihood of capturing as many species as possible and yielding the most complete data on species composition (Mengak and Guynn 1987).
Four trap lines of approximately 50 (range = 25 ~ 60) snap traps each were set per habitat type (Fig 7). All snap traps were baited with peanut butter, rolled oats, and bacon grease. Traps were baited in the evening before sunset and checked after sunrise the next morning.
|Figure 7. Location of snap and pitfall trapping sites on Sand Lake National Wildlife Refuge, Brown County, South Dakota.|
In some instances, several species of small mammals, including shrews, have been adequately caught in pitfall traps (Williams and Braun 1983, Szarro et al. 1988, Bogan et al. 1995). Williams and Braun (1983) also found that pitfall traps enable multiple captures of small mammals. Pitfalls can be effectively used without drift fences. Whitaker et al. (1994) placed pitfalls along runways or logs and achieved adequate samples of small mammals.
Eleven-liter plastic buckets without lids and handles were used as pitfall traps and placed in all habitats except agricultural fields. The pitfall traps were buried flush to the ground with trenches dug between them to act as runways for small mammals (D. Backlund, pers comm, SDGF&P, Pierre). Pitfall traps (n = 3 per transect) were placed in a straight line, approximately 5 m apart (Fig 8).
|Figure 8. Illustration of pitfall placement used for sampling small mammals at Sand Lake National Wildlife Refuge, Brown County, South Dakota.|
Pitfall trapping protocol was in compliance with the guidelines from the American Society of Mammalogists Ad hoc Committee (1987). A sufficient amount of liquid in each trap quickly drowned small mammals.
Opportunistic collection of some small mammals such as ground squirrels and pocket gophers also occurred throughout the study.
Trapped mammals were identified and recorded on data sheets and cross-referenced by trap and trap line number, date, and habitat type. Specimens were placed in moist paper towels and frozen. All specimens were verified to species, and representative samples of each species were prepared as museum voucher specimens (skull and skin) and deposited at the Natural History Museum, University of Kansas, Lawrence. Any former documentation of small mammal occurrence in the Sand Lake area prior to this study was considered a valid independent observation. Mammal species names (Appendix A) followed Banks et al. (1987).
Catch rates were calculated as the number of individuals captured/species/100 operable trapnights, and these were used as an index of relative abundance. Mean catch rates and standard errors (SE) of the mean were calculated. Snap trap data and pitfall trap data also were summarized and compared separately due to differential catch rates. Snap traps enable only one capture per night whereas pitfall types enable multiple captures. Percent species composition was calculated for each mammal species per habitat type per trap type. Small mammals are listed in phylogenetic order (Jones et al. 1985).
Correspondence analyses were performed for all species per habitat type for each trap type, using SAS (1990). Species with sum values less than 6.0 captures in snap traps and less than 10.0 in pitfall traps were not included in correspondence analyses.
Eleven species of nongame small mammals were represented in 800 captures at SLNWR when data were combined for both trap types. Captures were about equal between snap and pitfall trapping efforts.
Nine species and 447 individuals were captured with snap traps during 2,600 trapnights (TN) for an overall capture rate of 17.2 individuals/100 TN (Table 8).
For all habitats combined, the five most common species of small mammals captured in snap traps were the white-footed mouse, deer mouse, meadow vole, masked shrew, and meadow jumping mouse. The most common small mammal captured with snap traps (all habitats included) was the white-footed mouse, representing 24.4% of the total captures (Table 8).
Seven species and 135 small mammals were captured with snap traps in 1,101 trapnights in tame grassland habitats on SLNWR for an overall capture rate of 12.3 individuals/100 TN (Table 9). Masked shrews (22.2%) and meadow voles (21.5%) were the most frequently captured species in tame grasslands.
Seven species and 243 small mammals were captured with snap traps in 978 trapnights in woodland habitats with an overall catch rate of 24.9 individuals/100 TN (Table 10). White-footed mice (37.0%) and deer mice (15.6%) were the most common species that were captured in woodland habitats.
Five species and 29 small mammals were captured with snap traps in 230 total trapnights in wetland-edge habitats (Table 11) at a catch rate of 12.6 individuals/100 TN. Meadow voles, deer mice, and meadow jumping mice were the most common species captured in wetland-edge habitats.
Five species and 34 small mammals were captured in snap traps in 180 trapnights, for a catch rate of 18.9 individuals/100 TN, in cropland habitat (Table 12). The most common species captured in croplands was the deer mouse.
Only six individuals representing six species were captured in 111 trapnights in seeded native grassland habitats with snap traps, for a catch rate of 5.4 individuals/100 TN (Table 13). However, only two fields of seeded native grasslands were available for sampling.
Correspondence analysis graphically depicts species:habitat associations (Fig 9). Based on snap trap data, masked shrews and northern short-tailed shrews were closely associated with tame grasslands and somewhat associated with woodland habitats, whereas meadow jumping mice and meadow voles were closely associated with wetland environments. White-footed mice showed a positive affinity for woodland habitats, and deer mice were most closely associated with cropland habitats.
|Figure 9. Correspondence analysis for small mammals captured with snap traps at Sand Lake National Wildlife Refuge, Brown County, South Dakota. SC=Sorex cinereus, BB=Blarina brevicauda, PL=Peromyscus leucopus, PM=Peromyscus maniculatus, MP=Microtus pennsylvanicus, ZH=Zapus hudsonius. 1=woodland, 2=wetland, 3=native, 4=tame, 5=crop.|
Ten species and 353 small mammals were captured in 762 pitfall trapnights for an overall capture rate of 46.3 individuals/100 TN (Table 14). With all habitats combined, meadow jumping mice made up 49.0% and masked shrews 19.8% of total pitfall captures with all habitats combined.
Eight species and 117 small mammals were captured in 281 pitfall trapnights, resulting in an overall catch rate of 41.6 individuals/100 TN in tame grassland habitats (Table 15). Three species (meadow jumping mouse, masked shrew, and meadow vole) made up 91.5% of pitfall trap captures in tame grassland habitats. The western harvest mouse was captured only once during the study; this occurred in a pitfall trap in tame grassland.
Seven species and 143 small mammals were caught at an overall pitfall capture rate of 62.4 individuals/100 TN in woodland habitats (Table 16). Four species (meadow jumping mouse, masked shrew, white-footed mouse, and meadow vole) made up 93.7% of all captures in this habitat type.
Six species and 52 small mammals were captured in 132 pitfall trapnights in wetland-edge habitats at an overall catch rate of 39.4 individuals/100 TN (Table 17). Meadow jumping mice, meadow voles, and masked shrews were 90.4% of the total individuals in this habitat type.
Five species and 41 individuals were captured in 120 pitfall trapnights in native grasslands at an overall catch rate of 34.2 individuals/100 TN (Table 18). The two most abundant species captured in this habitat type were meadow jumping mouse and plains pocket mouse. Eleven plains pocket mice were captured in native grassland habitats with a mean catch rate of 5.7 ± 3.26. This higher standard error is partly due to the fact that this species was captured in every habitat type but in relatively high amounts in only one native grassland on SLNWR. Plains pocket mice were caught only with pitfall traps.
|Table 18. Number, percent composition, and mean capture rate (number of individuals/100 trapnights) of nongame small mammals captured with pitfall traps in reseeded native grassland habitats (n = 4) at Sand Lake National Wildlife Refuge, Brown County, South Dakota, 23 May - 17 August 1995 and 28 May - 22 July 1996.|
|Plains pocket mouse||11||26.8||5.65||3.26|
|Northern grasshopper mouse||4||3.0||11.11||11.11|
|Meadow jumping mouse||17||12.9||28.23||23.98|
|Overall capture rate/100 trapnights||34.2|
Correspondence analysis performed on pitfall trap data supports species:habitat associations (Fig 10). Northern grasshopper mice and plains pocket mice exhibited a positive association with native grasslands, whereas white-footed mice showed a high affinity for woodland areas. Masked shrews were closely associated with woodland habitats, whereas meadow jumping mice and meadow voles showed a positive association with tame grassland and wetland-edge habitats.
|Figure 10. Correspondence analysis for small mammals captured with pitfall traps at Sand Lake National Wildlife Refuge, Brown County, South Dakota. SC=Sorex cinereus, OL=Onychomys leucogaster, PF=Perognathus flavescens, PL=Peromyscus leucopus, MP=Microtus pennsylvanicus, ZH=Zapus hudsonius. 1=woodland, 2=wetland, 3=native, 4=tame.|
Nongame small mammals captured at Sand Lake NWR were representative of the small mammal populations of north-central South Dakota with a few exceptions. One of these is the prairie vole, which was not captured during this study.
Distribution maps (Jones et al. 1985) show this species inhabiting the entire state, and meadow voles and prairie voles are sympatric species in most cases. However, meadow voles prefer mesic sites, whereas prairie voles prefer xeric sites (Lewin 1968, Wrigley 1974). The high water during the past few years at SLNWR may have contributed to the lack of xeric sites and, hence, the absence of prairie voles in trap samples.
Another small mammal species not captured on SLNWR was the red-backed vole, even though it was frequently captured at Waubay NWR, Day County, about 70 km southeast of SLNWR (J. Koerner pers comm, USFWS, Columbia, S.D.). This species inhabits the very northern edge of north-central and northeastern South Dakota (Jones et al. 1985). Waubay NWR is located in the Prairie Couteau physiographic region, whereas SLNWR is located in the James River Lowland physiographic region of South Dakota.
The western harvest mouse was captured only once during this study. This species is described as statewide by Jones et al. (1985); however, Choate and Jones (1981) described its distribution in South Dakota proper as "restricted to relatively mesic habitats in the west."
Common species on the refuge were similar to those found by Searls (1974) in northwest Brookings County. Likewise, Pendleton (1984) reported that meadow voles, deer mice, meadow jumping mice, and masked shrews were 95% of total captures on Waterfowl Production Areas in northeastern South Dakota, findings very similar to our results. Additionally, species surveyed on the refuge (1936-1941) were similar to those found during this survey, with some exceptions (Table 19).
|Table 19. List of resident mammal species observed at Sand Lake National Wildlife Refuge, Brown County, South Dakota.|
|Large brown bat||X***|
|Little brown bat||X|
|Kit (Swift) fox||X***|
|Franklin's ground squirrel||X||X||X|
|Richardson's ground squirrel||X||X||X|
|Thirteen-lined ground squirrel||X||X|
|Plains pocket gopher||X||X***|
|Northern pocket gopher||X||X|
|Plains pocket mouse||X||X|
|Meadow jumping mouse||X||X***|
|* furbearer trapping for medium-sized
mammals only, and maintenance of a predator exclosure
** not trapped, but a roadkill was found by refuge personnel
*** listed as "noted locally and expected on Sand Lake Waterfowl Refuge, Columbia, South Dakota"
**** Baird white-footed mouse (Peromyscus maniculatus) probably both species of Peromyscus spp
Habitats at SLNWR harbored representative assemblages of small mammals common to the northern Great Plains. Woodland species used man-made shelterbelts, many of which were small in size and occurred as habitat islands. Grant (1971) reported that meadow voles frequent moist grassland habitats but can be found in woodlands as a result of intraspecific competition. This species was captured in grassland and woodland habitat types at SLNWR but not in great abundance in either.
Clark et al. (1987) wrote that the white-footed mouse is a woodland species that may inhabit adjacent grassland habitats if densities in woodlands are high enough. The white-footed mouse was the most abundant small mammal captured with snap traps in woodland areas, whereas capture rates were lower than expected in both tame and native grassland habitats, many of which were fragmented by multi-row shelterbelts. Only one white-footed mouse was captured in seeded native grasslands throughout the entire study period.
Cropland habitats (though only sampled with snap traps and with a low trapping effort) supported habitat for five species of small mammals. Often, initial cultivation of cropland habitats decreases the species richness and diversity of small mammals (Hayslett and Danielson 1994). Species richness in cropland habitats at SLNWR was similar to that of other habitat types. However, deer mice were nearly 75% of the total captures in croplands.