Small Mammal Trapping Along an Elevational Gradient in Bear Canyon

Transcription

1 Rocky Mountain College Small Mammal Trapping Along an Elevational Gradient in Bear Canyon A pilot study to gain baseline information of small mammal abundance and diversity in the Pryor Mountains. Field work and paper by Robert Beattie, Field Assistants Mary Schvetz and Kaila Acoba, Assistant Professor Kayhan Ostovar 4/29/2011

2 Introduction Small mammal trapping was conducted in the Pryor Mountains between May 13 th, and May 29 th, 2010 and September 17 th and September 20 th, The focus of the study was to analyze small mammal distribution, diversity and abundance along an elevational gradient in Bear Canyon. The Pryor Mountains are managed by the United States Forest Service (USFS) in the northern part of the range and the Bureau of Land Management (BLM) on the southern part of the range. The northeastern boundary is the Crow Indian Reservation and the Bighorn Canyon National Recreation Area is farther East. The Pryor Mountain Wild Horse Range is in the southeastern portion of the Pryor Mountains. Currently, there is a lot of controversy over the grazing of wild horses in this area, thus many scientific papers on the Pryor Mountains have focused on this issue. There has been little work done studying the small mammal population. Small mammals play an important role in the ecology of the Pryor Mountains, serving as seed and fungal spore dispersal agents, soil modifiers, and an important prey base for larger predators. There is also a lot of controversy over the degree of off road vehicle use and the closure of certain unplanned roads in the Pryor Mountains (United States Forest Service 2008). This study will contribute information on small mammal populations that can be considered by the USFS and BLM when creating travel management plans. Studies have shown that roads and trails have impacts on the species composition of small mammal communities, favoring generalist species and those that do well with human disturbance (Sauvajot 1998). With the trails and roads that cross through the Pryor Mountains, it is possible that motorized vehicles have an impact on the small mammal community. Pearson et al. (2001) showed that habitat generalists such as deer mice (Peromyscus maniculatus) are likely to benefit with habitat changes, such as the increase in exotic plant species that are frequently found near roads where vehicles travel.

3 The Pryor Mountains are an isolated mountain range, disconnected from the rest of the Rocky Mountains by prairie and agricultural lands to the southwest and from the Bighorn Mountains by the Bighorn River and canyon to the east. Previous cooling periods may have allowed species to extend their distributions to include the Pryor Mountain range from the Beartooth Mountains (Patterson 1986). Through climate change and habitat alteration of the space in between the ranges there is the potential for genetically unique populations and a composition of species different from what may be expected in other nearby ranges due to a low potential for emigration into the population and a higher potential for extirpation without recolonization (Patterson 1986) (Beever et. al. 2003). In light of various climate change scenarios, elevational studies that develop baseline data to allow monitoring of insular species distribution and presence in mountain ranges are becoming increasingly important (Beniston 2003). As global temperature increases, species are expected to follow their preferred habitat up the mountain in elevation. This could cause some species that can only live at high elevations to be pushed out by other species, as their suitable living areas decrease as the climate warms and suitable habitat conditions deteriorate (Peterson 2003). The extirpation of other species in the Pryor Mountains like white tailed prairie dogs (Cynomys leucurus) may also have an impact on the habitat suitability for a diverse small mammal community. Compared to grassland communities without prairie dogs, prairie dog communities have been documented to have higher species diversity of small mammals (Miller et al. 1994). This may be due to the increase in plant diversity that is also recorded in prairie dog towns (Reading et al.1989). The relocation of white-tailed prairie dogs to parts of the Pryor Mountain range, if successful, may increase habitat suitability for other species of small mammals.

4 Methods A total of 19 trap lines were completed in the Pryor Mountains. Fifteen of these trap lines were surveyed between May 13 th, 2010 and May 29 th, Another session with four more lines was completed in the fall between September 17 th and September 20 th, Fourteen of these trap lines were in Bear Canyon or in the lower elevations and drainage leading up to the canyon with an additional trap line set in a potential location for white-tailed prairie dog relocation. Finally, we surveyed sites along Wyoming Creek, Crooked Creek and another in a high elevation meadow. The additional trap lines were used to scout out locations for future survey work in different habitats at different elevations outside of the Bear Canyon vicinity. In May, we sampled lower elevation locations first and then moved progressively up in elevation into Bear Canyon. There were five trapping sessions. Each session consisted of three nights trapping with four trap lines consisting of 50 traps each. An exception to this was during the fourth trap session, a fourth trap line was not set due to destruction of most of an entire line of traps by a black bear. Locations were taken at the middle of each trap line with a GPS unit. The weather the day of the set and the conditions 24 hours prior to checking traps each day was recorded. Locations for the trap lines were chosen to achieve maximum species diversity. An attempt was made to cover a wide range of elevations and a wide range of habitat types with a specific focus on Bear Canyon. The standard protocol for small mammal trapping used by the state of Montana was followed for all trapping sessions. Following the protocol, each trap line was approximately 100m long consisting of 10 trap stations with 10m intervals per line. Each station consisted of five traps: a Sherman live trap, two Victor mouse traps, a rat trap, and alternating sizes of small and large pitfall traps. These traps were placed in a cross pattern at each station with the pitfall in the middle, Sherman in front, Victor to the left and right, and the rat trap behind. All snap traps were baited with a mix of peanut butter and rodent bait.

5 Sherman live traps were baited with sweet feed dry bait. Two small pitfalls were used at each station where there was not a large pitfall. When checking traps, if a trap was sprung with no capture, it was counted as not available. If a trap had not been sprung or was successful in capture, it was counted as available. All dead captures were identified, labeled by location, trap line, trap type and sealed in a ziplock bag. All live captures were released unless further lab analysis for species identification was needed. For calculation purposes, any unidentified Peromyscus were distributed to the counts for deer mouse and white-footed mouse in accordance to the overall ratio at which these species were captured. In order to analyze the data collected by elevation, trap lines were classified into one of three different elevation zones. The lowest elevation zone was between 4,400 and 4,999 feet, the middle elevation zone was 5,000 and 5,599 feet, and the highest elevation zone was between 5,600 and 6,200 feet. These categories were determined by the overall distribution of the trap lines. To compensate for the different number of trap lines at each elevational level, the species per trap line, captures per line, and captures per trap night were calculated. These calculations allow comparison between the elevational levels because the amount of effort is taken into account in the calculations. The number of species per line was calculated by taking the number of species at an elevational level and dividing the number of lines at that elevational level, captures per line was calculated in this manner also. The captures per trap night were calculated by averaging the number of captures per trap night at each line in an elevational zone. Also, the number of each trap type was not the same, creating different effort for each trap type. To compare trap types the number of captures per trap night was calculated to eliminate the bias of effort. Results Two trapping sessions were completed in the Pryor Mountains. The first was in May and the other in September. A total of 14 trap lines were in Bear Canyon and the Bear Canyon drainage (See Figures 1 & 2).

6 Figure 1 Location of trap lines in Bear Canyon and the lower drainage. Figure 2 Location of trap lines in Bear Canyon.

7 A total of 172 individuals and 11 species were captured during this survey. Of these 11 species, six are members of the Muridae family. These include the deer mouse (Peromyscus maniculatus), whitefooted mouse (Peromyscus leucopus), montane vole (Microtus montanus), prairie vole (Microtus ochrogaster), southern red-backed vole (Myodes gapperi), and bushy-tailed woodrat (Neotoma cinerea). Three species are members of the Sciuridae family. These include the least chipmunk (Tamias minimus), yellow-pine chipmunk (Tamias amoenus), and red squirrel (Tamiasciurus hudsonicus). The montane shrew (Sorex monticolus) was the only member of the Soricidae family, and the Ord s kangaroo rat (Dipodomys ordii) was the only member of the Heteromyidae family (See Table 1). Table 1 - Number of species captured by elevation. Species Total Deer mouse White footed mouse Kangaroo rat Wood rat Red backed vole Montane vole Prairie vole Least chipmunk Yellow pine chipmunk Red squirrel Montane shrew Total The deer mouse and white-footed mouse compromised 83% of all captures with 74 deer mice and 69 white-footed mice captured. The next most abundant species was the montane vole with eight captures followed by the kangaroo rat with six captures. All other species had four or less captures (Table 1).

8 Trap line 19, located along Crooked Creek, had the highest number of captures with 29 individuals, the highest captures per trap night (0.19) and four species (See Figure 2 & 3). Trap line 4, had the next highest number of captures with 23 individuals captured comprised of two species. Many lines had very low abundance with eight or less captures. The lowest number of captures was at line 7, 13 and 6 with two, three and three individuals captured respectively. Lines 5, 11, 9 and 19 each had four species captured. Line 6 was the only trap line that recorded just one species (See Figure 3 & 4). Figure 3 Number of captures for each trap line. Figure 4 Captures per trap night by trap line.

9 The Sherman large live trap had the highest number of captures per trap night at 0.17 captures per night, followed by the Sherman small live trap with 0.12 captures per night, and the mouse trap at 0.07 captures per night. The rat trap had the lowest number of captures per trap night at 0.02 captures per night, and the pitfall had the second lowest at 0.03 captures per night (Figure 5). Figure 5 Captures per trap night by trap type. The largest number of trap lines fell between 5600 and 6200 feet. This elevation zone also produced the highest number of captures, 91, and the highest number of species (eight) (See Table 2). The second largest number of trap lines fell between 5000 and 5599 feet. There were 51 captures and six species at this elevation zone. The smallest number of trap lines fell between 4400 and 4999 feet. There were 30 captures and four species at this elevation. The highest number of captures per line was at elevations between 5000 and 5599 feet, with 10.2 captures per line. This elevation also had the highest number of species per line, 1.2, and the highest number of captures per trap night, The second highest number of captures per line was at elevations between 5600 and 6200 feet, with 9.1 captures per line. This elevation also had the second highest number of captures per trap night, 0.06, but the lowest number of species per line, 0.8. The

10 lowest number of captures per line and captures per trap night was between 4400 and 4999 feet with 7.5 captures per line and 0.05 captures per trap night. This elevation fell in the middle with one species per line. Lines 9, 11 and 19 all fall between 5600 and 6200 feet, compromising 3 of the 4 trap lines that recorded four species (Table 2) (Figure 6). Table 2 Effort comparison of elevation levels. Elevation lines captures captures/line species species/line trap nights captures/trap night Figure 6 Species captured by elevation for each trap line. At each elevation zone, deer mice and white-footed mice compromised the majority of the captures, 73%, 92%, and 82% as elevation increases. The only other species found at all three elevation zones was the yellow-pine chipmunk. The species in second highest abundance between 4400 and 4999 feet was the Ord s kangaroo rat with 6 individuals captured. Only deer mice and white-footed mice were captured in abundances higher than one individual at elevations between 5000 and 5900 feet. The

11 species in second highest abundance between 5600 and 6200 feet was the montane vole with eight individuals captured. The Ord s kangaroo rat was the one species that was only caught between 4400 and 4999 feet. The red-backed vole and least chipmunk were the species that were only caught between 5000 and 5599 feet. The red squirrel, prairie vole, and montane vole were the species that were only caught between 5600 and 6200 feet (Figure 7). Figure 7 Species composition and number of species at different elevation zones. During this study we recorded all incidental herpetofauna observations and also experimented with a couple of remote camera trap stations. Of particular interest was the documentation of a peregrine falcon (Falco peregrinus) nest site at the campground in Bear Canyon. This site should be monitored again in 2011 to see if these birds return. The camera trap recorded a mountain lion (Puma concolor) as well as a black bear (Ursus americanus) in Bear Canyon. Greater short horned lizards (Phrynosoma hernandesi) were more frequently encountered in the flat open terrain outside of Bear Canyon below

12 5,000 ft., however, we did have one record at 6,018 ft. Most sage-brush lizards (Scelopoporus graciosus) were found at around 5,000 feet in Bear Canyon (See Table 3). Table 3. Incidental observations and camera trap records from Bear Canyon. Species Location Altitude (ft) Common sagebrush lizard N W Common sagebrush lizard N W Common sagebrush lizard N W Common sagebrush lizard N W Common sagebrush lizard N W Common sagebrush lizard N W Common sagebrush lizard N W Greater short-horned lizard N W Greater short-horned lizard N W Greater short-horned lizard N W Greater short-horned lizard N W Greater short-horned lizard N W Greater short-horned lizard N W Bullsnake N W Bullsnake N W Rattlesnake N W Eastern racer N W Black bear N W Mountain lion N W Peregrine Falcon N W Discussion The results of this study point to the middle elevation zone as having the highest abundance and diversity of species when effort is factored into the equation. Although the highest number of species and captures occurred in the highest elevation zone, the amount of effort there was greatest. When using the calculations that remove the bias of effort, the middle elevation zone appears to have been the most productive during this study. The middle elevation zone had the highest number of captures per line, species per line, and captures per trap night.

13 Clearly this shows that a significant level of effort is required to gather a more complete picture of species abundance and diversity at these sites. In our study as more effort was expended more species were recorded making it hard to accurately compare different elevation zones. Species that were not recorded at sites may still exist at these locations. One species that was captured at the highest elevation zone but not in the middle elevation zone, the red squirrel, was observed multiple times at the camp where researchers were staying which would have fallen into the middle elevation zone. The other two species that were captured at the highest elevation zone but not at the middle elevation zone were the prairie vole and the montane vole. The lone prairie vole captured during this study was from trap line 16, the lowest elevation trap line that falls within the highest elevation zone. All other voles captured, with the exception of one southern red-backed vole were at trap lines at least 200 feet higher. These were all montane voles. Montane and prairie voles are most commonly associated with dry grasslands. Where sympatric, the montane vole is generally found at higher elevations than the prairie vole (Foresman 103). This suggests that prairie voles may be found at lower elevations than the one recorded, as there appears to be a spike in the abundance of montane voles after a gain of approximately 200 feet. There was not much dry grassland habitat within Bear Canyon in the middle elevation zone, and it may be beneficial in the future to survey more preferable habitat within this elevation zone for prairie voles to determine if the abundance is higher in more open habitat outside of the canyon bottom. It is likely that either montane or prairie voles exist at the middle elevation as well, if not both. One concerning factor in the middle elevation zone is the dominance (92%) of Peromyscus sp. No other species was recorded in abundance greater than one in this zone. It may be beneficial at this elevation with such a high number of Peromyscus sp. to sample for more than 3 nights in the same location to remove some of the Peromyscus sp. to create a better chance of capturing some of the less abundant species. Some of the least diverse sites also had a dominance of Peromyscus sp. As mentioned

14 earlier Peromyscus sp. and may benefit with habitat changes, such as the increase in exotic plant species that are frequently found near roads where vehicles travel. Yahner (1992) and Pearson et al. (2001), both show that disturbances favor Peromyscus and other generalist species. A more thorough investigation of their distribution related to the level of vehicle traffic is warranted. The highest elevation zone had the trap line with the most captures (line 19), which ran parallel to Crooked Creek below where the tributary Wyoming Creek enters. The highest elevation zone also produced three lines which had four different species captured, while the middle elevation only had one such line. The lowest elevation zone never had more than three species occurring on a single trap line. This diversity can likely be attributed to the greater amount of water and moisture availability year round at higher elevations in the Pryor Mountains. Overall the lowest elevation zone was the poorest in terms of species diversity, with only four species, including the two species of Peromyscus sp. One of the noticeable differences between this elevation zone and the others is that there was less domination by Peromyscus sp. Trap line 13, at the site of a potential white-tailed prairie dog relocation, was the only trap line of the survey where there was a species (Ord s kangaroo rat) which outnumbered the Peromyscus sp. Ord s kangaroo rat is especially adapted to sandy arid environments and may be able to compete fairly well with the generalist Peromyscus sp. at lower elevations and modify habitats that are suitable for other species. The relocation of white-tailed prairie dogs may be an important step in reintroducing another key habitat modifier to the Pryor Mountains. Monitoring the small mammal diversity at these sites should be considered to document changes in the small mammal community related to white-tailed prairie dog restoration.

15 The documentation of 11 species of small mammals in the Pryor Mountains is an important first step in better understanding the habitat quality of the area. Since we focused on Bear Canyon for this study much is still unknown about overall species diversity in the Pryor Mountains. Our results showed a correlation with effort and the continued discovery of additional species. This highlights the important fact that more work still needs to be done to thoroughly understand the small mammal community in Bear Canyon, let alone the Pryor Mountains. The important role that small mammals play in the ecosystem deserves more attention through a greater survey effort of the Pryor Mountains. Literature Cited Beever, E. A., P. F. Brussard, and J. Berger Patterns of apparent extirpation among isolated populations of pikas (Ochotona Princeps) in the Great Basin. Journal of Mammology. 84: Beniston, M Climatic change in mountain regions: A review of possible impacts. Climatic Change 59: Foresman, Kerry Ryan. The Wild Mammals of Montana. Lawrence, KS: American Society of Mammalogists, Print. Miller, B., Gerarado Ceballos, and Richard Reading The prairie dog and biotic diversity. Conservation Biology. Volume 8 No Miller, D. Sterling and Mark Van Putten Prairie dogs: The case for listing. Wildlife Society Bulletin. 27(4): Patterson, B. D. and W. Atmar Nested subsets and the structure of insular mammalian faunas and archipelagos. Biological Journal of the Linnean Society 28:

16 Pearson, D. E., Y. K. Ortega, K. S. McKelvey and L. F. Ruggiero Small mammal communities and habitat selection in Northern Rocky Mountain bunchgrass: Implications for exotic plant invasions. Northwest Science 75: Peterson, A. T Projected climate change effects on Rocky Mountain and Great Plains birds: generalities of biodiversity consequences. Global Change Biology 9: Sauvajot, R. M., M. Buechner, and D. A. Kamradt Patterns of human disturbance and response by small mammals and birds in chaparral near urban development. Urban Ecosystems 2: United States Forest Service United States Forest Service Beartooth Travel Management Record of Decision Yahner, R. H Dynamics of a small mammal community in a fragmented forest. American Midland Naturalist 127: