1. Introduction Methods & Materials Results & Conclusions Habitat use is typically a non-random process; animals preferentially occupy patches where resources are available (Garshelis 2000). Habitat selection results from multiple choices made by individuals during their activities including foraging, escape from predators, mate searching, and refuge use (Prevedello et al. 2010). Behavioral habitat selection is a complicated phenomenon involving a perceptual selectivity by the individual to or from a specific habitat type (Baccus and Horton 1984). This paradigm also carries over to microhabitat use of small mammals, such as Peromyscus pectoralis, or the white-ankled mouse. Peromyscus pectoralis is relatively common within its distribution. Based on capture location data, P. pectoralis is commonly associated with rocky areas including cliffs, limestone outcrops, or talus slopes with some form of woody vegetation (Etheredge et al. 1989). Additionally this species has also been known to inhabit oak-juniper associations, arid and semiarid brush-covered foothills, and in Mexican populations (Eastern Durango) P. pectoralis has been collected in both grassland and desert habitats (Baker and Greer 1962). In New Mexican populations, P. pectoralis has been found to inhabit desert scrublands, arid grasslands, and piñon- juniper woodlands, captured in rocky situations on eroded walls of arroyos, in draws and canyons, and on nearly flat summits (Geluso 2004). A substantial amount of information exists in the literature about the habitat affinities of P. pectoralis (Baccus 2009); however, an in-depth study of vegetation associations and vegetative structure utilization has not been conducted within these broad habitat categories. At the Devils River State Natural Area (DRSNA) - Big Satan Unit (BSU) (formerly known as the ‘South’ unit), P. pectoralis is one of the dominant rodent species found within all habitat types sampled, and captured most commonly during preliminary trapping (64.8% of 105 rodent captures from Feb – Aug 2013). Three different level IV ecoregions meet at the BSU(Griffith et al. 2004). This mixing of floral communities has led to the generation of six main vegetation types assessed by Raven Environmental Services, Inc., in 2011. For the purpose of creating generalized macrohabitat types, this study will combine these six previously mentioned vegetation associations into four habitat types: woodland, shrubland, grassland, and rocky slope (Figure 2). To determine more refined habitat requirements, spool-and-line tracking will be used, with assessment of microhabitat components along the trap-line. Spool-and-line tracking can be an efficient, economical, and accurate mode of collecting data on animal movement patterns (Steinwald et al. 2006). Spool-and-line tracking uses a reverse-spun bobbin glued to the dorsal side (Attachment location depends on size of small mammal) of the individual which unspools as it moves throughout its environment. This method has been used to address both basic and conservation-related topics, including foraging behavior (Vernes and Haydon 2001), nest location (Woolley 1989), habitat use (Cox et al. 2000), and habitat search behavior (Zollner 2000). For the purpose of this study spool-and-line tracking will be used to assess microhabitat and vegetative structure utilization of P. pectoralis. The purpose of this study is to (1) delineate which microhabitat parameters are important to the microscale distribution of Peromyscus pectoralis; and if microhabitat selection patterns vary among the four aforementioned macrohabitat types, (2) if microhabitat selection at the BSU is uniform across the species, and (3) to test the efficacy of the spool-and-line tracking technique to determine microhabitat utilization and vegetative structure use for the species. References C LINT N. M ORGAN AND D R. R OBERT C. D OWLER Figure 2. Color coded vegetation map of Devils River State Natural Area – Big Satan Unit depicting the four macrohabitat types: Woodland - shown in green, Grassland - shown in white/green, Rocky Slope - shown in grey/white angled bars, and Shrubland - shown in blue. Locations of the 12 sampling locations (Three sampling sites per four habitat types) within DRSNA are shown. Figure 1. Map of Val Verde Co. and surrounding area in South Texas, showing the North (Del Norte) and South (Big Satan) units of the Devils River State Natural Area (DRSNA), north of the International Amistad Reservoir. ABSTRACT: The purpose of this study conducted at the Devils River State Natural Area – Big Satan Unit, in Val Verde County, Texas, is to delineate which of 21 selected microhabitat variables are important to the microscale distribution of the white-ankled mouse (Peromyscus pectoralis) and to determine if microhabitat selection patterns vary among four macrohabitat types (shrubland, woodland, grassland, and rocky slope). Data are collected on microhabitat by using the spool-and-line tracking technique. A preliminary set of three spool-and-line trials have been conducted (each with a randomized control line for comparison), in the shrubland (1) and rocky slope (2) macrohabitat types. Comparisons of microhabitat parameters across all mice spooled, the shrubland mouse and the combined rocky slope mice, and comparisons between rocky slope sites were made using a Student’s paired t-test. Out of 21 microhabitat variables examined, no statistically significant (P < 0.05) differences were found between habitats and control sites or between macrohabitat sites. These preliminary data suggest that the foraging pattern of mice at this study site does not differ from the expected, based on these analyses. Further data collection at all macrohabitats and larger sample sizes may reveal different patterns in microhabitat use. Additional statistical analyses including multivariate approaches also may show differences in the use of microhabitats by P. pectoralis. Data collection on microhabitat selection in this mouse species will continue through summer 2014. D EPARTMENT OF B IOLOGY, A NGELO S TATE U NIVERSITY, S AN A NGELO, TX Live-trapping Starting in January 2014, habitat-specific trap-lines will be placed in triplicate at three separate but similar trap sites, randomly selected within their respective macrohabitat type (Figure 2). Trapping will continue until our spool-and-line goals are met (5 spoolings/site; 60 total). Trap-lines (each consisting of 50 LFATDG Sherman traps) will be set out in each of the habitat types once a month and left open for two consecutive nights. Concentrated trapping effort will be conducted during the summer months of 2014. Traps will be set out each evening prior to sunset, and traps will be checked once in the night for captures, and again the following morning soon after sunrise. Upon capture, all rodents will be identified to species level, sexed, and evaluated for age class and reproductive conditions. Any juveniles captured will be released. Live mammal trapping and handling will conform to the guidelines of the American Society of Mammalogists (Sikes and Gannon 2011). A single P. pectoralis individual captured prior to the nighttime trap check on each trap-line, after processing, will be used for spool and line analysis. Spool-and-line Tracking Microhabitat use of P. pectoralis will be assessed via spool-and-line analysis using cocoon bobbins. The bobbin will be ≤ 5% of the total body weight as to not harm or hinder the rodent as it conducts its natural activities (Macdonald 1978). These bobbins will be wrapped in waterproof medical tape and then glued to the dorsal side of the rodent longitudinally (Steinwald et al. 2006; Cox et al. 2000). As P. pectoralis forages and travels in its respective habitat the line will spool out from the middle of the bobbin providing a way to observe its trail. A total of 10 microhabitat scores, one at each 5 m intervals starting at 10 m, will be used for each individual line. To ascertain microhabitat parameter selection, other microhabitats available to P. pectoralis must be assessed. At the site of release a 'random path‘, also with 10 points, will be generated for comparison. The path used by each mouse will additionally be examined for arboreal activity. Microhabitat Classification Microhabitat will be assessed and scored at selected spool-and-line points using 21 predetermined microhabitat parameters. The 21 microhabitat parameters in this study are adapted from Cox et al. (2000) and Doty and Dowler (2006), and are shown in Table 1. Each microhabitat parameter will be analyzed within a 0.5m radius from the selected spool-and-line point, using a rigid 0.5m radius vinyl-coated steel cable as shown in Figure 4. Table 1. Categories used to classify microhabitat parameters in a 0.5 m radius around selected spool-and-line points during live trapping for Peromyscus pectoralis at Devils River State Natural Area - Big Satan unit. Since January of 2014, four research trips have been made to DRSNA – BSU, and three mice have been successfully spooled and analyzed. One within the shrubland macrohabitat type, and the other two within the rocky slope habitat type, each with a randomized control line for comparison. Results of microhabitat parameter analysis is shown in Figure 3. Within the rocky slope habitat the spool-and-line analysis observed no arboreality, whereas in the shrubland macrohabitat we observed 16m of arboreality in tall woody vegetation. This tall woody vegetation is lacking in the rocky slope habitat type and explains why we observe this pattern. The distance traveled during one night of foraging ranged from 40m on Jan 25 th, to 58m on Jan 26 th. Comparisons of microhabitat parameters across all mice spooled, the shrubland mouse and the combined rocky slope mice, and comparisons between rocky slope sites were made using a Student’s paired t-test. Out of 21 microhabitat variables examined (Table 1.), there were no statistically significant (P < 0.05) differences found between microhabitats and control sites or between the two macrohabitat types (Shrubland and rocky slope). These preliminary data suggest that the foraging pattern of mice at this study site does not differ from the expected, based on these analyses. Given the limited current data, further data collection at all four macrohabitats is needed, and a larger sample size at each site may reveal differentiated patterns in microhabitat use. Additional statistical analyses including multivariate approaches also may show differences in the use of microhabitats by P. pectoralis. Data collection on microhabitat selection in this mouse species will continue through the summer months of 2014. MICROHABITAT PARAMETER (MP) DATA DATE LOCALITY (TEXAS: VAL VERDE CO., DRSNA-BSU, TYPEHabitat Averages of Microhabitat Parameters LEAF LITTER COVER (%) CANOPY COVER (%) ROCK COVER (%) SHRUB COVER (%) CACTUS COVER (%) FORB COVER (%) GRASS COVER (%) BARE SOIL COVER (%) # OF VERTICAL STEMS # OF GROUD STEMS # OF LOGS ALIVE TREES DEAD TREES # OF SHRUB SPP. LECHUGUILLA SOTOL BLACKBRUSH CENIZA GUAJILLO PRICKLY PEAR ASHE-JUNIPER Jan 25th NW Pila Spool & Line Rocky Slope 103200113200010110100 Random Rocky Slope 103111112200010000010 Jan 26th Devils Back Spool & Line Shrubland 221101113310010000000 RandomShrubland 001001221100000000000 Feb 8thBuzzard Roost Spool & Line Rocky Slope 102200112100010000000 Random Rocky Slope 003210112100010000010 N/A Rocky Slope Combined Spool & Line Rocky Slope 102200113200010000000 Random Rocky Slope 003110112200010000010 Figure 3. Chart displaying the adjusted (rounded to the nearest whole number) averages of each of the three preliminary spool-and-line trials conducted, also including the adjusted averages generated from combining the two rocky slope microhabitat parameter data. Figure 4. Image showing the 0.5m radius cable used, with center point of circle on a spool-and-line sampling point in shrubland macrohabitat type. 1.Baccus, J. T., J. M. Hardwick, D.G. Huffman, AND M. A. Kainer. 2009. Seasonal trophic ecology of the white-ankled mouse, Peromyscus pectoralis (Rodentia: Muridae) in central Texas. Texas Journal of Science 61:97-118. 2.Baccus, J.T., AND J.K. Horton. 1984. Habitat utilization by Peromyscus pectoralis in central Texas. Festschrift for Walter W. Dalquest in Honor of His Sixty-Sixth Birthday. Pp. 7-26. Midwestern State University, Wichita Falls, Texas. 3.Baker, R. H., AND J. K. Greer. 1962. Mammals of the Mexican State of Durango. 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Journal of Mammalogy 92:235-253. 13.Steinwald, M. C., B. J. Swanson, AND P. M. Waser. 2006. Effects of spool-and-line tracking on small desert mammals. Southwestern Naturalist 51:71-78. 14.Vernes, K., AND D. T. Haydon. 2001. Effect of fire on northern bettong (Bettongia tropica) foraging behaviour. Austral Ecology 26:649-659. 15.Woolley, P. A. 1989. Nest location by spool-and-line tracking of dasyurid marsupials in New Guinea. Journal of Zoology 218:689-700. 16.Zollner, P. A. 2000. Comparing the landscape level perceptual abilities of forest sciurids in fragmented agricultural landscapes. Landscape Ecology 15:523-533. Acknowledgments I would first like to thank the CITR foundation for granting me the Graduate Research Fellowship, as well as Angelo State University. I would also like to thank the Park Superintendent of DRSNA – BSU Joe Joplin, as well as the Texas Parks and Wildlife Department for providing an opportunity to pursue this research objective. A special thanks to the many research assistants and colleagues for field work assistance, Austin Osmanski, Grayson Allred, Laramie Lindsey, Zachary Ellsworth, Erin Adams, Stephanie Martinez, Dustin Tarrant, Miles Hubbell, Mark Lee, Ben Britton, Ross Kushnereit, and many others.