41 Vegetative Characteristics of Bachman’s Sparrow Habitat in the West Gulf Coastal Plain Robert Allen1,* and D. Brent Burt2 Abstract - While Peucaea aestivalis (Bachman’s Sparrow) will use several habitat types (e.g., pine savanna, pine plantations, clear cuts, abandoned fields), specific vegetative conditions must be present for a site to be acceptable. Bachman's Sparrow presence/absence was examined in forested (mature Pinus palustris [Longleaf Pine] forest and mid-aged pine plantations) and early successional habitats (clear cuts and three-year-old pine plantations) to determine which vegetation variables were best for predicting sparrow occurrence. Across all sampled habitats, the probability of Bachman’s Sparrow presence increased with increases in canopy cover and percent grass groundcover. Probability of presence decreased with increases in shrub-layer rating and percent bare ground. When considering only forested habitats, the probability of Bachman’s Sparrow presence increased with increasing canopy cover and percent grass groundcover, but decreased with increasing canopy height, shrub height, and stand basal area. In early successional habitats, the probability of Bachman’s Sparrow presence increased with greater grass groundcover and decreased with more bare ground. Also, there were more occupied sites in forested habitats than in early successional habitats. Introduction Peucaea aestivalis Lichtenstein (Bachman’s Sparrow) is endemic to North America, ranging throughout the southeastern and east-central portions of the US. Throughout its range, Bachman’s Sparrow is associated with open pine forests and early successional habitats. Bachman’s Sparrow occurs in several habitat types (e.g., pine savanna, pine plantations, clear cuts, abandoned fields), but specific vegetative conditions must be present for a site to be acceptable for this species (Dunning and Watts 1990). Dense herbaceous groundcover comprised of grasses and forbs up to 1.5 m tall is essential for the sparrow’s nesting habitat because this species nests exclusively on the ground (Dunning and Watts 1990, Meanley 1959, Plentovich et al. 1998). Nests are constructed at the bases of grass clumps or other low vegetation that provide concealment and, theoretically, increase the number of potential nest sites a predator must search (Haggerty 1988, Martin and Roper 1988, Weston 1968, Wolf 1977). Nest design varies from an open cup to a complete dome, and nest entrances often face north. Domed nests and north-facing entrances may aid in thermoregulation of nest contents by protecting them from extreme heat associated with direct sunlight (Haggerty 1995). Midstory and shrub-level foliage density also influence the presence/absence of Bachman’s Sparrow (Dunning and Watts 1990, Plentovich et al. 1998, Wan A. 1United States Fish and Wildlife Service, 506 Raguet Street, Nacogdoches, TX 75965. 2Department of Biology, Stephen F. Austin State University, PO Box 13003 SFA Station, Nacogdoches, TX 75962-3003. *Corresponding author - robert_allen@fws.gov. Manuscript Editor: Jerry Cook Proceedings of the 5th Big Thicket Science Conference: Changing Landscapes and Changing Climate 2014 Southeastern Naturalist 13(Special Issue 5):41–51 Southeastern Naturalist R. Allen and D.B. Burt 2014 42 Vol. 13, Special Issue 5 Kadir 1997). Sites with sparse midstory vegetation have a higher occupancy rate than sites with a high midstory vegetation density (Dunning and Watts 1990, Plentovich et al. 1998, Wan A. Kadir 1997). Dunning and Watts (1990) recorded a higher density of Bachman’s Sparrow territories associated with snags or sparse, tall shrubs than sites lacking these structures, which males use as singing perches, and which parents land on momentarily before returning to the nest (Dunning and Watts 1990, Haggerty 1995, Meanley 1959). Bachman’s Sparrow populations expanded northward in the early 20th century, as a result of the deforestation that accompanied agricultural development. Populations began to decline in the 1930s with a retraction of the species’ northern range and the localized extinction of populations in the South (Plentovich et al. 1998). Although the present range is similar to the historic range, the species continues to decline, becoming rare and locally distributed (Dunning and Watts 1990). Fire frequency reduction in the southeastern US is likely a key factor associated with the decline of the Bachman’s Sparrow (Conner et al. 2005). The USFWS lists the Bachman’s Sparrow as a species at risk (Hunter et al. 1993). The Nature Conservancy ranks the Bachman’s Sparrow as endangered in several southern states, including Texas, and rare in three others (Drilling 1985). The Texas Parks and Wildlife Department lists the Bachman’s Sparrow as threatened (Campbell 2003). The western boundary of this sparrow’s range coincides with the western limit of the southeastern pine forest ecosystem in Texas. Of the three described subspecies of Bachman’s Sparrow, only Peucaea aestivalis illinoensis Ridgway occurs in the western portion of the range. Characteristics of the Bachman’s Sparrow population in this region have been understudied when compared to eastern populations. Shortrotation pine management and fire suppression are common in this region, both of which are detrimental to this sparrow (Conner et al. 2005, Engstrom et al. 1984, Tucker et al. 1998). In this study, Bachman's Sparrow presence/absence was examined in forested (mature Longleaf Pine forest and mid-aged pine plantations) and early successional habitats (clear cuts and three-year-old pine plantations) to determine which vegetation variables are indicative of occupied sites and thus best for predicting occurrence in the western portion of the range. This information may assist land managers in their efforts to provide suitable habitat for this species. Field Site Description We conducted our study in eastern Texas on the Angelina National Forest and adjacent commercial timber industry lands in Jasper and Angelina counties. This area is known as Longleaf Ridge and is characterized by a mixture of federal and private lands. Federally managed pine forests in this area have rotation age of 80– 120 years and a prescribed burn cycle of 3–5 years, while commercially managed pine forests have a rotation age of 40–60 years and prescribed burns are infrequent. Upland pine forests are dominated by Pinus palustris P. Mill (Longleaf Pine) and Pinus taeda L. (Loblolly Pine) in the overstory, with Longleaf Pine, Loblolly Pine, Liquidambar styraciflua L. (Sweetgum) and various Quercus spp. (oak species) Southeastern Naturalist 43 R. Allen and D.B. Burt 2014 Vol. 13, Special Issue 5 sparsely distributed in the midstory. Shrub-layer vegetation is dominated by Ilex vomitoria Ait. (Yaupon), Callicarpa americana L. (American Beautyberry), and Sweetgum, while dominant groundcover species include Schizachyrium scoparium Michx. (Little Bluestem) and Pteridium aquilinum L. (Bracken Fern). Methods Seventy sample sites were established in our study area during the 2003 and 2004 breeding seasons. We chose sample sites randomly and divided them evenly among early successional and forest habitat-types. Early successional habitats consisted of clear cuts (25 sites) and a three-year-old pine plantation (10 sites). Forested habitats consisted of mature Longleaf Pine forest (25 sites) and a mid-aged pine plantation that was ≈50 years old (10 sites). Sites were circular with a radius of 50 m. A minimum of 100 m separated site perimeters from edges, and a minimum of 200 m separated adjacent sites. Audio data loggers (Johnson et al. 2002) were used to conduct point-count surveys at all sites. Data loggers were placed in the center of sample sites and they recorded avian vocalizations for one minute each day during the survey period at approximately one hour after sunrise. In 2003, surveys began 11 February and ended 11 July and in 2004, surveys began 3 February and ended 1 August. We collected tapes once every two weeks, and the data loggers were checked for malfunctions. Bachman’s Sparrow presence/absence and the number of singing detections (number of days singing was detected) were assessed for each site. To consider a site as occupied, we used a minimum of 5 detections in a breeding season. This criterion helped assure that occupied sites represented territories and prevented misclassification of sites used temporarily by floaters or transient migrants. One person (R. Allen) analyzed all tapes. Vegetation within sites was measured between May and July in both years. The sampling protocol was consistent across all habitat types. The data logger served as the center of the site, and we measured vegetation along four transects extending 50 m in the four cardinal directions. The following habitat variables were recorded at the site center and at 25-m increments. Groundcover was measured using an ocular tube (11.5 cm long by 5.0 cm in diameter) and percentages of grass, forb, bare ground, and leaf-litter cover were recorded. Groundcover height was measured using a meter stick. Percent canopy cover was also estimated with the ocular tube, and canopy height was recorded with a clinometer. Shrub-level vegetation was ranked using a scale of 1 to 5. A rank of 1 = absence of shrublayer, 2 = sparse shrub layer, 3 = half open, 4 = predominant shrub-layer, and 5 = closed shrub-layer. Shrub height was recorded using a meter stick. Stand basal area of all trees was measured at 25 m on each transect using a metric one-factor prism. Shrub density was measured with a density board (MacArthur and MacArthur 1961) in each cardinal direction from the 25-m mark along each transect. The number of stems (trees with a diameter at breast height >10 cm) within an 11.3-mradius plot centered at 25 m on each transect was measured using a diameter at breast height (dbh) tape. The number of snags and singing perches was counted Southeastern Naturalist R. Allen and D.B. Burt 2014 44 Vol. 13, Special Issue 5 within a 11.3-m-radius plot centered at 25 m on each transect. For this study, a singing perch is described as any object able to support the weight of a Bachman’s Sparrow (tree, shrub, snag, grass stalk, etc.). We developed predictive models that included combinations of habitat variables that best distinguished between sites with sparrows and sites without sparrows. These logistic regression models were developed using stepwise regression procedures. We used both forward-addition and backward-elimination methods to derive final models in which the coefficient of each retained habitat variable made a significant contribution to the model at P > 0.10. Models were developed using the entire data set (forested and early successional sites combined), and separately for forested habitats and early successional habitats. The ability of each model to correctly predict Bachman’s Sparrow occupancy was also evaluated by comparing model predictions to observed presence/absence patterns seen at each study site. We also tested whether occupied sites were evenly distributed between forest and early successional habitats using a chi-squared test. All statistical analyses were performed in JMP (version 8.0.2; JMP 2009). Results Shrub-layer rating, percent canopy cover, percent grass groundcover, and percent bare ground were retained in the logistic regression model that predicted Bachman’s Sparrow presence or absence among all sites (Table 1). The probability of sparrow presence increased with a reduced shrub layer and less bare Table 1. Logistic regression model results for habitat variables influencing Bachman’s Sparrow habitat occupancy during the 2003 and 2004 breeding seasons. Estimate = estimate of explanatory slope for habitat variables (β x); SE = standard error of slope estimate; c² = chi square statistic testing H0: slope estimate = 0; P > c² = probability to reject H0 Range observed Variable in this study Estimate SE c² P > c² All sites model n = 70 Intercept NA -0.886 1.703 0.27 0.602 c² = 37.307 Shrub-layer rating 1–4 -1.100 0.520 4.46 0.035 P > c² = <0.0001 Canopy cover (%) 0–58 7.269 2.655 7.49 0.006 R² = 0.384 Grass cover (%) 3–80 9.131 3.234 7.97 0.005 Bare ground (%) 0–35 -20.745 9.487 4.78 0.029 Forest sites model n = 35 Intercept NA 12.948 7.297 3.15 0.760 c² = 13.039 Stand basal area m2/ha 5.25–21 -0.482 0.277 3.02 0.082 P > c² = 0.004 Canopy height (m) 18.75–37.0 -0.237 0.138 2.95 0.086 R² = 0.311 Shrub height (m) 1.23–2.78 -6.755 2.927 5.33 0.021 Canopy cover (%) 13–58 26.648 12.258 4.73 0.030 Grass cover (%) 3–69 18.046 7.707 5.48 0.019 Early successional model n = 35 Intercept NA -2.635 2.018 1.70 0.191 c² = 15.121 Grass cover (%) 16–80 8.577 4.866 3.11 0.077 P > c² = 0.0005 Bare ground (%) 0–35 -32.163 14.99 4.60 0.032 R² = 0.361 Southeastern Naturalist 45 R. Allen and D.B. Burt 2014 Vol. 13, Special Issue 5 groundcover. Sparrow presence was also more likely with greater canopy cover and grass groundcover. The model correctly classified Bachman’s Sparrow presence in 27 of 35 (77.1%) sites with confirmed sparrow use, while absence was correctly classified in 26 of 35 (74.3%) sites where sparrows were not det ected (Fig. 1). The model for predicting Bachman’s Sparrow presence in forest sites retained stand basal area of all trees, canopy height, shrub height, percent canopy cover, and percent grass groundcover (Table 1). Probability of sparrow site use increased with reduced stand basal area of all trees and lower canopy and shrub heights. Sparrow site use also increased with greater percent canopy cover and percent grass groundcover. This model correctly classified Bachman’s Sparrow presence in 23 of 25 (92.0%) cases, while absence was correctly classified in 8 of 10 (80.0%) cases (Fig. 2). The model for predicting Bachman’s Sparrow presence in early successional sites retained percent grass groundcover and percent bare ground in the logistic regression model (Table 1). Increases in percent grass groundcover and decreases in percent bare groundcover were associated with an increase in the probability of sparrow site use. The model correctly classified Bachman’s Sparrow presence and absence in 8 of 10 (80.0%) and 24 of 25 (96.0%) cases, respectively (Fig. 3). Figure 1. Box plots showing the probabilities of site occupancy calculated from the logistic model built using all sites (forested and early successional habitats). Probabilities are partitioned between occupied and unoccupied study sites. Box ends represent 25th and 75th quantiles, while lines within boxes are median values. Southeastern Naturalist R. Allen and D.B. Burt 2014 46 Vol. 13, Special Issue 5 Occupancy by habitat type The ratio of sampled sites occupied by Bachman’s Sparrows differed significantly between forest (25 of 35) and early successional habitats (10 of 35) (c² = 20.701, df = 1, P < 0.001). There was a greater concentration of territories in the forest habitats than expected assuming an equal occupancy rate. Discussion Results from this study indicate two key points concerning Bachman’s Sparrow habitat-use patterns. First, attempts to generalize habitat-selection patterns in this species have limited potential for success. While increased grass cover is clearly an important vegetation feature common to all occupied sites in this study, few other generalizations are possible as indicated by the low predictive power of our general model (accuracy in classifying occupied [77.1%] and unoccupied [74.3%] sites; Fig. 1). However, patterns are apparent when forested and early successional habitats are considered individually. Sparrows use different vegetation characteristics to select territorial sites in forested and early successional habitats, and our habitat-specific models show much greater classification accuracy (forest Figure 2. Box plots showing the probabilities of site occupancy calculated from the logistic model built using only forested sites. Probabilities are partitioned between occupied and unoccupied study sites. Box ends represent 25th and 75th quantiles, while lines within boxes are median values. Southeastern Naturalist 47 R. Allen and D.B. Burt 2014 Vol. 13, Special Issue 5 sites: occupied = 92.0%, unoccupied = 80.0%; early successional sites: occupied = 80.0%, unoccupied = 96.0%; Figs. 2, 3). Second, a significantly greater proportion of sites was occupied in forest areas than in early successional areas. This suggests that although Bachman’s Sparrows establish territories in both forested and early successional habitats, they may prefer forest sites. Habitat-specific vegetation preferences In forested habitats, percent canopy cover, canopy height, and stand basal area of all trees were significant overstory variables useful in predicting Bachman’s Sparrow presence or absence. Increases in percent canopy cover indicated increased Bachman’s Sparrow presence. Additionally, a preference for some canopy cover is reflected in the sparrows’ preference for forest habitat over early successional habitat where tree canopy-cover was absent. In contrast to our findings, Haggerty (1998) found that sites with more canopy cover were less suitable breeding sites, and Plentovich et al. (1998) and Tucker et al. (1998) did not find a significant link between canopy cover and occupancy. The findings of our study may seem counterintuitive in that increases in canopy cover can result in increases in leaf litter and shade (i.e., negatively affecting other variables important for Bachman’s Sparrow habitat). However, it is important to note that in this study, the largest value for Figure 3. Box plots showing the probabilities of site occupancy calculated from the logistic model built using only early successional habitat sites. Probabilities are partitioned between occupied and unoccupied study sites. Box ends represent 25th and 75th quantiles, while lines within boxes are median values. Southeastern Naturalist R. Allen and D.B. Burt 2014 48 Vol. 13, Special Issue 5 canopy closure was only 58 percent, indicating a relatively open canopy. A threshold for percent canopy cover likely exists for Bachman’s Sparrow occupancy, but due to the percentages of canopy cover exhibited by forest habitats observed in this study, that threshold was not surpassed. In the western portion of the range, canopy cover may provide some beneficial aspect in habitat quality for the Bachman’s Sparrow. Haggerty (1988, 1995) theorized that nest design may aid in concealment and thermoregulation of nest contents due to higher percentages of domed nests in warmer southern latitudes. In eastern Texas, canopy cover may serve the same function by providing shade to the forest floor, thus, reducing the temperature and aiding individual and nest thermoregulation. As stand basal area increased in excess of 13.75 m²/ha, Bachman’s Sparrow presence decreased. This value for stand basal area is within the range recommended for management for Picoides borealis Vieillot (Red-cockaded Woodpecker), a federally listed species found sporadically throughout the forested sites in the study area. Higher levels of stand basal area in the study area were indicative of overstocked mature pine and pine-hardwood stands that did not exhibit an open park-like condition. High stand basal area is usually associated with significant tree canopy cover that blocks light from the forest floor and produces prodigious leaf litter, both of which inhibit the development of herbaceous groundcover, thereby reducing available forage plants and nest substrates. Increases in canopy height also indicated decreased Bachman’s Sparrow presence. It is unclear how canopy height influences Bachman’s Sparrow presence. Among forest sites, shrub height was the only significant shrub-layer variable useful in predicting Bachman’s Sparrow presence and absence. Increases in shrub height, likely the result of reduced fire frequency, decreased the probability of Bachman’s Sparrow presence. These findings concur with other studies of Bachman’s Sparrow breeding habitat (Dunning and Watts 1990; Gobris 1992; Haggerty 1998, 2000; Hardin et al. 1983; Plentovich et al. 1998). In early successional sites, no variable associated with shrub-layer vegetation was a significant predictor of Bachman’s Sparrow presence or absence. Percentage of grass groundcover was a significant predictor of Bachman’s Sparrow presence in all analyses. For all sites, an increase in grass groundcover was associated with increases in Bachman’s Sparrow presence. These findings concur with other studies of Bachman’s Sparrow breeding habitat (Dunning and Watts 1990; Gobris 1992; Haggerty 1998, 2000; Hardin et al. 1983; Plentovich et al. 1998; Tucker et al. 1998) that indicated an increase in grass groundcover provides more potential nesting sites (Haggerty 1995) and results in increased seed production and arthropod prey abundance (Collins et al. 2002). Percent bare ground was an additional significant predictor of Bachman’s Sparrow presence in analyses of early successional sites. Sparrow presence decreased with increased bare ground. There is a reduction in grass and forb groundcover with an increase in bare ground. Small amounts of bare ground may be desirable when associated with the patchy distribution of grass clumps necessary for nesting and foraging (Haggerty 2000). Southeastern Naturalist 49 R. Allen and D.B. Burt 2014 Vol. 13, Special Issue 5 Are forested habitats preferred? In this study, we found a higher proportion of Bachman’s Sparrow territories in forested sites. In eastern populations, Stober (1996) found significantly lower Bachman’s Sparrow densities in mature pine stands than in early successional habitats, while Dunning and Watts (1990) found higher densities of sparrows in clear cuts than in mature stands in one area and the opposite relationship in another. In these studies, mature pine stands associated with lower Bachman’s Sparrow densities were infrequently burned, resulting in less ground-layer vegetation and more mature shrub-layer vegetation (Dunning and Watts 1990). Mature pine stands associated with higher Bachman’s Sparrow densities were frequently burned and were characterized by dense groundcover (grass and forb) and a less-developed shrub layer (Dunning and Watts 1990). These conditions are similar to those examined in eastern Texas. Our data suggest that the early successional habitats in this study are suboptimal in some manner. Climatic differences between the eastern and western ranges may be responsible for the disparity in habitat occupancy. The absence of canopy cover in early successional habitats may negatively affect nestling thermoregulation in lower latitudes. Silvicultural site preparation methods, such as the use of herbicides to reduce competition between grasses and pine saplings, may also negatively influence habitat suitability. Also, sparrows in open habitats in eastern Texas may be susceptible to higher levels of predation. In eastern populations, Stober and Krementz (2000) found no significant difference in survival rates and nest success between mature and early successional habitats. Rakowitz (1983) found that Coluber constrictor L. (Eastern Racer), a documented Bachman’s Sparrow predator (Haggerty 1988), was more abundant in early successional habitats than in mature pine forest habitats in eastern Texas. Barber et al. (2001) found a greater abundance of Molothrus ater Boddaert (Brown-headed Cowbirds) and Corvus brachyrhynchos Brehm (American Crows) in early successional habitats than in mature pine forest habitats in Arkansas. The American Crow is a documented predator of the Bachman’s Sparrow, while the Brown-headed Cowbird is a documented nest parasite (Brooks 1938, Dunning 1993, Haggerty 1988, Weston 1968). Studies of Bachman’s Sparrow survival rate and nest success are needed in the western portion of its range to test these hypotheses. In conclusion, our results suggest that, across the Longleaf Pine ecosystem of eastern Texas, Bachman’s Sparrows establish territories in habitats with high percentages of grass groundcover. However, sparrows use different criteria to select sites within forest and early successional habitats. Individuals are found more often in forests with low levels of shrub-layer vegetation, intermediate levels of canopy cover and stand basal area, and dense grass groundcover. Sparrow occupancy of early successional sites increases in habitats with dense grass ground-cover and reduced bare ground. Higher occupancy rates in forest habitat may indicate that early successional habitats are suboptimal in comparison to nearby forest habitats. A comparison of mortality and reproductive data between these habitats would be useful in testing this hypothesis. Southeastern Naturalist R. Allen and D.B. Burt 2014 50 Vol. 13, Special Issue 5 Acknowledgments We are grateful to Dr. Dick Conner, Dr. Lance McBrayer, Dr. Cody Edwards, and Dr. Dan Saenz for their advice and contributions to this study. Also, we would like to recognize the United States Forest Service and Temple-Inland Forest Productions, Inc. for access to their properties. Cory Adams, Sally Allen, and Philip Blackburn were instrumental in data collection and technical assistance. Funding was provided by the USFWS, and both the Department of Biology and the STEM Research and Learning Center at Stephen F. Austin State University, Nacogdoches, TX. The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the US Fish and Wildlife Service. Literature Cited Barber, D.R., T.E. Martin, M.A. Melchiors, R.E. Thill, and T.B. Wigley. 2001. Nest success of birds in different silvicultural treatments in southeastern US pine forests. Conservation Biology 15(1):196–207. Brooks, M. 1938. Bachman’s Sparrow in the north-central portion of its range. Wilson Bulletin 50:86–109. Campbell, L. 2003. Endangered and Threatened Animals of Texas: Their Life History and Management. The University of Texas Press, Austin, TX. 140 pp. Collins, C.S., R.N. Conner, and D. Saenz. 2002. Influence of hardwood midstory and pine species on pine bole arthropods. Forest Ecology and Management 164:211–220. Conner, R.N., C.E. Shackelford, R.R. Schaefer, and D. Saenz. 2005. The effects of fire suppression on Bachman’s Sparrows in upland pine forests of eastern Texas. Bulletin of the Texas Ornithological Society. 38(1):6–11. Drilling, N.E. 1985. Aimophila aestivalis. Element stewardship abstract. Midwest Regional Office, the Nature Conservancy, Minneapolis, MN. Dunning, J.B. 1993. Bachman’s Sparrow (Aimophila aestivalis). No. 38, In A. Poole and F. Gill, (Eds.). The Birds of North America. The Academy of Natural Sciences, Philadelphia and American Ornithologists’ Union, Washington, DC. Dunning, J.B., and B.D. Watts. 1990. Regional differences in habitat occupancy by Bachman’s Sparrow. Auk 107:463–472. Engstrom, R.T., R.L. Crawford, and W.W. Baker, 1984. Breeding bird populations in relation to changing forest structure following fire exclusion: A 15-year study. Wilson Bulletin 96(3):437–450. Gobris, N.M. 1992. Habitat occupancy during the breeding season by Bachman’s Sparrow at Piedmont National Wildlife Refuge in central Georgia. M.Sc. Thesis. University of Georgia, Athens, GA. Haggerty, T.M. 1988. Aspects of the breeding biology and productivity of Bachman’s Sparrow in central Arkansas. Wilson Bulletin 100(2):247–255. Haggerty, T.M. 1995. Nest-site selection, nest design, and nest entrance orientation in Bachman’s Sparrow. Southwestern Naturalist 40(1):62–67. Haggerty, T.M. 1998. Vegetation structure of Bachman’s Sparrow breeding habitat and its relationship to home range. Journal of Field Ornithology. 69(1):45–50. Haggerty, T.M. 2000. A geographic study of the vegetation structure of Bachman’s sparrow (Aimphola aestivalis) breeding habitat. Journal of the Alabama Academy of Science. 71(3):120–127. Hardin, K.I., and G.E. Probasco. 1983. The habitat characteristics and life requirements of Bachman’s Sparrow. Birding15:189–197. Southeastern Naturalist 51 R. Allen and D.B. Burt 2014 Vol. 13, Special Issue 5 Hunter, W.C., D.N. Pashley, and R.E.F. Escano. 1993. Neotropical migratory landbird species and their habitats of special concern within the southeast region. Pp. 159–169, In D.M. Finch and P.W. Stangel (Eds.). Status and Management of Neotropical Migratory Birds. USDA Forest Service, General Technical Report-229. Fort Collins, CO. Johnson, J.B., D. Saenz, D.B. Burt, and R.N Conner. 2002. An automated technique for monitoring nocturnal avian vocalizations. Bulletin of the Texas Ornithological Society 35(2):8–12. JMP. 2009. Version 8.0.2. SAS Institute, Inc., Cary, NC, 1989–2009. Available online at http://www.jmp.com. Accessed 13 January 2011. MacArthur, R.H., and J.W. MacArthur. 1961. On bird species diversity. Ecology 42(3):594–598. Martin, T.E., and J.J. Roper. 1988 Nest and nest site selection of a western population of the Hermit Thrush. Condor 90:51–57. Meanley, B. 1959. Notes on the Bachman’s Sparrow in central Louisiana. Auk 76:232–234. Plentovich S., J.W. Tucker, Jr., N.R. Holler, and G.E. Hill. 1998. Enhancing Bachman’s Sparrow habitat via management of the Red-cockaded Woodpeckers. Journal of Wildlife Management. 62(1):347–354. Rakowitz, V.A. 1983. Comparison of the herpetofauna of four different aged stands in the Loblolly-Shortleaf Pine hardwood ecosystem of east Texas. M.Sc. Thesis. Stephen F. Austin State University, Nacogdoches, TX. Stober, J.M. 1996. Territory dynamics and basic biology of the Bachman’s Sparrow (Aimophila aestivalis) at the Savanna River Site, South Carolina. M.Sc. Thesis. University of Georgia, Athens, GA. Stober, J.M., and D.G. Krementz. 2000. Survival and reproductive biology of the Bachman’s Sparrow. Proceedings of the Annual Conference For the Southeastern Association of Fish and Wildlife Agencies 54:383–390. Tucker J.W., G.E. Hill, and N.R. Holler. 1998. Managing mid-rotation pine plantations to enhance Bachman’s Sparrow habitat. Wildlife Society Bulletin 26(2):342–348. Wan A. Kadir, W.R. 1987. Vegetation characteristics of early successional sites utilized for breeding by the Bachman’s Sparrow (Aimophila aestivalis) in Eastern Texas. M.Sc. Thesis. Stephen F. Austin State University, Nacogdoches, TX. Weston, F.M. 1968. Aimophila aestivalis bachmani (Audubon) Bachman’s Sparrow. Pp. 956–975, In A.C. Bent (Ed.), Life Histories of North American Cardinals, Grosbeaks, Buntings, Towhees, Finches, Sparrows, and Allies. Part 2. US National Museum Bulletin 237. Smithsonian Institution Press, Washington, DC. Wolf, L.L. 1977. Species relationships in the avian genus Aimophila. American Ornithological Union, Ornithological Monograph No. 23, Washington, DC. 220 pp.