2013 NORTHEASTERN NATURALIST 20(1):131–142 Nesting Success of Grassland Birds in Oak Barrens and Dry Prairies in West Central Wisconsin Susan M. Vos1 and Christine A. Ribic2,* Abstract - We investigated nesting success of grassland birds on dry prairie and oak barrens patches embedded within a forested matrix on Fort McCoy Military Installation. We monitored 280 nests of 9 grassland-bird species from mid-May to late July 2000–2002. Pooecetes gramineus (Vesper Sparrow) and Ammodramus savannarum (Grasshopper Sparrow) were the most abundant nesting species. Vesper Sparrow nest densities were highest on smaller grassland patches, while Grasshopper Sparrow nest densities were highest on the largest patches. Probability of fledging at least one young was 0.20 for Vesper Sparrow. For Grasshopper Sparrow, daily nest survival was higher for nests placed away from trees; probability of fledging at least one young was 0.28 for nests away from trees and 0.05 for nests near trees. Maintaining remnant native habitats is important, and management of woody features may help improve habitat quality for some grassland birds in Wisconsin. Introduction Grassland birds have faced extensive changes in habitat since settlement of North America by Europeans; native tallgrass prairie has been reduced to a fraction of its historical acreage in the US (Samson et al. 1998). In Wisconsin, approximately 809,400 ha of prairie (254,961 ha dry-mesic) occurred at the time of European settlement (1830–1850), and oak savannas once covered approximately 20% of the state (Curtis 1959). Sample and Hoffman (1989) reported that only 162 ha of dry-mesic prairie remained. As a result of these habitat changes, the widespread and steep population declines of many grassland bird species are of conservation concern at both state and federal levels (Askins et al. 2007). In addition to grassland birds, remnant habitats such as prairie have become an important conservation focus (Samson and Knopf 1996), and conservation efforts for grassland birds can contribute to this effort (Askins et al. 2007). Information on both bird density and reproduction on remnant prairies will be important for planning and understanding the success of prairie management actions. Unfortunately, information on grassland bird use of remnant prairies (Best et al. 1995, Chapman et al. 2004, Fletcher and Koford 2006, Fritcher et al. 2004, Ribic et al. 2009a, Vos and Ribic 2011) and reproduction in that habitat (Giocomo et al. 2008, Herkert et al. 2003, Johnson and Temple 1990, Ribic et al. 2012, Winter and Faaborg 1999) is limited. While information specific to native prairie habitats is limited, work on grassland bird reproduction in general 1DPTMS-DES (IMNW-MCY-PLT), 110 East Headquarters, Road Fort McCoy, WI 54656-5226. 2US Geological Survey, Wisconsin Cooperative Wildlife Research Unit, Department of Forest and Wildlife Ecology, University of Wisconsin, Madison, WI 53706. *Corresponding author - caribic@wisc.edu. 132 Northeastern Naturalist Vol. 20, No. 1 (Davis et al. 2006; Grant et al. 2006; Graves et al. 2010; Walk et al. 2010; Winter et al. 2000, 2006) has found that patch size and landscape features such as woody edges can influence nesting success. We focused on grassland birds nesting in dry prairie and oak barrens habitat in west-central Wisconsin; these communities are important for grassland birds (Sample and Hoffman 1989) but are rare in the state of Wisconsin (Sample and Mossman 1997). Our objectives were to (1) determine nest density and success of grassland birds in these habitats, and (2) determine the influence of within-patch vegetation, patch size, and woody features on nesting success. Methods Study area The study was conducted May–July 2000–2002 within grassland and savanna habitats on Fort McCoy Military Installation (hereafter Fort McCoy), WI. Fort McCoy covers approximately 24,281 ha, with 3561 ha available as habitat for grassland birds (Sample and Mossman 1997). Fort McCoy was converted into a military camp in 1909 before intense settlement and agriculture took an effect (Natural Resources Branch 2012). Consequently, Fort McCoy has a large amount of land considered to be relatively unchanged native grasslands. Fort McCoy is embedded within an extensive ridge complex (Natural Resources Branch 2012). From the 2001 National Land Cover Database (Homer et al. 2007), land cover within 5 km of Fort McCoy was 57% forest, 19% row crops, 7% pasture/hay, 7% developed, and 5% grassland/herbaceous cover. In general, a primary objective of land management on US military bases is to ensure that army activities and natural resource conservation measures are integrated within the context of federal stewardship requirements (Natural Resources Branch 2012). Fort McCoy is an active and important military base because it is the only army facility in the upper Midwest capable of full-spectrum training for combat (Natural Resources Branch 2012). The native habitats on Fort McCoy, like grasslands and oak savannas, are important for supporting various training scenarios. These habitats also are disturbance driven. Therefore, a comprehensive management program is used to maintain and expand grassland habitat if possible by using prescribed fire, exotic plant control, mowing, native-plant restorations, timber harvests, and brush removal (Natural Resources Branch 2012). Fort McCoy is located on the eastern edge of the Western Upland physiographic region of Wisconsin. Fort McCoy occurs south of the tension zone, a narrow band described by Curtis (1959) which marks the change from the northern coniferous forests to central deciduous forests. Much of the flora reaches its northern or southern limit within this zone, resulting in a diverse system (Natural Resources Branch 2012). Major tree species associated with the savanna habitat are Quercus velutina Lam. (Black Oak), Q. alba L. (White Oak), Q. macrocarpa Michx. (Bur Oak), Q. ellipsoidalis E.J. Hill (Northern Pin Oak), Pinus banksiana Lamb. (Jack Pine), P. strobus L. (White Pine), P. resinosa Aiton (Red Pine), Acer rubrum 2013 S.M. Vos and C.A. Ribic 133 L. (Red Maple), and Prunus serotina Ehrh. (Black Cherry). Understory plants consist of Corylus americana Walter (American Hazel), Vaccinium angustifolium Aiton (Lowbush Blueberry), Gaylussacia baccata (Wangenh.) K. Koch (Black Huckleberry), Lupinus perennis L. (Sundial Lupine), Amorpha canescens Pursh (Leadplant), Andropogon gerardii Vitman (Big Bluestem), Schizachyrium scoparium (Michx.) Nash (Little Bluestem), and Sorghastrum nutans (L.) Nash (Indiangrass) (Natural Resources Branch 2012). Common grass species found in the dry sand prairie community are Little Bluestem, Big Bluestem, and Koeleria macrantha (Ledeb.) Schult. (Junegrass). Common forbs are Asclepias syriaca L. (Common Milkweed), Euphorbia corollata L. (Flowering Spurge), Symphyotrichum ericoides (L.) G.L. Nesom (White Heath Aster), Rosa carolina L. (Carolina Rose), Geum triflorum Pursh (Prairie Smoke), and Tradescantia ohiensis Raf. (Ohio Spiderwort). Groundcover species include lichen and moss mixed with open sand patches. In less disturbed areas, a heavier and thicker cover of litter was found in among native grasses and forbs. Field methodology Nest searching was conducted in point-count survey plots set in grassland prairie patches to measure relative grassland bird abundance (Vos and Ribic 2011). The grassland patches ranged in size from 4 to 267 ha; 18 sites were less than 40 ha in size, and 7 sites were greater than 40 ha in size, with 2 sites greater than 100 ha. The largest grassland patch on Fort McCoy, the North Impact Area, was not surveyed due to the risk of encountering unexploded ordinance; this area is 2832 ha in size and closed to all Fort personnel. The North Impact Area is situated in the middle of Fort McCoy, and two study patches were directly adjacent to it. The rest of the grassland patches were scattered throughout Fort McCoy. Thirty-six plots in 16 patches were searched in 2000, 51 plots in 24 patches in 2001, and 44 plots in 17 patches in 2002. Area searched per plot averaged 10.3 ha (range = 2.0–32.4 ha) in 2000, 9.0 ha (range = 1.2–32.4 ha) in 2001, and 10.4 ha (range = 1.2–32.4 ha) in 2002. Each plot was searched on average twice (range = 1–2 searches) in 2000, 3 times (range = 1–11 searches) in 2001, and 3 times (range = 1–8 searches) in 2002. Nests were found primarily by technicians walking four or more abreast to flush birds from their nests. After a nest was found, a flag was placed 4 m north or south from the nest; the direction was chosen to reduce trampling of nest during subsequent nest checks. Nests were approached from different directions as much as possible in an effort to reduce a scent trail or path in the vegetation to the nest flag and nest. Nests were monitored every 3–5 days when possible. Same-day or next-day nest checks were conducted when the observer suspected a change in the nesting stage (e.g., eggs hatching or nestlings fledging). Observers recorded initiation date (if known; nest contents were not aged), clutch size, number of eggs or young, presence or absence of adults, and nest fate. Documentation of Molothrus ater Boddaert (Brown-headed Cowbird) eggs or young were recorded when applicable. Once nesting was finished, we interpreted fecal material, feather dust, and feather sheaths left in the nest cup as signs that the nestlings fledged 134 Northeastern Naturalist Vol. 20, No. 1 successfully. Behavioral cues such as chipping or feeding of young outside of the nest by parents were also used to help confirm fledgling success. We considered a nest lost to predators if the nest cup was empty with no eggs or nestlings present prior to the expected fledging date (if known). In some cases, the condition of the nest being disturbed also helped confirm predator activity at the nest (if nest was found empty prior to suspected fledging time). Nests were considered abandoned when the eggs were left cold and unattended by an adult for at least two to three nest checks after the clutch was considered complete. Mortality due to military training operations were considered when a nest was directly hit by military vehicles, military personnel, or by any military-related events. When nests were found with dead nestlings in saturated nest-cups immediately following heavy storms, we attributed mortality to weather. Brownheaded Cowbird parasitism was noted and considered a source of mortality only if direct destruction to the host eggs or nestlings occurred. We measured vegetation at the nests within 24 h after a nest failed or young fledged. A 20- by 50-cm frame was used to make visual estimates of cover; we estimated percent cover of grass, forb, and litter. Three random measurements of litter depth in cm were taken within the frame and averaged. A Robel pole was placed in the nest to measure vegetation height-density in dm (Robel et al. 1970). The pole was read at standing height (approximately 150-cm high) at 4-m away; we took 4 measurements in the cardinal directions and averaged the measurements. Nests were also characterized as being near woody vegetation or not; a nest was considered near woody cover if there were more than 2 trees and shrubs within a 10-m radius of the nest. All vegetation measurements were made by the first author. The native habitat patches were embedded in a matrix of dense shrubby/ woody vegetation (10–30 trees in a group) or pine plantations. Patch size (ha) and distance (m) of the nest to the nearest woody edge (where the tree canopy was greater than 30%) were measured in a geographic information system using Arc GIS 9.2 (Environmental Systems Research Institute 2007). Statistical analysis We calculated apparent nest density (nests/ha) by species, patch, and year; we did not have the data to adjust for imperfect detection of nests (see Grant et al. 2011). We averaged nest density by patch over the years to get an average nest density per patch for each grassland bird species. We also determined the number of grassland bird species that nested in each patch. We used linear regression to determine if average nest density and number of species varied by log(patch size). We used the square root transformation on the number of species to conform to the assumption of normality. To examine nesting success, we used the logistic exposure method (Shaffer 2004) for analysis of species with more than 50 nests. We were interested in understanding individual species’ nesting success in relation to nesting stage (incubation, nestling), year, within-patch vegetation, log(patch size), and distance to edge. We developed a priori models and used Akaike information 2013 S.M. Vos and C.A. Ribic 135 criterion corrected for small sample size (AICc) to rank the models (Burnham and Anderson 2002). Models within 2 AIC units of the minimum were considered competitive models, and we calculated Akaike weights for these models (Burnham and Anderson 2002). We developed models in three steps. First, we fit models for potential nesting stage and year effects. The minimum AIC model from this step was then used as a basis for investigating within-patch vegetation; these models were all combinations of the within-patch vegetation variables. Correlations of vegetation variables were <0.40. Using the minimum AIC model from step 2, we evaluated the importance of log(patch size) and distance to edge. Overall nesting success for each species was calculated using nesting-stage lengths based on data collected during the study. All analyses were done using the statistics package R (R Development Core Team 2007). Significance was assessed using an alpha of 0.05. Results We found 280 nests of 9 grassland bird species: 52 in 2000, 85 in 2001, and 143 in 2002. The most commonly found nests were from Pooecetes gramineus (Vesper Sparrow), Ammodramus savannarum (Grasshopper Sparrow), Spizella pusilla (Field Sparrow), and Spiza americana (Dickcissel) (Table 1). Less commonly found were nests of Spizella pallida (Clay-colored Sparrow), Sturnella magna (Eastern Meadowlark), Chondestes grammacus (Lark Sparrow), Bartramia longicauda (Upland Sandpiper), and Eremophila alpestris (Horned Table 1. Fate of nests for grassland bird species at Fort McCoy Military Installation May–July 2000–2002. Pred. = predation, Aband. = adult abandonment, Mil. Dist. = military disturbance, Weath. = weather, and Unk. = unknown. * = obligate grassland bird (Sample and Mossman 1997). Sources of nest mortality Total Total Mil. Species nests failed nests Pred. Aband. Dist Weath. Unk. Spiza americana Gmelin* 21 7 6 0 1 0 0 (Dickcissel) Spizella pusilla A. Wilson 22 13 12 1 0 0 0 (Field Sparrow) Ammodramus savannarum Gmelin* 85 45 40 3 1 1 0 (Grasshopper Sparrow) Pooecetes gramineus Gmelin* 119 78 59 11 3 5 3 (Vesper Sparrow) Spizella pallida Swainson 13 8 6 1 0 1 0 (Clay-colored Sparrow) Sturnella magna L. * 11 4 4 0 0 0 0 (Eastern Meadowlark) Chondestes grammacus Say 5 2 1 1 0 0 0 (Lark Sparrow) Bartramia longicauda Bechstein* 3 1 1 0 0 0 0 (Upland Sandpiper) Eremophila alpestris L. * 1 1 0 1 0 0 0 (Horned Lark) 136 Northeastern Naturalist Vol. 20, No. 1 Lark) (Table 1). The number of grassland bird species that nested on a patch increased with patch size (log-patch size coefficient = 0.36; F1,23 = 25.54, P < 0.001); average number of species on 7 patches of 9 ha or less was 1.1 (SE = 0.1), one-fourth the number of species that nested on 7 patches of 40 ha or greater (mean = 4.4 species, SE = 0.9). Across all years and species, over 80% of the failed nests were classified as taken by predators (Table 1). Six nests were lost to a single heavy rain event where cold eggs or young were found in inundated nest cups; five of the six nests belonged to Vesper Sparrow. Vesper Sparrow also had the most abandoned nests (Table 1). Few nests were directly destroyed by military training either by vehicles, training-related events, or equipment during maintenance of a range (Table 1). Brown-headed Cowbird parasitism rates were low (2%; 6 nests parasitized out of 280 nests). Direct destruction of eggs or of chicks by Brown-headed Cowbirds occurred in only two cases (one Eastern Meadowlark nest and one Field Sparrow nest), where one chick and one egg were destroyed, respectively; the rest of the young survived, making the final nest outcomes successful. Brown-headed Cowbirds laid eggs in two Vesper Sparrow nests, three Field Sparrow nests, and one Lark Sparrow nest; all of these nests were abandoned before the full clutch was laid. Monitored nests that had Brown-headed Cowbird eggs laid in them did not successfully produce Brown-headed Cowbird fledglings on Fort McC oy. Nest density Average nest density for all grassland birds was 0.26 nests/ha (SE = 0.03, n = 25 patches). Vesper Sparrow nests were found on all but 2 of the 25 patches. Average Vesper Sparrow nest density was 0.19 nests/ha (SE = 0.04, n = 25), and nest density was higher on smaller patches (log-patch size coefficient = −0.067; F1,23 = 4.47, P = 0.045). Specifically, average nest density on 7 patches of 9 ha or less was 0.29 nests/ha (SE = 0.11), almost three times that found on 7 patches of 40 ha or greater (mean = 0.11 nests/ha, SE = 0.03). In contrast, Grasshopper Sparrow nests were found on 9 of the 25 patches. Grasshopper Sparrow nest density was higher on the larger patches (log-patch size coefficient = 0.051; F1,23 = 5.15, P = 0.033). Specifically, average nest density on 7 patches of 9 ha or less was 0.01 nests/ha (SE = 0.01), almost one-fourth the density found on 7 patches of 40 ha or greater (mean = 0.05 nests/ha, SE = 0.01). Eastern Meadowlark and Dickcissel nests were only found on prairie patches 48 ha or larger (n = 4), while Horned Lark and Upland Sandpiper nests were only found on the largest prairie patch (267 ha). Nesting success For Vesper Sparrow, daily nest survival varied by nesting stage (Table 2). The other models within 2 AIC units of the minimum AIC model were simply the minimum AIC model with additional variables (Table 2); these additional variables were not significant (P > 0.15 for all variables). Daily nest survival during the nestling stage was higher than during incubation (nestling stage coefficient = 0.58, P = 0.024). Incubation was 13 days, and the nestling stage was 2013 S.M. Vos and C.A. Ribic 137 9 days for Vesper Sparrow on Fort McCoy. Probability of a Vesper Sparrow nest surviving through incubation was 0.31 (95% CI: 0.20, 0.43), while the probability of surviving the nestling stage was 0.63 (95% CI: 0.44, 0.78). Combining both stages, the overall probability of Vesper Sparrows fledging at least one young per nesting attempt was 0.20 (95% CI: 0.09, 0.34). For Grasshopper Sparrow, daily nest survival varied by nesting stage and placement near trees/shrubs (Table 3). The other models within 2 AIC units of the minimum AIC model were simply the minimum AIC model with additional variables (Table 3); these additional variables were not significant (P > 0.15 for all variables). Daily nest survival during the nestling stage was higher than during incubation (nestling stage coefficient = 0.87, P = 0.007). Daily nest survival for nests near trees/shrubs was lower than for nests placed away from trees/shrubs (trees/shrubs coefficient = −0.94, P = 0.02). Incubation was 11 days, and the nestling stage was 8 days for Grasshopper Sparrow on Fort McCoy. Probability Table 2. Minimum AIC model and models within 2 AIC units for survival of Vesper Sparrow nests found on Fort McCoy Military Base, WI, May–July 2000–2002. Exposure # of AIC Model days parameters AICc ΔAIC weight Nesting stage 921 2 306.56 0.00 0.18 Nesting stage + proportion forbs 921 3 306.72 0.16 0.16 Nesting stage + distance to woody edge 921 3 306.79 0.23 0.16 Nesting stage + proportion grass 921 4 307.07 0.51 0.14 + vegetation height-density Nesting stage + vegetation height-density 921 3 307.20 0.64 0.13 Nesting stage + proportion litter 921 3 307.33 0.77 0.12 Nesting stage + log(patch size) 921 3 308.36 1.80 0.07 Constant survival 921 1 309.63 3.07 0.04 Table 3. Minimum AIC model and models within 2 AIC units for survival of Grasshopper Sparrow nests found on Fort McCoy Military Base, WI, May–July 2000–2002. Exposure # of AIC Model days parameters AICc ΔAIC weight Nesting stage + nest near/away from trees and shrubs 683 3 210.07 0.00 0.19 Nesting stage + nest near/away from trees and shrubs 683 7 210.90 0.83 0.13 + average litter depth + proportion forbs + proportion grass + vegetation height-density Nesting stage + nest near/away from trees and shrubs 683 4 211.50 1.43 0.09 + proportion grass Nesting stage + nest near/away from trees and shrubs 683 4 211.50 1.43 0.09 + vegetation height-density Nesting stage + nest near/away from trees and shrubs 683 4 211.56 1.49 0.09 + log(patch size) Nesting stage + nest near/away from trees and shrubs 683 4 212.05 1.98 0.07 + distance to woody edge Nesting stage + nest near/away from trees and shrubs 683 4 212.06 1.99 0.07 + proportion forbs Constant survival 683 1 219.47 9.40 less than 0.001 138 Northeastern Naturalist Vol. 20, No. 1 of surviving incubation for nests placed away from trees/shrubs was 0.39 (95% CI: 0.23, 0.55) and 0.73 (95% CI: 0.51, 0.87) for the nestling stage, resulting in an overall probability of fledging at least one young of 0.28 (95% CI: 0.11, 0.47). For nests near trees/shrubs, probability of surviving incubation was 0.11 (95% CI: 0.01, 0.39) and 0.48 (95% CI: 0.14, 0.76) for the nestling stage, resulting in an overall probability of fledging at least one young of 0.05 (9 5% CI: 0, 0.30). Discussion The native dry sand prairie and barrens habitats of Fort McCoy appear to be important for grassland bird species of management concern (Sample and Mossman 1997, Vos and Ribic 2011). Of the 9 nesting grassland-bird species, 8 are species of management concern in Wisconsin, and 4 of those species (Lark Sparrow, Grasshopper Sparrow, Field Sparrow, and Eastern Meadowlark) are in the top ten of highest management concern (Sample and Mossman 1997). The dry sand prairie offers a mix of bare soil and patches of bunch grasses and diverse forbs, which allows a variety of ground nesting species such as Vesper and Grasshopper Sparrows the room to forage, conduct courtship activities, and nest (Sample and Mossman 1997). Patch size has been found to affect how some grassland birds use habitat patches (Askins et al. 2007, Ribic et al. 2009b). In our study, the patterns in grassland bird nest density are similar to what was found on Fort McCoy in regards to relative abundance of grassland birds (Vos and Ribic 2011). Both apparent nest density and relative abundance of Vesper Sparrow decreased with increasing patch size, nest density and abundance of Grasshopper Sparrow increased with increasing patch size, and Upland Sandpiper and Horned Lark and their nests were only encountered on the largest patch. However, we did not find that patch size affected daily nest survival rate for Grasshopper and Vesper Sparrows. This result is similar to findings for other grassland bird species (Davis et al. 2006, Winter et al. 2006). Information on nest density for grassland birds in general is limited; however, our result for Grasshopper Sparrow is consistent with other studies. Johnson and Temple (1990) found that Grasshopper Sparrow nests were more likely to be found on large (130–486 ha) than small (16–32 ha) tallgrass prairie patches. Herkert et al. (2003) found more Grasshopper Sparrow nests on large prairie fragments (>100 ha) compared to smaller patches (<100 ha). Vesper Sparrow is known to breed in areas with shrubby vegetation (Jones and Cornely 2002). Thus, our finding of higher Vesper Sparrow nest densities on small prairie patches which have shrubby/woody surrounding habitat is consistent with the ecology of the species. Small grassland patches as part of a native grassland-barrens/savanna complex may play an important role for species like Vesper Sparrow, Field Sparrow, Lark Sparrow, and Clay-colored Sparrow. Though conservation of large habitat patches is promoted for grassland birds, it is important to consider the location and function of small grassland patches in regards to the larger habitat complex of which the patches are part (Ribic et al. 2009b, Walk et al. 2010). 2013 S.M. Vos and C.A. Ribic 139 Overall nesting success for Vesper Sparrow in our study was lower than estimates observed in other systems. Wray et al. (1982) reported nesting success for Vesper Sparrow using reclaimed surface mines to be 0.31, while Grant et al. (2006) reported a rate of 0.45 in mixed-grass prairie. In contrast, overall nesting success for Grasshopper Sparrow in our study was in the 0.17–0.34 range reported in other studies working in tallgrass prairie and barrens systems (Giocomo et al. 2008, Ribic et al. 2012, Rohrbaugh et al. 1999, Winter and Faaborg 1999). Daily nest survival differed by nesting stage for both Vesper and Grasshopper Sparrows in our study; both sparrows had lower daily survival rates during incubation. Results for Grasshopper Sparrow from other studies are not consistent; survival during incubation was lower (Giacomo et al. 2008), higher (Patterson and Best 1996), and not different compared to the nestling stage (Ribic et al. 2012). Results for Vesper Sparrow are more consistent in regards to daily nest survival being lower during incubation compared to the nestling stage (Grant et al. 2005, Patterson and Best 1996). Grant et al. (2005) noted that it is difficult to know if a lack of consensus among studies reflects real biological differences or are spurious differences due to variation in methodology or sample size. Woody features in the landscape have been found to affect how grassland birds use habitat patches (Askins et al. 2007, Ribic et al. 2009b). In our study, Grasshopper Sparrow nesting success decreased when nests were placed near trees/shrubs. This result is similar to findings by Graves et al. (2010). Graves et al. (2010) found that mean daily survival rate for Grasshopper Sparrow nests was negatively associated with amount of woody vegetation surrounding nest locations. Unlike other studies (Grant et al. 2006, Johnson and Temple 1990, Ribic et al. 2012), we did not find that distance to woody edge affected daily nest survival of either Grasshopper or Vesper Sparrow. This inconsistency may be due to differences among the study sites. Our study took place along a prairie-savanna-forest ecotone with few hard edges; we had to define a woody edge by canopy cover. In contrast, the other studies were done where the woody habitat created hard edges (e.g., tree rows and wood lots in agricultural areas, aspen parkland). It is well established that predation is the major cause of nest failure, which we also found in our study, though the particular predators vary spatially and temporally (Pietz et al. 2012). In our study, Brown-headed Cowbird parasitism rates were low, comparable to that found by Grant et al. (2009) in an aspen parkland study area. This low rate is also typical of other grassland areas in Wisconsin (Ribic et al. 2012). The identities of the major nest predators on Fort McCoy remain unknown; we could not use video surveillance systems due to logistical constraints associated with an active military installation. However, visual observations indicated that potential nest predators are both woody-habitat-based predators (e.g., Procyon lotor L. [Raccoon], Odocoileus virginianus Zimmermann [White-tailed Deer], Buteo jamaicensis Gmelin [Red-tailed Hawk]), and grassland-based predators (e.g., Ictidomys tridecemlineatus Mitchill [Thirteen- lined Ground Squirrel], Taxidea taxus Schreber [American Badger], and Mintonius vulpinus Baird and Girard [Western Foxsnake]). These species have been documented as grassland bird nest predators in other grassland habitats in Wisconsin (Ribic et al. 2012). 140 Northeastern Naturalist Vol. 20, No. 1 Historically, southwest Wisconsin was the primary location for native prairies, but currently the remnant prairies in southwest Wisconsin are small and vulnerable to development (Sample and Mossman 1997). Fort McCoy Military Installation is the only relatively large landscape that offers greater than 3200 ha of dry-mesic prairie, barrens, and savanna habitat. It is also the only relatively large landscape in southern Wisconsin that is publicly owned and actively being managed to maintain these native habitat types. As the surrounding landscape outside of Fort McCoy changes (e.g., in 2012, a hydrofracking sand mine was developed just east of Fort McCoy’s southeast boundary), Fort McCoy’s diverse landscape may become a refuge for the flora and fauna of oak barrens and dry sand prairie in Wisconsin. Acknowledgments We thank the staff biologists at Fort McCoy for their invaluable help: K. Mello, D. Beckmann, B. Friedl, and T. Wilder. We would like to acknowledge the radio staff in Range Control and the schedulers M. Stelzner (Ranger) and D. Wetuski (Ski), and T. Hoff for coordinating with the field team and providing invaluable guidance while conducting research on Fort McCoy. In addition, we would like to thank the technicians involved in the study: M. Guzy, T. Backus, A. Weber, J. Cianciolo, D. Williams, M. Weindant, K. Ruekheim, K. Sash, K. Repyack, L. Braggs, and D. Jones. D. Sample provided important advice in establishing this project. We thank R. Koford, D. Rugg, and two anonymous reviewers for their comments on previous versions of this manuscript. This work was supported by the US Department of Defense Legacy Project as a subcontract with the University of Tennessee; additional funding was provided by the Wisconsin Department of Natural Resources and the US Geological Survey Wisconsin Cooperative Wildlife Research Unit. Mention of trade names or commercial products does not constitute endorsement for use by the US Government. We thank the Department of Forest and Wildlife Ecology, University of Wisconsin-Madison, for assistance with publication expenses. Literature Cited Askins, R.A., F. Chavez-Ramirez, B.C. Dale, C.A. Haas, J.R. Herkert, F.L. Knopf, and P.D. Vickery. 2007. Conservation of grassland birds in North America: Understanding ecological processes in different regions. Ornithological Monographs No. 64. 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