Northeastern Naturalist 10 L. Murray 22001155 NORTHEASTERN NATURALIST V2o2l.( 12)2:,1 N0–o1. 91 Success and Predation of Bird Nests in Grasslands at Valley Forge National Historical Park Les Murray* Abstract - Populations of grassland birds are declining in the Northeast due to habitat loss and fragmentation. Fragmentation of grasslands can contribute to lower breeding success of grassland birds by altering local predator communities. Using miniature video cameras, I estimated nest success and identified nest predators in grassland fragments at Valley Forge National Historical Park in southeastern Pennsylvania. Estimated nest-success probability for Sturnella magna (Eastern Meadowlark) at Valley Forge was 0.25 (0.04–0.65, n = 7) and similar to estimates from the Midwest, but slightly lower than other studies in the Northeast. Nest success for Spizella pusilla (Field Sparrow; 0.77 [0.31–0.98, n = 8]) and Agelaius phoeniceus (Red-winged Blackbird; 0.48 [0.18–0.80, n = 10]) was higher than estimates from other studies. The local predator community identified at Valley Forge was less diverse than documented in other studies, with only 4 species depredating 8 of 25 monitored nests. The primary predator was Odocoileus virginianus (White-tailed Deer; 38% of nest predation events) followed by Vulpes vulpes (Red Fox; 25%); Procyon lotor (Raccoon; 13%), and a probable Mustela sp. (weasel; 13%). I never detected nest predation by small mammals or snakes, which are important nest predators in the Midwest. The impact of White-tailed Deer on grassland birds at Valley Forge is uncertain, therefore further research is needed to fully understand local predator–prey community dynamics. Introduction Grassland-bird populations are declining throughout North America (Sauer et al. 2014). In the Northeast (New England and Mid-Atlantic states), 56% of grasslandbreeding species have significantly declined in abundance since their populations were first monitored in 1966 (Sauer et al. 2014). Population declines in the Northeast are associated with loss of grassland habitat due to succession to woodland habitat, changes in agricultural practices, and human development (Murphy 2003, Perlut 2014, Vickery and Dunwiddie 1997). Grassland habitat in New England and New York has declined by 60% since the 1930s (V ickery et al. 1994). In addition to a reduction in available breeding areas, habitat loss leads to fragmentation of habitats resulting in smaller grasslands and more habitat edge. Increased predation in smaller fragments and near edges has been reported in other studies (Balent and Norment 2003, Gates and Gysel 1978, Herkert et al. 2003, Johnson and Temple 1990, Winter and Faaborg 1999, Winter et al. 2006). Several proposed hypotheses explain increased predation near edges including increased predator activity or abundance near edges (Faaborg et al. 1995, Johnson and Temple 1990) and greater predator-species richness in edge habitats (Heske 1995, Vander *Division of Science and Engineering, Penn State Abington, Abington, PA 19001; ldm12@ psu.edu. Manuscript Editor: Peter Paton Northeastern Naturalist Vol. 22, No. 1 L. Murray 2015 11 Haegen and Degraaf 1996). However, the effects of fragmentation on nest predation vary depending on the local predator community (Chalfoun et al. 2002, Heske et al. 2001, Tewksbury et al. 1998). Thus, identification of local nest predators is important to understanding causes of nest failure in fragmented landscapes (Heske et al. 2001, Thompson and Ribic 2012). Several studies have used video cameras to investigate patterns of grassland-nest predation in the Midwest and Great Plains (see Ribic et al. 2012b), but predators of grassland bird nests in the Northeast have not been documented using video recording. I monitored nests of Sturnella magna L. (Eastern Meadowlark), Spizella pusilla Wilson (Field Sparrow), and Agelaius phoeniceus L. (Red-winged Blackbird) in restored grasslands in Valley Forge National Historical Park (hereafter Valley Forge) in southeastern Pennsylvania in 2011 and 2012. One objective of my study was to estimate nesting success in Valley Forge to compare with estimates in other studies in the Northeast and Midwest. The second objective was to identify predators of grassland-bird nests using miniature video cameras. Field-Site Description Valley Forge park (1293 ha) is a mixture of forests and fields, including grassland habitat (541 ha), surrounded by residential development and roads. Valley Forge is managed to preserve the natural and cultural resources of the area and is one of the few large, contiguous, protected areas in southeastern Pennsylvania. Valley Forge is located in Chester and Montgomery counties within the Northern Appalachian Piedmont ecological region. The long-term average temperature during May and June for the area is 20 °C, with 18.1 cm of precipitation on average during the 2-month period (NOAA National Climatic Data Center 2013). Prior to the breeding season, grasslands within the park are maintained by annual mowing to maintain the appearance of small-grain agriculture that was present on the landscape during the late 18th Century. The grassland areas are dominated by non-native grass species; Festuca rubra L. (Red Fescue) and Festuca pratensis Huds. (Meadow Fescue) are the most widespread grasses. Native warm-season grass species (e.g., Andropogon L. spp. [bluestems]) are less abundant. Maintenance of areas of Rubus cuneifolius Bailey (Sand Blackberry), a state-endangered plant in Pennsylvania, create a shrub component within some grasslands. In addition, invasive vines and shrubs (i.e., Celastrus orbiculatus Thunb. [Oriental Bittersweet] and Lonicera japonica Thunb. [Japanese Honeysuckle]) are found in many grasslands at Valley Forge. Methods We searched for nests in 6 grassland patches (min–max = 24 –75 ha) at Valley Forge during May and June of 2011 and 2012. Typically, 2 researchers conducted nest searches each day using random walks and behavioral cues with variable effort in patches based on bird abundance and activity. The grassland-bird community at Valley Forge predominantly consisted of Eastern Meadowlarks, Field Sparrows, and Red-winged Blackbirds (Murray 2014a). Nest-searching effort was directed Northeastern Naturalist 12 L. Murray 2015 Vol. 22, No. 1 towards Eastern Meadowlarks and Field Sparrows because these were species of conservation concern that commonly nested at Valley Forge. Researchers recorded nest locations using a handheld GPS, marked nests with a surveyor flag placed 5 m from the nest, and monitored the nests every 3 days. Nests were continuously recorded using video equipment similar to Ribic et al. (2012a) and following the recommendations of Richardson et al. (2009). Researchers placed a miniature (3 cm x 10 cm) weatherproof infrared digital video camera near most nests within 3 days of finding the nest. Cameras were mounted on wooden stakes (30–90 cm above the ground) and placed approximately 30 cm from the nest. The camera was connected by a 20-m cable to a waterproof-cased portable DVR that constantly recorded digital video. The camera and DVR were powered by a 12-V sealed lead–acid battery. We painted the camera casings, stakes, waterproof cases, and batteries with a flat green paint to decrease visibility (Herranz et al. 2002). To conceal them from predators and park visitors, we placed cameras and stakes below the height of the vegetation surrounding the nest and covered the cable with grass and litter. A researcher visited the nest every 3 days to change the memory card and battery. All Field Sparrow and Eastern Meadowlark nests were equipped with a video camera as soon as possible, but two Field Sparrow nests fledged young before a camera could be installed. Approximately half of the Red-winged Blackbird nests found were not monitored by cameras to increase the number of nesting intervals without cameras for estimation of the effects of cameras on daily nest success. We chose Red-winged Blackbird nests for our examination of camera effects because they were abundant. We maximized the number of Eastern Meadowlark and Field Sparrow nests equipped with cameras in order to identify predators of species of management concern. We reviewed captured video to determine if each nest fledged young or was depredated and to identify nest predators. Apparent nest success (proportion of successful nests) is reported for each species for comparison to other studies. However, apparent nest success can be a misleading metric of reproductive success because nests that are active longer (i.e., successful) are more likely to be found. Thus, I also estimated daily nest survival by using the logistic exposure method (Shaffer 2004) in R (R Core Team 2013) for each species. Effects of cameras on Red-winged Blackbird nest survival were tested by comparing a model including a variable for presence or absence of a camera during a nesting interval with an intercept-only model using Akaike’s information criterion corrected for small sample size (AICc) (Burnham and Anderson 2002). In addition, profiled log-likelihood 95% confidence intervals for the estimated coefficient for camera effects were examined to determine if the interval included zero. Red-winged Blackbird daily nest survival was calculated for nests with and without cameras separately only if the model with camera effects had a lower AICc score than the null model and the confidence interval for camera effects excluded zero. The low number of nest-check intervals without cameras for Eastern Meadowlark nests (7 intervals) and Field Sparrow nests (9 intervals) did not allow for evaluation of camera effects for these species. Nest success for the entire nesting period was estimated by raising daily nest survival to the exponent of the typical number of Northeastern Naturalist Vol. 22, No. 1 L. Murray 2015 13 days in the nesting cycle (incubation and nestling) reported in the literature for each species (Eastern Meadowlark = 24.5 days, Field Sparrow = 19 days, Red-winged Blackbird = 24.5 days; Carey et al. 2008, Jaster et al. 2012, Yasukawa and Searcy 1995, respectively). Results We found a total of 26 nests, but one Red-winged Blackbird nest was abandoned and not considered in our analyses. We monitored 7 Eastern Meadowlark nests for a total of 76 days with cameras at nests for 80% of the active nesting days, 8 Field Sparrow nests for a total of 73 days with cameras at nests for 68% of the days, and 10 Red-winged Blackbird nests for a total of 140 days with cameras at nests for 35% of the days. Apparent nest success for all nests was 0.42. We did not detect effects of cameras on nesting success in the logistic exposure analysis for Red-winged Blackbirds (n = 49 nest-check intervals). The AICc values were less for the camera-effects model than the null model (camera model: AICc = 28.63, null model: AICc = 29.39), but the 95% confidence interval for the coefficient of camera effects included zero (-4.85, 0.26), therefore daily nest survival was calculated independent of the presence of cameras. Daily nest survival and nest-success estimates from logistic exposure models were highest for Field Sparrow and lowest for Eastern Meadowlark (Table 1). Uncertainty in estimates of daily nest survival and overall nest success was high for all 3 species (Table 1). Nestsuccess estimates for the entire nesting period from the logistic exposure model were 13–42% lower than apparent nest success (Table 1). All nest failures were a result of predation; brood parasitism was not observed for nests of any species. Predation events were video recorded for 7 of the 9 nests that failed. In addition, video evidence of a partial nest predation was recorded at a Field Sparrow nest that fledged a single young. All predator visits except one were by mammals and occurred between 2203 and 0437. Odocoileus virginianus Zimmermann (White-tailed Deer) depredated 3 nests (38% of depredated nests where the predator was identified) and were the most common nest predator. White-tailed Deer depredated all 5 eggs from an Eastern Meadowlark nest, all but 1 egg from a Field Sparrow nest, and 4 five-day-old nestlings from another Field Sparrow nest. Nestlings and eggs Table 1. Apparent nest success (the proportion of nests that successfully fledged at least one young) and estimated nest success from logistic exposure models for grassland bird nests at Valley Forge National Historical Park in southeastern Pennsylvania in 2011 and 2012. Intervals = the number of nest-check intervals used in the logistic-exposure model. Nest success was estimated by raising the DSR to the number of days in the entire nesting cycle for the species. Logistic-exposure models Apparent nest Daily survival rate Nest success Species success (n) Intervals (95% CI) (95% CI) Eastern Meadowlark 0.43 (7) 30 0.9443 (0.8752–0.9824) 0.25 (0.04-0.65) Field Sparrow 0.88 (8) 28 0.9861 (0.9403–0.9992) 0.77 (0.31–0.98) Red-winged Blackbird 0.60 (10) 49 0.9706 (0.9329–0.9908) 0.48 (0.18–0.80) Northeastern Naturalist 14 L. Murray 2015 Vol. 22, No. 1 from 2 Eastern Meadowlark nests (25% of depredated nests) were depredated by Vulpes vulpes L. (Red Fox). Procyon lotor L. (Raccoon) depredated 3 four-day-old Red-winged Blackbird nestlings. Six-day-old Eastern Meadowlark nestlings were depredated, but the predator knocked over the camera while pursuing the adult bird, thus precluding collection of conclusive evidence for identification; the triangularshaped head and small black eyes with no eye-shine were suggestive of a Mustela L. sp. (weasel). In addition, a female Red-winged Blackbird committed infanticide of a lone 5-day-old Red-winged Blackbird nestling (Murray 2014b). We were unable to identify a predator that knocked over the camera before depredating a Red-winged Blackbird nest. Discussion Estimates of nest success for grassland birds in Valley Forge were similar or higher than those reported in other studies. Eastern Meadowlark nest success was lowest among the species observed in this study, but was similar to estimates from the Midwest (Granfors et al. 1996, Lanyon 1957, McCoy et al. 2001, Rahmig et al. 2008, Ribic et al. 2012a, Roseberry and Klimstra 1970, Winter and Faaborg 1999). McCoy et al. (1999) estimated that nest survival of 0.30 was sufficient to maintain a population of Eastern Meadowlarks in Missouri Conservation Reserve Program. Therefore the estimated 0.25 nest success at Valley Forge is near levels needed to maintain a stable population, but estimates of fledgling survival at Valley Forge are necessary to calculate overall reproductive success. Our small sample size for Eastern Meadowlark nests and uncertainty in the estimate warrant caution in concluding that Valley Forge is a source habitat. Estimates of Eastern Meadowlark nest success in other areas in the Northeast were higher than those documented during this study (0.46 in New York [Norment et al. 2010], 0.70 in West Virginia [Warren and Anderson 2005]). Eastern Meadowlark nest success at Valley Forge could be negatively impacted by the local predator community (e.g., high White-tailed Deer density), greater urbanization, or smaller patch sizes causing lower nest success at Valley Forge than was estimated in New York and West Virginia. Red-winged Blackbird nest success in grasslands at Valley Forge was higher than estimates reported for other upland habitats. No impact of the presence of a camera on nest survival was found in this study, but the confidence interval was skewed toward a negative effect of cameras at nests. Nest survival for the entire nesting period ranged from 0.15 to 0.39 for Red-winged Blackbird populations in the Midwest and Northeast (Blakely 1976; Camp and Best 1994; McCoy et al. 1999, 2001; Patterson and Best 1996; Robertson 1972; Warren and Anderson 2005) compared with 0.48 for Valley Forge. Brood parasitism by Molothrus ater Boddaert (Brown-headed Cowbird) was a substantial contributor to nest failure for Red-winged Blackbirds in most populations, with up to 25% of nests parasitized in Conservation Reserve Program fields in Iowa (Patterson and Best 1996). The proportions of Red-winged Blackbird nests that failed due to predation, however, were similar between Valley Forge (0.40) and fields in Connecticut (0.30; Robertson 1972), when nests that were abandoned with eggs were excluded. Northeastern Naturalist Vol. 22, No. 1 L. Murray 2015 15 Field Sparrow nest success was the highest among the 3 species monitored in this study and higher than estimates in other studies. Nest-survival estimates ranged from 0.10 to 0.47 for studies in Illinois, Missouri, and Wisconsin (Best 1978; Burhans et al. 2002; McCoy 1999, 2001; Thompson and Burhans 2003; Vos and Ribic 2013), but brood parasitism was a contributing factor to nest failure in these other studies that was not observed at Valley Forge. Nest-predation rates away from edges in Michigan (0.05–0.10) were similar to those observed in our study (0.12), but were higher near edges (0.40–0.50) (Gates and Gysel 1978). Variation in predation rates among studies likely is driven by local predator communities; Best (1978) and Thompson et al. (1999) both identified snakes as frequent predators of Field Sparrow nests, but snakes were not observed depredating nests i n Valley Forge. Fewer nest-predator species were identified in Valley Forge than in other studies using video cameras to identify grassland-nest predators. At least 10 species were identified depredating nests in each of 4 studies in the Midwest (Pietz and Granfors 2000a, Renfrew and Ribic 2003, Ribic et al. 2012a, Thompson et al. 1999) compared to 4 species identified in this study (including the unconfirmed Mustela sp.). Overall, video evidence of nest predation by at least 18 mammal species, 7 bird species, and 5 snake species were reported in the Midwest (Pietz et al. 2012). All 4 predator species identified in this study have depredated nests in other studies; infanticide by Red-winged Blackbirds had not been previously recorded (see Murray 2014b for a detailed description). The small number of predation events recorded by video surveillance at Valley Forge partially explains the low diversity of predators detected, and I would expect additional predator species (e.g., snakes, birds) to be identified with further nest monitoring. The predominance of mammalian nest predators in Valley Forge parallels nest predation in other studies (e.g., Pietz and Granfors 2000a, Ribic et al. 2012a), but small-mammal predators were more common in the Midwest (Pietz et al. 2012). Valley Forge, however, is outside of the range of Ictidomys tridecemlineatus Mitchill (Thirteen-lined Ground Squirrel), which is the most common smallmammal predator in the Midwest (Grant et al. 2006, Pietz and Granfors 2000a, Ribic et al. 2012a). Several snake species known to depredate nests (e.g., Coluber constrictor L. [North American Racer], Lampropeltis triangulum Lacépède [Milk Snake], and Thamnophis sirtalis L. [Common Garter Snake]) occur at Valley Forge (Tiebout 2003) but were not detected in this study. Predators of grassland-bird nests in the Northeast had not been previously identified using video cameras, and thus, comparison of predator communities within the Northeast is not possible. Nest predation (0.38) by White-tailed Deer at Valley Forge was higher than reported from other studies (Grant et al. 2006 [0.07], Ellison et al. 2013 [0.05], Pietz and Granfors 2000b [0.08]). Because nest predation by White-tailed Deer is thought to occur opportunistically (Pietz and Granfors 2000b), the relatively high density of White-tailed Deer at Valley Forge (70 per km2, National Park Service 2009) likely contributed to the high rate of nest predation by White-tailed Deer. In addition, competition for food among White-tailed Deer in a high-density situation might make it more likely for these animals to consume high-protein, calorie-dense foods such as eggs and chicks when opportunities occur. In the fall of 2010, the Northeastern Naturalist 16 L. Murray 2015 Vol. 22, No. 1 National Park Service implemented a plan to reduce the White-tailed Deer population because of the negative effects of high densities on forest regeneration in the park (National Park Service 2009). I would expect less nest predation by Whitetailed Deer following herd reduction. However, the overall effects of White-tailed Deer removal on nest success is difficult to predict because it is possible that nest predation is compensatory and thus, reduction of one nest predator might allow opportunities for other predators and not affect overall nesting success (Ellis-Felege et al. 2012, Ellison et al. 2013). A comparison of the nest-predator community before and after reduction of the White-tailed Deer herd would provide insight into potential compensatory shifts in nest-predation risk among predators at Valley Forge and potentially give insight on how White-tailed Deer grazing on vegetation influences nest success. In conclusion, nest success for Eastern Meadowlarks, Field Sparrows, and Redwinged Blackbirds at Valley Forge was similar to reported nest success from other studies. The diversity of nest predators in Valley Forge is lower than those reported in other studies, but continued sampling likely would increase the number of nestpredator species documented because several unconfirmed potential nest predators occur in Valley Forge (e.g., birds and snakes). Previous conclusions about grassland- nest predators in the Northeast were based on likely predators in the area and predator activity or cues at the nest (e.g., Ardizzone and Norment 1999, Vickery et al. 1992). Video evidence, however, has shown that nests are depredated by diverse species and that cues at the nest cannot be used to accurately identify nest predators (Pietz and Granfors 2000a, Thompson et al. 1999). Therefore, continued research on local predator communities in grasslands of the Northeast is important for better understanding factors that can affect the stability of grassland-bird populations and managing habitat in the region. Acknowledgments I thank Valley Forge National Historical Park for granting me access to their meadows as research sites. I am particularly grateful to K.M. Heister and M.K. Jensen for their help in identifying suitable study areas. J.D. Dadisman provided invaluable guidance on video system components. M.K. Jensen, P. Paton, C.A. Ribic, F. Servello, and anonymous reviewers provided useful feedback on previous versions of this manuscript. Work done at Valley Forge National Historical Park was conducted under Scientific Research Permits VAFO-2011-SCI-0002 and VAFO-2012-SCI-0002 for Study VAFO-00026 issued by the U. S. Department of Interior, National Park Service. All research activities were approved by the Pennsylvania State University Institutional Animal Care and Use Committee (IACUC# 34156). Financial support was provided by Penn State Abington. Literature Cited Ardizzone, C.D., and C.J. Norment. 1999. Experimental analysis of nest predation in a New York grassland: Effects of habitat and nest distribution. Studies in Avian Biology 19:122–127. Balent, K.L., and C.J. Norment. 2003. Demographic characteristics of a Grasshopper Sparrow population in a highly fragmented landscape of western New York State. Journal of Field Ornithology 74:341–348. Northeastern Naturalist Vol. 22, No. 1 L. Murray 2015 17 Best, L.B. 1978. Field Sparrow reproductive success and nesting ecology. Auk 95:9–22. Blakely, N.R. 1976. Successive polygyny in upland-nesting Red-winged Blackbirds. Condor 78:129–133. Burhans, D.E., D. Dearborn, F.R. Thompson III, and J. Faaborg. 2002. Factors affecting predation at songbird nests in old fields. Journal of Wildlife Management 66:240–249. Burnham, K.P., and D.R. Anderson. 2002. Model Selection and Multimodel Inference: A Practical Information-theoretic Approach, 2nd Edition. Springer-Verlag, New York, NY. 488 pp. Camp, M., and L.B. Best. 1994. Nest density and nesting success of birds in roadsides adjacent to rowcrop fields. American Midland Naturalist 131:347–358. Carey, M., D.E. Burhans, and D.A. Nelson. 2008. Field Sparrow (Spizella pusilla). Number 103, In A. Poole and F. Gills (Eds.). The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, NY. Available online at http://bna.birds.cornell.edu.bnaproxy. birds.cornell.edu/bna/species/103. Accessed 29 August 2013. Chalfoun, A.D., M.J. Ratnaswamy, and F.R. Thompson III. 2002. Songbird-nest predators in forest–pasture edge and forest interior in a fragmented landscape. Ecological Applications 12:858–867. Ellis-Felege, S.N., M.J. Conroy, W.E. Palmer, and J.P. Carroll. 2012. Predator-reduction results in compensatory shifts in losses of avian ground nests. Journal of Applied Ecology 49:661–669. Ellison, K.S., C.A. Ribic, D.W. Sample, M.J. Fawcett, and J.D. Dadisman. 2013. Impacts of tree rows on grassland birds and potential nest predators: A removal experiment. PLos ONE 8: e59151. Doi:10.1371/journal.pone.0059151. Faaborg, J., M. Brittingham, T. Donovan, and J. Blake. 1995. Habitat fragmentation in the temperate zone. Pp. 357–380, In T.E. Martin and D.M. Finch (Eds.). Ecology and Management of Neotropical Migratory Birds: A Synthesis and Review of Critical Issues. Oxford University Press, New York, NY. 489 pp. Gates, J.E., and L.W. Gysel. 1978. Avian nest dispersion and fledging success in field–forest ecotones. Ecology 59:871–883. Granfors, D.A., K.E. Church, and L.M. Smith. 1996. Eastern Meadowlarks in rangelands and Conservation Reserve Program fields in Kansas. Journal of Field Ornithology 67:222–235. Grant, T.A., E.M. Madden, T.L. Shaffer, P.J. Peitz, G.B. Berkey, and N.J. Kadrmas. 2006. Nest survival of Clay-colored and Vesper Sparrows in relation to woodland edge in mixed-grass prairies. Journal of Wildlife Management 70:691–701. Herkert, J.R., D.L. Reinking, D.A. Wiedenfeld, M. Winter, J.L. Zimmerman, W.E. Jensen, E.J. Finck, R.R. Koford, D.H. Wolfe, S.K. Sherrod, M.A. Jenkins, J. Faaborg, and S.K. Robinson. 2003. Effects of prairie fragmentation on the nest success of breeding birds in the midcontinental United States. Conservation Biology 17:58 7–594. Herranz, J., M. Yanes, and F. Suárez. 2002. Does photo-monitoring affect nest predation? Journal of Field Ornithology 73:97–101. Heske, E.J. 1995. Mammalian abundances on forest–farm edges versus forest interiors in southern Illinois: Is there an edge ef fect? Journal of Mammalogy 76:562–568. Heske, E.J., S.K. Robinson, and J.D. Brawn. 2001. Nest predation and neotropical migrant songbirds: Piecing together the fragments. Wildlife Society Bulletin 29:52–61. Jaster, L.A., W.E. Jensen, and W.E. Lanyon. 2012. Eastern Meadowlark (Sturnella magna). Number 160, In A. Poole (Ed.). The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, NY. Available online at http://bna.birds.cornell.edu/bna/species/160. Accessed 29 August 2013. Johnson, R.G., and S.A. Temple. 1990. Nest predation and brood parasitism of tallgrassprairie birds. Journal of Wildlife Management 54:106–111. Northeastern Naturalist 18 L. Murray 2015 Vol. 22, No. 1 Lanyon, W.E. 1957. The Comparative Biology of the Meadowlarks (Sturnella) in Wisconsin. Publications of the Nuttall Ornithological Club. Nuttall Ornithological Club, Cambridge, MA. 66 pp. McCoy, T.D., M.R. Ryan, E.W. Kurzejeski, and L.W. Burger, Jr. 1999. Conservation Reserve Program: Source or sink habitat for grassland birds in Missouri? Journal of Wildlife Management 63:530–538. McCoy, T.D., M.R. Ryan, L.W. Burger, Jr., and E.W. Kurzejeski. 2001. Grassland-bird conservation: CP1 vs. CP2 plantings in Conservation Reserve Program fields in Missouri. American Midland Naturalist 145:1–17. Murphy, M.T. 2003. Avian population trends within the evolving agricultural landscape of eastern and central United States. Auk 120:20–34. Murray, L.D. 2014a. Bird-habitat relationships in restored meadows in southeastern Pennsylvania. Ecological Restoration 32:197–203. Murray, L.D. 2014b. Video evidence of infanticide by a female Red-winged Blackbird. Wilson Journal of Ornithology 126:147–151. National Oceanic and Atmospheric Administration (NOAA), National Climatic Data Center. 2013. 2012 Local climatological data annual summary with comparative data, Philadelphia, PA (KPHL). Available online at http://www.ncdc.noaa.gov/. Accessed 24 July 2013. National Park Service. 2009. Final White-tailed Deer management plan and environmental impact statement for Valley Forge National Historical Park. Available online at http:// parkplanning.nps.gov/document. Accessed 18 November 2013. Norment, C.J., M.C. Runge, and M.R. Morgan. 2010. Breeding biology of grassland birds in western New York: Conservation and management implications. Avian Conservation and Ecology 5:3 Available online at http://dx.doi.org/10.5751/ACE-00399-050203. Accessed 26 January 2014. Patterson, M.P., and L.B. Best. 1996. Bird abundance and nesting success in Iowa CRP fields: The importance of vegetation structure and composition. American Midland Naturalist 135:153–167. Perlut, N.G. 2014. Grassland birds and dairy farms in the northeastern United States. Wildlife Society Bulletin. 38:574–579. Pietz, P.J., and D.A. Granfors. 2000a. Identifying predators and fates of grassland passerine nests using miniature video cameras. Journal of Wildlife Management 64:71–87. Pietz, P.J., and D.A. Granfors. 2000b. White-tailed Deer predation on grassland-songbird nestlings. American Midland Naturalist 144:419–422. Pietz, P.J., D.A. Granfors, and C.A. Ribic. 2012. Knowledge gained from video-monitoring grassland passerine nests. Pp. 3–22, In C.A. Ribic, F.R. Thompson III, and P.J. Pietz (Eds.). Video Surveillance of Nesting Birds. Studies in Avian Biology (Number 43), University of California Press, Berkeley, CA. 224 pp. R Core Team. 2013. R: A language and environment for statistical computing. R Foundation for Statistical Computing. Vienna, Austria. Available online at http://www.R-project. org. Accessed 4 November 2013. Rahmig, C.J., W.E. Jensen, and K.A. With. 2008. Grassland-bird responses to land management in the largest remaining tallgrass prairie. Conservation Biology 23:420–4 32. Renfrew, R.B., and C.A. Ribic. 2003. Grassland passerine nest predators near pasture edges identified on videotape. Auk 120:371–383. Ribic, C.A., M.J. Guzy, T.J. Anderson, D.W. Sample, and J.L. Nack. 2012a. Bird productivity and nest predation in agricultural grasslands. Pp. 119–134, In C.A. Ribic, F.R. Thompson III, and P.J. Pietz (Eds.). Video Surveillance of Nesting Birds. Studies in Avian Biology (Number 43), University of California Press, Berke ley, CA. 224 pp. Northeastern Naturalist Vol. 22, No. 1 L. Murray 2015 19 Ribic, C.A., F.R. Thompson III, and P.J. Pietz (Eds.). 2012b. Video Surveillance of Nesting Birds. Studies in Avian Biology (Number 43), University of California Press, Berke ley, CA. 224 pp. Richardson, T.W., T. Gardali, and S.H. Jenkins. 2009. Review and meta-analysis of camera effects on avian nest success. Journal of Wildlife Management 73:287–293. Robertson, R.J. 1972. Optimal niche space of the Red-winged Blackbird (Agelaius phoeniceus). I. Nesting success in marsh and upland habitat. Canadian Journal of Zoology 50:247–263. Roseberry, J.L., and W.D. Klimstra. 1970. The nesting ecology and reproductive performance of the Eastern Meadowlark. Wilson Bulletin 82:243–267. Sauer, J.R., J.E. Hines, J.E. Fallon, K.L. Pardieck, D.J. Ziolkowski, Jr., and W.A. Link. 2014. The North American breeding bird survey: Results and analysis 1966–2012. Version 02.19.2014. USGS Patuxent Wildlife Research Center, Laurel, MD. Available online at http://www.mbr-pwrc.usgs.gov/bbs/. Accessed 26 January 2015. Shaffer, T.L. 2004. A unified approach to analyzing nest success. Auk 121:526–540. Tewksbury, J.J., S.J. Hejl, and T.E. Martin. 1998. Breeding productivity does not decline with increasing fragmentation in a western landscape. Ecology 79:2890–2903. Thompson III, F.R., and D.E. Burhans. 2003. Predation of songbird nests differs by predator and between field and forest habitats. Journal of Wildlife Management 67:408–416. Thompson III, F.R., and C.A. Ribic. 2012. Conservation implications when the nest predators are known. Pp. 23–34, In C.A. Ribic, F.R. Thompson III, and P.J. Pietz (Eds.). Video Surveillance of Nesting Birds. Studies in Avian Biology (Number 43), University of California Press, Berkeley, CA. 224 pp. Thompson III, F.R., W. Dijak, and D.E. Burhans. 1999. Video identification of predators at songbird nests in old fields. Auk 116:259–264. Tiebout III, H.M., 2003. An inventory of herpetofauna of Valley Forge National Historical Park. Technical Report NPS/PHSO/NRTR-03/088, US National Park Service, Philadelphia, PA. 54 pp. Vander Haegen, W.M., and R.M. Degraaf. 1996. Predation on artificial nests in forested riparian buffer strips. Journal of Wildlife Management 60:542–550. Vickery, P.D., and P.W. Dunwiddie. 1997. Introduction. Pp. 1–13, In P.D. Vickery and P.W. Dunwiddie (Eds.). Grasslands of Northeastern North America. Massachusetts Audubon Society, Lincoln, MA. 297 pp. Vickery, P.D., M.L. Hunter, Jr., and J.V. Wells. 1992. Evidence of incidental nest predation and its effects on nests of threatened grassland birds. Oikos 63:281–288. Vickery, P.D., J.L. Hunter, Jr., and S.M. Melvin. 1994. Effects of habitat area on the distribution of grassland birds in Maine. Conservation Biology 8:1087–1097. Vos, S.M., and C.A. Ribic. 2013. Nesting success of grassland birds in oak barrens and dry prairies in west central Wisconsin. Northeastern Naturalist 20:131–142. Warren, K.A., and J.T. Anderson. 2005. Grassland songbird nest-site selection and response to mowing in West Virginia. Wildlife Society Bulletin 33:285–292. Winter, M., and J. Faaborg. 1999. Patterns of area sensitivity in grassland-nesting birds. Conservation Biology 13:1424–1436. Winter, M., D.H. Johnson, J.A. Shaffer, T.M. Donovan, and W.D. Svedarsky. 2006. Patch size and landscape effects on density and nesting success of grassland birds. Journal of Wildlife Management 70:158–172. Yasukawa, K., and W.A. Searcy. 1995. Red-winged Blackbird (Agelaius phoeniceus). Number 184, In A. Poole (Ed.). The Birds of North America Online. Cornell Lab of Ornithology, Ithaca, NY. Available online at http://bna.birds.cornell.edu/bna/species/184. Accessed 29 August 2013.