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Nest-site Fidelity in Grassland Birds on Mowed Versus Unmowed Areas on a Reclaimed Surface Mine
Danny J. Ingold, James L. Dooley, and Nicole Cavender

Northeastern Naturalist, Volume 17, Issue 1 (2010): 125–134

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2010 NORTHEASTERN NATURALIST 17(1):125–134 Nest-site Fidelity in Grassland Birds on Mowed Versus Unmowed Areas on a Reclaimed Surface Mine Danny J. Ingold1,*, James L. Dooley1, and Nicole Cavender2 Abstract - We monitored return rates of 324 color-banded Ammodramus savannarum (Grasshopper Sparrow), 138 Passerculus sandwichensis (Savannah Sparrow), and 49 Dolichonyx oryzivorus (Bobolink) on mowed and unmowed areas on a reclaimed surface mine during seven breeding seasons. We observed 61 returns among Grasshopper Sparrows, 40 returns among Savannah Sparrows, and 11 returns among Bobolinks. Grasshopper Sparrows and Savannah Sparrows returned to mowed and unmowed areas at about equal rates (21 vs. 18% and 26 vs. 31%, respectively), while Bobolinks returned to unmowed areas at a higher rate than mowed areas (28% vs. 17% respectively). When hatching-year birds were excluded, overall return rates increased slightly for Grasshopper Sparrows and Bobolinks (19 to 20% and 22 to 23%, respectively), but more substantially for Savannah Sparrows (from 29 to 36%). Sixteen of 51 returning Grasshopper Sparrows (31%), 12 of 27 Savannah Sparrows (44%), and 2 of 10 Bobolinks (20%) were observed during multiple years. These observations support previous findings that reclaimed surface mines provide suitable nesting habitat for these species. Early-season mowing did not appear to influence the return rates of Grasshopper Sparrows or Savannah Sparrows, although it may have influenced Bobolink returns. Introduction Populations of several grassland bird species in the Appalachian region of the eastern United States are declining (Helzer and Jelinski 1999, Sauer et al. 2005, Swanson 1996), largely as a result of habitat loss and fragmentation (Askins 2002, Vickery et al. 2005). Reclaimed surface mines, although heavily disturbed systems, are often vast and secluded and provide potentially suitable nesting habitat for several obligate-grassland bird species which might not be able to persist in regions otherwise lacking in extensive grasslands (Bajema et al. 2001, DeVault et al. 2002, Ingold 2002, Swanson 1996). The nesting success of several grassland bird species on reclaimed surface mines has been shown to be comparable to that on a variety of unmined lands (Galligan et al. 2006, Monroe and Ritchison 2005). Populations of Dolichonyx oryzivorus (L.) (Bobolink), Passerculus sandwichensis (Gmelin) (Savannah Sparrow), and Ammodramus henslowii (Brewster) (Henslow’s Sparrow), which have steadily declined in the glaciated portions of Ohio (Sauer et al. 2005), have increased in the southeastern, unglaciated 1Department of Biology, Muskingum College, New Concord, OH 43762. 2The Wilds, 14000 International Road, Cumberland, OH 43732. *Corresponding author - ingold@ muskingum.edu. 126 Northeastern Naturalist Vol. 17, No. 1 counties where reclaimed surface mines are common (Peterjohn 1989, Peterjohn and Rice 1991). In addition to demography and habitat association (see DeVault et al. 2002, Galligan et al. 2006, Monroe and Ritchison 2005), nest-site fidelity can also be used to assess habitat quality of reclaimed surface mines for breeding grassland birds. Nest-site fidelity, the proclivity for individuals to return to breed at a previous breeding site, has been documented in several species (Bollinger and Gavin 1989, Gavin and Bollinger 1988, Greenwood 1980), and its presence in grassland birds has been positively associated with hatching and/or fledging success of breeding individuals during the previous year (Gavin and Bollinger 1988). There are few studies that focus on nestsite fidelity in grassland birds, and even fewer that have examined the return rates of grassland birds on reclaimed surface mines. Among the nest-site fidelity studies that have been conducted, reports for grassland bird species seem to indicate highly variable return rates which may, in some cases, vary as a function of habitat quality (Balent and Norment 2003, Bollinger and Gavin 1989, Gill et al. 2006, Perlut et al. 2008, Wheelwright and Mauck 1998) or geographic area (Jones et al. 2007). Two studies have specifically quantified nest-site fidelity in grassland birds on a reclaimed surface mine. Skipper (1998) found that 5 of 27 (18.5%) color-banded male Henslow’s Sparrows and 0 of 7 color-banded females returned to nest in the same location as in the previous year in Maryland. Monroe and Ritchison (2005) reported that 2 of 9 (22%) marked male Henslow’s Sparrows returned to the same location on one study site and that 2 of 18 (11%) males returned to a second study site, both in Kentucky. Both of these studies, however, were relatively short-term (two and four years, respectively). A number of extrinsic factors that influence grassland habitat structure (e.g., mowing, hay-cropping, burning, and grazing) could affect reproductive success and/or nest-site fidelity on reclaimed surface mines. Numerous studies have shown that mowing and hay-cropping, particularly between May and August, adversely affect reproductive success of several grassland bird species in the Midwest and northeastern United States (Bollinger et al. 1990, Frawley and Best 1991, Ingold 2002). However, Ingold (2002) reported that Ammodramus savannarum (Gmelin) (Grasshopper Sparrow) and Savannah Sparrows on a reclaimed surface mine frequently nested on plots that were mowed in mid-April prior to onset of nesting. In general, few studies, particularly on reclaimed surface mines, have examined the effects of early- (prior to 1 May) or late-season (after 1 Aug) mowing on grassland bird breeding density, reproductive success, or return rates (but see Herkert 1994a, b; Ingold 2002; Ingold et al. 2009). Our objective was to quantify and compare long-term return rates of Grasshopper Sparrows, Savannah Sparrows, and Bobolinks on areas mowed in mid-April versus unmowed areas on reclaimed surface mine habitat. 2010 D.J. Ingold, J.L. Dooley, and N. Cavender 127 Methods Study area The Wilds (International Center for the Preservation of Wild Animals) is a 3700-ha center for conservation research and education located on reclaimed mined land overlapping portions of Muskingum, Guernsey, and Noble counties in southeastern Ohio. The landscape was initially mined for coal by the Ohio Power Coal Company in the 1940s and 1950s. After a 10– 15 year hiatus, the land was again mined from 1969–1984 and subsequently reclaimed. Today, the landscape is comprised of hilly non-native grasslands with scattered wood lots, drainage ponds, lakes, and a large wetland area. See Ingold (2002) for a description of the predominant vegetation types that comprised our study site. Field methods We established eight 210- x 90-m rectangular plots in 1999 along the western boundary of the Wilds. Four plots were mowed during mid- April each year from 2000 to 2007, and four plots were left undisturbed. After our first year of data collection, we determined that our sample size of marked birds on these plots would be limited. Thus, during the subsequent six field seasons (2001–2006), we captured and color-banded birds not only on the plots, but on several unmowed areas between them. Each plot, as well as the areas between them, was surrounded on at least three sides by a minimum of 10 ha of additional open grasslands with some scattered Elaeagnus umbellata Thunb. (Autumn Olive) trees. The same plots were mowed each year in most cases; however, there were some years in which a few previously mowed plots were left unmowed, and a few previously unmowed plots were mowed. Because of our decision to expand the sampling area, our intention shifted from conducting an inferential experiment, to reporting return rates of these species on readily available mowed and unmowed areas. Grasshopper and Savannah Sparrows and Bobolinks were captured using 2.6- x 12-m mist nets and play-back tapes. Captured individuals were fitted with 3 plastic color bands (randomly chosen color combinations) and a US Geological Survey aluminum band (2 color bands on one leg and a color band and an aluminum band on the other leg) to facilitate individual identification in subsequent breeding seasons. Netting and searching for color-banded birds was conducted on each mowed and unmowed area on a weekly or biweekly basis between 0800 and 1200 hrs (EDT) from early May through mid-July 2000–2007. The amount of time spent netting birds was relatively uniform across each area. Typically, four nets were placed in an area, usually near one or more singing males. We were fairly thorough in our capture efforts, but did not attempt to capture every individual in every area, nor did we spend much time netting in those portions of study areas in which birds were consistently absent. Captured birds were classified to gender and 128 Northeastern Naturalist Vol. 17, No. 1 as hatching year or adult. Location and general habitat attributes associated with the capture site were recorded. Recaptured or resighted birds were identified from previous records, and returning individuals were considered to have exhibited site fidelity if they were sighted or captured within 100 m in any direction of the original point of capture. Analyses Return rates were calculated by dividing the total number of returns we observed in a given species in a particular habitat (mowed vs. unmowed) by the total number of individuals that were banded in that habitat. Detection and survival probabilities were estimated for Grasshopper and Savannah Sparrows using Pradel routines (Pradel 1996) available within Program MARK (White and Burnham 1999) and are reported ± SE. Small sample sizes precluded estimating detection and survival probabilities for Bobolinks. Birds that returned to plots in which the treatment had inadvertently been changed between years (e.g., unmowed plots that were mowed or mowed plots that were left unmowed) were not included in our return-rate calculations or in our detection and survivorship probability estimations. Results We captured and color-banded 324 Grasshopper Sparrows, 138 Savannah Sparrows, and 49 Bobolinks from 2000–2006 and documented 112 total returns across all species from 2001–2007 (Table 1). We documented 61 returns among Grasshopper Sparrows (Table 2), 40 returns among Savannah Sparrows (Table 3), and 11 returns among Bobolinks (Table 4). About equal percentages of Grasshopper and Savannah Sparrow returns were to mowed versus unmowed areas (21% vs 18% and 26% vs. 31%, respectively; Table 1), while a slightly higher percentage of Bobolink returns were to unmowed vs. mowed areas (28% vs. 17% respectively; Table 1). Mean (±SD) estimated detection probabilities were largely similar between habitats for Grasshopper Sparrows (x̅ = 0.786 ± 0.048 and 0.693 ± 0.077 in mowed vs. unmowed plots, respectively). Detection probabilities were higher in mowed relative to unmowed habitats for Savannah Table 1. Numbers of Grasshopper Sparrow (GH), Savannah Sparrow (SA), and Bobolink (BO) returns to the same location (within 100 m2) and habitat type (mowed vs. unmowed) in which individuals were originally banded. Number of individuals Number of returns Returns to Returns to banded (2000–2006) observed mowed areas unmowed areas GH 324 61 (19%) 26/126 (21%) 35/198 (18%) SA 138 40 (29%) 14/53 (26%) 26/85 (31%) BO 49 11 (23%) 4/24 (17%) 7/25 (28%) 2010 D.J. Ingold, J.L. Dooley, and N. Cavender 129 Sparrows (x̅ = 0.869 ± 0.066 and 0.594 ± 0.119, respectively); however, in many cases, the variation around estimates for particular years was large (ranging from near zero to 0.9999). Mean annual apparent survival probabilities for Grasshopper Sparrows were higher in mowed areas (x̅ = 0.81 ± 0.055 and 0.676 ± 0.095 in mowed vs. unmowed plots, respectively), while mean annual apparent survival probabilities for Savannah Sparrows were similar in mowed and unmowed habitats (x̅ = 0.733 ± 0.079 and 0.773 ± 0.118, respectively). Table 4. Number banded (n) and recaptures/resightings of all Bobolinks banded from 2000–2006 on a reclaimed surface mine (the Wilds) in Ohio. Recaptures/resightings by breeding season (habitat types combined) Year banded n 2000 2001 2002 2003 2004 2005 2006 2007 2000 4 - 0 0 0 0 0 0 0 2001 3 2 0 0 1 0 0 2002 6 1 0 1 0 0 2003 9 1 1 0 0 2004 5 0 0 0 2005 13 2 0 2006 9 2 Table 3. Number banded (n) and recaptures/resightings of all Savannah Sparrows banded from 2000–2006 on a reclaimed surface mine (the Wilds) in Ohio. Recaptures/resightings by breeding season (habitat types combined) Year banded n 2000 2001 2002 2003 2004 2005 2006 2007 2000 18 - 7 2 1 0 0 0 0 2001 23 1 5 2 1 0 0 2002 18 5 2 2 2 0 2003 35 3 2 1 0 2004 14 0 0 0 2005 8 1 1 2006 22 2 Table 2. Number banded (n) and recaptures/resightings of all Grasshopper Sparrows banded from 2000–2006 on a reclaimed surface mine (the Wilds) in Ohio. Recaptures/resightings by breeding season (habitat types combined) Year banded n 2000 2001 2002 2003 2004 2005 2006 2007 2000 18 - 6 3 2 0 0 0 0 2001 29 7 0 1 0 0 0 2002 43 4 2 2 1 0 2003 47 4 3 2 0 2004 61 5 3 1 2005 61 8 3 2006 65 4 130 Northeastern Naturalist Vol. 17, No. 1 Eleven, twenty-six, and four percent of the Grasshopper Sparrows, Savannah Sparrows, and Bobolinks, respectively, were captured during their hatching year (Table 5). Return rates of these individuals were low (6% Grasshopper, 8% Savannah, and 0% Bobolinks), and when excluded from our calculations, the overall return rates of each species increased (Table 5). Sixteen of 51 (31%) returning Grasshopper Sparrows, 12 of 27 (44%) Savannah Sparrows, and 2 of 10 (20%) Bobolinks were observed during multiple years (Tables 2–4). Four Grasshopper Sparrows were seen during three consecutive years, and two Savannah Sparrows were observed during four consecutive years. Discussion Our findings suggest that reclaimed surface mines provide suitable nesting habitat for Grasshopper Sparrows, Savannah Sparrows, and Bobolinks. Our return rates, in some cases, are comparable to those reported for these species on unmined lands. Our 21% overall Grasshopper Sparrow return rate is lower than the 28% overall return rate reported for this species during a three-year study in western New York (Balent and Norment 2003), and notably lower than the rates reported from a six-year study on Conservation Reserve Program fields in Maryland (Gill et al. 2006). In contrast, our return rates for Grasshopper and Savannah Sparrows were substantially higher than those reported for these species during a nine-year study in Montana, which was conducted on a large, undisturbed native prairie landscape (Jones et al. 2007). Our overall return rate for Bobolinks (24%) was lower than those reported by Gavin and Bollinger (1988) and Bollinger and Gavin (1989) on low-quality sites (44% male returns and 25% female returns). We concur with Bollinger and Gavin (1989), who suggested that Bobolink return rates at a particular location are likely influenced by their density at that location, and therefore return patterns should not be generalized across sites. Densities, in turn, are likely influenced by habitat quality and patch size (Herkert 1997). Patch size on our study site was comparable to those in Bollinger and Gavin’s (1989) study, but it is possible that the quality of habitat on our site (a highly disturbed reclaimed surface mine) Table 5. Numbers of Grasshopper Sparrows (GH), Savannah Sparrows (SA), and Bobolinks (BO) captured during their hatching year (HY) on all areas, and overall return rates (2001– 2007) of these species when hatching-year birds are excluded. Number banded during Total return rates Return rates with HY (2000–2006) with HY birds HY birds excluded GH 34/324 (11%) 61/324 (19%) 59/290 (20%) SA 36/138 (26%) 40/138 (29%) 37/102 (36%) BO 2/49 (4%) 11/49 (22%) 11/47 (23%) 2010 D.J. Ingold, J.L. Dooley, and N. Cavender 131 was lower than that in central New York (unmined pastures and meadows; Bollinger and Gavin 1989). That observed return rates were similar and apparent survival rates actually higher on mowed vs. unmowed areas for Grasshopper Sparrows suggests that our spring mowing regime did not adversely affect this species. That return rates and apparent survival rates for Savannah Sparrows were also comparable between habitats also suggests April mowing was not detrimental. Similarity in return rates of Grasshopper Sparrows and Savannah Sparrows to mowed vs. unmowed areas in this study were likely in part a result of their generalized habitat requirements (Madden et al. 2000, Vickery 1996, Warren and Anderson 2005, Wheelwright and Rising 1993), and the preference of both species to nest in medium to short vegetation (Balent and Norment 2003, Gill et al. 2006, Ribic and Sample 2001, Whitmore 1979). The return rates for Bobolinks to mowed vs. unmowed areas across this seven-year period contrasted slightly (28% vs. 20%, respectively), although our sample sizes were small. These results are consistent with those reported by Ingold (2002), in which Bobolink densities on mowed plots were lower and nests were uncommon. Bobolinks are generally associated with tall grasses and legumes (Herkert 1997, Madden et al. 2000, Renken and Dinsmore 1987), and the extent to which vegetative growth occurred between the time of mowing and the onset of nesting likely influenced whether Bobolinks returned to mowed plots in this study. This growth, in turn, was likely in part a function of plant species composition, which varied somewhat across our study area. Relatively few Grasshopper and Savannah Sparrows and Bobolinks (6%, 8%, and 0%, respectively) banded during their hatching year were observed to return to their natal area in subsequent years. Return rates of hatching-year individuals among these species in other studies have generally been low as well (Balent and Norment 2003, Jones et al. 2007, Wheelwright and Rising 1993), although Gill et al. (2006) reported a 12% return rate in hatching-year Grasshopper Sparrows in Maryland. Results from this investigation are consistent with previous work suggesting that reclaimed surface mines can provide useful habitat for these species of grassland birds (Bajema et al. 2001, DeVault et al. 2002, Monroe and Ritchison 2005, Galligan et al. 2006). Nonetheless, developing longterm strategies for successful conservation of these species will likely require addressing a number of additional questions. Though mowing did not appear to negatively impact return rates for Grasshopper and Savannah Sparrows, there are other management strategies that might prove important in enhancing habitat quality for these species, as well as for Bobolinks (e.g., providing perch sites, particularly in situations in which restoration work may involve removing invasive shrubs; see Gill et al. 2006). 132 Northeastern Naturalist Vol. 17, No. 1 Acknowledgments We are indebted to Evan Blumer for encouraging and promoting conservation research of native species at the Wilds. Jason Larson, Richard Yost, Charlotte Worstall, Aaron Binckley, Daniel Hollenbaugh, John Treasure, Jarrod Girod, Ashley Campbell, Paul Gledhill, Elena Gledhill, Lauren Harding, Jessica Turner, Adam Cirone, and Don Ingold all assisted in the field work. Funding was provided through Muskingum College and the Homer A. Anderson Distinguished Professor of Natural Sciences Endowment. Literature Cited Askins, R.A. 2002. Restoring North America’s Birds: Lessons from Landscape Ecology, 2nd Edition. Yale University Press, New London, CT. Bajema, R.A., T.L. DeVault, P.E. Scott, and S.L. Lima. 2001. Reclaimed coal mine grasslands and their significance for Henslow’s Sparrows in the American Midwest. Auk 118:422–431. 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. Bollinger, E.K., and T.A. Gavin. 1989. 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