Northeastern Naturalist L.R. Cassidy and G. Kleppel 2017 86 Vol. 24, Special Issue 8 The Effect of Grazing Regime on Grassland Bird Abundance in New York State Lisa R. Cassidy1,* and Gary Kleppel1 Abstract - Grassland breeding bird abundances in New York State mirror a national downward trajectory as land-use changes degrade, destroy, and fragment suitable habitat. We quantified and compared bird abundances on pastures that were subject to continuous grazing, minimal rotation, or holistic resource management. We hypothesized that grassland bird abundance varied systematically with pasture management approaches. We measured grassland bird abundances using 40-m radius point counts performed on 27 pastures. Further, we assessed vegetation and environmental parameters to characterize the available habitat on each pasture. Holistic resource managed pastures had 1.5 and 4.5 times higher average abundances of obligate grassland birds than minimally rotated or continuously grazed pastures, respectively. Overall, our results indicate that farms can employ strategies that promote grassland bird habitat and may therefore have a positive influence on grassland bird metapopulations in New York State. Introduction Native grassland ecosystems in North America have declined by nearly 80% due largely to agricultural intensification since the late 1800s (Askins 1993, Brennan and Kuvlesky 2005, Knopf 1994, Noss et al. 1995). Consequently, grassland birds have experienced more severe and precipitous population declines than any other avian guild in North America. Paradoxically, farmland and rangeland have become critical secondary habitats for grassland birds, serving as surrogates for native landscapes with which they co-evolved (Brennan and Kuvlesky 2005). Grasslands in northeastern North America were historically embedded within a heterogeneous landscape, with forests as the dominant cover type (Norment 2002). Following European settlement, a substantial portion of existing forests were cleared for agriculture, which resulted in large expanses of open, grassland habitat. This shift led to an increase in the diversity and abundance of grassland birds in the regions as western populations expanded into the Northeast and native grassland species increased in numbers (Askins 1999, Brennan and Kuvlesky 2005, Norment 2002). The current decline in native and naturalized grassland bird species in the Northeast is due primarily to reforestation, increased intensity of land use on farms, and urban and suburban development (American Farmland Trust 2016, Farmland Information Center 2014). Some grassland specialists, such as Ammodramus henslowii (Audubon) (Henslow’s Sparrow), listed as near threatened on the IUCN red list (BirdLIfe International 2016), and 1 Department of Biological Sciences, University at Albany, Albany, NY 12222. *Corresponding author - lrcassidy@albany.edu. Manuscript Editor: Peter Paton Natural History of Agricultural Landscapes 2017 Northeastern Naturalist 24(Special Issue 8):86–98 Northeastern Naturalist 87 L.R. Cassidy and G. Kleppel 2017 Vol. 24, Special Issue 8 Bartramia longicauda (Bechstein) (Upland Sandpiper) have experienced local extirpation (Askins 2000, Brennan and Kuvlesky 2005, Norment 2002). Farming practices in the region have intensified, resulting in monoculture and row crops, confined animal feeding operations, and increased pesticide/herbicide use. These changes have led to the reduction of native grasslands, contributed significantly to environmental degradation, and had negative impacts on local grassland bird populations by reducing available food resources and nesting habitat (Brennan and Kuvlesky 2005, Matson et al. 1997, Wilson et al. 2005). Finally, changes in the timing and frequency of hay cutting, as well as the overgrazing of pastures by livestock (typical attributes of conventional farming) have led to negative impacts on grassland bird habitat (Bollinger et al. 1990, Brennan and Kuvlesky 2005, Smith and Owensby 1978). Changes in haying and grazing practices are of particular concern because grasslands become “ecological traps” that attract high densities of breeding birds that have low productivity (W iens 1974). Given that agricultural land is, of necessity, secondary habitat for grassland breeding birds, it is critical that conservationists consider agricultural best management practices that protect grassland bird habitat. While much work has been done in New York State to change agricultural practices on hayfields (Bollinger 1995, Perlut et al. 2006), less effort has been made to understand how different pasture management and grazing strategies affect grassland bird populations. In New York, nearly 500,000 ha are managed as pastures (USDA 2007), where various types of livestock are managed by utilizing different grazing strategies and intensities. Overgrazing and intensive trampling degrades the pasture, potentially diminishing its ecological integrity and capacity to support avian foraging and breeding activities and conceal adults and chicks from predators. Therefore, many species of birds are absent from intensively grazed pastures (Brennan and Kuvlesky 2005, Cody 1968, Fondell and Ball 2004). Numerous studies have investigated the effects of domestic grazing on vegetation, soil microbes, and wildlife (Briske et al. 2008, Kleppel and LaBarge 2011, Teague et al. 2011). Grazing impacts on grassland birds can be categorized into direct effects such as trampling of nests, and indirect effects such as alteration of vegetation and soil topography. It is apparent that birds discern differences in grassland management techniques. Perlut et al. (2006) found that Dilichonyx oryzivorus L. (Bobolink) were more likely to re-nest on a pasture that was disturbed by grazing than one that was hayed. Additionally, certain species, such as Upland Sandpipers and Sturnella magna L. (Eastern Meadowlark), show a preference for grazed pasture (Derner et al. 2009, Roseberry and Klimstra 1970). Derner et al. (2009) regard livestock as “ecosystem engineers”, suggesting that current practices reduce heterogeneity on the landscape and thus grassland bird diversity. However, certain livestock management approaches can promote the conservation and restoration of grasslands and habitat for certain avian species. This study focused on the use of grazed lands by grassland birds. The overarching goal was to identify potential differences in avian abundance on pastures managed by different grazing methods and to create a model that incorporated the Northeastern Naturalist L.R. Cassidy and G. Kleppel 2017 88 Vol. 24, Special Issue 8 most important environmental variables that influenced avian abundances. We hypothesized that different livestock management strategies (i.e., holistic resource management, minimal rotation, and continuous grazing) would support varying abundances of obligate grassland birds. Study Area We conducted field work from 25 May to 31 July 2015 in Albany, Columbia, Green, and Schoharie counties, NY. We surveyed 27 pastures on 10 farms for birds and vegetation attributes (Fig. 1). Each pasture was managed following one of 3 strategies: holistic resource management (n = 13), minimal rotation (n = 10), and continuous grazing (n = 4) (Table 1). All pastures were grazed by beef or dairy cattle. Holistic resource management (HRM) is a comprehensive, adaptive framework used by farmers to make decisions that promote ecosystem health by mimicking the behavior of wild grazers that co-evolved on grasslands (Savory 1999, Voisin 1959). HRM seeks to mimic this behavior with high stocking densities, frequent (less than 1–3 day) rotations, and long periods (up to 60 days) of pasture rest, while also accounting for local environmental, social, and financial considerations to develop an adaptive decision-making framework that is specific to the resources and conditions that exist on the farm. We defined minimal rotation as infrequent pasture rotation with little attention to stock density, in which only vegetation height was used to determine when the livestock were moved. This system results in relatively high numbers of “animal days” on pasture. Continuous grazing includes pastures Figure 1. Location of pastures where avian point count were conducted in Schoharie, Albany, Columbia, and Green counties in New York State. Northeastern Naturalist 89 L.R. Cassidy and G. Kleppel 2017 Vol. 24, Special Issue 8 Table 1. Paddock size, number of animals, stocking density, animal days, and number of point count stations for pastures in each management type (continuous grazing, minimal rotation, and holistic resource management). Each point count station represents one pasture surveyed. Numbers for paddock size, number of animals, and stock density are derived from averaging those values for each case per management strategy. Therefore, stock density cannot be calculated from the means of paddock size and number of anim als in this table. # of point- Grazing Paddock size (ha) Number of animals Stock density (head/ha) Animal days/study period count management type Min–max Mean SD Min–max Mean SD Min–max Mean SD Min–max Mean SD stations Continuous 6.78–18.58 13.31 5.3 16–25 20.75 4.26 0.79–2.36 1.72 0.48 58–60 61.5 3.8 4 Minimal rotation 1.34–11.17 4.53 2.7 20–32 23.81 5.54 4.50–9.10 7.43 4.67 10–25 19.6 8.4 13 Holistic 0.10–2.57 1.12 0.9 23–65 41.18 17.60 65.00–316.29 120.30 126.77 1–4 3.3 2.2 10 Northeastern Naturalist L.R. Cassidy and G. Kleppel 2017 90 Vol. 24, Special Issue 8 that were grazed without rest at relatively low stock densities for the entire study, which resulted in the highest number of animal days on pasture. Methods Bird sampling We conducted fixed-radius (40-m) point counts at permanent survey stations in each pasture following the New York State Department of Environmental Conservation Grassland Bird Survey Protocol. We randomly located survey stations using a 1-m grid superimposed on a map of each pasture with the restrictions that survey stations were at least 100 m from an adjacent habitat or public road, at least 250 m from any other survey station, and located in grasslands of at least 5 ha. We visited each survey station during 3 times periods (25 May to 14 June, 15 June to 14 July, and 15 July to 31 July) . The first 2 periods corresponded to the birds’ arrival to breeding grounds and egg incubation period, and the incubation to early fledging period, respectively. The third survey period aligned with the period of post-natal disperal the onset of prebasic molt.. Upon arrival at each survey station, we waited 5 min before starting the point count to allow the birds to habituate to our presence. A 5-min point-count was then conducted that was subdivided into two 2-min intervals and a 1-min interval (adapted from Farnsworth et al. 2002). We conducted surveys between sunrise and 10 AM EDT under suitable weather conditions (i.e., no strong winds or precipitation) and varied the order in which stations were surveyed on each farm to reduce bias associated with differences in sampling time. Each bird associated with the pasture (e.g., perched, actively foraging) was identified, assigned to the appropriate time interval based on first detection, and placed into a distance category (0–19 m, 20–40 m) . Differences in detection probability (p) were not accounted for in this study, as bird observations were restricted to a 40-m radius. We assumed that detection probability was close to 1.0 due to birds’ proximity to the observer and reductions in the effect of landscape heterogeneity on birds present (Hutto 2016). Vegetation and landscape plots We sampled vegetation height and litter depth in 3 randomly selected 3-m radius plots within 10 m of each survey station. The percentage of each 3-m radius plot covered by grasses, forbs, woody vegetation, bare ground, and litter were estimated visually and averaged for each station. We also recorded distance to the nearest shrub, made a visual obstruction reading (VOR) of the vegetation with a Robel Pole (Robel et al. 1970), and noted the dominant grass species, dominant forb species, and any invasive plant species on each plot. To determine the area of cover types within the surrounding landscape of each bird census station, we obtained 4-band, digital ortho-imagery with a resolution of 0.33 m for all pastures from the New York State Geographic Information Systems Clearinghouse (http://gis.ny.gov) to quantify the proportion of each cover type (i.e., open, wooded, residential, water, and shrub) within 2.5 km of each survey station. We used ARCMap10.2 to perform a supervised classification using maximum likelihood procedures to determine the area of each cover type. Northeastern Naturalist 91 L.R. Cassidy and G. Kleppel 2017 Vol. 24, Special Issue 8 Data analyses To estimate the effects of grazing regimes on avian abundance, we averaged over all surveys for each type of pasture management from the 27 point-count stations. Differences in abundances, or the average number of individuals per management type, of the most commonly occurring grassland bird species were assessed using a non-parametric Kruskal-Wallis H test. We conducted pair-wise comparisons on bird counts using a 1-way ANOVA and tested time and management- specific differences in vegetation height, VOR, and percent cover using a 2-way ANOVA. We performed all statistical analyses with GraphPad Prism 7. Results The most commonly observed grassland bird species at our survey stations were Bobolinks, Passerculus sandwichensis (Gmelin) (Savannah Sparrow), Eastern Meadowlarks, and Charadrius vociferous L. (Killdeer). HRM pastures had 1.5 times higher average abundances of obligate grassland birds than minimally rotated pastures and 4.5 times more obligate grassland birds than continuously grazed pastures (Fig. 2). Savannah Sparrow abundances (Fig. 3A) varied significantly among management regimes (Kruskal-Wallis test: P = 0.008), while Bobolink (P = 0.26; Fig. 3B) and Eastern Meadowlark (EAME; P = 0.78; Fig. 3C) abundances did not differ with management regime, due to the large, within-group variability evident in these species. Pair-wise comparisons of Killdeer abundances over the 3 management regimes showed no significant difference among management regimes (P > 0.05; Fig 3D). However, there was a significant difference between Killdeer abundances overall (Kruskal-Wallis test: P = 0.049). Grass was the overwhelmingly dominant cover type in all pastures (P < 0.0001; Fig. 4), regardless of management strategy. Mean cover (vegetation) heights across grazing regimes on each visit are given in Table 2. The vegetation in HRM pastures Figure 2. Mean (SE) abundance of obligate grassland birds within a 40-m radius across continuous, minimally rotated, and holistic resource management pastures in New York. Means with different letters are significantly different based on a 1-way ANOVA. Northeastern Naturalist L.R. Cassidy and G. Kleppel 2017 92 Vol. 24, Special Issue 8 was 70% and 43% higher than on continuously grazed or minimally rotated pastures, respectively (2-way ANOVA: P = 0.009; Fig. 5). Variability in vegetation height was not affected by the time of sampling (i.e., visit number), nor did the interaction of these 2 factors affect vegetation height. While the timing of visitation (visit number) did not affect the visual obstruction reading (VOR), the differences between mean VOR in holistically managed Figure 3. Mean (SE) abundance within a 40-m radius of (A) Bobolinks (BOBO), (B) Savannah Sparrows (SAVS), (C) Eastern Meadowlarks (EAME), and (D) Killdeer (KILL) across continuous, minimally rotated, and holistic resource management pastures in New York. Means with different letters are statistically different based on a 1-way ANOVA. Table 2. Mean (SE) vegetation height (cm) for 3 visits to pastures under different grazing regimes in New York: C = continuous grazing, M = minimal rotation, H = holistic resource management. Visit 1 Visit 2 Visit 3 Mean SE n Mean SE n Mean SE n C 24.9 10.2 4 17.1 6.2 5 13.2 2.6 4 M 19.7 3.8 13 24.4 4.9 12 21.5 3.7 13 H 36.1 3.8 10 35.4 5.1 8 22.3 2.6 10 Northeastern Naturalist 93 L.R. Cassidy and G. Kleppel 2017 Vol. 24, Special Issue 8 pastures and other pasture management strategies was significant (P = 0.009; Fig. 6). VORs on holisticly managed pastures were 146% and 36.4% higher than on continuously grazed and minimally rotated pastures, respecti vely. Discussion During this study, we documented that the overall abundance of all grassland- obligate birds was higher on HRM pastures than on minimally rotated and continuously grazed pastures. However, the abundances of Bobolinks and Eastern Figure 4. Mean (SE) percent cover of grasses, forbs, bare soil, litter, and woody vegetation across c o n t i n u o u s , minimally rotated, and holistic resource management pas t u r es in New York. Figure 5. Mean (SE) vegetation height across c o n t i n u o u s , minimally rotated, and holistic resource management pastures in New York Northeastern Naturalist L.R. Cassidy and G. Kleppel 2017 94 Vol. 24, Special Issue 8 Meadowlarks did not differ as a function of grazing regime, whereas Savannah Sparrow and Killdeer abundances did differ among grazing regimes. The absence of within-group (i.e., grazing management strategy) variability for Bobolinks and Eastern Meadowlarks may be partially due to inter-station and seasonal variability in the abundances of these species, as well as the way different farms applied specific grazing strategies, which may have obscured differences among grazing regimes (Herkert 1994, Walk and Warner 2000, Winter et al. 2006). Killdeer were present in continuously grazed and minimally rotated pastures, and did not occupy the taller vegetation found in HRM pastures. Killdeer are not grassland-obligate species but nest in open habitats, including intensely grazed pastures that have bare patches (Jackson et al. 2000). Most previous research found that grazing can have a positive impact on grassland birds. Skinner et al. (1974) found that grazed grasslands had significantly more individual birds than ungrazed grasslands (see also Bignal and McCracken 1996, Roseberry and Klimstra 1970). Walk and Warner (2000) reported that light to moderate grazing created a heterogeneous grassland structure that benefitted a variety of grassland obligate species such as Eastern Meadowlarks, Ammodramus savannarum (Gmelin) (Grasshopper Sparrow), and Henslow’s Sparrows. In contrast, Smith and Owensby (1978) found that intensive stocking techniques reduced biodiversity over the landscape and gave the vegetation little opportunity to recover. Differences in vegetation characteristics among farms utilizing the 3 grazing regimes in this study were substantial. HRM pastures had taller grass and higher VOR measurements than both continuously grazed and minimally rotated pastures. Bobolink, Savannah Sparrow, and Eastern Meadowlark prefer grass heights of 20–30 cm, >13 cm, and ~25 cm for nesting activities, respectively (Renfrew et al. 2015). Figure 6. Mean (SE) visual obstruction readi n g s ( V O R ) across continuous, minimally rotated, and holistic resource ma n a g eme n t pastures in New York. Northeastern Naturalist 95 L.R. Cassidy and G. Kleppel 2017 Vol. 24, Special Issue 8 Based on these height preferences, we documented seasonal variation in nest-site habitat suitability among grazing regimes. During our first survey period, the mean grass heights for all 3 grazing regimes were suitable for Bobolinks because many pastures were not yet being grazed due to sparse precipitation at the start of the 2015 growing season (National Weather Service, n.d.) resulted in the delay of cattle releases onto pastures. However, by the second and third survey periods, vegetation was tall enough for nesting Bobolinks only in minimally rotated pastures and HRM pastures. All 3 grazing regimes provided suitable grass heights for Eastern Meadowlarks throughout the entirety of the study, but vegetation height in continuously grazed pastures was almost too short by the third survey period. Grass height requirements for Savannah Sparrows suggest that early in the breeding season (period 1), continuously grazed and HRM fields provided suitable habitat, but by periods 2 and 3 only HRM pastures were suitable. Overall, HRM pastures retained a healthy vegetation height for all obligate grassland bird species for the entirety of this study. VOR was significantly higher on HRM pastures than on minimally rotated and continuously grazed pastures. Bobolinks, Savannah Sparrows, and Eastern Meadowlarks selected sites that had high values in vertical vegetation density for concealment and cover for their chicks (Renfrew et al. 2015). Eastern Meadowlarks prefer heterogeneous territories with densely vegetated sites for nesting and shorter vegetation for foraging (Jaster et al. 2012). Overall, HRM pastures appear to include important vegetation characteristics for the grassland specialists we studied, including increased vegetation height and VOR. Fuhlendorf and Smeins (1999) suggested that the long-term grazing impacts on landscape heterogeneity was dependent on grazing intensity. Since landscape heterogeneity is a major factor influencing diversity and abundance of grassland birds (Cody 1985, Knopf 1994, Wiens 1974), grazing could potentially be used as a conservation tool. Fuhlendorf and Engle (2001) suggest that livestock can be used for grassland conservation by mimicking Bison bison L. (Bison) behavior on the landscape to create a shifting mosaic that will foster grassland bird diversity. Most grassland bird studies that have assessed grazing strategies tend to categorize grazing management as either light, moderate, or intensive grazing (Bock and Webb 1984, Fondell and Ball 2004, Shustack et al. 2010). However, visually assessing pastures at 1 point in time does not account for temporal effects of livestock distributions and movements on the landscape. Determining how livestock can be moved to optimize bird habitat on seasonal, annual, and higher temporal scales may allow for the development of conservation plans to incorporate livestock as a conservation tool on agricultural landscapes. It is critical that biologists and farmers develop grazing regimes that promote grassland birds and are both conducive to wildlife and economically viable for farmers. This study provides a simple pasture management classification system that allows one to discern differences among management approaches. Biologists should understand how varying stocking densities, animal days, and rest time for pastures could interact to create suitable habitat for grassland breeding birds. Northeastern Naturalist L.R. Cassidy and G. Kleppel 2017 96 Vol. 24, Special Issue 8 Further, this study occurred on farms that were outside of New York’s current important bird areas for grassland birds. We detected only 3 obligate grassland bird species: Bobolinks, Eastern Meadowlarks, and Savannah Sparrows, but New York has 7 other species of grassland birds that are in need of management actions including Circus cyaneus L. (Northern Harrier), Asio flammeus (Pontopiddan) (Short-eared Owl), Eremophila alpestris L. (Horned Lark), Cistothorus platensis (Latham) (Sedge Wren), Pooecetes gramineus (J.F. Gmelin) (Vesper Sparrow), Grasshopper Sparrow, and Henslow’s Sparrow (New York State Department of Environmental Conservation 2016). Conservation efforts in the future may begin to provide habitat for some of these once locally abundant grassland bird species. In order to promote bird-favorable habitat characteristics on such landscapes, it is prudent to use as a guide, natural landscapes on which wild grazers and grassland birds not only coexist, but coevolved. While the Northeast is not a region where birds and grazers co-evolved, the modifications to native ecosystems created by agriculture (i.e., clearing of forests, creation of grasslands and deployment of herd-forming ungulates) require that we seek physical models of habitats in which such features exist naturally, and manage our “created grasslands” to accommodate bird–ungulate coexistence. Acknowledgments We are grateful to J. Kirchman and A. Strong for assistance with the design of the project and analysis of the data. 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