Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 252 Canaan Valley & Environs 2015 Southeastern Naturalist 14(Special Issue 7):252–260 Invertebrate Biomass in Mowed and Unmowed Fields of Canaan Valley Kelly A. Chadbourne1,2 and James T. Anderson1,* Abstract - Few data exist on invertebrate populations in farmland habitats of the Appalachian Mountains. However, invertebrate biomass and taxonomic composition may influence the potential for birds to reproduce. We collected invertebrates using sweepnets on 3 idle pastures and 3 idle hayfields in the Canaan Valley National Wildlife Refuge, WV. To evaluate the effects of mowing on invertebrate biomass, half of each field was mowed in August 1999 after grassland birds had finished nesting. In 2000, we collected terrestrial invertebrates on the mowed and non-mowed portions of each field. We documented 25 invertebrate families from 12 orders. Taxa in the orders Coleoptera (beetles), Diptera (flies), Homoptera (leafhoppers), and Orthoptera (grasshoppers and crickets) were the most abundant. Invertebrate biomass (g/150 passes of a sweep net) was similar (P = 0.763) between mowed (mean = 0.4302, SE = 0.0509) and unmowed (mean = 0.4704, SE = 0.0716) treatments. Biomass was similar between hayfields and pastures for each month (P > 0.05). We conclude that mowing did not influence the composition or biomass of our collections, which were comprised of invertebrate taxa from orders commonly consumed by breeding grassland birds. Introduction Studies of grassland invertebrates are necessary to assess the food resources for grassland birds and to evaluate the effects of management activities. The biomass and community composition of invertebrates influence avian productivity, survival, and nesting success (Cody 1985, Miller et al. 1994, Strehl and White 1986). For example, Passerculus sandwichensis (Gmelin) (Savannah Sparrow) nestlings in Alaska showed increased growth rates during years of high invertebrate production (Miller et al. 1994). Agelaius phoeniceus L. (Red-winged Blackbird) generally fledge more young during years with high invertebrate availability (Nero 1984, Strehl and White 1986). Grasslands in Canaan Valley (hereafter, the Valley), Tucker County, WV, provide important habitat for several grassland bird species, including Dolichonyx oryzivorus L. (Bobolink), Sturnella magna L. (Eastern Meadowlark), and Savannah Sparrows (Warren and Anderson 2005). Information concerning the abundance and composition of invertebrate food items is required to fully evaluate the importance of the Valley’s grasslands for birds. We could find no other studies detailing invertebrate abundance and composition in the Valley. Management of idle pastures, defined as open areas formerly grazed by livestock, and idle hayfields, which were formerly managed for hay production 1Wildlife and Fisheries Resources Program, Division of Forestry and Natural Resources, West Virginia University, PO Box 6125, Morgantown, WV 26506. 2Current address - US Fish and Wildlife Service, Great Bay National Wildlife Refuge, 100 Merrimac Drive, Newington, NH 03801. *Corresponding author - jim.anderson@mail.wvu.edu. Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 253 through mowing and baling, can improve habitat quality for grassland birds by controlling woody vegetation, lowering vegetative height, and reducing litter build-up (Sample and Hoffman 1989). If performed prior to or after nesting, mowing temporarily halts succession and provides nesting habitat for grasslandnesting birds (McCoy et al. 2001). Mowing may also impact food resources, particularly arthropods and seeds for adults and nestlings. For example, invertebrate composition and abundance varied between mowed and unmowed fields in England (Morris and Plant 1983). However, invertebrate richness was not influenced by mowing in Colorado (Collinge 2000) or Australia (Parker and Mac Nally 2002). The timing of mowing can also impact invertebrate species diversity and relative abundance. In England, grasslands mowed in July, or in both May and July, had lower invertebrate species diversity than grasslands mowed only in May (Morris and Plant 1983). Because invertebrates are a primary food source for grassland birds, we studied invertebrate biomass of idle hayfields and pastures and of mowed and unmowed portions of these fields in the Valley. The specific objectives of our study were to (1) compare total invertebrate biomass between mowed and unmowed fields to determine the effects of mowing on invertebrate biomass, (2) compare total invertebrate biomass between hayfields and pastures to determine if grassland type impacted invertebrate biomass, and (3) compare total invertebrate biomass among months (June, July, and August) and years (1999 and 2000) to determine the temporal variation in invertebrate abundance. Field Sites This study was conducted on 6 grasslands (mean = 121.6 ac/field, SE = 31.4; [49.2 ha/field, SE = 12.7]), range = 39.5–230 ac [16–93 ha]) of the Canaan Valley National Wildlife Refuge (herein called “the Refuge”) in the Valley. Grasslands had not been pastured or mowed for 6–7 years prior to the start of this study. The dominant grassland vegetation on the Refuge consisted of Dactylis glomerata L. (Orchard Grass), Danthonia compressa (Austin) (Mountain Oat Grass), Anthoxanthum odoratum L. (Sweet Vernal Grass), Agropyron repens L. (Quackgrass), Phleum pratense L. (Timothy), Solidago uliginosa (Nutt.) (Bog Goldenrod), Solidago rugosa (Mill.) (Wrinkle-leaved Goldenrod), Hypericum densiflorum (Pursh) (Bushy St. Johnswort) , and Spiraea alba (Du Roi) (White Meadowsweet) (Warren 2001). Summers in the Valley are typically cool, averaging 75–79 °F (24–26 °C) during the day and 50–55 °F (10–13 °C) at night (NOAA 1999). Due to its cool climate, the Valley’s floral composition includes plants with northern distributions, some of which are at the southernmost extent of their range (Fortney 1993). Normal rainfall in the Valley is about 45 in/y (114 cm/y) (NOAA 1999). During 1999, total rainfall was lower than average (38 in [96 cm]), with the largest deviation from average (9 in [22 cm]) occurring during May–August. In 2000, total rainfall (44 in [113 cm]) was similar to that of a normal year (NOAA 2000). Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 254 Methods Experimental design During 1999 and 2000, we collected invertebrates on grasslands that had previously been managed as 3 hayfields, known as the Beall, Harper, and Thompson tracts, and as 3 pastures, known as the Cortland, Freeland, and Herz tracts. At the end of 1999’s grassland-bird breeding-season (mid–late August; Warren 2001), one-half of each of the Beall, Cortland, Freeland, Harper, and Thompson tracts was mowed to determine the effects of habitat manipulation on breeding-bird nesting success (Warren 2001) and to evaluate impacts on invertebrate biomass. Herz was not mowed because it was too wet. Invertebrate sampling We sampled invertebrates according to the methods in O’Leske et al. (1997). We collected samples using standard canvas-bag sweep-nets (15-in [38-cm] diameter) once monthly in June, July, and August of 1999 and 2000 along line transects (Anderson et al. 2013). Transects ran the length of each field, were located 164 ft (50 m) from the field’s edge, and were spaced 328 ft (100 m) apart to facilitate bird, invertebrate, and plant sampling (Warren 2001). We collected invertebrates by walking the entire length of each transect during 1000–1500 hours on days when cloud cover was less than 50%, wind speed was less than 12 mph (20 km/ hr), and ambient temperature was 61–82 °F (16–28 °C) (O’Leske et al. 1997, Robel et al. 1996). On each field, we made 3 collections, each consisting of 50 full sweeps through the upper level of vegetation. The 3 collections were combined to create 1 sample per field per month. Thus, each sample included the catch from 150 passes of the sweep net. The same person collected all samples to reduce bias (Robel et al. 1996). We placed the contents of the sweep net in ethyl-acetate kill jars and then transferred the specimens to labeled plastic bags and froze them. We determined invertebrate numbers and biomass by separating thawed invertebrates from vegetative debris, allowing them to air dry , and sorting them to family or order (O’Leske et al. 1997). Once sorted, we dried samples to a constant mass at 158 °F (70 °C) for 48 hours and recorded the mass to the nearest 0.0001 g. We could not identify all invertebrates to family or order; however, unknown invertebrates were included in the total biomass calculations. Statistical analyses We checked data for normality using the Shapiro-Wilk statistic and for homogeneity of variances by plotting residuals (Cody and Smith 1991). When the distributions proved to be non-normal, we log (x + 1)-transformed invertebrate biomass data to improve normality. For the 2000 data, we analyzed total invertebrate biomass data (dry mass/150 sweeps) by three-way analysis of variance (ANOVA) using a model that included habitat type (hayfields, pastures), treatment (mowed, unmowed), and month (June, July, August). The model also consisted of habitat type, year, and month for 1999 and 2000 data (Robel et al. 1996). We considered all tests significant at P < 0.05. Following a significant ANOVA, we used Tukey’s multiple comparison test to separate means. Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 255 Results We collected 12 orders of invertebrates, all of which were insects except Araneae (spiders) and Palpigradi (microwhip scorpions). The samples included at least 25 families (Table 1). In 2000, the total invertebrate biomasses were similar between mowed (mean = 0.4302 g/150 sweeps, SE = 0.0509) and unmowed Table 1. Mean biomass (g/150 sweeps of a sweep net) of invertebrate families collected on mowed and unmowed grasslands of the Canaan Valley National Wildlife Refuge, Tucker County, WV, during June, July, and August 2000. Mowed Unmowed Order/Family Mean SE Mean SE Araneae 0.0097 0.0022 0.0180 0.0067 Coleoptera 0.0184 0.0054 0.0196 0.0019 Carabidae 0.0000 0.0000 0.0008 0.0008 Cerambycidae 0.0000 0.0000 0.0005 0.0005 Chrysomelidae 0.0079 0.0038 0.0072 0.0027 Coccinellidae 0.0022 0.0007 0.0046 0.0018 Curculionidae 0.0007 0.0006 0.0007 0.0004 Phalacridae 0.0003 0.0003 0.0000 0.0000 Dermaptera 0.0004 0.0004 0.0000 0.0000 Forficulidae 0.0004 0.0004 0.0000 0.0000 Diptera 0.0267 0.0046 0.0101 0.0023 Syrphidae 0.0132 0.0039 0.0049 0.0008 Tephritidae 0.0000 0.0000 0.0004 0.0004 Hemiptera 0.0347 0.0164 0.0694 0.0356 Lygaeidae 0.0102 0.0081 0.0198 0.0139 Miridae 0.0101 0.0052 0.0428 0.0218 Nabidae 0.0010 0.0005 0.0022 0.0018 Pentatomidae 0.0044 0.0026 0.0021 0.0014 Reduviidae 0.0034 0.0018 0.0024 0.0017 Homoptera 0.1632 0.0213 0.1640 0.0362 Cercopidae 0.1396 0.0282 0.1151 0.0369 Cicadellidae 0.0307 0.0121 0.0144 0.0059 Dictyopharidae 0.0012 0.0012 0.0002 0.0002 Flatidae 0.0021 0.0021 0.0038 0.0023 Membracidae 0.0021 0.0013 0.0139 0.0067 Hymenoptera 0.0625 0.0028 0.0119 0.0074 Braconidae 0.0010 0.0009 0.0000 0.0000 Formicidae 0.0017 0.0010 0.0089 0.0059 Larvae (Unknown) 0.0109 0.0046 0.0124 0.0036 Lepidoptera 0.0157 0.0039 0.0069 0.0026 Neuroptera 0.0002 0.0002 0.0000 0.0000 Chrysopidae 0.0002 0.0002 0.0000 0.0000 Orthoptera 0.0162 0.0059 0.0289 0.0111 Acrididae 0.0130 0.0052 0.0316 0.0129 Tettigoniidae 0.0004 0.0004 0.0000 0.0000 Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 256 (mean = 0.4704 g/150 sweeps, SE = 0.0716) treatments (F1, 7 = 0.10, P = 0.763). However, not all invertebrates occurred in both mowed and unmowed fields (Table 1). For the combined 1999 and 2000 data, we detected a three-way interaction among year, habitat type, and month (F2, 24 = 4.23, P = 0.027). During 1999, there were no differences in invertebrate biomass, in terms of dry mass/150 sweeps, between hayfields and pastures for June (F1, 4 = 2.84, P = 0.167), July (F1, 4 = 1.85, P = 0.246), or August (F1, 4 = 0.12, P = 0.751) (Table 2). In 2000, there also were no differences in invertebrate biomass between hayfields and pastures for June (F1, 4 = 0.03, P = 0.876), July (F1, 4 = 2.76, P = 0.172), or August (F1, 4 = 6.37, P = 0.065) (Table 2). There were no differences in total invertebrate biomass among months in 1999 for hayfields (F2,6 = 0.52, P = 0.621) or pastures (F2,6 = 4.91, P = 0.055) (Fig. 1). However, in 2000, biomass varied among months for hayfields (F2,6 = 5.98, P = 0.037) but not for pastures (F2,6 = 0.07, P = 0.932) (Fig. 1). Invertebrate biomass was higher in July 2000 than August 2000, but both months were similar to June 2000. Most orders were represented in both hayfields and pastures, but Dermaptera (earwigs) were absent in pasture collections, and Palpigradi were absent from hayfield collections (Table 3). Discussion Sweep-netting is a standard procedure for sampling invertebrate populations in grassland habitats (Robel et al. 1996). This method, like most techniques, has advantages and disadvantages (Cooper and Whitmore 1990). A main disadvantage is that different people sweep differently and comparisons among treatments may be biased if numerous people collect the samples (Ausden 1996). We reduced this bias by having the same person collect all of the samples in the same manner. Therefore, biases should be similar between habitats, treatments, years, and months. Although we believe that sweep-net samples provided an accurate picture of the invertebrates inhabiting vegetation, we do not believe this method adequately sampled ground-dwelling invertebrates such as carabid beetles. With several exceptions, the taxonomic composition of invertebrates was similar among mowed and unmowed plots and hayfields and pastures. Dermaptera were not present in collections from pastures or from unmowed hayfields; Table 2. Mean biomass (g/150 sweeps of a sweep net) of invertebrates collected from idled pastures and idled hayfields of the Canaan Valley National Wildlife Refuge, Tucker County, WV, during June, July, and August 1999–2000. June July August Year Habitat type Mean SE Mean SE Mean SE 1999 Hayfields 0.6932 0.3586 0.3145 0.2657 0.4814 0.0523 Pastures 0.0988 0.0096 0.8285 0.2733 0.5234 0.1082 2000 Hayfields 1.1014 0.2765 1.7121 0.3026 0.5080 0.1089 Pastures 1.2210 0.4466 1.1595 0.0837 1.3287 0.3277 Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 257 Neuroptera (net-winged insects) were not present in collections from pastures. Overall, vegetative composition and structure were similar between hayfields and pastures (Warren 2001). Indeed, although invertebrate biomass differed Figure 1. Total invertebrate biomass by month for hayfields and pastures on the Canaan Valley National Wildlife Refuge, WV, for 1999 and 2000. Table 3. Mean biomass (g/150 sweeps of a sweep net) of invertebrate orders collected from idled pastures and idled hayfields of the Canaan Valley National Wildlife Refuge, Tucker County, WV, during June, July, and August 1999–2000. Hayfield Pasture Order Mean SE Mean SE Araneae 0.03740 0.00240 0.03720 0.00380 Coleoptera 0.03700 0.00300 0.03240 0.00600 Dermaptera 0.00280 0.00280 0.00000 0.00000 Diptera 0.02080 0.00940 0.01900 0.00560 Hemiptera 0.00480 0.01180 0.04780 0.01280 Homoptera 0.13420 0.02660 0.12320 0.05960 Hymenoptera 0.01340 0.00240 0.02020 0.00440 Larvae (unidentified) 0.04640 0.00740 0.03760 0.01000 Lepidoptera 0.05040 0.01060 0.02100 0.00780 Neuroptera 0.00100 0.00010 0.06000 0.05840 Orthoptera 0.09760 0.01096 0.07820 0.00580 Palpigradi 0.00000 0.00000 0.00500 0.00500 Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 258 slightly among months for hayfields in 2000, we detected no significant differences among months for hayfields and pastures. Insect orders present in our samples that may provide important food for grassland birds and their nestlings on the Refuge were adult forms of Coleoptera (beetles), Homoptera (leafhoppers), and Lepidoptera (moths and butterflies), as well as the larvae of Diptera (flies), Coleoptera, and Lepidoptera. All of these orders are important to nesting grassland birds in other regions of the US (Kobal et al. 1998, Lanyon 1995, Martin and Gavin 1995, Meunier and Bedard 1984, Wheelwright and Rising 1993). Although information does not exist on the insect orders fed to nestlings on the Refuge, the dominant foods in the above studies were the same dominant orders collected during our sweep-net sampling. Odonata (dragonflies and damselflies) were not captured in our study, and may be underrepresented in sweep-net samples (Ausden 1996). Although avian nesting success ranged from 19.4% for Bobolinks to 70% for Eastern Meadowlarks, most nests (82%) were lost to predators (Warren 2001), indicating that food was likely not limiting for nestlings. Management implications Mowing had limited impacts on the abundance and composition of plantdwelling invertebrates during the summer. Mowing probably reduced the overall abundance of invertebrates (Morris and Plant 1983), but we did not measure this response. The use of mowing as a management tool to slow succession (McCoy et al. 2001) in grassland habitats appears to have mostly positive impacts and may be suitable for future manipulation of the Refuge’s grasslands. Additional studies on food resource availability, specifically invertebrates and seeds, and their uses will determine which grassland sites are providing adequate resources for the Refuge’s grassland birds. It would be useful to incorporate invertebrate sampling with observations of grassland birds carrying food to their nestlings to determine the foods being fed to nestlings and whether the Refuge is providing adequate food resources. These data should be combined with studies of energetics, productivity, and survival models to determine the long-term sustainability of the Refuge’s grassland bird populations. Acknowledgments We are grateful for funds provided by the US Fish and Wildlife Service (Canaan Valley National Wildlife Refuge); the West Virginia Division of Natural Resources; the West Virginia University Division of Forestry and Natural Resources; the Davis College of Agriculture, Natural Resources, and Design at West Virginia University (Brown Faculty Development Fund); and the West Virginia Agricultural and Forestry Experiment Station (McIntire-Stennis). We thank S.K. Reilly and C.A. Rhoads for assisting with data collection and laboratory work. We also thank C.A. Davis, W.C. Conway, and J.D. Osbourne for reviewing the manuscript. This is manuscript number 3202 of the West Virginia University Agricultural and Forestry Experiment Station. Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 259 Literature Cited Anderson, J.T., F.L. Zilli, L. Montalto, M.R. Marchese, M. McKinney, and Y.-L. Park. 2013. Sampling and processing aquatic and terrestrial invertebrates in wetlands. Pp. 142–195, In J.T. Anderson, and C.A. Davis (Eds.). Wetland Techniques. Volume 2: Organisms. Springer, New York, NY. 332 pp. Ausden, M. 1996. Invertebrates. Pp. 139–177, In W.J. Sutherland (Ed.). Ecological Census Techniques: A Handbook. Cambridge University Press, Cambridge, UK. 336 pp. Cody, M.L. 1985. Habitat selection in grassland and opencountry birds. Pp. 191–226, In M.L. Cody (Ed.). Habitat Selection in Birds. Academic Press, Orlando, FL. 558 pp. Cody, R.P., and J.K. Smith. 1991. Applied Statistics and the SAS Programming Language, 3rd Edition. Elsevier Scientific Publications, New York, NY. 403 pp. Collinge, S.K. 2000. Effects of grassland fragmentation on insect species loss, colonization, and movement patterns. Ecology 81:2211–2226. Cooper, R.J., and R.C. Whitmore. 1990. Arthropod sampling methods in ornithology. Studies in Avian Biology 13:29–37. Fortney, R.H. 1993. Canaan Valley: An area of special interest within the upland forest region. Pp. 47–65, In S.L. Stephenson (Ed.). Upland Forests of West Virginia, Mc- Clain Printing Company, Parsons, WV. 295 pp. Kobal, S.N., N.F. Payne, and D.R. Ludwig. 1998. Nestling food habits of 7 grassland bird species and insect abundance in grassland habitats in Northern Illinois. Transactions of the Illinois Academy of Science 91:69–75. Lanyon, W.E. 1995. Eastern Meadowlark (Sturnella magna). No. 160, In A. Poole and F. Gill (Eds.). The Birds of North America. The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists’ Union, Washington, DC. Martin, S.G., and T.A. Gavin. 1995. Bobolink (Dolichonyx oryzivorus). No. 176, In A. Poole and F. Gill (Eds.). The Birds of North America. The Academy of Natural Sciences, Philadelphia, PA and The American Ornithologists’ Union, Washington, DC. McCoy, T.D., E.W. Kurzejeski, L.W. Burger, Jr., and M.R. Ryan. 2001. Effects of conservation practice, mowing, and temporal changes on vegetation structure on CRP fields in northern Missouri. Wildlife Society Bulletin 29:979–987. Meunier, M., and J. Bedard. 1984. Nestling foods of the Savannah Sparrow. Canadian Journal of Zoology 62:23–27. Miller, C.K., R.L. Knight, L.C. McEwen, and T.L. George. 1994. Responses of nesting Savannah Sparrows to fluctuations in grasshopper densities in interior Alaska. Auk 111:962–969. Morris, M.G., and R. Plant. 1983. Responses of grassland invertebrates to management by cutting. Journal of Applied Ecology 20:157–177. Nero, R.W. 1984. Redwings. Smithsonian Institution Press, Washington, DC. 160 pp. National Oceanic Atmospheric Administration (NOAA). 1999. National climatological data: Canaan Valley, West Virginia. US Department of Commerce, Washington, DC. NOAA. 2000. National climatological data: Canaan Valley, West Virginia. US Department of Commerce, Washington, DC. O’Leske, D.L., R.J. Robel, and K.E. Kemp. 1997. Sweepnet-collected invertebrate biomass from high- and low-input agricultural fields in Kansas. Wildlife Society Bulletin 25:133–138. Parker, M., and R. MacNally. 2002. Habitat loss and the habitat fragmentation threshold: An experimental evaluation of impacts on richness and total abundances using grassland invertebrates. Biological Conservation 105:217–229. Southeastern Naturalist K.A. Chadbourne and J.T. Anderson 2015 Vol. 14, Special Issue 7 260 Robel, R.J., B.L. Henning, K.W. Johnson, K.E. Kemp, and K.E. Church. 1996. Effects of seasonal disking on seed production and invertebrate biomass. The Southwestern Naturalist 41:403–408. Sample, D.W., and R.M. Hoffman. 1989. Birds of dry-mesic and dry prairies in Wisconsin. Passenger Pigeon 51:195–208. Strehl, C.E., and J. White. 1986. Effects of super-abundant food resources on breeding success and behavior of the Red-winged Blackbird. Oecologia 70: 178–186. Warren, K.A. 2001. Habitat use, nest success, and management recommendations for grassland birds of the Canaan Valley National Wildlife Refuge, West Virginia. M.Sc. Thesis. West Virginia University, Morgantown, WV. 146 pp. 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. Wheelwright, N.T., and J.D. Rising. 1993. Savannah Sparrow (Passerculus sandwichensis ).No. 45, In A. Poole and F. Gill (Eds.). The Birds of North America. The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists’ Union, Washington, DC.