Snakes are Important Nest Predators of Dickcissels in an Agricultural Landscape Author(s): Page E. Klug, L. LaReesa Wolfenbarger, and John P. McCarty Source: The Wilson Journal of Ornithology, 122(4):799-803. 2010. Published By: The Wilson Ornithological Society DOI: 10.1676/09-203.1 URL: http://www.bioone.org/doi/full/10.1676/09-203.1

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The Wilson Journal of Ornithology 122(4):799–803, 2010

Snakes are Important Nest Predators of Dickcissels in an Agricultural Landscape

Page E. Klug,1,2,3 L. LaReesa Wolfenbarger,1 and John P. McCarty1

ABSTRACT.—We used video cameras to monitor 33 remains (Samson and Knopf 1994). Grassland Dickcissel (Spiza americana) nests during 2003–2004 nesting in the remaining grasslands often in the highly-fragmented, agricultural ecosystem of experience low reproductive success due to eastern Nebraska and western Iowa. Nine nests fledged landscape features in agroecosystems that attract young, 20 were completely depredated, three were partially depredated, and one was abandoned due to a diversity of nest predators (Bergin et al. 2000). ants. Nine snakes, six small mammals, six common Previous studies have identified predators of raccoons (Procyon lotor), two Brown-headed Cowbirds grassland nests, but more studies are (Molothrus ater), and one American mink (Neovison necessary to understand how predator communi- vison) were documented as nest predators. These results ties differ among regions and what factors may suggest a diversity of predators is responsible for contribute to these differences (Weatherhead and depredation of Dickcissel nests with snake predation Blouin-Demers 2004). At least two video studies being an important cause of nest failure. Received 21 December 2009. Accepted 24 May 2010. of nesting birds that have occurred in North American grasslands were in areas that could be considered tallgrass prairie, but were conducted at Nest predation is the leading cause of repro- the edge of the historical tallgrass prairie range. ductive failure for many bird species across Thompson and Burhans (2003) documented numerous regions and (Martin 1993), predators of shrub-nesting birds in old fields in and may be an important factor in avian Missouri, and Renfrew and Ribic (2003) docu- population declines (Heske et al. 2001). Grassland mented predators of five grassland species in birds are of special concern because they have grazed pastures in the Driftless Area of Wiscon- undergone declines greater than any group of sin; both studies were conducted along the birds in North America (Knopf 1994) and have ecotone with eastern deciduous forests. Pietz and shown decreasing reproductive rates with in- Granfors (2000) studied nest predation on 10 creased fragmentation (Herkert et al. species of grassland and Grant et al. (2006) studied two species in mixed- 2003). Nearly 80% of grasslands in the Great Plains of North America have been converted to grass prairie in North Dakota. To date, no studies have been conducted in the highly fragmented, agricultural use, and ,4% of the tallgrass prairie agricultural ecosystem in the core of the former tallgrass prairie biome. Our objective was to 1 Department of Biology, University of Nebraska at identify predators of Dickcissel (Spiza americana) Omaha, Omaha, NE 68182, USA. 2 Current address: Department of Biology, University of nests within small grassland patches interspersed Notre Dame, Notre Dame, IN 46556, USA. within intensive row crop agriculture. Dickcissels 3 Corresponding author; e-mail: [email protected] are of conservation concern and have shown 800 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 122, No. 4, December 2010

TABLE 1. Nest predators recorded on video with corresponding number of Dickcissel nests depredated at incubation and nestling stages.

Predator Incubation Nestling # Events Snakes Fox snake (Elaphe vulpina)325 Plains garter snake (Thamnophis radix)022 Eastern yellowbelly racer (Coluber constrictor flaviventris)011 Bullsnake (Pituophis catenifer)101 Small mammals Thirteen-lined ground squirrel (Spermophilus tridecemlineatus)213 Franklin’s ground squirrel (S. franklinii)011 Cricetid rodent (Peromyscus spp.) 2 0 2 Mid-sized mammals Common raccoon (Procyon lotor)426 Other Brown-headed cowbird (Molothrus ater)112 American mink (Neovison vison)011 Totals 13 11 24 population declines similar to other grassland production (e.g., corn or soybeans). Grasslands passerines, but their predator community has not covered 2–43% (x¯ 6 SE 5 17.8 6 2.5) and trees been documented on video. Dickcissels are an 6–42% (x¯ 6 SE 5 15.7 6 2.5) of the landscape. ideal model for understanding how nest predator Human development covered 0.5–22% (x¯ 6 SE 5 communities vary among regions, landscapes, or 4.0 6 1.7), and roads ,2% (x¯ 6 SE 5 1.2 6 0.1), habitat types because they inhabit marginal whereas wetlands and water bodies covered 1– grasslands in extremely fragmented landscapes 14% (x¯ 6 SE 5 5.4 6 1.0) of the landscape. as well as relatively unfragmented landscapes. We used 24-hr time-lapse video systems to monitor nests and identify predators removing or METHODS consuming eggs and nestlings. We constructed six We monitored Dickcissel nests at DeSoto battery-powered video systems, which included a National Wildlife Refuge, Boyer Chute National camera (V-1214-IR Weatherproof Bullet Camera Wildlife Refuge, Allwine Prairie Preserve, Cum- with infrared illumination, Marshall Electronics, ing City Cemetery and Nature Preserve, and a El Segundo, CA, USA) attached to a time-lapse privately owned Conservation Reserve Program video recorder (SSC-960 Time Lapse VCR, (CRP) parcel in eastern Nebraska and western Samsung Electronics America Inc., Ridgefield Iowa (Klug et al. 2009). The grasslands were Park, NJ, USA) by 8.5 m of cable (buried under managed with prescribed burning but no livestock vegetation and litter) and powered by a sealed grazing. Vegetation in the grasslands was either lead acid battery connected by a power converter dominated by native warm-season grasses or by (375w PowerVerter, Tripp-Lite World Headquar- exotic cool-season grasses with variation in forb ters, Chicago, IL, USA). The camera was attached density (Klug 2005). We video-documented to a wood dowel and placed within 10 cm of the predators of Dickcissel nests in 15 grassland nest so the camera was completely obscured by fragments ranging from 4 to 45 ha (x¯ 6 SE 5 20.3 vegetation, but vegetation did not completely 6 3.1). The landscape within 1,600 m of obscure the field of view. We minimized grassland fragments included six major land cover disturbance at the nest by setting up the system types based on the evaluation of orthophotographs in ,20 min between 1000 and 1600 CST, in dry, in ArcMap GIS (scale of 1:1500) by Klug et al. moderate temperatures. We set up systems during (2009). We classified the landscape as an both incubation and nestling stages, but only after agroecosystem because 20–64% (x¯ 6 SE 5 52.5 females had incubated for 3–5 days to minimize 6 3.9) of the surrounding land was in crop abandonment. Nest contents were checked re- SHORT COMMUNICATIONS 801

TABLE 2. Nest predators of grassland passerines documented on video in Nebraska/Iowa, North Dakota, Missouri, and Wisconsin.

Nebraska North North Predator Iowaa Dakotab Dakotac Missourid Wisconsine Snake (Elaphe vulpina, E. obsoleta, Thamnophis spp., Coluber constrictor, Lampropeltis getula, L. calligaster, Pituophis catenifer)92333 Common raccoon (Procyon lotor)6148 Squirrel (Spermophilus tridecemlineatus, S. franklinii, Sciurus niger) 4 13 11 1 4 Brown-headed Cowbird (Molothrus ater)22511 Mouse or vole (Peromyscus spp., Zapus spp., Microtus spp.) 2 2 3 2 Long-tailed weasel/American mink (Mustela frenata, Neovison vison)11 1 American badger (Taxidea taxus)232 Bird of prey (Buteo spp., Circus cyaneus, Tyto alba)2132 Red fox/coyote/domestic dog (Vulpes vulpes, Canis latrans, C. lupus familiaris)2 1 Domestic cat (Felis catus) 1 Striped skunk (Mephitis mephitis) 1 Virginia opossum (Didelphis virginiana)1 White-tailed deer (Odocoileus virginianus)22 Unidentified 1 2 1 Totals 24 27 30 46 24

a This study. b Pietz and Granfors (2000). c Grant et al. (2006). d Thompson and Burhans (2003). e Renfrew and Ribic (2003). motely by attaching a portable monitor to the survival of 0.333 6 0.07 if we extrapolated to a system every 24 hrs given that the tape ran out 20-day nesting cycle (i.e., the average length of a after 24 hrs. We archived the tape to identify the Dickcissel nesting cycle). The probability of predator using a high-resolution monitor and slow predation for nests with cameras was similar to motion function if the contents differed from the nests not monitored with video systems (DSR 5 previous day. We recorded time, nest stage, nest 0.934 6 0.005, overall survival rate 5 0.255 6 contents, and contents removed for each depre- 0.03). Twenty of the nests monitored completely dation event. failed due to depredation, three nests were We estimated daily survival rates (DSR) for partially depredated before eventual fledging of nests using Program MARK with the design young, nine nests fledged young with no depre- matrix tools and the logit-link function (Dinsmore dation, and one nest was abandoned after an ant et al. 2002), and calculated variance using the infestation. Delta method (Powell 2007). We also estimated Nine snakes, six small mammals, six common DSR for nests without video systems to better raccoons (Procyon lotor), two Brown-headed understand the influence of the equipment on nest Cowbirds (Molothrus ater), and one American survival. Means 6 SE are presented. mink (Neovison vison) were documented as nest predators (Table 1). We documented one instance RESULTS of a multiple predation at one nest (i.e., a Brown- We video-monitored 33 nests over 2 years headed Cowbird removed three Dickcissel eggs (2003 5 15 nests, 2004 5 18 nests) for 287 prior to a thirteen-lined ground squirrel [Spermo- observation days during incubation (n 5 148 days) philus tridecemlineatus] consuming the remaining and nestling (n 5 139 days) stages. Nests were 2 Brown-headed Cowbird and 1 Dickcissel egg). monitored an average of 12.9 6 1.0 days. We We documented partial predation by a fox snake placed cameras at 19 nests that recorded both (Elaphe vulpina) late in the nesting cycle at two incubation and nestling stages, 11 nests during the nests, which caused the surviving nestlings to incubation stage only, and three nests during the fledge prematurely. A fox snake at another nest nestling stage only. The DSR of nests monitored was documented consuming one egg and leaving with video was 0.946 6 0.01 for an overall three, which later hatched and fledged. We 802 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 122, No. 4, December 2010 observed one female Brown-headed Cowbird has revealed considerable nest predation by removing Dickcissel nestlings without laying snakes and ground squirrels, which are essential eggs. We recorded 13 and 11 depredations at the members of prairie communities (Table 2). Rec- incubation and nestling stages, respectively (Ta- ommendations directed at decreasing the influ- ble 1). Depredation by cricetid rodents and ence of resident predators in grasslands where raccoons were nocturnal, whereas depredation birds are nesting are not straightforward given that by ground squirrels, mink, and cowbirds were many of these species are also targets of diurnal. All depredations by snakes were diurnal conservation. For example, fox snakes and except two by fox snakes, which were nocturnal. Franklin’s ground squirrels (Spermophilus frank- linii) are native members of the tallgrass prairie DISCUSSION (Martin et al. 2003) and efforts to control these The potential predator community in agricul- predators to increase bird populations must tural systems is diverse; thus, the composition of proceed with caution. the community, and identity of the dominant predator, will ultimately dictate nest predation ACKNOWLEDGMENTS risk (Klug et al. 2009). We found at least 10 We thank the staff of Boyer Chute and DeSoto National species responsible for predation of Dickcissel Wildlife refuges for their support. We also thank the nests, including both obligate grassland species American Museum of Natural History Frank M. Chapman (e.g., ground squirrels and snakes) and more wide- Memorial Fund, Sigma Xi Grants-In-Aid of Research, ranging habitat generalists (e.g., common raccoon Center for Great Plains Studies Grant-In-Aid for Graduate and Brown-headed Cowbird; Table 1). Our sam- Students, University of Nebraska at Omaha, USDA ple size of video-monitored nests (n 5 33) is Biotechnology Risk Assessment Research Grants Program, and the U.S. Fish and Wildlife Service for financial support. consistent with other studies in the grasslands of North America (Table 2), but it is likely that additional predator species would be detected LITERATURE CITED with a larger sample size. For example, striped BERGIN, T. M., L. B. BEST,K.E.FREEMARK, AND K. J. skunk (Mephitis mephitis), Virginia opossum KOEHLER. 2000. Effects of landscape structure on nest (Didelphis virginiana), American Crow (Corvus predation in roadsides of a midwestern agroecosystem: brachyrhynchos), and coyote (Canis latrans) have a multiscale analysis. Landscape Ecology 15:131–143. been documented as nest predators (Renfrew and DINSMORE, S. J., G. C. WHITE, AND F. L. KNOPF. 2002. Advanced techniques for modeling avian nest survival. Ribic 2003, Peterson et al. 2004, Staller et al. Ecology 83:3476–3488. 2005), but were not documented at our study sites GRANT, T. A., E. M. MADDEN,T.L.SHAFFER,P.J.PIETZ, regardless of their presence on predator surveys G. B. BERKEY, AND N. J. KADRMAS. 2006. Nest (Klug et al. 2009). However, given the consisten- survival of Clay-Colored and Vesper sparrows in cy of snake events across years, it is unlikely a relation to woodland edge in mixed-grass prairies. larger sample would change our conclusion that Journal of Wildlife Management 70:691–701. snakes are among the most important nest HERKERT, J. R., D. L. REINKING,D.A.WIEDENFELD,M. WINTER,J.L.ZIMMERMAN,W.E.JENSEN,E.J.FINCK, predators for grassland birds in this region. R. R. KOFORD,D.H.WOLFE,S.K.SHERROD,M.A. Information about the predator community is JENKINS,J.FAABORG, AND S. K. ROBINSON. 2003. important for understanding variation in nest Effects of prairie fragmentation on the nest success of predation and to increase productivity of nesting breeding birds in the midcontinental United States. birds (Lahti 2009). However, recognizing the Conservation Biology 17:587–594. importance of the predator community also brings HESKE, E. J., S. K. ROBINSON, AND J. D. BRAWN. 1999. Predator activity and predation on nests on challenges. Studies that document predation of forest-field edges in east-central Illinois. Landscape grassland bird nests consistently discover wide- Ecology 14:345–354. ranging generalist predators including Brown- HESKE,E.J.,S.K.ROBINSON, AND J. D. BRAWN. 2001. Nest headed Cowbird and common raccoon. Thus, predation and neotropical migrant : piecing efforts directed at increasing reproductive success together the fragments. Wildlife Society Bulletin 29:52–61. of birds have often focused on decreasing the KLUG, P. E. 2005. The effects of local grassland habitat and surrounding landscape composition on the predators of population size of species that have increased due grassland bird nests. Thesis. University of Nebraska, to agricultural land use (Heske et al. 1999, Omaha, USA. Kosciuch and Sandercock 2008). Our study, and KLUG, P., L. L. WOLFENBARGER, AND J. P. MCCARTY. other nest predation studies in grassland habitats, 2009. The nest predator community of grassland birds SHORT COMMUNICATIONS 803

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