Multi-Isotopic (δ2H, δ13C, δ15N) Tracing of Molt Origin for Red-Winged Blackbirds Associated with Agro-Ecosystems

RESEARCH ARTICLE Multi-Isotopic (δ2H, δ13C, δ15N) Tracing of Molt Origin for Red-Winged Blackbirds Associated with Agro-Ecosystems Scott J. Werner1*, Keith A. Hobson2,3, Steven L. Van Wilgenburg4, Justin W. Fischer1 a11111 1 United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, 4101 LaPorte Avenue, Fort Collins, CO, United States of America, 80521, 2 Environment Canada, 11 Innovation Boulevard, Saskatoon, SK, Canada, S7N 3H5, 3 Department of Biology, University of Western Ontario, 1151 Richmond St. N., London, ON, Canada, N6A 5B7, 4 Environment Canada, Prairie and Northern Wildlife Research Center, Canadian Wildlife Service, 115 Perimeter Road, Saskatoon, SK, Canada, S7N 0X4 * Abstract OPEN ACCESS Citation: Werner SJ, Hobson KA, Van Wilgenburg SL, Fischer JW (2016) Multi-Isotopic (δ2H, δ13C, δ15N) Tracing of Molt Origin for Red-Winged Blackbirds Associated with Agro-Ecosystems. PLoS ONE 11(11): e0165996. doi:10.1371/journal. pone.0165996 Editor: Roberto Ambrosini, Universita degli Studi di Milano-Bicocca, ITALY Received: February 28, 2016 Accepted: October 23, 2016 Published: November 15, 2016 Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Data Availability Statement: All relevant data are within the paper and its Supporting Information File (S1 Table) which can be publically accessed at https://dx.doi.org/10.6084/m9.figshare.3860772. Funding: SW and KH received Blue Sky Grant from USDA’s National Wildlife Research Center for this study. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. We analyzed stable-hydrogen (δ2H), carbon (δ13C) and nitrogen (δ 15N) isotope ratios in feathers to better understand the molt origin and food habits of Red-winged Blackbirds (Agelaius phoeniceus) near sunflower production in the Upper Midwest and rice production in the Mid-South of the United States. Outer primary feathers were used from 661 after-secondyear (ASY) male blackbirds collected in Minnesota, Montana, North Dakota and South Dakota (spring collection), and Arkansas, Louisiana, Mississippi, Missouri and Texas (winter collection). The best-fit model indicated that the combination of feather δ2H, δ13C and δ15N best predicted the state of sample collections and thus supported the use of this approach for tracing molt origins in Red-winged Blackbirds. When considering only birds collected in spring, 56% of birds were classified to their collection state on the basis of δ2H and δ13C alone. We then developed feather isoscapes for δ13C based upon these data and for δ2H based upon continental patterns of δ2H in precipitation. We used 81 birds collected at the ten independent sites for model validation. The spatially-explicit assignment of these 81 birds to the δ2H isoscape resulted in relatively high rates (~77%) of accurate assignment to collection states. We also modeled the spatial extent of C3 (e.g. rice, sunflower) and C4 (corn, millet, sorghum) agricultural crops grown throughout the Upper Midwest and MidSouth United States to predict the relative use of C3- versus C4-based foodwebs among sampled blackbirds. Estimates of C3 inputs to diet ranged from 50% in Arkansas to 27% in Minnesota. As a novel contribution to blackbird conservation and management, we demonstrate how such feather isoscapes can be used to predict the molt origin and interstate movements of migratory blackbirds for subsequent investigations of breeding biology (e.g. sex-specific philopatry), agricultural depredation, feeding ecology, physiology of migration and sensitivity to environmental change. Competing Interests: The authors have declared that no competing interests exist. PLOS ONE | DOI:10.1371/journal.pone.0165996 November 15, 2016 1 / 22 Multi-Isotopic Tracing of Molt Origin in Red-Winged Blackbirds Introduction Conservation and management of migratory wildlife is dependent upon our understanding of species-specific spatial ecology, reproductive biology and sensitivity to environmental change. Although generally abundant, some subpopulations of the Red-winged Blackbird (Agelaius phoeniceus) have experienced declines since 1965 [1]. Although the Red-winged Blackbird (hereafter blackbird) is one of the most studied wild birds in North America, current research priorities for this species include sex-specific philopatry, net impacts to agricultural crop production, feeding ecology during the nonbreeding season and aspects of physiology related to migration [2]. Producers of U.S. rice, corn and sunflower commodities have experienced agricultural depredation caused primarily by blackbird damage to their newly-planted and ripening crops [3, 4, 5]. Managing bird damage to agricultural crops by blackbirds within the U.S. currently involves various lethal and non-lethal approaches as part of an integrated pest management strategy [4]. Non-lethal management strategies include propane cannons, chemical repellents, decoy crops and modified agricultural practices. Such practices include changing to crops not affected by birds, synchronized planting or planting larger fields, delaying the plowing of harvested grains to provide alternative food, and herbicide and insecticide applications [4]. Lethal management strategies often include the use of avicides and trapping at sites associated with depredation. Clearly, the efficacy of each of these management strategies would be enhanced if the subpopulations, movements and food habits of blackbirds associated with agro-ecosystems could be identified and monitored. Previous attempts at tracing movements of blackbirds associated with damage to agricultural crops involved use of fluorescent markers [6]. However, this approach and other conventional techniques such as banding are extremely limited as means of evaluating structure and movement of small passerines at continental scales [7]. Reliable applications of cost-effective methods are needed for blackbird control as are accurate evaluations of control efforts within the context of the overall conservation and management of blackbirds. The use of intrinsic markers such as naturally occurring stable isotopes of the light elements (carbon, nitrogen, hydrogen, sulfur) in animal tissues provides an additional or complimentary means of tracking migratory movements of birds and other animals that can be useful in species conservation and management [8]. Stable-carbon (δ13C) and hydrogen (δ2H) isotope ratios in feathers were previously used to delineate geographic origins among 64 blackbirds collected along a latitudinal gradient from Louisiana, USA, to Saskatchewan, Canada [9]. Stable-hydrogen isotope values from primary feathers (...truncated)