Matching geographical assignment by stable isotopes with African non-breeding sites of barn swallows Hirundo rustica tracked by geolocation

RESEARCH ARTICLE Matching geographical assignment by stable isotopes with African non-breeding sites of barn swallows Hirundo rustica tracked by geolocation Nina Seifert 1*, Roberto Ambrosini2, Luana Bontempo3, Federica Camin3, Felix Liechti4, Diego Rubolini5, Chiara Scandolara4,5, Nicola Saino5, Steffen Hahn4 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 1 Michael Succow Foundation for the Protection of Nature, Greifswald, Germany, 2 Department of Earth and Environmental Sciences (DISAT), University of Milano Bicocca, Milano, Italy, 3 Dipartimento Qualità Alimentare e Nutrizione, Fondazione E. Mach—Istituto Agrario di San Michele all’Adige, San Michele all’Adige, Italy, 4 Department of Bird Migration, Swiss Ornithological Institute, Sempach, Switzerland, 5 Dipartimento di Bioscienze, Univ. degli Studi di Milano, Milano, Italy * OPEN ACCESS Citation: Seifert N, Ambrosini R, Bontempo L, Camin F, Liechti F, Rubolini D, et al. (2018) Matching geographical assignment by stable isotopes with African non-breeding sites of barn swallows Hirundo rustica tracked by geolocation. PLoS ONE 13(9): e0202025. https://doi.org/ 10.1371/journal.pone.0202025 Editor: Suzannah Rutherford, Fred Hutchinson Cancer Research Center, UNITED STATES Received: December 19, 2017 Accepted: July 26, 2018 Published: September 14, 2018 Copyright: © 2018 Seifert et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All data files are available from the dryad digital repository database (doi:10.5061/dryad.72q5723 Data files: Seifert_et_al_Data_Barnswallows). Funding: The study was co-funded by the EU INTERREG program (project ID 15 7624065), Fondazione Cariplo (grant UNIAGI 13357 to NS), Milan Univ. (grant 2009-ATE-0015 to DR), Univ. of Milano-Bicocca (grant 2011-ATE-0272 to RA) and the German Ornithological Union (travel grant to Abstract Knowledge on whereabouts within the annual cycle of migratory species is prerequisite for many aspects in ecology and biological conservation. Spatial assignments of stable isotopes archived in tissues allows for later inference on sites where the specific tissue had been grown. It has been rarely tested whether spatial assignments match directly tracked non-breeding residences, especially for migratory songbirds. We here compare assignments of stable isotopes from feathers of Palaearctic Barn swallows Hirundo rustica with their African non-breeding residence sites tracked by geolocation.Assignments based on δ2H, δ13C and δ15N isotope compositions delineate three main non-breeding regions: a main cluster in central Africa, a second in West Africa, and the third cluster in Northern Africa. Using δ13C, δ15N only, non-breeding sites ranged from clusters in West/Southwest Africa to South East Africa with a centre in Central Africa. The non-breeding areas (50% and 75% Kernel density estimates, KDE) of the birds tracked by geolocation stretched from West Africa via central Africa to southern Africa. We found little overlap of 0.3% (assuming a 1:1 odds ratio) to 1.4% (3:1 odds ratio) in the three element assignments and KDEs for only 2 and 13 individuals out of 32 birds. Assignment maps for two elements (δ13C, δ15N) and KDEs showed higher consistencies with an overlap of 3.6 and 8.5% for 12 and 18 birds. We argue that the low matching between stable isotope assignments and non-breeding sites in our study arise from insufficient baseline data for Africa (concerning both isoscapes and specific discrimination functions). However, other factors like aerial foraging habit of the species, and a potential mismatch of non-breeding site location and the spatial origin of aerial plankton might further hamper accurate assignments. Finally we call for concerted analyses of tissues i.e. feathers and claws of birds which are grown at known sites across the continent and from species with various ecological requirements (diverse habitats, foraging behaviours, and diet compositions) to establish isoscapes for general applicability. PLOS ONE | https://doi.org/10.1371/journal.pone.0202025 September 14, 2018 1 / 16 Matching of multiple stable isotope assignments and geolocation tracking of barn swallow NiS). The Swiss federal office for environment contributed financial support for the development of the data loggers (UTF-Nr. 254, 332, 363, 400). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Introduction Individual residence sites outside the breeding season are still fragmentary known for many populations of migratory animals. Underlying reasons are e.g. body size constraints which impede the adoption of transmitting devices such as GSM and ARGOS PTTs, low recapture rates of individuals marked with archival tags (GPS, geolocators) [1] or even the low numbers in rare species. This lack of knowledge is unsatisfactory as migratory species are assumed to be prone to divergent changes in various environments during their annual cycle [2] and thus their actual distribution should be identified urgently to be able to track ongoing and future distributional shifts [3]. During the last decade, indirect methods for the identification of the distribution in longdistance migrants such as small passerine birds or insects became progressively more sophisticated and nowadays enable an outline of the species’ whereabouts on a very fine geographical scale [4]. The accuracy of localisation attempts seems especially crucial when targeted conservation actions subsequently are planned within the identified areas. The analysis of naturally occurring stable isotopes archived in animal tissues is one of the most widely adopted indirect tracking method developed to date [5]. Stable isotope analyses are very powerful tools to observe various ecological phenomena in animals, related to food and water intake, metabolism and finally the incorporation of chemical elements into the animal’s tissues. Herein, the tissue’s isotopic composition mirrors the source composition of the diet in a predictable manner [6]. Moreover, various tissues in a broader sense differentially archive this information on temporal scales from hours, like the composition of breath and blood plasma [7], to very long times in metabolically inert tissues like teeth [8], keratin in claws and feathers [9,10] or in hair of ancient mummies [11]. Additionally, the distribution of many stable isotopes like δ13C, δ2H and δ18O shows distinct spatial pattern across broad geographical scales, allowing for geographical assignments of archive stable isotope compositions and thus inference on animal [12]. Today this approach is frequently used especially in the study (...truncated)