DOI: 10.5061/dryad.np5hqbzqd
title: Data from: Trophic niche similarities of sympatric Turdus thrushes determined by fecal contents, stable isotopes, and bipartite networks approaches

description: An ecological niche has been defined as an n-dimensional hypervolume
 formed by conditions and resources that species need to survive, grow and
 reproduce. In practice, such niche dimensions are measurable and describe
 how species share resources, which has been thought to be a crucial
 mechanism for coexistence and a major driver of broad biodiversity
 patterns. Here, we investigate resource partitioning and trophic
 interactions of three sympatric, phylogenetically related and
 morphologically similar species of thrushes (Turdus spp.). Based on one
 year of data collected in southern Brazil, we investigated niche
 partitioning using three approaches: diet and trophic niche assessed by
 faecal analysis, diet and niche estimated by stable isotopes in blood and
 mixing models, and bipartite network analysis derived from direct diet and
 mixing model outputs. Approaches revealed that the three sympatric
 thrushes are generalists that feed on similar diets, demonstrating high
 niche overlap. Fruits from C3 plants were one of the most important food
 items in their networks, with wide links connecting the three thrush
 species. Turdus amaurochalinus and T. albicollis had the greatest trophic
 and isotopic niche overlap, with 90% and 20% overlap, respectively. There
 was partitioning of key resources between these two species, with a shared
 preference for fig tree fruits - Ficus cestrifolia (T. amaurochalinus
 PSIRI% = 11.3 and T. albicollis = 11.5), which was not present in the diet
 of T. rufiventris. Results added a new approach to the network analysis
 based on values from the stable isotope mixing models, allowing
 comparisons between traditional dietary analysis and diet inferred by
 isotopic mixing models, which reflects food items effectively assimilated
 in consumer tissues. Both are visualized in bipartite networks and show
 food-consumers link strengths. This approach could be useful to other
 studies using stable isotopes coupled to network analysis, particularly
 useful in sympatric species with similar niches.
description: Birds were captured with 6 mist nets, 36 mm mesh size (12 m × 2.6
 m), settled in locations adjacent or inside forest patches, in shadow
 areas, where intense transit of birds of interest had been observed. Nets
 were open 30 min before sunrise and closed 30 min after sunset. Captured
 birds were identified and placed in cotton bags for 15 min for the
 collection of faeces and regurgitated material. Faecal
 samples were individually stored in vials with 70% ethanol, in the
 laboratory faeces were screened in a stereomicroscope, identified at the
 lowest taxonomic level possible using identification guides and
 consultations with experts. Food items were first counted individually,
 and then, their reconstituted volume was estimated based on the average
 volume of items of similar size in a reference collection. To quantify the
 items present in the diet, the volumetric method was used following
 Hellawell & Abel (1971) that was modified by Bastos et al. (2013).
 With a millimetric paper under a Petri dish, food items were compacted
 with glass slides, forming blocks of 1
 mm<sup>3</sup>. A total of 100–200 µl of
 blood from the brachial or tarsal vein of birds was collected with a
 syringe and needle (4 mm), stored in plastic vials and frozen. Blood
 samples were lyophilized for 8 h, homogenized, weighed and placed in
 sterilized tin capsules (5 × 9 mm). Samples were analysed in isotope ratio
 mass spectrometer at the Stable Isotope Center at the University of New
 Mexico (UNM) in the USA. To determine the isotopic values of consumers,
 the isotopic ratio (R) of each element in the samples
 (<sup>13</sup>C/<sup>12</sup>C and
 <sup>15</sup>N/<sup>14</sup>N), represented in
 delta notation (<i>δ</i>) and expressed in parts per thousand
 (‰), was obtained. Atmospheric air and Vienna Pee Dee belemnite (VPDB)
 were the international standards for N and C, respectively. Isotopic
 reference materials were interspersed with samples for drift calibration,
 and the precision of the measurements was 0.08‰ and 0.03‰ for
 <i>δ</i><sup>15</sup>N and
 <i>δ</i><sup>13</sup>C, respectively.