Trophic Niches and Feeding Relationships of Shorebirds in Southern Brazil
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Aquat Ecol (2018) 52:281–296 https://doi.org/10.1007/s10452-018-9663-6 (0123456789().,-volV)(0123456789().,-volV) Trophic niches and feeding relationships of shorebirds in southern Brazil Fernando Azevedo Faria . Ede´lti Faria Albertoni . Leandro Bugoni Received: 18 October 2017 / Accepted: 19 October 2018 / Published online: 30 October 2018 Ó Springer Nature B.V. 2018 Abstract Niche theory predicts that sympatric community was sampled to determine potential prey species should differ in some ecological characteristic, and ascertain feeding preferences of birds. Coleoptera to allow co-existence and reduce competition for key was the most abundant taxon in the feces of all resources. Food is critical on wintering grounds and shorebirds. Trophic niche overlap in the diets was stopover areas for migratory species that need to high, with the widest trophic niche found for the buff- accumulate reserves in order to complete their migra- breasted sandpiper Calidris subruficollis. Isotopic tion. Wetlands of the Rio Grande do Sul coastal plain, mixing models indicated differences in the main food in southern Brazil, host several species of shorebirds sources of shorebirds. The isotopic niche breadth was with similar morphology, foraging methods and diet. widest for the American golden-plover Pluvialis When these species are in sympatry, some trophic dominica. These species, as well as the resident niche overlap is expected. Diets and trophic niches of southern lapwing Vanellus chilensis, consumed some migratory and resident shorebirds were investigated prey in higher proportions over others, although they during the austral summer on Torotama Island, Lagoa had generalist diets. Migratory species with generalist dos Patos Estuary, Brazil. Complementary methods habits benefit from heterogeneous environments such were used to determine the trophic ecology of three as floodplains during the non-breeding season. shorebird species; diet was determined through anal- ysis of feces and food samples, using stable isotopes of Keywords Diet Á Feeding ecology Á carbon and nitrogen. The local invertebrate Macroinvertebrates Á Plover Á Sandpiper Á Stable isotopes Handling Editor: Piet Spaak. F. A. Faria (&) Á L. Bugoni Introduction Laborato´rio de Aves Aqua´ticas e Tartarugas Marinhas, ˆ ´ Instituto de Ciencias Biologicas, Universidade Federal do During their annual cycle, migratory animals inhabit Rio Grande - FURG, Campus Carreiros, Rio Grande, RS 96203-900, Brazil and feed in different environments, where it is to their e-mail: [email protected] advantage to exploit a wide range of food resources (Skagen and Knopf 1994; Skagen and Oman 1996; F. A. Faria Á E. F. Albertoni Davis and Smith 1998). Shorebirds perform some of Laborato´rio de Limnologia, Instituto de Cieˆncias Biolo´gicas, Universidade Federal do Rio Grande - FURG, the longest migratory journeys on the planet (Johnson Campus Carreiros, Rio Grande, RS 96203-900, Brazil 123 282 Aquat Ecol (2018) 52:281–296 2003; Gill-Jr. et al. 2005). Several shorebird species how species of the same community utilize these that breed in the Northern Hemisphere migrate south resources in different ways (Schoener 1974). Investi- to spend their non-breeding season in the Southern gations of resource partitioning are important to Hemisphere during the austral summer. On their understand the mechanisms that influence the struc- wintering grounds, shorebirds rest, molt their feathers ture of communities. If a given resource is superabun- and feed, storing energy for the next step of the dant, even with high trophic niche overlap, migration (Piersma et al. 1996; Piersma and Wiersma competition between different species will not occur 1996). (Pianka 1981). Wetlands are the environments most intensively Several studies have analyzed the diet and trophic used by migratory shorebirds during the staging and niche of shorebirds by using fecal analysis (e.g., Smith wintering periods. Wetlands are dynamic habitats, and Nol 2000; Gillings and Sutherland 2007; Lour- changing with variation in rainfall, tide and seasonal- enc¸o 2007). This technique allows a large number of ity (Davis and Smith 2001). Commonly, wetlands are samples to be collected with relatively limited effort also areas with high productivity and a diversity of and minimal disturbance to the birds, although it may invertebrates (Anderson and Davis 2013). Due to the underestimate the amounts of easily digestible food dynamic nature of these environments, shorebirds items (Ralph et al. 1985). feeding at these sites probably encounter variations in Since the 1990s, studies on trophic relationships the availability of food resources. In response to these have used stable isotope analysis (SIA) in tissues of characteristics, most migratory shorebirds are thought consumers and their potential prey as a complemen- to use generalist dietary regimes to supply their tary methodology to conventional dietary analysis nutritional requirements (Skagen and Knopf 1994; (Karnovsky et al. 2012). While conventional methods Skagen and Oman 1996; Davis and Smith 1998). In such as fecal analysis provide information on recently wintering areas, shorebirds must share resources with eaten food items, SIA indicates the food assimilated at resident species, i.e., those that remain in the area different timescales, depending on the turnover rates throughout the year (Belton 1994; Piersma and of the tissues analyzed (Peterson and Fry 1987). Wiersma 1996; Vooren 1998). Stable isotopes of nitrogen (15N/14N, or d15N) provide Coastal plains in the southern Brazilian state of Rio information about the trophic level of individuals Grande do Sul, including the estuarine region of the (Hussey et al. 2014), while stable isotopes of carbon Lagoa (= Lagoon) dos Patos, are important sites for (13C/12C, or d13C) are used to distinguish the origins of migrant birds (Vooren 1998; Bencke et al. 2006). food resources, such as marine versus freshwater Previous studies suggest that the estuary is used as a environments (Fry 2006; Barrett et al. 2007). In recent non-breeding area by thousands of shorebirds, espe- years, researchers have proposed the use of SIA as a cially Nearctic plovers and sandpipers (Vooren 1998; tool to answer questions on trophic niches of species Ferreira et al. 2005; Dias et al. 2017) that use the area (e.g., Bearhop et al. 2004; Newsome et al. 2007, 2012; from late September to early March (Vooren and Catry et al. 2015). Ecological studies using stable iso- Chiaradia 1990). topes present their data in Cartesian spaces, where the Shorebirds feed on several types of invertebrates axes represent the relative abundance of each element including annelids, insects, crustaceans and mollusks (Newsome et al. 2007). The area occupied in this space (Brooks 1967; Isacch et al. 2005). However, it is is known as the ‘‘isotopic niche’’ and can be consid- necessary to understand more clearly how these ered as an isotopic proxy for the ecological niche resources are shared, and the importance of each prey (Pe´rez et al. 2008). type for different shorebird species. One way to Based on the information above, the present study characterize the structure of communities is through aimed to describe and compare the trophic niches and the analysis of trophic niches (Bearhop et al. 2004). diets of one resident and two migratory shorebird Hutchinson (1957) defined the ecological niche of a species in temporary flooded grasslands in an estuarine species as an n-dimensional hypervolume, where the area of southern Brazil, using the complementary dimensions are environmental resources and condi- methods of fecal analysis and SIA. We hypothesized tions. Occupied niches represent the use of resources that trophic niches of the three most common coex- (Bearhop et al. 2004), and ecologists are interested in isting shorebirds overlap to some degree, making use 123 Aquat Ecol (2018) 52:281–296 283 of abundant food resources, and that these birds have specially from mid-October to early February generalist habits as a consequence of their life strategy (Piersma et al. 1996). and the need to adapt to different environments during their annual cycle. Macroinvertebrate sampling To determine the potential prey of shorebirds, the Materials and methods macroinvertebrate community was sampled monthly from December 2014 to February 2015 through Study area complementary methods to cover different microhab- itats, aiming to sample most invertebrates available on The study was conducted in a 60-ha wet grassland area the soil surface, water and upper soil, also accounting on Torotama Island (31°550S; 052°100W), Lagoa dos for efficiency of each trapping method to different Patos Estuary, in southern Brazil (Fig. 1). This estuary taxa. The study site was divided into three transects, has an area of approximately 970 km2 (Asmus 1998). 200 m apart. On each transect, 3 sampling points Lunar tides are only 0.5 m at maximum, and thus the 200 m apart were established, with the three methods flooding regime is influenced by wind and rainfall used at each point. Each month, we installed a total of upstream, which ultimately affect the outflow and the 10 pitfalls in each point to collect invertebrates that water level of the lagoon as a whole, as well as their move on the soil surface (Triplehorn and Johnson margins (Garcia 1998). Salt marshes occupy intertidal 2011). These traps consisted of plastic pots 6 cm in zones of the estuary and its islands, including Toro- diameter and 10 cm high, containing a solution of tama Island. Most of the interior and shores of these water, ethanol and detergent; and remained active for estuarine islands are periodically flooded salt marshes, 96 h before removal. We also collected 27 samples of with Spartina densiflora and Bolboschoenus mar- sediment each month, with a 5-cm-diameter corer, to a itimus predominating. The sampling site near the shore depth of 5 cm (Brandimarte et al. 2004) to capture of Torotama Island is characterized as intermittently benthic invertebrates; and 27 additional environmen- flooded grassland, where the vegetation is kept low by tal samples with a kick-net (D-shaped, 30 cm wide, intensive livestock grazing (Marangoni and Costa 250-lm mesh, covering 1 m; Maltchik et al.