Quantitative analysis of foraging habitat use by ciconiiformes in the upper Paraná river Floodplain, Brazil

415 Vol.54, n. 2: pp. 415-427, March-April 2011 ISSN 1516-8913 Printed in Brazil BRAZILIAN ARCHIVES OF BIOLOGY AND TECHNOLOGY A N I N T E R N A T I O N A L J O U R N A L Quantitative Analysis of Foraging Habitat Use by Ciconiiformes in the Upper Paraná River Floodplain, Brazil Márcio Rodrigo Gimenes1* and Luiz dos Anjos2 1 Universidade Estadual de Maringá; Av. Colombo, 5790; 87020-900; Maringá - PR - Brasil. 2Departamento de Biologia Animal e Vegetal; Universidade Estadual de Londrina; C. P.: 6001; 86051-970; Londrina - PR - Brasil ABSTRACT The aim of this study was to analyze the seasonal variations in habitat selection and abundance of Ciconiiformes species in four foraging habitats (rivers, channels, connected and disconnected lagoons) on the upper Paraná River floodplain, Brazil, and to conduct the surveys of wading birds in 2002 and 2003. The largest number of species and highest abundances of most species were observed in the connected lagoons. Snowy Egrets (Egretta thula), Wood Storks (Mycteria americana), Roseate Spoonbills (Platalea ajaja), and Jabirus (Jabiru mycteria) frequently used connected lagoons (habitat with the highest fish abundance) and abandoned the areas during floods, suggesting that they were able to find high quality patches for foraging. Cocoi Herons (Ardea cocoi), Great Egrets (Ardea alba), and Rufescent Tiger-Herons (Tigrisoma lineatum) used habitats with lower fish abundance and did not totally abandon these areas during floods, suggesting they were not dependent on high quality patches. Differences in foraging techniques and social behavior explained the difference between the two groups. The results showed that opportunism did not totally explain the foraging habitat selection and in low water level seasons there were higher differences in foraging behavior among the species. Key words: Wading birds, Ciconiiformes, prey availability, floodplain, Paraná river INTRODUCTION The floodplains of the central/southern portion of South America are among the world’s largest in size and in terms of their importance for the aquatic birds (Antas, 1994). The Paraná River is approximately 3800 km long and drains the southcentral part of South America (Agostinho et al., 1995). The Paraná River basin has suffered from strong human impacts, mainly deforestation and the construction of dams. The 230-km stretch of river between the mouth of the Paranapanema River (its main tributary) and the town of Guaíra, Brazil, in the upper Paraná River is the only * significant segment in Brazil that is free from dams (Agostinho et al., 1994). Although upstream dams have altered the natural river regime, the flood pulse is the principal factor acting on the communities of that area (Thomaz et al., 1997). On the east bank (State of Paraná) of this section of the river, with relatively high elevations, there are limited flooded areas and semideciduous forests have almost all been converted to pasture. On the west bank (State of Mato Grosso do Sul), with low land elevation, there is a fairly wellpreserved floodplain with numerous braided secondary channels, lagoons, and rivers (SouzaFilho and Stevaux, 1997). Author for correspondence: Braz. Arch. Biol. Technol. v.54 n.2: pp. 415-427, Mar/Apr 2011 416 Gimenes, M. R. and Anjos, L. Wading birds (Ciconiiformes) are conspicuous elements of these ecosystems, fully adapted to the flood-drought cycle (Kushlan et al., 1985; González, 1996b), but sensitive to anthropogenic perturbations in the hydrologic regime (Russell et al., 2002). The results of previous studies have suggested that the spatio-temporal fluctuations in the populations and seasonal variation in the habitat used by the wading birds resulted from variation in water levels and prey availability (Smith, 1997a; Strong et al., 1997; Young and Chan, 1997; Gaines et al., 1998; Maccarone and Brzorad, 1998; Butler and Vennesland, 2000; Gaines et al., 2000; Wong et al., 2001; Tourenq et al., 2003). For foraging, most of these birds choose the areas with shallow water and high prey densities (Kushlan, 1976; Master et al., 1993; Battley et al., 2003) that tend to be ephemeral and irregularly distributed in the floodplains (Fasola, 1994). Thus, Ciconiiformes use an extensive area for foraging, frequently changing locales (Custer and Osborn, 1978; Hoffman et al., 1994). Consequently, the studies on Ciconiiformes habitat use must employ large spatio-temporal scales (McCrimmon et al., 1997; Strong et al., 1997). In addition, most Ciconiiformes prey primarily on the fishes (Del Hoyo et al., 1992), whose distribution is strongly influenced by water levels (Erwin, 1985; Gawlik, 2002). This opportunistic way of habitat selection is commonly described in the wading bird literature (Fasola, 1986; 1994). However, more recent studies have observed important differences among the species (Smith, 1997b; Gawlik, 2002; Russell et al., 2002), and questions are arising on how hydrologic cycle and variation in prey availability influence the foraging behaviors. Consequently, the studies on foraging habitat selection by Ciconiiformes need more empiric information and must employ large spatiotemporal scales (McCrimmon et al., 1997; Strong et al., 1997). In this study, the structure and composition of Ciconiiformes communities in foraging habitats on the floodplain of the upper Paraná River were analyzed, and seasonal variation in the habitat selection and abundance were examined. The results can help to understand whether in the wading bird communities, foraging habitat selection is really simply opportunistic or whether there are differences among the species, and how the hydrologic cycle influence this process. There have been few studies on Ciconiiformes in Brazil (Willis, 1995; Petry and Hoffmann, 2002; Bouton and Frederick, 2003; Gimenes and Anjos, 2006; Mestre et al., 2007). But this is the first study to quantitatively analyze the use of foraging habitats by the community. MATERIALS AND METHODS Study area The climate in the study area (22°40’S to 22°52’S and 53°12’W to 53°38’W) is classified as tropicalsubtropical, with an average annual temperature of 22°C (summer average 26°C and winter average 19°C) and an average annual rainfall of 1500 mm (Centrais Elétricas do Sul do Brasil, 1986). In 2002 and 2003, the water levels of the Paraná River were highest between mid-January and April, with several short-duration flood pulses. During the last half of 2003, the water level was slightly higher than in the same period of 2002, occasionally reaching 3.0-3.5 m, when the water began to overflow the levee and connect the river to the lateral vegetation and some isolated lagoons (Fig. 1). For data collecting, four habitats were selected where wading birds were known to forage, including rivers, channels (semi-lotic water bodies connecting two rivers or two stretches of the same river, between 20-30 m wide), disconnected lagoons (not connected to rivers or channels, except during f (...truncated)