Hydrological Constraints on Tricolored Heron and Snowy Egret Resource Use

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

“…Thus, species more dependent on highquality patches are more susceptible to the reductions in the floodplain area or alterations of the hydrologic regime that reduce the quality of foraging sites. Not surprisingly, the populations of the four species in this study that were constrained in the habitat use were declining in large floodplains suffering from strong anthropogenic alterations, such as the Everglades (Hoffman et al, 1994;McCrimmon et al, 1997;Strong et al, 1997) and Venezuelan Llanos (González, 1996a;1997). The habitat selection by Maguari Storks and Striated Herons seemed to be more influenced by the prey density and less by water depth because these species clearly selected connected lagoons and used those areas during the floods.…”

“…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).…”

“…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.…”

Influence of lagoons size and prey availability on the wading birds (Ciconiiformes) in the upper Paraná river floodplain, Brazil

“…In spite of the flood to be the period of highest fish productivity in floodplains (Loftus and Eklund, 1994;Vazzoler et al, 1997b), the fishes were more dispersed and less vulnerable to the birds due to the high connectivity among the water bodies. Thus, independent of the amount of fishes, the shortage of adequate habitats available and the low fish vulnerability turned this environment inhospitable for Ciconiiformes in the flood, a fact verified in flooded areas elsewhere also (Custer and Osborn, 1978;Erwin, 1983;Powell, 1987;Smith and Breininger, 1995;Custer et al, 1996;González, 1996;Strong et al, 1997;Russell et al, 2002). In the study area, only Green-backed Heron, capable to forage in deep waters, was abundant in this period.…”