Adolfo H. Beltzer

Diversity of Anurans Across Agricultural Ponds in Argentina

We examined the anuran diversity of 31 ponds (30 located on the border of soybean cropland and one within a protected forest) in mid-western Entre Ríos Province (Argentina). Moreover, each species found was characterised with respect to its vertical location. Using principal component (PCA) and canonical correspondence analyses (CCA) we quantified associations between species diversity and habitat and spatial variables. A total of 21 anuran species belonging to four families (Microhylidae, Bufonidae, Leptodactylidae and Hylidae) were detected in ponds surrounded by soybean croplands. PCA generated three principal components, which together explained variation in anuran diversity across the agricultural ponds and control site. Negative values of PC-1 described the smaller ponds with narrower hedgerow and monospecific shore vegetation. PC-2 had high loading on pond depth, and PC-3 had negative loading on air temperature. CCA showed a very strong association between the two data sets. We found all guilds related with pond area. Indeed, we found that arboreal species were recorded in large ponds with higher values of shore vegetation index and presence of wider hedgerow. Moreover, a higher number of terrestrial species was found to relate to large pond areas and greater shore vegetation diversity. Finally, aquatic species were related to pond area, shore vegetation index and depth. Anuran diversity across agricultural ponds of mid-western Entre Ríos Province can be affected by local habitat factors such as reduction in pond size and depth, shore vegetation richness, width of hedgerow and air temperatures. Management of anurans to reverse recent declines will require defining high-quality habitat for individual species or group of species, followed by efforts to retain or restore these aquatic habitat. The maintenance of shore vegetation of ponds and hedgerows may increases the number of species and diversity of anurans within agricultural landscapes.

Aspects of the Foraging Ecology of the Waders Tringa flavipes, Calidris fuscicollis and Charadrius collaris (Aves: Scolopacidae; Charadriidae) in Del Cristal Pond (Santa Fé, Argentine)

The results of a comparative study of a trophic spectre of three species of shorebirds (Tringaflavipes. Calidrisfuscicollis and Charadrius collaris), are given in this contribution. They show the mechanisms of isolation despite sharing the same source of food. Considering the diversity of food, the mechanisms of isolation can be shown in the trophic as well as in special dimension of the ecological niche. Specialization on certain types of food and different types of habitat use are the prevalent strategies to avoid competitive exclusion.

Local conditions vs regional context: variation in composition of bird communities along the Middle Paraná River, an extensive river-floodplain system of South America

We studied spatial changes in species composition (i.e., beta diversity) of local assemblages of birds along ∼450 km of the Middle Parana River, an extensive fluvial system of South America. Point counts were used to survey birds at 60 plots located in shrub swamps and marshes of the floodplain within four sites (15 plots per site). Two sites were surrounded by each of the two upland ecoregions. Beta diversity of bird assemblages was high and was more important than alpha diversity in shaping regional diversity (i.e., gamma diversity) of the fluvial system. Compositional changes were related to species turnover among plots, while nestedness dissimilarity was not important for shaping diversity patterns. Variation-partitioning analysis showed that local conditions (i.e., landscape composition within a radius of 200 m from the center of each plot) accounted for more spatial variation in assemblage composition than did location along the fluvial system. Adjacent upland ecoregions did not account for spatial changes in bird composition within the fluvial system. In conclusion, environmental heterogeneity created by flood pulses is an important factor for sustaining regional diversity of birds within the fluvial system through effects on beta diversity.

Song structure of the golden-billed saltator (Saltator aurantiirostris) in the middle Parana river floodplain

Bird communication is a growing field of study in ethology and evolutionary biology; however, most known studies were conducted only in the northern hemisphere. We measured six temporal and structural features of golden-billed saltator (Saltator aurantiirostris) song and recorded 57 vocalizations at Parque San Martín reserve (Argentina). Results indicated that the prelude represented between two and four syllables, while the trill was composed of one to three. The complete song always contained six syllables. Maximum and minimum frequencies were higher in the trill. The duration of prelude and trill did not differ between vocalizations. Modifications and differences observed in vocalizations may be explained by the acoustic adaptation hypothesis, which predicts higher frequencies in open habitats. Our results broaden and supplement the data available for this species in Argentina, representing useful information for studies intended to assess the effect of different habitats on birds vocalizations in southern South America.

Diet of Cattle Egrets ( Bubulcus ibis ibis ) in the flood valley of the Paraná River, northern Argentina

We analysed the feeding ecology of Cattle Egrets (Bubulcus ibis ibis) based on 30 individuals captured on the Carabajal island, Santa Fe, Argentina (31°39′S, 60°42′W), determining the minimum sample, index of relative importance (IRI), size of prey, feeding efficiency, dietary selectivity, amplitude of the trophic niche, standardisation, circadian rhythm of feeding activity and habitat preference. The trophic spectrum was made up of 17 taxonomic entities, mainly insects (IRI = 15,000), among which orthopterans were the most numerous followed by spiders and amphibians (IRI = 250). The highest percentage of prey size was found in the interval 21-30 mm. The amplitude of the trophic niche ranged between 1.98 and 3.45, and the feeding efficiency between 89 and 92%. In relation to dietary selectivity, the correlation between abundance of prey in stomachs and abundance of prey in the study area yielded no significant results (rs = 0.84, P.0:001). The rhythm of feeding activity responded to the bell-shaped model, which meant a peak in its feeding behaviour pattern at the noon hours. The pastures were the units of vegetation and environment selected more frequently.

Ecología alimentaria de batará grande taraba major (aves: Formicariidae) en el valle aluvial del río paraná medio, Argentina

The diet of the Great Antshrike Taraba major was investigated using 40 specimens collected on the Carabajal island, Parana river, in the province of Santa Fe, Argentine, from 1984 to 1986. The stomach content was composed of seeds, crustaceans, insects, arachnids, molluscs and small mammals. A seasonal change was found between summer‐autumn and winter‐spring. The animal part was more pronounced during winter, but ants of the genus A cromyrmex were present throughout the year. In summer and autumn the seeds taken then contributed to an omnivorous type of diet. High quality habitat for the Great Antshrike consists of tracts of riverine forests rich in creepers and vines (enriedales), where there are food, protection, breeding and sleeping places.

Bird communities in wetlands along the Lower Parana ´ River, Entre Rõ´os, Argentina

The Paraná River develops a wide and complex floodplain with a vast heterogeneity of habitats, which allows the existence of diverse biotic communities adapted to aquatic conditions. The specific composition of bird populations in different ecosystems depends on the factors that operate in a spatio-temporal level. The aim of this work was to describe the bird communities in part of the Lower Parana Valley. We detected in the area of study, 7,462 birds belonging to 129 species of 39 Families and 14 Orders. In relation to the phenology of the detected species, 97 species are resident. This rich diversity is associated with the local environmental characteristics facilitating the presence of a large number of species. Each environmental unit presents a particular group of birds, which could indicate that species respond to spatial heterogeneity according to the requirements of the habitat.

Contribución al conocimiento de la dieta del pato picazo (Netta peposaca) en cultivos de arroz (Oryza sativa) (Prov. Santa Fé, Argentina)

Food selection of 24 captured Rosy‐billed Pochards, which had visited rice fields in the alluvial valley of the Parana river in Argentine during the months from March to May in 1989, has been studied in order to compare the results with others from natural settings. A qualitative‐quantitative analysis provided the typical herbivorous pattern with grains of the rice (Oryza sativa) and other grain‐bearing species, i.e. Panicum sp., Polygonum sp., Paspalum sp. and Echinochloa sp. with rice being the pre‐dominant species. The quantitative results are given in the tables.

Notes on the food of the rufescent tiger heron Tigrisoma lineatum (Aves: Ardeidae) in the Middle Paraná River Floodplain, Argentine

Rufescent tiger herons feed on aquatic insects, small fish and occasionally on colubrid snakes in the floodplain of the Parana River in Argentine. The results are given in the table and figures.

Consideraciones sobre la ecología alimentaria del Chiviro de Isla Saltator coerulescens coerulescens y el Chiviro de Corbata Saltator aurantiirostris aurantiirostris (Aves: Emberizidae) en el valle aluvial del Río Paraná Medio (Argentina)

Food composition of the Greyish and the Golden‐billed Saltator was studied by examination of stomach contents in the course of the year. These emberizine birds living near the Parana river in Argentine show a relatively broad spectrum of food items both from seeds and insects, but plant seed are most important. Food niche overlap is considerable and amounts to 44% (index of overlap). The results are shown for both species for the different seasons in the figs.