Rodrigo Ezequiel Lorenzón

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.

Breeding biology of the White-rumped Swallow (Tachycineta leucorrhoa; Hirundinidae) in a wetland: A comparative approach

We studied the reproductive biology of the White-rumped Swallow (Tachycineta leucorrhoa) in a colony of 50 nests boxes located in a wetland of the Paraná River, Santa Fe, Argentina between 2004 and 2006. The nest boxes were checked regularly and reproductive parameters, as well as morphological data of eggs and nestlings, were recorded. The species had an average clutch size of 4.7 eggs whose volumes and weight means were 2.04 cm3 and 2.17 g. respectively. The incubation period averaged 15.9 days and decreased with the clutch size. The mean nestling period was 23.8 days. Clutch size, number of nestlings per nest and the nestling period decreased with the advance of the breeding seasons, while the incubation time increased. Breeding parameters showed a similarity with those reported for the population from Chascomús site, although the eggs were 5% heavier, the incubation period took one more day and the reproductive success was also higher. With the closely related species Tachycineta meyeni, the studied species showed a lower clutch size. Finally, considering another closely related species Tachycineta bicolor, the White-rumped Swallow showed the reproductive life history traits characteristic of species in the southern hemisphere. We provide new information for this species nesting on wetlands, a fact that contributes to the understanding of changes in the life history of the Tachycineta genus along the American continent.

Spatial variation in bird assemblages are linked to environmental heterogeneity in agricultural landscapes in the province of Entre Ríos, Argentina

Natural environments have been altered by many human actions and during the last decades this process has been hastened in an alarming way. In the Pampean and Espinal ecoregions of Argentina, agriculture was the major contributor, producing a homogeneous landscape of cultivated lands interrupted by few small, isolated pieces of natural environment or noncultivated lands. We studied bird assemblages in two types of agricultural landscapes, one with crops located within a heterogeneous landscape matrix, such that crops were bordered by different types of noncultivated environments, and the other with crops located within a homogeneous landscape matrix away from noncultivated areas. The main objective was to compare the bird assemblage structure and composition between these two landscapes to test the hypothesis that heterogeneous agricultural landscapes support greater bird diversity than do homogeneous landscapes. We recorded 33% of the total abundance in the crops within a homogeneous matrix (CHOM) and 67% of the total abundance in the crops within a heterogeneous matrix (CHEM). The CHEM points had greater species richness, and composition of species differed between CHOM and CHEM. Thus, the results support the hypothesis that environmental heterogeneity increases bird diversity in agricultural areas, with important consequences for ecosystem services that biodiversity provides to agricultural ecosystems and for the conservation value of these systems. The fact that the protected areas by themselves are not sufficient to guarantee biodiversity conservation emphasises the important role that areas under cultivation can play. Our data provides evidence that the presence of uncultivated environments can increase the importance of agricultural lands for biodiversity conservation and, at the same time, can benefit agroecosystems by supporting bird species that can function as biological control agents of agricultural pests.

Reproductive Biology of Striated Heron (Butorides striata) in Argentina

Abstract The reproductive biology of the Striated Heron (Butorides striata) was studied in the lagoon of the Reserve of the Universidad Nacional del Litoral, Santa Fe, Argentina, during two breeding seasons: September 2012–February 2013 (n = 77) and September 2013–March 2014 (n = 125). All nests (n = 202) were built on waxy-leaf nightshade (Solanum glaucophyllum) at 0.99 ± 0.27 m above water level. The incubation period was 20–23 (21.71 ± 1.57) days; laying and hatching took place on successive days. An average of 2.63 ± 0.60 (Range = 2–4) opaque pale blue eggs were recorded per nest. Length, width and weight of eggs did not differ between seasons. Double (n = 43) and triple (n = 47) broods were recorded. A total of 631 eggs were monitored; no differences were detected in breeding, hatching, nesting, or fledging success between seasons. The time spent by chicks in the nest was 14.6 ± 2.16 days, and the average number of chicks per nest was 2.15 ± 0.55. Age-specific mortality rate for eggs was 22% and 38% and for chicks 47% and 35% for the first and second seasons, respectively. Sixty-one percent of nest failures were related to the disappearance of eggs or chicks from the nests, possibly due to predation or climatic factors.

Temporal variation of bird assemblages in a wetland: influence of spatial heterogeneity

The temporal variation of bird assemblages at three sites within a wetland of the Parana River was examined. The aim was to obtain an overview of the influence of spatial heterogeneity on communities in such a variable environment as the wetlands. We recorded 1,662 individuals belonging to 139 species from 40 families. There were no significant differences between sites in richness, abundance nor diversity. Species richness in the first year was greater than during the second year. Number of resident and migrant species decreased in the second year. Community composition differed between the two years of study and was significantly different among seasons. Species were grouped into 19 trophic guilds. In this study, number of species and their abundances were not significantly different among sites; there were differences in the composition of birds among sites. Thus, the structure of the environments influenced the composition of assemblages in different areas. Guild composition remained fairly constant between years and among seasons. Geomorphological and hydrological dynamics of the river produce a heterogeneous availability of habitats and resources that affect the composition of bird assemblages. Annual and seasonal changes in meteorological variables can lead to changes in the structure and/or composition of those assemblages.