Pamela F. Olguin

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.

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.