Abstract Acoustic communication plays a key role in the life of birds and it is useful in phylogenetic and evolutionary investigations. This study described the structure and function of Polioptila dumicola´s call repertoire in riparian environments from the Mid-eastern of Argentina. Male calls (N=644) were recorded in the field during the pairs nuptial interactions; nests exploration and previously capture of male. Then, specific function was assigned to different calls using standardized methods of acoustic classification and behavioral observations. Twelve different types of calls were classified. Alert and call to female were the most frequent calls and they represented 12.04% and 10.24% of recordings. Anguish call was also recorded in this species. These are the first results regarding to the calls and repertoire of P. dumicola. These data could be used for new studies on environmental selection pressures and for conservation of this species and its habitats.

Abstract The whistling heron (Syrigma sibilatrix) is a neotropical species that inhabits aquatic environments, rural areas and groves. We studied the diet of 19 birds in Carabajal Island (31°39´S, 60°42´W) from 1999 to 2003. The trophic spectrum was composed of 14 taxonomic units of animal taxa. Trophic diversity ranged between 0.23 and 2.15. Index of relative importance was of 10 780 for insects, 1 800 for arachnids and crustaceans, and 1 750 for vertebrates. Most of the prey were represented by individuals included in the 0-20 mm (45%) and 21-40 mm (35%) size intervals. Trophic niche breadth was of 1.98 in spring, 2.34 in summer, 2.21 in autumn, and 1.99 in winter; standardized values were of 0.075 in spring, 0.10 in summer, 0.09 in autumn, and 0.076 in winter. Feeding efficiency was 96.01% in spring, 98.3% in summer, 89.9% in autumn and 92.34% in winter. No evidence was found of food selectivity. The highest percentage of site fidelity (69%) corresponded to the grassland environment. In the floodplain of the Middle Parana River, S. sibilatrix primarily feeds on insects from grasslands.

Resumen Se estudió la dieta de Syrigma sibilatrix (n=19) en la isla Carabajal (31°39’ S y 60°42’ O) desde 1999 hasta 2003. El espectro trófico resultó integrado por 14 entidades taxonómicas de la fracción animal. El índice de diversidad trófica de Brillouin varió entre 0,23 - 2,15. Los valores del índice de importancia relativa fueron: insectos = 10 780, arácnidos y crustáceos= 1 800 y vertebrados= 1 750. La mayoría de las presas estuvieron representadas por organismos comprendidos en los intervalos 0-20 mm (45%) y 21-40 mm (35%). Los valores de la amplitud del nicho trófico por estación fueron de 1,98 en primavera, 2,34 en verano, 2,21 en otoño y 1,99 en invierno mientras que los valores estandarizados fueron de 0,075 en primavera, 0,10 en verano, 0,09 en otoño y de 0,076 en invierno. La eficiencia alimentaria fue de 96,01% en primavera, 98,3% en verano, 89,9% en otoño y 92,34% en invierno. No se encontró evidencia de selectividad dietaria. El mayor porcentaje de uso de hábitat (69%) correspondió a la unidad ambiental de pastizal. En conclusión, los resultados indicaron que en la planicie de inundación del río Paraná medio, S. sibilatrix tiene una dieta basada principalmente en insectos que obtiene principalmente en la unidad ambiental de pastizal.

We examined the diet of the Rosy-billed Pochard, Netta peposaca (Vieillot, 1816), (n = 59) during the autumn of 2010 in Santa Fe province, Argentina. Were analyzed a total of 59 ducks (n = 37 females and n = 22 males) to assess their gastrointestinal contents. The trophic spectrum was composed of 16 taxa (plant fraction: animal fraction 9 and 7). The contribution of each food category estimated using the IRI was: Echynochloa sp. (Poaceae) = 4301, Polygonum sp. (Polygonaceae) = 956, and unidentified graminoid species = 53 (females: Echynochloa sp. = 4313, Polygonum sp. = 1095 and males: Echynochloa sp. = 5522, Polygonum sp. = 814). No significant differences were found between females and males in diet composition (Fisher's test, p < 0.05). Moreover, the diversity index (H') was significantly (Mann-Whitney, p < 0.05) different between sexes. The Rosy-billed Pochard showed a predominantly phytophagous feeding habit in autumn. Likewise, this is the first contribution on the sexual differences in the feeding biology of the Rosy-billed Pochard.