Abstract:
Brow-breasted Pygmy-Tyrant (Hemitriccus obsoletus) was registered two times at the Iguazú National Park, being the first records for Argentina.

Resumen:
El descubrimiento de Macá Tobiano (Podiceps gallardoi), en 1974, generó preocupación por el reducido número de ejemplares encontrados en una laguna de la provincia de Santa Cruz.Sumado a esto, los primeros estudios indicaban un éxito reproductivo nulo. Frente a tal situación, la Fundación Vida Silvestre Argentina (FVSA) inició un proyecto con el propósito de conocer el estado de conservación y ciclo biológico de la especie.En la actualidad, y en base a la información publicada y la obtenida por el proyecto de la FVSA, puede afirmarse que la especie es una de las aves acuáticas más comunes de las mesetas santacruceñas, pero también que subsisten importantes dudas sobre su posibilidad de supervivencia a largo plazo.Dado el desconocimiento parcial de su rango de distribución geográfica, y total de su patrón la dispersión estacional y paradero invernal, hasta tanto no se disponga de mayores datos, se propone que el Macá Tobiano siga siendo considerada una especie rara y de distribución restringida.

Abstract:
Update on the distribution, biology and conservation status of the Hooded Grebe (Podiceps gallardoi ). Discovery of the Hooded Grebe in 1974 was followed by concern due to its low population size and almos zero reproductive success. In 1979, Fundación Vida Silvestre Argentina (FVSA) started a project intending to evaluate species conservation status and to better knows its life cicle. According to data obtained along that project and to publish information, it can be said the Hooded Grebe is one the most common acquatic birds found over the santacruean plaeau. However, given the lack of information on some aspects of its range, seasonal dispersion pattern and wintering grounds, it still remain important doubts about its survival in the long term. Up to more information is available, it es proposed to continue considering the Hooded Grebe a rare species with a restricted range.

Abstract:
The feeding ecology of Galllinula chloropus galeata was studied collecting seasonal samples (spring, summer and winter). Twenty eight stomachs were analized. In each one the volume of each taxonomic entity was registered. The Weighted Resultant Index (Mohan and Sankaran 1988) and Seasonal amplitude of the niche (Levins 1968) were calculated. This study revealed for Galllinula chloropus galeata an oportunistic behavior. The trophic breath of the niche did not show seasonal variations.

Abstract:
The Rock Shag (Phalacrocorax magellanicus) is an endemic species from the Patagonian coast. We estimated a total of 1,792 breeding pairs in 27 colonies along the Province of Chubut coast. The number of colonies and relative abundance of Rock Shags increased lo the south. Aproximately 90% of colonies were located on rocky slopes close to the water, at an average distance from the high tide line of 13.4 m (s.d. = 9.6) At Islas Isabel and Galiano, nest building started between the second and third weeks of October, while the eggs were laid between the first and third weeks of Decernber in both 1989 and 1990. During 1990, average clutch size was 2.3 (s.d. = 1.1).

Abstract:
In this note, I report on the occurrence of albinistic eggs (i. e., lacking shell pigmentation) in a population of House Wrens (Troglodytes aedon) in Colombia. In a study site encompassing about 15 wren territories, two females laid albinistic eggs during a two-and-a-half year periodo One female laid 17 completely white eggs during the study. The second case involved a progretive 1088 of eggshell pigmentation. This female laid normally pigmented eggs at the beginning of the study, but her eggshells became progressively albinistic, and the end of the study she was laying completely white eggs.

Abstract:
The breeding cycle in estancia "El Cuadro" (47º 40' S, 68º W) begins in september and ends in january. Five of six nests found were placed in basaltic cliff holes, the remaining in an abandoned dove col. The mean height of the nests was 4,7 m. while the density of nesting pairs was 0,038/km2. There productive success of five nests was of 3,2 nestlings nest. Finally we describe some aspects of reproductive behavior.

Abstract:
Physiological and ethological mechanisms allow a widespread distribution of vertebrates through different bioclimatic areas. E. elegans occupies an extensive region in Argentina; probably as a consecuence of its special biological characteristics and strategies. This paper describes the circadian activity of the species and the seasonal variation and identifies factors influencing it, in the Monte desert. Active specimens censused in different hours, on succesive days each season, were related to day length and environmental temperature. lt is concIuded that the length and the intensity of the activity are deterrnined by the light and the temperature, respectively. Predominantly diurnal, crested tinamou activity is favored near 20"C temperatures. This renders unimodal activity curves in winter and bimodal curves in the other seasons. This behaviour is similar to that of other desert vertelxates and likely reflects an ethological adaptative strategy for the species.

Abstract:
Presence of the White-tipped Swift (Aeronautes montivagus) in Parque Nacional Calilegua, Jujuy province, becomes fírst record for Argentina.

Abstract:
First records of the Magellanic Plover (Pluvianellus socialis) wintering in southem Buenos Aires Province are given.

Resumen:
En este estudio se examina la productividad de Tyto alba (lechuza de campanario) en nidos artificiales instalados en agrosistemas pampeanos. Se instalaron nidos artificiales en Diego Gaynor, provincia de Buenos Aires, en los cuales T. alba presentó un tamaño medio de puesta de 5,6 ± 0,5 huevos,una media de eclosiones de 4,4 ± 1,1 y un éxito reproductivo de 4,4 juveniles/puesta. La mortalidad de pichones fue nula. La producción en nidos artificiales fue mayor que en nidos naturales (esta última obtenida en base a datos presentados en este estudio y otros de bibliografía). El 29% de los pichones nacidos en los nidos naturales considerados murieron debido a la baja calidad de los sitios de anidación. La calidad de los sitios de anidación puede ser manipulada a traves de la instalación de nidos artificiales, incrementando la producción de T. alba en agrosistemas pampeanos.

Abstract:
We examined the productivity of Tyto alba in nest boxes in Pampean agrosystems of Argentina. Nest boxes were setup in trees in Diego Gaynor, Buenos Aires Province. Mean clutch size was 5.6 ± 0.5 eggs,mean hatching per nest was 4.4 ± 1.1, and reproductive success was 4.4 fledges/clutch. No mortality of chicks was recorded. Productivity in nest boxes was greater than in natural nests (the latter based on results obtained from this study and from past studies). Twenty nine percent of the mortality which occurred in the natural nests was caused by the low quality of nest sites. Thus, tbe quality of nest sites rnay be manipulated, by setting nest boxes, to increase reproductive success of T. alba in Pampean agrosystems.

Abstract:
First record for Argentina of the Carbonated Flower-piercer (Diglossa carbonaria) is reported for neighbourhoods east of La Quiaca, Jujuy province.

Resumen:
Observaciones realizadas en nidos mostraron que Speotyto cunicularia presentó un tamaño medio de puesta de 4,8 ± 1,2 huevos, un tamaño medio de carnada de 3,5 ± 2,4 pichones y un éxito reproductivo de 0,3 juveniles/puesta. La máxima tasa de mortalidad correspondió a los huevos y pichones mayores de 30 días. Los principales factores de mortalidad de huevos fueron las labores agrícolas y la predación, y los de pichones fueron la predación humana y las enfermedades. El tamaño de carnada afectó el crecimiento de los pichones. Los nidos artificiales no presentaron signos de ocupación.

Abstract:
Observation conducted in nests showed Ihe mean clutch size of Speotyto cunicularia was 4.8 ± 1.2 eggs, Ihe mean hatching per nest was 3.5 ± 2.4, and the reproductive success was 0.3 fledges/clutch. High mortality of eggs and young fledges was recorded, mainly due to agricultural practices, predation, and illnesses. Brood size affected Ihe growlh of chicks. The artificial nest burrows were not used by the owls.

Abstract:
In this paper we describe a case of poliginy in the American Kestrel (Falca spatverius). Two females had their nests within the territory of a male. The male copulated with the two females and defended their territory against intruders. The male played the usual male role with one female (primary) but never was seen feeding the other one (secondary). Secondary female managed to go through incubation and part of the nestling period (at least up to day 10 of nestling's life) without the aid of the male.

Abstract:
In this paper we analyze the differences in hábitat use among Fulica armillata, F. leucoptera and Gallinula chloropus during spring, in relation to their abundances and activities. This work was carried out in an artificial pond located in the Parque Natural y Reserva Ecologica Costanera Sur. G. chloropus mainly use the coastal zone and the totoral, while Fulica species are more frequent in open water. Both Fulica coots are associated in the use of open water zones during feeding and of muddy vegetated coastal zone during resting. They differ in the use of the totoral (F. armillata doesn't use it), and emergent vegetation for rest. We discuss the differences exhibited by these species through analysis of morphology, behavior and ecological segregation.

Abstract:
A new breeding colony of Eudyptes crestatus was described and censed during six breeding seasons. This rockhopper penguin colony is located 35 km from Puerto Deseado (Santa Cruz, Argentina). Data presented in this paper show a clear population increase in the number of breeding adults (27% annual). Hypothesis are presented to explain some annual variation observed.

Resumen:
Se documenta la dieta del caburú grande o chuncho (Glaucidium nanum) a nivel cuantitativo y se analiza su composición en diferentes estaciones, en dos afios consecutivos, en una localidad cercana a Illapel, IV Regibn, Chile. Se comparan las disttibuciones de frecuencias de las presas en la dieta con sus abundancias respectivas en el ambiente. El análisis de 311 egagrópilas arrojó 670 presas y otras 110 fueron detectadas en restos. En promedio (por número), las aves componian el 33,2% de las presas, seguidas por micromamíferos (31,9%), insectos (30,9%), reptiles (2,4%) y arácnidos (1,6%). Se encontró gran variabilidad estacional e interanual en la composición dietaria. Además hubo grandes diferencias en la dieta para las estaciones correspondientes en los dos años. El consumo de distintas presas parece ser independiente de sus abundancias en el medio, y las diferencias interanuales se podrían explicar por cambios en la vulnerabilidad de ciertas presas debido a extremos climáticos. Considerando la abundancia de las presas mamíferos con su consumo, en algunos períodos el caburé se comporta como un depredador oportunista y en otros selecciona lo que come. De acuerdo a los ciclos diarios de actividad conocidos de las diferentes presas consumidas, parece cazar tanto de día como de noche.

Abstract:
We report the met of the Austral Pygmy-Owl (Glaucidium nanum) at a quantitative level, and analyze it by season In two consecutive years in a locality near Illapel, IV Region, Chile. We compared the frequency distribution of different prey In the diet of the owl with their respective abundances In the field. Among 311 pellets we found 670 prey Items. Another 110 prey were found as remains. On average, birds made up 33.2% of the diet by number, followed In decreasing order by small mammals (31.9%), insects(30.9%), reptiles (2.4%) and arachnids (1.6%). We detected large variability In the diet composition between years and between seasons. For the same season in two dfferent years, the diet of the owl changed substantially. The consumption of different prey appears to be independent of their respective abundances in the field, so that interannual differences may be explained by changes in the vulnerability of certain prey due to climatic extremes. By relating the abundance of mammalian prey wlth thelr respective consumption by the owl, it appears that In some periods the owl behaves as an opportunistic,and in others as a selective predator. Accordng to the kown daily actlvlty periods of prey, the Pygmy-Owl hunts both in the daytime and durig the night.

Resumen:
Algunas especies de aves coloniales se dispersan de sus dormideros nocturnos en flujos continuos mientras que otras lo hacen en una serie de éxodos interrumpidos por un lapso más o menos regular. Discutimos el patrón de dispersióndel tordo renegrido (Molothrus bonariens is) de dormideros urbanos en la ciudad de Paraná, Entre Ríos. Las aves se dispersaron en flujos discontinuos,separados por intervalos de 2 a 5 minutos.Estos intervalos se mantuvieron en la ruta de vuelo hacia los sitios de alimentación en áreas agrícolas. Si bien se desconoce el significado biológico de tal comportamiento, en especies con patrón de dispersión similar, tal como el estornino hay un componente social, ya que en dormideros monoespecíficos, los estorninos machos adultos predominan en los éxodos más tempranos mientras que hembras juveniles en los más tardíos. Planteamos el interés por analizar la persistencia de éste patrón en dormideros mixtos de tordos en Norteamérica o bienen estorninos cuando éstos se agregan en dormideros con tordos.