Resumen:
Se investigó el papel del aprendizaje en el desarrollo del canto del chingolo, mediante la comparación de los cantos primarios desarrollados por 10 sujetos capturados a diferentes edades y criados en aislación acústica o entrenados con tutores grabados conespecíficos. Los sujetos capturados antes de los 10 días de vida, y privados de modelos de canto para escuchar, desarrollaron cantos anormales, carentes de introducción (tema) y trino. En contraposición, los sujetos capturados y aislados a partir de los 35-40 días de vida desarrollaron buenas copias de los cantos de su población natal. Estos hechos sugieren que la exposición a los cantos de los adultos del área donde se crían los pichones es suficiente para la imitación del dialecto. Los sujetos capturados y expuestos tempranamente a grabaciones de canto, desarrollaron cantos con algunas de las características del modelo utilizado, lo cual muestra la importancia de la experiencia acústica temprana en el aprendizaje del canto. No se hallaron evidencias de la copia del tutor grabado con posterioridad a los 40 días de vida.

Abstract:
The role of learning in the development of the Rufous-collared Sparrow's song was investigated comparing the primary song of 10 subjects captured at different ages and raised in acoustic isolation or trained with conspecific tape-tutors, The subjects captured before day 10 of age and deprived of song models developed abnormal songs, lacking introduction (theme) and trill, In contrast, subjects captured and isolated after day 35-40 of age developed good copies of the song of their natal population, These facts suggest that the acoustical experience with the song from their natal area is sufficient for the imitation of their natal dialecto Subjects captured as nestlings and tape-tutored with natal and alien dialects developed songs with some features of the models, indicating the importance of the early acoustic experience in development of songoNo evidences of song copying were found when tape-tutoring started after day 40 of age.

Abstract:
Within seabirds, terns are frequently affected by foodrobbing. We document the occurrence of kleptoparasitism at a mixed-species colony ofRoyal (Sterna maxima) and Cayenne (S. eurygnatha) terns at Punta León, Chubut. In two seasons we observed both inter- and intra-specific food robbing by adult terns. The amount of food lost to pirates was relatively low, only 2% of prey brought back by the terns (n = 1127). Intra-specific food robbing was higher than inter-specific kleptopatasitism in the Royal Tern and similar in the Cayenne Tern. The percentage of food lost topirates in thecolony(2.1%,n = 921)wassimilarthan in groupsoftem chicksat the beach(2.4%, n = 206). Kleptoparasitismbetweentems at PuntaLeón appears to be of 1ittle importance with respect to its effectsonbothtem populations.

Resumen:
Registré la abundancia de especies de aves en el Chaco Paraguayo central, Agosto de 1989 hasta Agosto de 1990, para investigar la variación estacional al nivel de grupo funcional o gremio (guild). Las características usadas para definir grupos funcionales fueron la dependicia del agua o la dieta primaria. El numero de especies (abundancia: raro) por grupo funcional son: insectívoras (21 :35), granívoras and folívoras (20:6), faunívoras (14:13), especies asociadas al agua (4:28), detritívoras (3: 1), nectarívoras (1: 1), y frugívoras (0:5). El grupo con la variación estacional mayor fue las insectívoras (SD = 1.63), siguiéndoles las especies asociado al agua, (SD = 1.43), las nectarívoras (SD = 1.41), faunívoras (SD = 1.33), granívoras and folívoras (SD = 1.20), y detritívoras (SD = 0.50). Pruebas de chi cuadrado indican que la diferencia entre especies abundantes y raras son muy significativas para las insectívoras (P < 0.01), granívoras (P < 0.005), y especies asociadas al agua (p < 0.005). Los resultados se interpretan en términos de procesos, de ecología y evolución.

Abstract:
Abundances of different species of birds were recorded in the central Paraguayan Chaco from August 1989 to August 1990 to investigate seasonal variation at the guild level. Species were grouped into guilds based upon primary diet or water dependence. The number of species (abundant : rare) in each guild is as follows: insectivores (21 :35), granivores and foliovores (20:6), faunivores (14: 13), hydrophilic species (4:28), detrivores (3: 1), nectarivores (1: 1), and frugivores (0:5). Insectivores show the strongest seasonality (SD = 1.63) folIowed by hydrophilic species (SD = 1.43), nectarivore (SD = 1.41), faunivores (SD = 1.33), granivores and foliovores (SD = 1.20), and detrivores (SD = 0.50). Chi-square tests indicated that differences between numbers of abundant versus rare insectivores (P < 0.0 1), granivores (P < 0.005), and hydrophilic species (P < 0.005) were highly significant. Results are intrepreted in light of ecological and evolutionary processes.

Resumen:
La estación reproductiva del Ñandú ( Rhea americana ) presenta una variación temporal entre los estados del sur y del centro oeste y nordeste de Brasil. Este estudio tuvo como objetivo identificar la fenologia reproductiva de la especie en Rio Grande do Sul, a través del análisis de las diferentes etapas reproductivas. Se ha constatado un retraso de 30 dias aproximadamente, de diferencia en el inicio de la reproducción, con relación a las poblaciones del centro-oeste y nordeste de Brasil. Los machos demuestran preferencia por construir sus nidos en los cultivos de soja. La predación animal y la interferencia humana fueron las principales causas de abandono de los nidos por parte de los machos incubantes. Los factores climatológicos influenciaron grandemente en el éxito de las eclosiones y en la supervivencia de los pichones. Se hizo además, la biometría de nidos, huevos y pollos encontrados.

Abstract:
The reproductive season ofthe Greater Rhea (Rhea americana) occurs at different times at the southern, central-western and northeastern states of Brazil. The start of reproduction in the Greater Rhea at Rio Grande do Sul shows a delay of aproximately 30 days with relation to the populations in Central-east and North-east of Brazil. Males show a preference to build nests in fields of wheat and soybeans. Human and animal predation is the main cause of nest desertion by the incubating male, and the c1imatic variables are the most influential factors over hatching succes and chick survival. The biometry of nests, eggs and chicks is discussed.

Abstract:
The first record on the nesting ofthe South American Bittern (Botaurus pinnatus) for Argentina is given. The nest and eggs are described and commented.

Abstract:
We describe a nest with eggs of Phegornis mitehelli found at 2850 m in the Andes of Mendoza Province. It is the first nest of the species described for Argentina.

Resumen:
Se describen dos híbridos intergenéricos entre Cardenal Amarillo ( Gubernatrix cristata ) y Diuca Común ( Diuca diuca minar ) capturados en un área de simpatría, al este de la Provincia de Río Negro (República Argentina), donde estos híbridos son conocidos como «Plomitos». Además se dan a conocer otros 15 híbridos entre estas especies, la mayoría registrados en localidades del extremo SE de La Pampa, S de Buenos Aires y E de Río Negro. Dado que un avicultor logró en cautiverio cruzar estas dos especies, se confirma que se trata de un fenómeno de hibridación, posiblemente desencadenado por una sobrecaptura de machos de Gubernatrix cristata para el mercado ilegal de mascotas. Los híbridos son viables, pero no se conoce su grado de fertilidad. Se sugiere: a) investigar las experiencias de cría en cautiverio; b) realizar análisis genéticos de los híbridos para disponer de mayor información sobre la relación taxonómica entre ambas taxas; c) estudiar en el área de hibridación la relación ecológica de las especies parentales y los posibles efectos de la hibridación para Gubernatrix, dado que es una especie clasificada como amenazada de extinción.

Abstract:
Two intergeneric hybrids between the Yellow Cardinal (Gubernatrix cristata) and the Common Diuca Finch (Diuca diuca minar) are described. The hybrids were captured in the area of sympatry between Gubernatrix cristata and Diuca diuca in E Río Negro Province (Argentina), where they are locally named «Plomitos ». Other 15 hybrid specimens are reported from localities in SE La Pampa, S Buenos Aires and E Río Negro Provinces. A bird breeder was able to cross both species and obtained hybrids in captivity; thus makingit clear that the similar birds described hererepresent a phenomenon of hybridization. We believe that hybridization was «triggered» by the capture of more males than females Gubernatrix cristata for the illegal pet trade. The hybrids are viable, but their degree of fertility is unknown. We suggest: a) to investigate captive breeding programs b) to carry out genetic analyses of the hybrids in order to obtain data on the taxonomic relationship of the parent taxa; e) to undertake field studies in the zone of hybridization to determine the ecological relationships between these two species and to assess the possible effects of this hybridization on Gubernatrix, a species currently classified as threatened.

Abstract:
We provide new records, data on habitat and abundance of the Speckled Crake (Coturnicops notata) and Dot-winged Crake (Porzana spiloptera), and measurements and stomach contents of one C. notata. The study area was Mar Chiquita Reserve, Buenos Aires Province. Records were gathered as follows: between 1983-84, 1992-97 during monthly censuses at different habitats (but mainly on grassland), and in 1995-96 during 1000 m transects in grasslands of Spartina densiflora and Juncus acutus (c1imax state and postfire succession). The Speckled Crake was recorded in four opportunities, on three different habitats: grasslands of S. densiflora, J. acutus and a patch of Scirpus americanus. The Dot-winged Crake was recorded in 26 opportunities (41 individuals), two on J. acutus grassland and the rest on mature grassland of S. densiflora. The Speckled Crake has a wider distribution, it's apparently more plastic in habitat requirements but rarer; the Dot-winged Crake has a narrower distribution, it's habitat specific (occurs mostly with S. densiflora), and locally more frequent (but uncommon).

Resumen:
En dos áreas con bosque de Nothofagus del Parque Nacional Nahuel Huapi (Puerto Blest y Quetrihué) el picaflor rubí Sephanoides sephaniodes, la única especie local de su familia, visitó flores de 11 y tres especies de plantas, respectivamente. En el pico y cabeza de 48 picaflores se encontró polen de 12 especies de plantas; siete plantas nativas con flores ornitófilas estaban representadas en cantidades abundantes. Estas siete plantas, en los géneros Embothrium, Tristerix, Fuchsia, Campsidium, Desfontainia, Mitraria y Asteranthera, tienen flores ornitófilas con néctares de alta concentración de azúcar (entre 23,02 y 37,97 o Brix). Existe una correlación positiva entre la abundancia de picaflores y la de estas flores. En Quetrihué una de estas plantas, Tristerix (Lorantáceas), tiene floración invernal, lo que permite la presencia permanente de algunos picaflores. Por su morfología Sephanoides se asemeja a otros picaflores territoriales, pero los datos de campo sugieren un comportamiento variable.

Abstract:
In two areas at Nahuel Huapi National Park the Firecrown Hummingbird Sephanoides sephaniodes , the only local hummingbird, visited 11 and three plant species, respectively. Pollen loads in the bills and head feathers of 48 hummingbirds contained pollen of 12 plant species; pollen of seven native plants was abundant. The seven plants, in the genera Embothrium, Tristerix, Fuchsia, Campsidium, Desfontainia, Mitraria and Asteranthera, had ornithophilous flowers with nectars rich in sugars (23.02 to 37.97 o Brix). A positive correlation between the abundance of these flowers and hummingbirds was found. Wintering hummingbirds ocurred at the locality having the winter-blooming mistletoe Tristerix. Morphological data for Sephanoides suggests territorial forraging, but field data indicate variable behaviour.

Abstract:
We report the location and size of reproductive colonies of cormorant species in the Deseado estuary (Argentina). Five colonies of Red-legged Cormorants (Phalacrocorax gaimardi), Rock Cormorants (P. magellanicus), and Neotropic Cormorants (P. olivaceus) were counted. The Red-legged Cormorant is the most abundant and more widely distributed cormorant species within the estuary. Estimated reproductive populations are 588,306 and 186 individuals for the Redlegged Cormorant, Neotropic Cormorant and Rock Cormorant, respectively. Although Rock Cormorants nest in a cliffused also by Red-Iegged Cormorants, limits between their colonies are well established. Given their magnitude, cormorant colonies at Puerto Deseado should be highlighted for conservation purposes.

Abstract:
The first record of the Plushcap ( Catamblyrhynchus diadema) for Salta province is given based in a collected specimen. New records for Jujuy province are reported. A immature plumage is described and information about the habits is discussed by means ofthe bibliography and field notes.

Abstract:
From 1991 to 1995 11 species of oceanic birds were registered at two sites in SE Buenos Aires Province, Argentina, by means of regular observations from the shore. Nine species corresponded to the order Procellariiformes and 2 species to the family Stercorariidae.

Abstract:
We describe a breeding co1ony of South American Tern Sterna hirundinacea in an island of the Río Negro river, 45 km NW of the city of Viedma, Argentina. It is the first record of a breeding colony of this species in a riverine environment.

Abstract:
Wereporta nest of Black Vultures,the first for Buenos Aires Province.It was found on the ground in a coastal sand dune,covered by the endemic bush Neosparton darwinii.

Resumen:
Un total de 182.810 aves marinas pertenecientes a 50 especies fueron censadas en diferentes localidades de Antártida y Océano Atlántico Sur en las temporadas de verano 1987 a 1995. Los censos fueron hechos a bordo de buques siguiendo la metodología recomendada por el S.C.A.R., realizando 9.281 observaciones de 10 minutos cada una. Fueron definidas seis subáreas antárticas y subantárticas. Las mayores abundancias fueron obtenidas en las sub áreas de las Islas Orcadas del Sur y Arco de Scotia e Islas Shetland del Sur. Las abundancias fueron comparadas con las distintas sub áreas y con factores ambientales tomados al momento del censo (temperatura del aire y cobertura de hielo). Se discute la influencia que estos factores ambientales ejercen en la distribución de las especies.

Abstract:
A total number of 182,810 seabirds of 50 species was recorded at Antarctica and South Atlantic Ocean in consecutive summers from 1987 to 1995. 9,281 ten minute censuses were made onboard ships following S.C.A.R. methodology. Six Antarctic and Subantarctic sub-areas were considered for study. The largest abundance was recorded at South Orkney Is. and South Shetland Is. Abundance were compared with all sub-areas and with some environmental factors such air temperature and ice-cover. The influence between those environmental factors and species distribution is discussed.

Abstract:
A Green Violetear Colibri thalassinus was mistnetted in Alnus acuminata forest at Catamarca province, northwestem Argentina. The previous record for this hummingbird was Olrog (1963) for Tucumán province. The individual captured was an adult, with neither molt nor brood patch.

Resumen:
Se presentan datos de cría del Petrel Damero (Daption capense), obtenidos en la localidad Cerro Mossman, Isla Laurie, Orcadas del Sur, desde la formación de la pareja en Noviembre 1989 hasta la partida de los últimos pichones en los primeros dias de Marzo 1990. En un periodo de cincuenta dias entre Enero y Marzo los pichones llegaron a doblar el peso del adulto (registrado durante éste trabajo). La media máxima a los 30 dias de edad resultó de 496,3 g. descendiendo al momento de la partida a una media de 337,5 g. De las 20 parejas, cinco no fueron reproductivas; dos pichones fueron predados y uno de los quince huevos resultó infertil.

Abstract:
I present data on breeding of Cape Pigeons (Daption capense) at Cerro Mossman, Laurie Island, South Orkneys. The adults paired in November 1989 and the latest chicks departed in March 1990. In a 50 - day period, between January and March, chicks were able to duplicate the adult weight (as registered during this work). The maximum mean mass at 30 days of birth, was 496.3 g. At departure the chick's weight declined to 337.5 g. Five of twenty pairs were non-reproductive. Two chicks were predated and only one on fifteen eggs was infertile.

Abstract:
The presence of Thinocorus rumicivorus bolivianus is confirmed, from the extreme north of Argentina to the Northwest of Mendoza, where a pair was taken during the breeding season. The geographieal distribution of Thinocorus orbignyianus ingae is extended further to the south, in Northwestern Mendoza, and we show that the typical subspecies ranges from the south of Argentina to the south center of that province.

Abstract:
The presence of Anthus hellmayri is confirmed for the Sierras of Cordoba province, based on specimens, sightings and sound recordings by the author and others. Sonograms of this species and A.jurcatus are given for comparison, as both speeies are sympatric in the area of observations and can be confused.

Abstract:
An infrared sensor, as a new method for localization of Wilson's Storm Petrel nests, was tested at Cierva Point, Gerlache Strait, in the Antarctic Peninsula. It detects the heat emitted by breeding birds benneath debris. To test its effectiveness, we used the sensor in an area where nests had already been located, finding 100% ofthe nests. Afterwards, seven eoastal sites with an average area of 548 m' were sampled. The infrared sensor was highly sensitive to the presence of birds benneath rocks; no obvious error sources were found. Besides providing reliable density values, the use of infrared sensors reduced the human impact on colonies because no traumatic methods were used for finding nests.

Abstract:
We recorded the annual variation in abundance of Blue-crowned Conures (Aratinga acuticaudata) at the Chancaní Reserve, Córdoba, Argentina. This parrot was more frequently recorded during the breeding season (August, October and December) than in the non breeding season (March and May), possibly because of movements to more suitable feeding areas. The Chancani Reserve, a mature Chaco woodland, could be a source habitat that keeps populations stable at the regional level, as it provides suitable nest cavities, scarce in the surrounding agropastoral landscapeso.