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SummaryThe north-east of Argentina contains a high number of globally threatened grassland birds and is increasingly managed for livestock, with annual burning in remaining natural grasslands. The Strange-tailed Tyrant Alectrurus risora, a globally threatened grassland specialist, has suffered a 90% contraction in its original range. From 1996 to 2008 we monitored a breeding population in Formosa, north-east Argentina, and explored the effect on breeding of four accidental and one prescribed fires. The plant most frequently used for nesting was Imperata brasiliensis, but the frequency of use was lower after a fire than before. In years with a fire, the height of the plant used for nesting and the height of the nest were lower than in those without a fire. Females avoided nesting in the burned plot in the breeding season immediately after the prescribed fire, but they started to return to the burned plot by the second breeding season and did not discriminate between plots by the third breeding season after the fire. Movements of females after the prescribed fire did not affect nest survival, clutch size, hatchability or chick survival indicating this species was adapted to regular fires. However, our results also show that annual burning in the grassland negatively affects the settlement for reproduction of Strange-tailed Tyrants and that the intervals between burns in the same grassland should be longer than two years. ResumenLos pastizales del noreste de Argentina presentan un alto número de aves de pastizales globalmente amenazadas y en los últimos años está aumentando la actividad ganadera con quemas anuales. El Yetapá de Collar Alectrurus risora, un ave globalmente amenazada y especialista de pastizales, ha sufrido una disminución del 90% de su distribución original. Desde 1996 hasta 2008 monitoreamos una población reproductiva en Formosa, noreste de Argentina, y estudiamos el efecto de cuatro fuegos accidentales y uno prescripto sobre la nidificación. La planta usada con mayor frecuencia para nidificar fue Imperata brasiliensis, pero la frecuencia de uso fue menor después de los incendios. En años con fuego, la altura de la planta utilizada para nidificar y la altura del nido fue más baja que en años sin fuego. Las hembras evitaron nidificar en el área quemada durante la temporada reproductiva inmediatamente después del fuego prescripto, pero comenzaron a volver a dicha área durante la segunda temporada reproductiva, pero ya no discriminaron las parcelas quemada y no quemada durante la tercera temporada reproductiva después del fuego prescripto. Los movimientos entre parcelas de las hembras después del fuego prescripto no afectaron la supervivencia de nidos, el tamaño de postura, el éxito de eclosión o la supervivencia de pichones, indicando que esta especie estaría adaptada a fuegos regulares en los pastizales. Sin embargo, nuestros resultados también muestra que la quema anual de pastizales tiene un efecto negativo en el establecimiento de grupos reproductivos del Yetapá de Collar y que los intervalos ent...

SummaryThe Marsh Seedeater Sporophila palustris is one of the most endangered and least known of the capuchino seedeaters. Breeding populations are patchy, occurring in north-east Argentina, southern Brazil, and Uruguay. We present data on the breeding biology of the species, and describe nests and eggs, behaviour (including courtship, nesting, incubation and parental care), breeding sites and food items. Marsh Seedeaters breed in well-preserved grasslands with wet soils and tall vegetation. In general, these habitats are used for extensive livestock ranching. Main threats are overgrazing, widespread use of fire, conversion of grasslands to pastures of exotic grasses and rice fields, afforestation, and illegal trapping. Most breeding sites are located in Important Bird Areas, but only one in Brazil and one in Argentina are protected. We propose a series of actions to promote the conservation of Marsh Seedeaters and other endangered birds that coexist in grassland habitats.

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