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ARTHROPOD PREY AVAILABILITY AND BREEDING OF THE THREATENED STRANGE‐TAILED TYRANT (ALECTRURUS RISORA)
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ABSTRACT ∙ The Strange‐tailed Tyrant (Alectrurus risora) is an insectivorous flycatcher (Tyrannidae) endemic to the natural tall grasslands of northern Argentina and southern Paraguay. Alectrurus risora has a polygynous mating system and the abundance of arthropods could be a major factor determining the establishment of male breeding territories and the extent of the breeding season, which is shorter than in most other reported tyrant flycatchers. To investigate this hypothesis, we examined the abundance of arthropods in upland and lowland breeding habitats. Upland habitats seem to be preferred for breeding, and usually harbour more nests. Data from one year showed that, for both grasslands, the beginning of the breeding season coincides with a greater availability of arthropods, and that the short reproductive season of A. risora coincides with a general lower availability of prey during February and March in the year we conducted the study. In upland territories, males attracted more females and had more active nests than males holding territories in lowland grasslands. However, the abundance and biomass of total arthropods and of potential prey were higher in lowland than in upland grasslands, with the exception of the abundance of Orthoptera, which was higher in upland habitat and could represent one of the major prey items. Therefore, we conclude that 1) female preference for males in upland grasslands cannot be explained by higher arthropod prey availability, and 2) the availability of arthropod prey may be important in determining the extent of the breeding season, although further, multiannual studies are required to corroborate this hypothesis. RESUMEN ∙ Disponibilidad de artrópodos presa asociados a territorios de reproducción de un ave en peligro de extinción, el Yetapá de Collar (Alectrurus risora) El Yetapá de Collar (Alectrurus risora) es un tiránido insectívoro endémico de los pastizales altos naturales del norte de Argentina y sur de Paraguay, que posee una temporada reproductiva más corta que aquella reportada para la mayoría de los tiránidos. Alectrurus risora posee un sistema de apareamiento poligínico, y la abundancia de artrópodos podría representar un factor determinante en el establecimiento de los territorios de los machos y en la duración de la temporada reproductiva. Con el fin de investigar esta hipótesis examinamos la abundancia de artrópodos en hábitats reproductivos de pastizales altos y bajos. Los pastizales altos parecen ser más utilizados durante la época reproductiva y usualmente albergan un mayor número de nidos activos. Los datos de un año de muestreo mostraron que el inicio de la temporada reproductiva coincide con el pico de abundancia de artrópodos en ambos pastizales, y que su corta duración coincide, para el área en estudio durante el año analizado, con una menor disponibilidad de presas durante los meses de febrero y marzo. En los territorios ubicados en el pastizal alto los machos atrajeron más hembras y tuvieron más nidos activos que en los territorios de pastizal bajo. Sin embargo, la abundancia y biomasa de artrópodos totales y de presas potenciales fueron mayores en el pastizal bajo, con la excepción de la abundancia de Orthoptera, que podría representar uno de los tipos principales de presa. A partir de estos resultados, concluimos que 1) la preferencia de las hembras por machos en el pastizal alto no puede ser explicada por una mayor disponibilidad de artrópodos presa, y 2) la disponibilidad de artrópodos presa podría representar un factor importante en la determinación de la extensión de la temporada reproductiva, pero se requieren estudios adicionales, plurianuales, para corroborar esta hipótesis.
Neotropical Ornithological Society
Title: ARTHROPOD PREY AVAILABILITY AND BREEDING OF THE THREATENED STRANGE‐TAILED TYRANT (ALECTRURUS RISORA)
Description:
ABSTRACT ∙ The Strange‐tailed Tyrant (Alectrurus risora) is an insectivorous flycatcher (Tyrannidae) endemic to the natural tall grasslands of northern Argentina and southern Paraguay.
Alectrurus risora has a polygynous mating system and the abundance of arthropods could be a major factor determining the establishment of male breeding territories and the extent of the breeding season, which is shorter than in most other reported tyrant flycatchers.
To investigate this hypothesis, we examined the abundance of arthropods in upland and lowland breeding habitats.
Upland habitats seem to be preferred for breeding, and usually harbour more nests.
Data from one year showed that, for both grasslands, the beginning of the breeding season coincides with a greater availability of arthropods, and that the short reproductive season of A.
risora coincides with a general lower availability of prey during February and March in the year we conducted the study.
In upland territories, males attracted more females and had more active nests than males holding territories in lowland grasslands.
However, the abundance and biomass of total arthropods and of potential prey were higher in lowland than in upland grasslands, with the exception of the abundance of Orthoptera, which was higher in upland habitat and could represent one of the major prey items.
Therefore, we conclude that 1) female preference for males in upland grasslands cannot be explained by higher arthropod prey availability, and 2) the availability of arthropod prey may be important in determining the extent of the breeding season, although further, multiannual studies are required to corroborate this hypothesis.
RESUMEN ∙ Disponibilidad de artrópodos presa asociados a territorios de reproducción de un ave en peligro de extinción, el Yetapá de Collar (Alectrurus risora) El Yetapá de Collar (Alectrurus risora) es un tiránido insectívoro endémico de los pastizales altos naturales del norte de Argentina y sur de Paraguay, que posee una temporada reproductiva más corta que aquella reportada para la mayoría de los tiránidos.
Alectrurus risora posee un sistema de apareamiento poligínico, y la abundancia de artrópodos podría representar un factor determinante en el establecimiento de los territorios de los machos y en la duración de la temporada reproductiva.
Con el fin de investigar esta hipótesis examinamos la abundancia de artrópodos en hábitats reproductivos de pastizales altos y bajos.
Los pastizales altos parecen ser más utilizados durante la época reproductiva y usualmente albergan un mayor número de nidos activos.
Los datos de un año de muestreo mostraron que el inicio de la temporada reproductiva coincide con el pico de abundancia de artrópodos en ambos pastizales, y que su corta duración coincide, para el área en estudio durante el año analizado, con una menor disponibilidad de presas durante los meses de febrero y marzo.
En los territorios ubicados en el pastizal alto los machos atrajeron más hembras y tuvieron más nidos activos que en los territorios de pastizal bajo.
Sin embargo, la abundancia y biomasa de artrópodos totales y de presas potenciales fueron mayores en el pastizal bajo, con la excepción de la abundancia de Orthoptera, que podría representar uno de los tipos principales de presa.
A partir de estos resultados, concluimos que 1) la preferencia de las hembras por machos en el pastizal alto no puede ser explicada por una mayor disponibilidad de artrópodos presa, y 2) la disponibilidad de artrópodos presa podría representar un factor importante en la determinación de la extensión de la temporada reproductiva, pero se requieren estudios adicionales, plurianuales, para corroborar esta hipótesis.
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