Breeding behavior and reproductive success of Strange-tailed Tyrants (Alectrurus risora) differ between two types of grasslands

DI GIACOMO, A.S.; DI GIACOMO, A.G.; REBOREDA, J.C.

Cusco

Congreso; IX Congreso de Ornitología Neotropical; 2011

The Strange-tailed Tyrant (Alectrurus risora) is a threatened obligate grassland bird that inhabits savannas, wet grasslands and marshes in southern Paraguay and northeastern Argentina. At our study site (Reserva El Bagual, province of Formosa, Argentina) they breed in two types of grasslands: upland fields dominated by Imperata brasiliensis (uplands) and lowland fields dominated by Paspalum intermedium (lowlands). More than 90% of the area suitable for breeding is lowlands, but most nesting attempts occur in uplands. We evaluated the extent of social polygyny, main measures of reproduction and nesting success in both types of grasslands. We expected higher reproductive success in the less abundant, more preferred habitat. Most females that nested in consecutive breeding seasons did so in the same grassland. There were no differences between grasslands in clutch size, hatching success, chick survival and chick weight at the time of fledging. However, number of females per male, number of nesting attempts per female and nesting success were higher in uplands than in lowlands. As a result of this, the reproductive success of females and males was higher in uplands than in lowlands. Our results suggest that higher quality females and males that disproportionately contribute to the recruitment of new individuals occupy less abundant habitat. Thus, it is imperative to protect this upland habitat for the conservation of this species.