Male and female reproductive success in a threatened polygynous species: the Strange-tailed Tyrant, Alectrurus risora.

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

THE CONDOR

COOPER ORNITHOLOGICAL SOC

Año: 2011 vol. 113 p. 619 - 628

0010-5422

The Strange-tailed Tyrant (Alectrurus risora) is an endangered obligate grassland bird that inhabits savannas, wet grasslands and marshes in southern Paraguay and northeastern Argentina. We evaluated the extent of social polygyny, main reproductive parameters (i.e. clutch size, hatching success and chick survival), and factors that influence nesting success in this species. We also estimated the reproductive success of females and males by measuring the number and fate of nesting attempts by banded females and the number of females per male’s territory. More than 80% of the males were polygynous. Males defended contiguous territories of 2-2.5 ha that included the territories of up to four females. Females built the nest, incubated the eggs and brooded and fed the chicks. On average, successful nests fledged 2.3 chicks. Nest survival through the nesting cycle was 0.23 and decreased with nest age and time of breeding. Most females had 2-3 nesting attempts per breeding season and they bred in the same area for 2-3 consecutive years. In contrast, males rarely were seen in the same area more than one year, suggesting sexual differences in mortality. As a result of this, the reproductive succcess during the study period was similar for females and males. Our findings indicate that although males are highly polygynous and females have a low nesting success, the high turnover of males across breeding seasons and the high probability of renesting by females within and across breeding seasons reduce the variance in reproductive success of males and females.