Age-specific variation in reproduction of the threatened Strange-tailed Tyrant (Alectrurus risora) in Formosa, Argentina

ADRIAN S. DI GIACOMO; DI GIACOMO, ALEJANDRO G.

Puerto Iguazú

Congreso; Ornithological Congress of the Americas; 2017

Aves Argentinas

The knowledge on variation in reproductive performance in relation to age is important for making more accurate population viability models of threatened species. The aim of this study was to evaluate the longevity and reproductive parameters variation in relation to the age of the Strange-tailed Tyrant, a threatened bird that inhabits subtropical grasslands (25-29° S). The study was conducted over 13 years (2004-2016) in Reserva El Bagual, Formosa, Argentina. A total of 79 females were marked with metallic numbered bands and colored bands during their stage of nestlings, or in the case of adults, when they were captured with mist-nets in their breeding territories. All the reproductive attempts of these marked females were monitored year after year (N = 292). Most females began to reproduce in their second year of life; the minimum age of reproduction was one year and the maximum nine years. The number of breeding attempts increased with the age of the females (from 1 to 2.5 nests per year). The clutch size remained stable throughout the life of females (2.5 to 2.9 eggs per nest), however the number of fledglings produced reached a maximum at the age of 2 and 3 years (1.5 and 1.1 fledglings per nest) and then decreased to an average of 0.5 for the rest of life. These results indicate that in this population of Strange-tailed Tyrant there is a variation of the reproductive parameters in function of age that should be considered for conservation management.