Social and genetic polygyny in the strange-tailed tyrant (Alectrurus risora).

DI GIACOMO, ALEJANDRO G.; MAHLER, BETINA; DI GIACOMO, ADRIÁN S.; REBOREDA, JUAN C.

Campos do Jordao

Congreso; 25th International Ornithological Congress, Campos do Jordao, Sao Paulo, Brasil, Agosto 22-28, 2010.; 2010

The strange-tailed tyrant (Alectrurus risora) is a globally threatened flycatcher that inhabits savannas, wet grasslands and marshes in southern Paraguay and northeastern Argentina. This species is highly sexually dimorphic, with males having a long tail with modified outer feathers, a contrasting black-and-white plumage and notable bare red skin on the throat during the breeding season. Variation in the extent of sexual dimorphism and dichromatism among birds is attributed to sexual selection and differences in mating system. On the basis of observations of unbanded breeding birds it has been suggested that this species is socially polygynous. However, the predominant mating system of tyrant flycatchers is social monogamy with biparental care of the chicks. We examined the social and genetic mating system of strange-tailed tyrants and evaluated the extent of parental care by females and males. During five consecutive breeding seasons we followed the nesting attempts of banded females and males and collected blood samples from chicks and parents in a protected area of the humid Chaco, in Formosa Province, Argentina. The social mating system was polygyny. Males defended contiguous territories of 2- 2.5 ha that included the territories of 1-3 females. Females bred in the same territory over several years, but males rarely remained in the area more than one year. Parental care was provided exclusively by the female, who builds the nest, incubates the eggs and broods and feeds the chicks without male‘s assistance. Genetic analysis of 8 microsatellite loci confirmed that males were polygynous, but also showed extra-pair fertilizations.