Social and genetic polygyny in a fluvicoline flycatcher, the Strange-tailed Tyrant, Alectrurus risora

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

Campos do Jordao, Brasil

Congreso; 25th International Ornithological Congress; 2010

International Ornithological Society

The Strange-tailed Tyrant (Alectrurus risora, Tyrannidae) is a fluvicoline flycatcher that inhabits savannas, wet grasslands and marshes in southern Paraguay and northeast Argentina. This species is highly sexually dimorphic. Males have 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. Females have brown plumage with an outer pair of rectrices also elongated and finishing in a ´racquet´. Variation in the extent of sexual dimorphism and dichromatism among birds is attributed to sexual selection and differences in the social mating system. On the basis of observations of a group of unbanded breeding birds it has been suggested that this species is polygynous. However, the predominant mating system of tyrant flycatchers in both, temperate and tropical zones is social monogamy with biparental care of the chicks. In this work we examined the social and genetic mating system of Strange-tailed Tyrants and evaluated the extent of parental care by males and females. During five consecutive breeding seasons we followed the nesting attempts of banded females and males and collected blood samples from chicks and putative parents. The social mating system was social polygyny. Males defended contiguous territories of 2 ha that included the territories of 2-4 females. Females bred in the same area over several years, but males rarely bred in the same area in consecutive years. 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 the presence of extra-pair fertilizations. Our results show that the Strange-tailed Tyrant is a socially and genetically polygynous flycatcher with uniparental female care.