Data from: Extra-pair paternity in two populations of the socially monogamous Thorn-tailed Rayadito Aphrastura spinicauda (Passeriformes: Furnariidae)

Studies on extra-pair paternity (EPP) are key to understanding the
ecological and evolutionary drivers of variation in avian mating
strategies, but information is currently lacking for most tropical and
sub-tropical taxa. We describe the occurrence of EPP in two populations of
a South American socially monogamous bird, the Thorn-tailed Rayadito,
based on data from 266 broods and 895 offspring that were sampled during
six breeding seasons in north-central and southern Chile. In the northern
population, 21% of the broods contained at least one extra-pair young and
14% of all offspring were sired by an extra-pair male, while in the
southern population, we detected extra-pair offspring (EPO) in 14% of the
broods, and 6% of all offspring were EPO. Variation in the frequency of
EPP could stem from population differences in the duration of the breeding
season or the density of breeding individuals. Other factors such as
differences in breeding synchrony and variation in food availability need
to be evaluated. More reports on EPP rates are necessary to determine the
patterns of taxonomic and geographic variation in mating strategies in
Neotropical birds, and to better understand the differences in ecological
dynamics between northern and southern hemisphere populations.