Extra-pair paternity enhances the reproductive fitness of urban Chinese blackbird

Urbanization is a human-induced process of rapid habitat change that can
affect the reproductive success of animals. The occurrence of
extra-partial paternity (EPP) may be sensitive to changes in urban
ecological conditions. In this study, the Chinese blackbird (Turdus
mandarinus), a common breeding bird in southern Chinese cities, was
selected as the focus species to explore the EPP patterns of monogamous
birds in developing cities and their relationship. Over four breeding
seasons, 316 Chinese blackbird nestlings and 20 adults in both urban and
rural areas were monitored and genotyped for 11 microsatellite loci to
determine progeny affinity. We confirmed that both the brood size and
hatching rate of EPP nests were significantly larger than those of
within-pair paternity (WPP) nests. The body mass, beak length, head
length, and body length of 12-day age extra-pair offspring (EPO) were
significantly greater than those of within-pair offspring (WPO) suggesting
important benefits of EPP. However, according to the analyses of nest
ecological variables, we concluded that EPP occurs most often in areas
with low urbanization levels indicating some constraints for this
reproductive strategy in cities. Our findings provide interesting new
insights into how this growing human-induced landscape change affects
mating behavior in birds, an important aspect of avian ecology and
evolution.