Females often invest more in parental care than males, but in socially monogamous systems, males invest as much as females in caring for their offspring, and male contribution is believed essential for reproductive success in these systems. Here we describe the number of visits, the feeding rate to their nestlings, and the time on the nest invested by each sex of the socially monogamous songbird, the Clay-colored Thrush (Turdus grayi), for 16 nests in San José, Costa Rica. Both males and females fed their nestlings at a similar rate, but females visited the nests more frequently than males. The feeding rate of both females and males was also similar when controlled by age of nestling. The feeding rate was highly variable across males (minimum 1, maximum 15 visits per 2 h), possibly related to the probability of males fathering the offspring of the attended nest. Females spent more time on the nest than males, but males tended to remain near the nest to defend it from predators. Moreover, male contribution during the nestling period correlated with the reproductive success.

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