Neither paternity loss nor perceived threat of cuckoldry affects male nestling provisioning in grass wrens.

Extra-pair paternity (EPP) is frequent in socially monogamous birds with biparental care. However, males should avoid providing care to unrelated offspring. In this study, we first analyzed the relationship between parental care and paternity loss, and secondly, we evaluated if males adjust parental care to a perceived threat of cuckoldry. Over three breeding seasons, we intensively studied a color-banded population of south temperate grass wrens Cistothorus platensis. We monitored nests attended by socially monogamous males, collected blood samples from adults and nestlings, and recorded male provisioning rates to the nestlings. Paternity was assigned genetically using SNP markers. We simulated territorial intrusions during the female fertile period (egg-laying) to manipulate males' perceived threat of cuckoldry. Neither the proportion of extra-pair offspring nor the presence/absence of extra-pair offspring in the nest affected male provisioning rates, suggesting that males did not adjust parental effort to actual paternity loss. Simulated territorial intrusions revealed that males were more likely to approach and attack a conspecific than a heterospecific stuffed decoy. However, experimental and control males provided food to their nestlings at similar rates. Retaliatory reduction of paternal care might not have evolved in grass wrens given the low frequency of extra-pair paternity (23%). Alternatively, males may rely predominately on precopulatory strategies (e.g., territoriality and mate guarding) to prevent females from obtaining extra-pair fertilizations. Significance statement: A central tenet in the study of extra-pair behavior in birds is that males should reduce their parental contribution when females engage in extra-pair copulations. Males are thought to use indirect clues (female absences, male intrusions) and direct clues (observation of copulations) to gauge paternity loss. We studied the relationship between extra-pair behavior and male contribution to feeding nestlings in a Neotropical population of grass wrens. We found that males did not adjust their contribution to paternal care based on actual paternity loss. Moreover, simulated male intrusions during the female fertile period, which influence a male's perceived threat of cuckoldry, did not affect paternal care. Our results suggest that male grass wrens do not indirectly retaliate against females who engage in extra-pair behavior by reducing parental care. [ABSTRACT FROM AUTHOR]