Sex-dependent recognition and behavior against nest predators and brood parasites by Chestnut-capped Blackbird Chrysomus ruficapillus

Brood parasitism and nest predation are among the main causes of breeding failures in passerine birds. Brood parasites threaten to the nest, while predatory birds threaten to both the nest and the parents. The objective of this study was to experimentally evaluate whether male and female Chestnut-capped Blackbirds, Chrysomus ruficapillus, recognize and respond to different nest threats during the breeding stages. For this purpose, we presented taxidermy models of a brood parasite, Molothrus bonariensis; a nest predator, Caracara plancus; and a non-predator species, Colaptes campestris, on the nest of C. ruficapillus. Additionally, we filmed nests without the display models to compare them with the nests exposed to taxidermy mounts. We assessed whether parents returned to the nest for each sex based on nest attention, visit frequency, and visit duration through the filming of a total of 44 nests. The parental return to the nest in the experimental trials varied between the sexes and breeding stages. During the incubation stage, males increased their nest attention and frequency of visits in the presence of the non-predator and brood parasite models. Females also increased their frequency of visits in the presence of the non-predator model in relation to the predator and brood parasite models. During the nestling stage, males extended the duration of their visits in the presence of the predator model compared to nests without the display model. Meanwhile, females showed no differences in their behavior during this stage. Overall, the Chestnut-capped Blackbirds parents demonstrated the ability to recognize the presented models and responded differently to different threats at different stages of the breeding cycle. The flexible responses they exhibited may be consistent with the `threat-sensitive predator avoidance´ hypothesis.