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

Abstract

Brood parasitism and nest predation are among the main causes of breeding failures in passerine birds. Brood parasitesthreaten to the nest, while predatory birds threaten to both the nest and the parents. The objective of this study was toexperimentally evaluate whether male and female Chestnut-capped Blackbirds, Chrysomus ruficapillus, recognize andrespond to different nest threats during the breeding stages. For this purpose, we presented taxidermy models of a broodparasite, 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 nestsexposed to taxidermy mounts. We assessed whether parents returned to the nest for each sex based on nest attention, visitfrequency, and visit duration through the filming of a total of 44 nests. The parental return to the nest in the experimentaltrials varied between the sexes and breeding stages. During the incubation stage, males increased their nest attentionand frequency of visits in the presence of the non-predator and brood parasite models. Females also increased their frequencyof visits in the presence of the non-predator model in relation to the predator and brood parasite models. Duringthe nestling stage, males extended the duration of their visits in the presence of the predator model compared to nestswithout the display model. Meanwhile, females showed no differences in their behavior during this stage. Overall, theChestnut-capped Blackbirds parents demonstrated the ability to recognize the presented models and responded differentlyto different threats at different stages of the breeding cycle. The flexible responses they exhibited may be consistent withthe `threat-sensitive predator avoidance´ hypothesis.