Birds have the potential to be considered valuable bioindicators of the quality of ecosystems and the environmental impact of pollutants. The aims of this study were to determine the micronuclei frequency and other nuclear abnormalities in erythrocytes by analyzing a wild bird community from central Monte desert (Argentina) and to clarify if there were any differences among certain species. Frequencies of nuclear abnormalities were determined in 73 wild birds belonging to 17 species and two orders (Passeriformes and Columbiformes). A high proportion of individuals, 90.4 and 80.9 %, had erythrocytes with micronuclei and nuclear buds, respectively. Notched nuclei, binucleated cells, nuclear tails, and nucleoplasmic bridges were also recorded. Certain species appeared to be more informative than others with regard to the possibility of being used as bioindicators of genetic damage. Saltator aurantiirostris and Columbina picui were the only species that showed significantly different frequencies of nuclear alterations, in comparison with the other species. The frequencies here presented are the first reported for these bird species from the orders Passeriformes and Columbiformes. This research supports the notion that the use of these biomarkers could be effectively applied to evaluate spontaneous or induced genetic instability in wild birds.

Grass Wrens Cistothorus platensis build two types of non‐breeding nest structures: platforms and dummy nests. Platforms are rudimentary accumulations of grasses concealed between vegetation. Dummy and breeding nests are dome‐shaped with a similar structural layer. We used a nest‐removal experiment and observational data to evaluate several hypotheses regarding the adaptive significance of building multiple nests in a south temperate population of Grass Wrens. Building non‐breeding nests was not a strategy of males to attract additional females, as most of these nests were built after pair formation and both sexes collaborated during building. Building non‐breeding nests was not a post‐pairing display as the presence of multiple nests did not increase female investment in the breeding attempt: clutch size and female provisioning to nestlings did not differ between experimental and control territories where no non‐breeding nests were removed. Similarly, in non‐manipulated territories, clutch size and female provisioning were not correlated with the number of non‐breeding nests or with males’ nest‐building effort. Contrary to this hypothesis, the number of non‐breeding nests was associated with delayed clutch initiation and reduced hatching success. The presence of non‐breeding nests did not reduce nest predation and brood parasitism, which did not differ between experimental and control territories. We did not detect differences in concealment between non‐breeding and breeding nests, suggesting that non‐breeding nests were not the result of abandonment before egg‐laying to reduce subsequent nest predation. Dummy nests did not provide shelter; they were not used frequently for roosting over the breeding season and were not maintained during the non‐breeding season. We suggest that building non‐breeding nests may be an attempt by males to manipulate the decision of females to breed with a mate they might otherwise reject or to start reproduction earlier than optimal for the females.

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