Breeding Performance and Effects of Nest Site Features on Nest Survival of Chestnut- Capped Blackbird Chrysomus ruficapillus (Passeriformes: Icteridae).

The Chestnut-capped Blackbird Chrysomus ruficapillus is a neotropical species that nests in wetlands, which are abundant in South America. However, many of these wetlands face threats of disappearance and degradation, with potential consequences for the species inhabiting them. Here, we carried out a detailed study of the breeding biology of this species and examined variables that influence daily nest survival rates (DSR). We described nest site features, nest morphometry, breeding parameters, estimated the growth curves of nestlings, and recorded the causes of nest failure. We evaluated the effects of nest site features, nest morphometry, nest age and timing of breeding season on the DSR of Chestnut-capped Blackbirds. We expected that DSR would increase with greater nests and higher nest concealment at the beginning of the breeding season. Additionally, we predicted that larger nests would have higher nest survival. We studied the breeding performance of 138 nests in a wetland in central Argentina over three consecutive breeding seasons. Nests were placed 80 ± 21.53 cm above the water. The clutch size was 2.75 ± 0.67 eggs (n = 84 nests), and the brood size was 2.28 ± 0.79 nestlings (n = 49 nests). The most frequent cause of nest failures was predation (60%). The daily nest survival rate (DSR) was 0.96, and the cumulative probability of nest survival in a 29-day breeding cycle was 0.31 (n = 85 nests). As expected, we found a positive association between nest height above the water and DSR, suggesting that nests built further away from the water have increased survival rates. However, we found no effects of nest morphometry or the timing of breeding season on DSR. We emphasize the importance of understanding the breeding performance and the influence of nest site features on the survival of species inhabiting wetlands to implement actions to conserve and protect the population.