Diagnosing cryptic species has long posed a challenge in ornithology. However, advances in vocal and molecular analyses have significantly enhanced species recognition. In the Amazon, the sister species Turdus hauxwelli and T. fumigatus epitomize this difficulty. Previous studies on plumage suggested the existence of an intergradation zone in southern Central Amazonia and Mato Grosso. However, similarities in their songs have often led to misidentifications that obscure their true distributions. This study sought to evaluate whether acoustic characteristics could refine the geographic boundaries of these species, particularly in Central Amazonia and Mato Grosso, and to reevaluate specimens for potential plumage differences. We analyzed recordings of both species, conducted multivariate analyses of vocal characteristics, and performed morphometric and visual assessments of specimens. Our vocal analyses identified two call types - single-note and multiple-note calls - with each species predominantly using one type as its primary call. These calls allowed clear differentiation between the species. Additionally, our data showed that recordings from Mato Grosso pertain exclusively to T. hauxwelli, contradicting prior reports of T. fumigatus in the region and refuting the previously proposed intergradation zone (based on plumage alone). In contrast, neither morphometric analyses nor plumage patterns effectively distinguished the two species. Some T. hauxwelli specimens from Mato Grosso exhibited plumage characteristics indistinguishable from those of T. fumigatus, likely contributing to earlier misclassifications. Our findings emphasize the taxonomic value of vocalizations in thrushes and highlight the need for integrating diverse datasets to improve our understanding of species identity and distribution.

Cavity-nesting birds, such as the endangered vinaceous-breasted Amazon (Amazona vinacea), are particularly vulnerable to habitat loss and nest-site competition. Released amazons may face challenges to form mating pairs and choose a nest site. This study documents a rare case of two released pairs of A. vinacea sharing the same artificial nest box in the surroundings of the Araucárias National Park, Brazil. Behavioral interactions were monitored using camera traps over 65 days. The implications for reproductive success were evaluated, and management strategies to mitigate nest competition in reintroduction programs were proposed. Both pairs frequently visited the same nest box, occasionally with different partners, and exhibited aggressive interactions. A female laid two eggs that failed to hatch. These findings suggest that limited availability of artificial nest boxes may elicit atypical behaviors in released individuals, potentially influenced by captivity related factors. To improve reproductive success, it is recommended to install nest boxes ≥ 300 m apart, adopt weather-resistant designs and promote local engagement in monitoring through citizen science.

Abstract The breeding success of birds is crucial for their survival and development, with nest features and nest-site selection playing a significant role in the reproductive process. This study investigated the nest features of the giant babax, the key environmental factors influencing its nest-site selection, and the factors affecting its reproductive success. We conducted field research at four sample plots in Lhasa, Xizang, from March to October 2023. Examining a total of 34 nests, 26 (76.5%) were successful, while 8 (23.5%) failed. Principal component analysis (PCA) revealed that the primary environmental factors influencing nest-site selection of the giant babax were altitude, distance to water, distance to houses, canopy density, nesting tree height, and DBH. Binomial logistic regression analysis revealed that canopy density significantly influenced both nest-site selection and reproductive success. Additionally, the number of helpers had a significant effect on reproductive success.