Experimentally elevated corticosterone increases song output and complexity in common mynas.

Vocalization is an important communication tool that can reflect many aspects of an individual's internal and external condition. This is especially true for birds. Previous research has shown that bird calls and songs change in response to a variety of potential stressors, although the extent and direction of the changes depend on the nature of the stressor and the environment. Circulating glucocorticoids, such as corticosterone, often increase in response to stressors and mediate some of the observed changes via alterations of the individual's physiological state. Acute elevations of corticosterone often occur as a physiological response to short-term stressors; however, the effects of this elevation on adult vocalizations have not been well documented. Here, we experimentally elevated corticosterone at two different levels using a noninvasive method and examined the effects on the vocal communication of male and female adult common mynas (Acridotheres tristis). Corticosterone elevation temporarily increased song output and some measures of song complexity, while call output decreased. These effects were dosage dependent (higher corticosterone levels had a stronger effect), most evident 40 min after ingestion, and some vocal changes were sex-specific. Future studies should investigate whether the changes in vocal performance due to elevated glucocorticoids have consequences for the birds' behavior, reproductive success, and survival.

Blood parasites in passerine birds from the Brazilian Atlantic Forest / Hemoparasitos em passeriformes da Mata Atlântica Brasileira

Parasites may lead bird species to extinction, affect host temporal and spatial population dynamics, alter community structure and alter individuals’ social status. We evaluated blood parasite prevalence and intensity according to bird families and species, among 925 birds that were caught in 2000 and 2001, in the Atlantic Forest in the State of Minas Gerais, Brazil. We applied Giemsa staining to thin blood smears, to detect blood parasites. The birds (n = 15.8%) in 11 families, were infected by at least one parasite genus, especially Muscicapidae (28.3%) and Conopophagidae (25%). Among the 146 infected birds, Plasmodium was detected in all bird families and had the highest prevalence (54.8%). Trypanosoma, Haemoproteus and microfilaria had lower prevalence rates (23.3, 23.3 and 2.1%, respectively). Birds caught during the rainy season were more infected than birds caught during the dry season. The overall low prevalence of blood parasites in birds is similar to the patterns found elsewhere in the Neotropical region.

Parasitos podem levar espécies de aves à extinção, afetar as dinâmicas temporais e espaciais dos hospedeiros, alterar a estrutura de comunidades e o status social de indivíduos. Avaliou-se a prevalência e a intensidade de parasitos em famílias e espécies de 925 aves capturadas, entre 2000 e 2001, na Mata Atlântica de Minas Gerais. Foram coradas com Giemsa extensões de sangue para detectar parasitos hematozoários. As aves (n= 15,8%) 11 famílias estavam infectadas por pelo menos um gênero de parasito, especialmente Muscicapidae (28,3%) e Conopophagidae (25%). Entre as 146 aves infectadas, Plasmodium foi detectado em todas as famílias e possuiu a maior prevalência (54,8%). Trypanosoma,Haemoproteus e microfilaria possuíram baixas prevalências (23,3, 23,3 e 2,1%, respectivamente). Aves capturadasdurante a estação chuvosa estavam mais infectadas do que aves capturadas durante a estação seca. A baixa prevalência geral de parasitos do sangue das aves é semelhante aos padrões encontrados em outras localidades da região Neotropical.