Quando encontrar aves na Amazônia Central: variação da atividade vocal em duas escalas temporais

Abstract

In temperate regions, bird vocal activity concentrates on the early morning of spring and summer days, but in the tropics, where high diversity results in a variety of dial and seasonal activity patterns, vocal activity is less predictable. We document quantitative patterns of temporal variation in vocal activity of 160 central Amazon tropical forest species, assessing variation between days throughout the dry season and between clock times throughout the morning. To span an area of approximately 500 km2 we sampled bird vocalizations using autonomous recording devices deployed over 170 points, and built a database of more than 4,500 recording hours. To quantify temporal variation we modeled our data with a multi-scale occupancy model fitted in a Bayesian framework. Our model formally separates site occupancy from species detection at two separate temporal scales – season and morning – using quadratic functions to represent the temporal variation of sound-based detection throughout the season and throughout the morning. By representing species as random effects of a community-level mean, we identify community-wide vocal activity peaks in August, towards the middle of the dry season, and approximately 40 minutes after sunrise, at the morning scale. Species-specific results identify a majority of species without obvious variation of vocal activity throughout the dry season, and a few species with morning activity peaks before dawn or late in the morning. Our results offer a basis to optimize the timing of central Amazon bird surveys and a robust quantitative assessment of vocal behavior that can be compared with other species traits.