Vocal activity of lowland forest birds in eastern Ecuador varies by foraging strata, guild, and species during the first hours of the morning

Abstract

Patterns of vocal activity vary among tropical bird species, with some tending to sing before or close to dawn (“dawn chorus”) whereas others are more likely to vocalize later in the morning. Timing of vocal activity can, therefore, affect the results of bird counts which often rely heavily on vocalizations for species identification. Passive acoustic monitoring (PAM), which uses autonomous recording units (ARUs) to record vocalizations at a set schedule, allows birds to be sampled at multiple points simultaneously and can be set to record over extended time periods at single points. Thus, monitors provide an effective way to document vocal activity patterns during the morning when birds are typically most active. I used ARUs to record vocal activity of birds at a lowland forest site in eastern Ecuador during 2013-2017 on two 100-ha study plots. Monitors were set to record for 10-min periods followed by a 5-min break from 0545 to 0810. Species were identified by listening to the recordings, with presence of species noted during each 10-min period. Activity (number of species occurrences per period) was examined by strata (understory, canopy), guild, and by individual species. Overall patterns of activity (all species combined) increased rapidly from before dawn to about 0630 and then gradually decreased. The pattern was the same on both plots and consistent across years on each plot. Activity patterns differed among strata, guilds, and individual species. Understory birds peaked in activity before canopy birds and then declined to a point where there was less vocal activity than among canopy birds. Terrestrial granivores, omnivores, and frugivores all showed an early morning peak followed by a rapid decrease in contrast to arboreal species that increased in activity throughout the morning. Terrestrial insectivores did not differ from bark insectivores in their patterns of activity even though bark insectivores forage at higher strata. Substantial variation among species within different guilds also was apparent and illustrates that patterns of activity can vary even among species that forage in similar ways. Passive acoustic monitoring is a useful method for sampling bird activity because multiple monitors can be active at the same time across multiple points.

Keywords

• activity
• autonomous recorder
• lowland forest
• passive acoustic monitoring
• temporal activity