Changes in the bird communities of Nothofagus forests in a long-term plot in Tierra del Fuego

Abstract

Long-term studies have proven to be important to characterize animal communities and analyse the ecological responses to climate and environmental changes. These studies are necessary to determine the natural community variability (e.g., richness and density) to develop better conservation strate-gies to face climate changes. Here, we analysed the natural changes in the structure and functional traits of bird communities over 13 consecutive years (2010–2022) and determined the number of years of sampling needed to ob-tain a good estimation of the community structure variables in deciduous high latitude Nothofagus forests. Using point counts, we studied closed (80% of can-opy cover) and open (40% of canopy cover) forests inside the Tierra del Fuego National Park. Species richness, density, biomass, and functional traits (migra-tory status, trophic groups, nest type, and feeding strata) were analysed using generalized linear models with forest type (closed and open) and year (2010–2022) as the main factors, while the standard error (SE) of sampling obtained from one to 12 sampling years was compared. Richness was significantly higher in open forests (p< 0.01), while density and biomass were higher in closed for-ests. Additionally, density and biomass significantly varied among years in both forest types (e.g., lower density in 2013, 2014 and 2015, and higher in 2019). The density of birds for some functional traits also varied among years and forest types (e.g., higher values of cavity nesters in closed forests during 2019). Five to six years of sampling were needed to have an acceptable estimation of richness (20% SE), between 10 and 12 years for density, and >12 years for biomass. This study highlights the importance of long-term studies to visualize natural varia-tions in undisturbed habitats along time