The relationship between habitat breadth, climate, local species diversity, and avian body condition in the Atlantic Forest Biome

Body condition serves as a critical indicator not only of an individual’s overall health but also provides valuable insights into the strategies adopted by organisms in response to factors like resource availability, climate, and biological interactions. In this study, we dove into a comprehensive dataset sourced from the Atlantic Forest Biome, encompassing 4152 individuals spanning 114 bird species across 27 families and 8 orders. Here, we tested the macro-ecological determinants of body condition, assessed through the scaled mass index, a metric derived from body mass and length. Our analytical approach involved hypothesis testing, considering several factors as predictors, including forest cover, local species diversity, mean annual temperature, mean annual rainfall, and habitat breadth. We employed a phylogenetic generalized linear mixed model (PGLMM) to investigate the impact of these factors on body condition. Our findings reveal a negative association between habitat breadth and body condition, suggesting that habitat-specialist species might reap the rewards of enhanced resource predictability or wield a competitive edge over generalist species, thereby potentially elevating their body condition. Furthermore, we discovered an important association: individuals in habitats with higher local diversity exhibited lower levels of body condition. We discuss potential explanations for this, such as increased competition, heightened susceptibility to pathogens, or a higher vulnerability to diseases. Lastly, we found a positive association between mean annual rainfall and body condition, suggesting that potentially increased food and water availability in areas with greater rainfall could contribute to enhanced body condition. Our study highlights the crucial role of species interactions and habitat usage in influencing the body condition. These findings have significant implications for conservation strategies, offering insights that can guide targeted interventions in areas where bird populations show lower body condition, indicating potential vulnerability to disturbances.