A link between increased temperature and avian body condition in a logged tropical forest

The combined effects of anthropogenic disturbances, such as logging and climate change, remain poorly understood; yet, they are the main threats to tropical biodiversity. Most tropical African countries lack long-term climate data, so climate impacts on biodiversity cannot be assessed. However, individuals experience weather, rather than climate, such that climate effects could be seen as the cumulative effects of weather over time. We used morphometric data collected in 1996-2000 and 2017-2021 on understory birds in the Budongo Forest, Uganda, to assess how logging history and short-term weather variations affected the body condition (body condition index [BCI]) of birds. Birds were captured in mist nets in logged and unlogged sites. We analyzed data with Bayesian mixed-effects models. The BCI values were lower in logged forests and decreased as maximum temperatures increased, irrespective of the sensitivity of the birds to logging. Birds responded quickly to increasing temperatures and precipitation (within 1 week), and the longer a hot period was, the worse the effect on birds in heavily logged forests, suggesting reduced thermal buffering. Contrary to our expectations, BCI values for 2017-2021 were higher than values for 1996-2000, indicating possible forest recovery. Our findings underscore the importance of short-term weather data to predict climate change impacts. Such predictions can inform tropical forest management and restoration measures.