Thermal adaptation and the potential anticipation of overnight weather in the nesting decisions of chimpanzees.

We investigated the nesting behavior of eastern chimpanzees in relation to fine-scale microclimatic variation. We recorded in situ measurements of temperature, humidity, wind speed, and rainfall at the time of nest construction and during the subsequent overnight period. Then, we modeled how these microclimatic factors influenced the nesting site selection, nest structure, nest insulation, and the characteristics of the nesting tree. Chimpanzees preferentially constructed nests in warmer, less windy microclimates, built thicker and deeper nests under cooler or wetter conditions, and selected taller trees with denser canopy cover prior to rainy nights. Across analyses, models that incorporated overnight weather consistently outperformed those that incorporated weather variables at the time of nest construction, indicating that nesting decisions align more closely with overnight conditions than with conditions at the time of nest building. This outcome is consistent with the possibility that chimpanzees adjust nest-building behavior in relation to expected overnight thermal conditions, potentially using proximate cues, although it does not provide conclusive evidence of anticipatory decision-making. These findings suggest flexible thermoregulatory responses and possible integration of environmental cues in nesting decisions, offering new insight into the cognitive foundations of behavioral adaptation under variable climatic conditions.