Abstract ID: 3.13821 | Accepted as Poster | Poster | TBA | TBA

Mountain environments pose significant climatic challenges for breeding birds, including strong temperature fluctuations and exposure to harsh weather. Nest-site selection can help mitigate these stressors and improve fitness. Rock cavities may offer thermal advantages by buffering external temperature variation. We monitored alpine bird nests in two volcanoes of the temperate Andes during the 2024–2025 breeding season in southern Chile (~39°S, 71°W). A total of 40 nests from six treeline-breeding species were studied: Blue-and-white Swallow (Pygochelidon cyanoleuca, n = 23), White-browed Ground-Tyrant (Muscisaxicola albilora, n = 8), Ochre-naped Ground-Tyrant (Muscisaxicola flavinucha, n = 1), Buff-winged Cinclodes (Cinclodes fuscus, n = 7), Plumbeous Sierra Finch (Geospizopsis unicolor, n = 1), and Upucerthia saturatior (n = 1). To assess microclimatic conditions, thermal sensors (Hobo Temp) were placed inside and outside 20 nest cavities (n = 40). External sensors were positioned in stone stacks, facing north, and shielded from direct sunlight, up to 130 cm from cavity entrances. Temperature was recorded every 10 minutes for 42 hours per cavity. Temperature differences between interior and exterior were analyzed for four species: P. cyanoleuca (n = 9), M. albilora (n = 6), C. fuscus (n = 4), and U. saturatior (n = 1). Across species, temperatures were generally higher inside at night and lower in the evening. However, variation in magnitude and direction was species-specific. For M. albilora, all cavities were warmer inside at night and cooler in the evening, while three were warmer outside at twilight and one in the morning. C. fuscus followed the same pattern, with two cavities warmer outside at twilight and one in the morning. P. cyanoleuca showed significant nighttime differences, with higher temperatures inside. Five cavities differed at twilight, only one being warmer inside. Additionally, four cavities were warmer in the morning. U. saturatior showed temperature differences in all periods except the morning. These findings suggest that mountain-top species may select rock cavities for their microclimatic benefits, indicating an adaptive response to thermal conditions.