Anna's hummingbird (Calypte anna) physiological response to novel thermal and hypoxic conditions at high elevations

Many species have not tracked their thermal niches upslope as predicted by climate change, potentially because higher elevations are associated with abiotic challenges beyond temperature. To better predict if organisms can continue to move upslope with rising temperatures, we need to understand their physiological performance when subjected to novel high elevation conditions. Here, we captured Anna’s hummingbirds – a species expanding their elevational distribution in concordance with rising temperatures – from across their current elevational distribution and tested their physiological response to novel abiotic conditions. First, at a central aviary within their current elevational range, we measured hovering metabolic rate to assess their response to oxygen conditions and torpor use to assess their response to thermal conditions. Second, we transported the hummingbirds to a location 1200 meters above their current elevational range limit to test an acute response to novel oxygen and t...