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


Spence, Austin; LeWinter, Hannah; Tingley, Morgan (2022), Anna's hummingbird (Calypte anna) physiological response to novel thermal and hypoxic conditions at high elevations, Dryad, Dataset,


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 thermal conditions. Hummingbirds exhibited lower hovering metabolic rates above their current elevational range limit, suggesting lower oxygen availability may reduce performance after an acute exposure. Alternatively, hummingbirds showed a facultative response to thermal conditions by using torpor more frequently and longer. Finally, post-experimental dissection found that hummingbirds originating from higher elevations within their range had larger hearts, a potential plastic response to hypoxic environments. Overall, our results suggest lower oxygen availability and low air pressure may be difficult challenges to overcome for hummingbirds shifting upslope due to rising temperatures, especially if there is little to no long-term acclimatization. Future studies should investigate how chronic exposure and acclimatization to novel conditions, as opposed to acute experiments, may result in alternative outcomes that help organisms better respond to abiotic challenges associated climate-induced range shifts.


This manuscript contains two types of data: metabolic data and organ mass data. The metabolic data was collected using a Field Metabolic System from the company Sable Systems. Hummingbird torpor and hovering metabolic rate was collected at two different elevations. Additionally, hummingbird organs were collected through dissection to look at dry mass of different organ systems. These were dried to remove any water content and weighed on precise scales.

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National Science Foundation, Award: DGE-1747453