Our study that started in 2017 has finally been published! Congratulations to Dr. Erich Eberts, who was project lead for this project while he was finishing his undergraduate degree at Loyola Marymount University, and who stuck with the writing, analysis, and manuscript handling. It is rather apt that the study was accepted and In Press around about the same time that Dr. Eberts defended his PhD!

Here is the abstract:

Reproduction entails a trade-off between short-term energetic costs and long-term fitness benefits. This is especially apparent in small endotherms that exhibit high mass-specific metabolic rates and live in unpredictable environments. Many of these animals use torpor, substantially reducing their metabolic rate and often body temperature to cope with high energetic demands during non-foraging periods. In birds, when the incubating parent uses torpor, the lowered temperatures that thermally sensitive offspring experience could delay development or increase mortality risk. We used thermal imaging to noninvasively explore how nesting female hummingbirds sustain their own energy balance while effectively incubating their offspring. We located 67 active Allen’s hummingbird (Selasphorus sasin) nests in Los Angeles, California and recorded nightly time-lapse thermal images at 14 of these nests for 108 nights using thermal cameras. We found that nesting females usually avoided entering torpor, with one bird entering deep torpor on two nights (2% of nights), and two other birds possibly using shallow torpor on three nights (3% of nights). We also modeled nightly energetic requirements of a bird experiencing nest temperatures vs. ambient temperature and using torpor or remaining normothermic, using data from similarly-sized broad-billed hummingbirds. Overall, we suggest that the warm environment of the nest, and possibly shallow torpor, help brooding female hummingbirds reduce their own energy requirements while prioritizing the energetic demands of their offspring.

Citation

Eberts, ER, Tattersall, GJ, Auger, PJ, Curley, M, Morado, MI, Strauss, EG, Powers, DR, Camacho, NM, Tobalske, BW, and Shankar, A. 2022. Free-living Allen’s hummingbirds (Selasphorus sasin) rarely use torpor while nesting. Journal of Thermal Biology. Available online 5 December 2022, 103391. https://doi.org/10.1016/j.jtherbio.2022.103391

Acknowledgements

We thank the numerous undergraduate assistants who completed much of the nest searching, equipment maintenance, and data collection, CURes, the LMU grounds and facilities maintenance staff for assisting with the location of and access to nests. We also thank Susan Wethington for providing broad-bill hummingbird nests. We also thank Welch lab members (University of Toronto) for helpful discussions. We especially thank our crowdfunding campaign donors who participated in the Experiment.com crowd-source campaign and FLIR Systems for their support.