Heterothermy and torpor as energy saving strategies in Antarctic storm-petrel nestlings
Final Report Abstract
Wilson’s storm-petrels (Oceanites oceanicus) are the smallest marine birds breeding in Antarctica, where events like snowstorms often prevent parents from providing food daily for their offspring. To minimize energy expenses, Wilson’s storm-petrel chicks can reduce their metabolism and body temperature by entering hypothermia. Chick development in a breeding colony of Wilson’s stormpetrels on the South Shetland Islands was monitored daily during three consecutive summers by recording chicks’ body mass and temperature, as well as environmental parameters. Provisioning, and body conditions were highest in 2017, and chicks became hypothermic most frequently in 2016. Body temperature was influenced by age, mass, body condition, and minimal nocturnal temperatures. While most chicks were able to maintain stable body temperatures when not fed for one day, some chicks’ body temperatures decreased by up to 21°C. Age did not differ between those two groups, but chicks maintaining their active body temperatures had higher body conditions. Snowstorms were typically followed by several days of unreliable food provisioning and continuous days of fasting. Most chicks were hypothermic during this time, and were hence able to survive periods of food shortages, reverse their low body temperatures after the next feeding event, and regained body mass. Overall, the effects of torpor events on growth and physiological parameters were relatively mild. Although Wilson’s storm-petrel chicks showed some depletion in lipid metabolites after periods of torpor, they did not suffer measurably effects of torpor on immunocompetence, but had reduced growth rates. We conclude that hypothermia is a strong survival strategy to endure times of fasting, which might be necessary for Antarctic storm-petrel chicks to survive to reach fledging. Further analyses suggested a mild impact of hypothermia during development on important life functions (growth, immune capacity). However, future scenarios suggest more frequent snowstorms due to climate change, and thus malnourishment could lead to more frequent use of hypothermia, which could affect chicks’ development more strongly than currently observed.
