Anyone who has seen the movie March of the Penguins knows that these animal undergo long periods of fasting. There are actually 3 stages of fasting in birds.
Phase I: This is a short phase in which they burn stored fat for energy.
Phase II: In this long phase, animals are constantly losing body mass and trying to spare proteins. Fat continues to be the main source of energy.
Phase III: Animals enter this phase if fat reserves start running low. This is when changes in hormones and metabolism occur resulting in a switch from using fats to using proteins for energy. Along with the metabolic changes come behavioral changes that may include abandoning their eggs and increased movement presumably driving the animals to seek out food.
Researchers in France have been studying phases II and III of fasting in Adélie penguins (Pygoscelis adeliae). They found a significant reduction in body mass and fatty acids during these later stages of fasting. Levels of the stress hormone corticosterone and locomotion were significantly increased as fasting progressed similar to what is seen in other species of penguins (king and emperor). Since these birds were studied in captivity, these data show that the responses in captivity are similar to those observed in the wild. The researchers then wanted to know whether corticosterone was responsible for controlling the phase III responses in Adélie penguins.
To test this, birds were administered various doses of the hormone and the responses were again measured. What they found was that birds treated with corticosterone responded by increasing locomotion and shifting their substrate use from fats to proteins. Therefore, their findings support the role of this stress hormone in the phase III fasting response which drives the search for food in starving penguins.
I can relate. When I feel stressed, I also feel the need to search for food.
You now have free access to the article! You can read it here.
Spée M, Marchal L, Thierry A,Chastel O, Enstipp M, Le Maho Y, Beaulieu M, Raclot T. Exogenous corticosterone mimics a late fasting stage in captive Adélie
penguins (Pygoscelis adeliae). Am J Physiol Regul Integr Comp Physiol 300: R1241-R1249, 2011.