Exogenous corticosterone mimics a late fasting stage in captive Adélie

26 Fasting is part of penguin’s breeding constraints. During prolonged fasting three 27 metabolic phases occur successively. Below a threshold in body reserves, birds enter phase 28 III (PIII), which is characterized by hormonal and metabolic shifts. These changes are 29 concomitant with egg abandonment in the wild and increased locomotor activity in captivity. 30 Because CORT enhances foraging activity, we investigated the variations of endogenous 31 CORT, and the effects of exogenous CORT on the behavioral, hormonal, and metabolic 32 responses of failed breeder Adélie penguins. 33 Untreated and treated captive male were regularly weighed and sampled for blood 34 while fasting, and locomotor activity was recorded daily. Treated birds were implanted with 35 various doses of CORT during phase II. 36 Untreated penguins entering PIII had increased CORT (3.5-fold) and uric acid (4-fold; 37 reflecting protein catabolism) levels, concomitantly with a rise in locomotor activity (2-fold), 38 while prolactin (involved in parental care in birds) levels declined by 33 %. In CORT-treated 39 birds, an inverted-U relationship was obtained between CORT levels and locomotor activity. 40 The greatest increase in locomotor activity was observed in birds implanted with a high dose 41 of CORT (C100), locomotor activity showing a 2.5-fold increase, four days after implantation 42 to a level similar to that of birds in PIII. Moreover, uric acid levels increased 3-fold in C10043 birds, while prolactin levels declined by 30 %. 44 The experimentally-induced rise in CORT levels mimicked metabolic, hormonal, and 45 behavioral changes characterizing late fasting, thus supporting a role for this hormone in the 46 enhanced drive for refeeding occurring in long-term fasting birds. 47 48 49