Physiology of Prolonged Fasting in Greater Snow Geese (Chen caerulescens atlantica)

Greater Snow Geese (Chen caerulescens atlantica) may face periods of complete food deprivation during incubation in the High Arctic.We studied the ability of these birds to withstand a prolonged fast.We measured rate of mass loss, patterns of carbohydrate, lipid and protein utilization, and changes in resting metabolic rate in 11 captive geese subjected to complete food deprivation.Geese lost 44% of their initial body mass during fasting periods that ranged from 19 to 42 days (mean 34 days).The rate of mass loss reflected the three phases commonly associated with the changing rates of lipid and protein catabolism in homeothetins.Phase I (11 days) was characterized by a decreasing rate of body-mass loss and a rapid increase in plasma fl-hydroxybutyrate level, indicating body-lipid mobilization.During phase II (22 days), the rate of body-mass loss stabilized at a low level.Plasma concentration of fl-hydroxybutyrate peaked in the first half of phase II and then decreased.Plasma uric-acid level, an index of protein catabolism, increased during the second half.Resting metabolic rate of fasting geese was reduced by 38% below the pre-fast value, more than predicted from body-mass decrease alone.Phase III (3 to 4 days) was characterized by an increase in the daily rate of mass loss.Plasma concentration of uric acid increased markedly, while fl-hydroxybutyrate values remained low and stable.Glycemia and total plasma protein level also started to fall.Greater Snow Geese did not tolerate fasting as long as larger birds, like penguins, probably because they were less efficient in sparing their protein reserves during phase II.Greater Snow Geese endurance of fasting may be limited by their use of flight, which ultimately limits their capacity to carry the large fat reserves required for prolonged fasting.