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Various bird species regularly fast in connection with breeding, migration, or drastic climatic conditions. The metabolic response of penguins and domestic geeseto fasting has been studied in detail. These large birds, in contrast to smallspecies, do not become torpid when they are fasting. Nevertheless, they reduce their rate of energy expenditure by decreasing both resting metabolic rate and locomotor activity. From changes in the loss of body mass, the fast of penguins and geese has been divided into three phases: I, the loss of body mass decreases;II, it remains at a minimum level; and III, it increases. These phases reflect metabolic adjustments. Phase I is a rapid phase of adaptation, marked by a decrease in protein catabolism and mobilization of lipids. Phase II is a phase of economy, during which more than 90% of the energy expenditure derives from lipids, while protein catabolism remains at a minimum level. In phase III there still arelipid reserves and this phase is reversible; it is, however, critical because proteins are no longer spared. Data in the literature suggest that these three phases may also be used to describe how a wide variety of wild and domestic birdsadapt to fasting.

Physiology and biochemistry of long-term fasting in birds

Yves Cherel, Jean-Patrice Robin, Yvon Le Maho

NUTRITION, PHYSIOLOGY, AND STABLE ISOTOPES: NEW INFORMATION FROM FASTING AND MOL

TING PENGUINS

Yves Cherel1,,4, Keith A. Hobson2, Frdric Bailleul1, and Ren Groscolas31Centre d'Etudes Biologiques de Chiz, UPR 1934 du CNRS, BP 14, 79360 Villiers-en-Bois, France

2Prairie and Northern Wildlife Research Centre, Environment Canada, SaskatchewanS7N 0X4 Canada

3Centre d'Ecologie et Physiologie Energtiques, CNRS, 67087 Strasbourg Cedex 02, France

Stable isotopes are increasingly used in animal ecology, but little attention ha

s been paid to the underlying physiological processes accounting for changes in15N/14N and 13C/12C ratios, for example, the influence of protein balance on 15Nvalues. We investigated a professional faster, the King Penguin (Aptenodytes patagonicus), to test the effect of long-term food deprivation on the isotopic signature of tissues that can be nondestructively sampled, i.e., blood and feathers. Fasting for 25 days induced a tissue 15N enrichment, thus leading to a moderate increase in the apparent trophic levels of penguins. As expected, 15N enrichmentwas higher in tissues with high protein turnover rates (e.g., plasma, 0.70) thanin those with low turnover rates (e.g., blood cells, 0.24). Fasting decreased the13C value of plasma, which was due to an increase in its lipid content, as indicated by a concomitant rise in plasma C/N ratio. Finally, food deprivation induced a 15N enrichment in keratin (1.68), as indicated by the lower nitrogen signature for portions of new feathers that were synthesized at sea than for those parts

grown on land, thus illustrating the different pathways for resource allocation(dietary vs. endogenous reserves) in molting birds. The study also emphasized the usefulness of collecting whole blood (or blood cells) in the field to overcome both the fasting and lipid effects observed in plasma.

Read More: http://www.esajournals.org/doi/abs/10.1890/05-0562