All animals face the possibility of limitations in food resources that could ultimately lead to starvation-induced mortality. The primary goal of this review is to characterize the various physiological strategies that allow different animals to survive starvation. The ancillary goals of this work are to identify areas in which investigations of starvation can be improved and to discuss recent advances and emerging directions in starvation research. The ubiquity of food limitation among animals, inconsistent terminology associated with starvation and fasting, and rationale for scientific investigations into starvation are discussed. Similarities and differences with regard to carbohydrate, lipid, and protein metabolism during starvation are also examined in a comparative context. Examples from the literature are used to underscore areas in which reporting and statistical practices, particularly those involved with starvation-induced changes in body composition and starvation-induced hypometabolism can be improved. The review concludes by highlighting several recent advances and promising research directions in starvation physiology. Because the hundreds of studies reviewed here vary so widely in their experimental designs and treatments, formal comparisons of starvation responses among studies and taxa are generally precluded; nevertheless, it is my aim to provide a starting point from which we may develop novel approaches, tools, and hypotheses to facilitate meaningful investigations into the physiology of starvation in animals.

Starvation physiology: reviewing the different strategies animals use to survive a common challenge.

The nutrition of animals involves procurement of food, digestion and absorption of component nutrients, metabolism and (or) assimilation of absorbed nutrients, and elimination of resulting waste products. Adequate nutrition is essential to an organism’s survival and reproductive success (i.e., fitness). Determining what constitutes adequate nutrition for free-living animals poses a challenge. An animal’s nutritional status depends on (1) its nutrient needs, (2) nutrient accessibility, and (3) the metabolic, physiological, morphological, and behavioral plasticity that the animal can invoke either to avert or to minimize discrepancies between demand and accessibility, or to resolve conflicting demands through the course of its annual or life cycle (e.g., adaptive anorexias; Mrosovsky and Sherry 1980). This chapter focuses on these three elements of the nutritional budgets of birds. An exhaustive review of the literature germane to this topic is neither practical nor possible. This chapter is intended only to provide an overview and some direction for future research. For the sake of brevity, reviews and recent reports have been preferentially cited here. Two sources of notable value, because of their scope and attention to avian nutrition, are Scott et al. (1982) and Robbins (1993).

Nutrition and Metabolism

Stable isotopes are increasingly used in animal ecology, but little attention has been paid to the underlying physiological processes accounting for changes in 15N/14N and 13C/12C ratios, for example, the influence of protein balance on δ15N values 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, ie, 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 enrichment was higher in tissues with high protein turnover rates (eg, plasma, 070‰) than in those with low turnover rates (eg, blood cells, 024‰) Fasting decreased the δ13C 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 (168‰), as indica

Nutrition, physiology, and stable isotopes: new information from fasting and molting penguins

The validity of the haematocrit or packed cell volume as an indicator of condition in wild birds has recently been questioned. We reviewed over 300 published papers on haematocrit values for wild birds. These studies show that changes in haematocrit could be caused by a number of different natural factors that include age, sex, geographical elevation, energy expenditure, parasitism, nutrition and genetics. Haematocrit also increased with age from hatching, due to increased erythropoiesis, so that adult birds generally have greater haematocrit values than nestlings or juveniles. Haematocrit values were either independent of elevation or increased with elevation. A meta-analysis of 36 studies showed no difference in haematocrit between the sexes. Relationships between haematocrit value and both energy expenditure and parasitic infection vary between studies. In temperate climates, haematocrit tended to be higher in winter than in summer, which may be due to dehydration or increased oxygen demand caused by thermogenesis, moult or acquisition of reproductive status. Our review indicates that the use of haematocrit as a sole indicator of condition or health could lead to incorrect conclusions if natural factors that can affect haematocrit are not taken into consideration.

Sources of variation in haematocrit in birds

Plasma protein electrophoresis is now commonly recognized to be a very reliable diagnostic tool in avian medicine. However, the influence of circannual phenomena such as molt on protein electrophoregrams is poorly documented. Yet, the molt is a period of heavy hormonal and metabolic change in birds. The purpose of this study was to investigate the effects of molt on total protein concentration and electrophoresis patterns in birds. Nineteen bar headed geese (Anser indicus) were blood sampled from mid May to mid August, at 15 day intervals. At the same time, the birds’ molting stage was checked. Total protein concentrations were measured and plasma agarose gel electrophoresis were performed on these samples. The geese were chosen as a model, because these birds molt over a very short period. The total protein concentration, albumin, alpha-2, beta and gamma fractions were at their minimum values during molt, whereas the prealbumin and alpha-1 fractions rose to their maximum levels. This study provides baseline information relevant to changes occurring in avian proteinograms throughout the molt. The increase in the prealbumin and alpha-1 fractions may be related to an increase in plasma thyroid hormones during molt. The decrease observed in albumin, alpha-2, beta and gamma fractions may be related to a protein and energy shift, directed towards feather growth, as well as to an expansion of the circulatory system located around the feather follicles. From a clinical point of view, the observed changes associated with molting were less significant than initially expected, and are not likely to be strong enough to mislead the practitioner.

http://www.afvpz.com/IMG/pdf/These_de_3o_cycle_Yannick_ROMAN.pdf

Juan C Carrillo

Papers

Metabolic responses of Buteo buteo to long-term fasting and refeeding

Hematocrit and blood chemistry values in captive raptors (Gyps Fulvus, Buteo Buteo, Milvus m ig Ra` s, Aquila Heliaca)