Endogenous Reserves Research Articles

Body-mass Dynamics of King Eiders During Incubation

Several studies have demonstrated the importance of maintaining parental body reserves to successfully complete incubation or to raise offspring without affecting parental survival (e.g. Tombre and Erikstad 1996, Merila and Wiggins 1997, Zicus 1997). Restraint in use of reserves could be favored if females with greater reserves after laying had higher reproductive success or survival. Erikstad and Tveraa (1995) suggested that optimal clutch size in Common Eiders (Somateria mollissima) is determined by an interaction between allocation of endogenous reserves to egg production and energy needed for incubation and brood rearing. Depletion of reserves before hatching may lead to nest failure through nest abandonment or decreased nest attentiveness. Moreover, high nest attentiveness may reduce predation by reducing the amount of time that nests are unattended and by reducing incubation duration (Milne 1976, Aldrich and Raveling 1983). Nest failure during incubation, therefore, may be a consequence of nest abandonment or predation, either of which may be linked to female body condition. Gloutney and Clark (1991) found that female Mallards (Anas platyrhynchos) and Northern Shovelers (A. clypeata) that nested successfully were heavier than unsuccessful females, but this pattern was absent in Blue-winged Teal (A. discors). Canvasbacks (Aythya valisineria) and Redheads (Aythya americana) used stored reserves during egg production and incubation, but body mass during late incubation predicted nesting success only for yearling Canvasbacks (Arnold et al. 1995). Blums et al. (1997) investigated this hypothesis in a large sample of Common Pochards (Aythyaferina) and Tufted Ducks (A. fuligula); late-incubation body mass predicted nesting success in Tufted Ducks and adult Common Pochards, but not in yearling Common Pochards. Hence, whereas all three studies documented effects of body mass on nesting success, in at least some species and/or age groups, these effects did not apply. Because arctic-nesting species contend with colder temperatures and possibly lower food availability

Body size and age of recruitment in Snow Geese Anser c. caerulescens

'At what age to start breeding?' is a question fundamental to analysis of life histories. VVhile there has been considerable interest in the theoretical aspects of age of first breeding, comparatively little work has been done on the problems of estimating recruitment rates in wild populations. Most studies to date have relied on ad hoc methods that rely on one or more assumptions which may be generally untenable. Recently, it has been suggested that mark-recapture analysis can provide a robust, statistically formal approach for the analysis of recruitment, by using 'reverse capture-histories' to estimate the probability of entering the population over a given interval. We applied this approach to data from the arctic-breeding Lesser Snow Goose Anser c. caerulescens¸, using data from a long-term study in subarctic Canada. We tested the hypothesis that recruitment rate in this species was influenced by structural size. Since arcticnesting geese rely heavily on endogenous nutrient reserves for reproduction, structurally smaller birds may be less able to recruit at a young age than larger birds. However, despite significant long-term changes in body size, and significant annual variation in recruitment rate, we found no evidence of correspondence between the two.

Improving ecological fitness and environmental stress tolerance of the biocontrol yeast Candida sake by manipulation of intracellular sugar alcohol and sugar content

Candida sake was cultured on nutrient yeast dextrose broth, which was diluted and/or modified by the addition of either glycerol, glucose to 0.96 or trehalose to 0.97 water activity ( a w ) to modify endogenous sugar alcohol and sugar content. Sugar alcohols (glycerol, erythritol, arabitol and mannitol) and sugars (trehalose and glucose) were extracted from the yeast cells and quantified using HPLC. Total polyol and sugar content varied significantly between treatments. The total intracellular concentrations in NYDB medium were significantly increased in NYDB + glucose media. The major intracellular polyols/sugars in cells grown on unmodified NYDB were arabitol, trehalose and glucose with small amounts of glycerol and erythritol. This was changed by reducing a w of the growth medium, particularly with glucose or glycerol. The major polyols in C. sake cells grown on glucose-modified media were arabitol and the low mol wt polyol glycerol, with smaller amounts of glucose. In glycerol-amended full strength normal and diluted media, glycerol was the major intracellular polyol with lower amounts of the other polyols and sugars. The viability of the yeast cells with modified polyols/sugars was significantly improved at lowered a w level (0.935 and 0.95) when compared to unmodified yeast cells. Improvements in water stress tolerance was better in yeast cells grown for 48 than 24 h, especially in those from NYDB modified with either glucose, glycerol or trehalose. Such modifications of endogenous reserves were also shown to preserve or improve the biocontrol potential of the yeast against Penicillium expansum rot of apples. Thus physiological manipulation of intracellular polyol and sugar content may provide a means for developing biocontrol agents with improved ecological fitness in field environments.

Endogenous Reserves and the Collapse of the Exchange Rate Mechanism: A Stochastic Analysis

This work develops an alternative interpretation of the Exchange Rate Mechanism (ERM) Crises occurred in 1992. The model outlined in the paper assumes that the endogeneity of the reserves with respect to the deviation of the nominal exchange from the central parity exacerbates the size of the speculative attack. By considering a continuous-time stochastic velocity shock in the demand for money equation, it is possible to take into account the feedback effects from the exchange rate to the fundamental in the resulting model with saddle path dynamics. The main result in presence of an irreversible switch of regime is that the size of the attack is amplified. The issue of sustainability of the target zone increases as a time-varying realignment probability is considered in the basic stochastic system.

Ecophysiological responses of the biocontrol yeast Candida sake to water, temperature and pH stress

N. T EIXIDO ´, I. VINAS, J. USALL, V. SANCHIS AND N. MAGAN. 1998.The growth responses of the biocontrol agent Candida sake to changes in water activity (aw), temperature and pH and their interactions, and accumulation of sugars (glucose, trehalose) and sugar alcohols (glycerol, erythritol, arabitol and mannitol) were determined in vitro in nutrient yeast dextrose based media. The aw temperature profile for growth was between 0·995 and 0·90 and 4‐37 °C with the non-ionic solute glycerol, and between 0·995 and 0·92 and 10‐30 °C with the ionic solute NaCl. Regardless of solute, there was a longer lag time prior to growth as aw was reduced, and at marginal temperatures for growth. Relative growth rates were compared at different aw levels and temperatures and it was found that aw, temperature, solute and two and three‐way interactions were statistically significant. By contrast, C. sake was tolerant of a wide range of pH levels (3‐7) regardless of aw, although growth rates were reduced at marginal temperatures and aw. In non-stressed basal NYDB, glucose and arabitol were the predominant endogenous reserves accumulated in the cells of C. sake. However, when nutrient status was diluted (75%) and stressed by the addition of glycerol or NaCl (0·98 and 0·96 aw), significant changes in the accumulation of sugars and sugar alcohols occurred. In glycerol-stressed media, glucose and glycerol were the major compounds accumulated, with markedly lower arabitol and little trehalose or mannitol present. With NaCl-stressed media, glycerol was the only sugar alcohol accumulated, with very low levels of the sugars and other sugar alcohols. This study has defined the ecological niche within which C. sake would be active as a biocontrol agent for the first time and suggests that endogenous reserves can be significantly modified by nutrient and aw stress; these changes may be useful for improving environmental competence of such micro-organisms in the environment.

The fats of Escherichia coli during infancy and old age: regulation by global regulators, alarmones and lipid intermediates.

The fluidity and phase state of bacterial lipid bilayers commonly change in response to ambient environmental conditions to maintain the critical functions of the envelope as a semipermeable and selective boundary. A special, and intricate, set of alterations in membrane lipid metabolism is elicited by conditions causing growth arrest. Under such conditions, specific alterations in the membrane lipid-fatty acid composition are required for survival of the cell and, concurrently, the membrane lipids are suggested to serve as endogenous reserves providing carbon/energy for maintenance requirements. It appears that the global regulator FadR is required for both of these activities to be performed properly and that the FadR regulon is interconnected to the universal stress response of Escherichia coli. FadR, in conjunction with long-chain fatty acyl-CoA, long-chain acyl-ACP, ppGpp and cAMP, are key players in regulating the activities of enzymes and expression of genes involved in fatty acid and phospholipid metabolism in dividing and ageing E. coli cells.

Effect of Incubation Body Mass on Reproductive Success and Survival of Two European Diving Ducks: A Test of the Nutrient Limitation Hypothesis

The nutrient limitation hypothesis postulates that variation in nutrient reserves during egg laying and incubation are important predictors of future reproductive success of female waterfowl. We tested one component of this hypothesis in two European diving ducks, Common Pochard (Aythya ferina) and Tufted Duck (Aythya fuligula), relating body masses of incubating females to subsequent nest success, and to duckling and adult survival. We based our analyses on 3,224 Common Pochards and 1,812 Tufted Ducks captured and weighed during the last two weeks before ducklings hatched at Engure Marsh, Latvia, in 1978-1993. Adult (ASY) females from successful nests weighed significantly more than those from abandoned nests, but differences in body masses between two categories of nest fates were negligible for yearlings (SY). For both species, survival (measured as apparent return rate) of females (SY + ASY) was unrelated to their body masses. Duckling recruitment was independent of adult female body mass for both species, but yearling Common Pochards that provided recruits weighed more than those that produced none. Results of our study support the nutrient limitation hypothesis and we conclude that nutrient reserve levels may be important determinants of nest success in female ducks in general, especially for species that rely heavily on endogenous reserves during incubation.

Body condition, territory ownership and age‐related reproductive performance in Spruce Grouse Dendragapus canadensis hens

Adult Spruce Grouse Dendragapus canadensis hens show better reproductive performance (i.e. larger clutch size, earlier clutch initiation, higher frequency of renesting) than year‐lings. Body and breast muscle weights, condition indices and relative body composition were compared between adult and yearling birds from northeastern Ontario, Canada, to determine whether differences in endogenous reserves mobilized for egg production and (or) territory ownership could explain these differences in reproductive performance. Adults and yearlings showed similar declines in body‐weight, breast muscle weight and condition indices from the pre‐laying to the post‐laying period, but no significant interage differences emerged at any stage of the breeding season. Changes in body composition, especially gut structure, were similar in all birds; this result is consistent with a dietary shift in both age classes from a fibrous winter diet to more succulent foods in spring. Non‐territory‐holding (replacement) yearlings also had similar body‐weights and breast muscle weights and were in similar condition to territory holders (residents) in the pre‐laying period. My findings do not support the hypothesis that differences in body condition and territory occupancy can account for differences in age‐related reproductive performance in Spruce Grouse.

Optimizing nutritional conditions for the liquid culture production of effective fungal biological control agents

Spores of fungal pathogens of weeds and insects are unique in their ability to actively infect and kill their pest host. While these capabilities are advantageous in terms of their use as a contact biological control agent, or biopesticide, they also require special consideration during spore production. Directed approaches to medium optimization must consider not only spore yield but also spore qualities such as desiccation tolerance, stability as a dry preparation, and biocontrol efficacy. Nutritional conditions during culture growth and sporulation should direct the accumulation of appropriate endogenous reserves so that newly formed spores possess these advantageous qualities. Studies with the bioherbicidal fungus Colletotrichum truncatum and with the bioinsecticidal fungus Paecilomyces fumosoroseus have demonstrated the impact of nutrition on spore ‘fitness’ for use as a biological control agent. The optimization strategy used in these nutritional studies as well as a comparison of the results are presented.

Changes in Trumpeter Swan (Cygnus buccinator) Activities from Winter to Spring in the Greater Yellowstone Area

Trumpeter swans (Cygnus buccinator), in the winter, primarily, slept 42% of the time, fed 30%, swam 12%; and preened 7%. Comparisons of swan activities among die periods during the winter indicated they increased feeding throughout the day into night, when they fed at their highest rate. Swans spent more time sleeping as winter temperatures decreased; feeding mostly ceased when temperatures fell below approximately -17 C. Dominant activities in spring included feeding (45%), sleeping (17%), swimming (13%); and preening (12%). During spring, swans fed at a high rate throughout day and night, suggesting that spring use-areas may be important to swans depositing endogenous reserves before nesting.

Long-term foraging optimization in northern shovelers

In this paper I attempt to explain the seasonal foraging strategy employed by male northern shovelers ( Anas clypeata). Through the use of dynamic-optimization modeling I demonstrate that male shovelers are optimizing total foraging time over the entire summer by foraging heavily when resources (cladocerans) are abundant and utilizing endogenous reserves during times when resources are in short supply. Additionally, I construct predictive long-term models based on cladoceran dynamics and show that observed values for shoveler body mass and foraging dynamics agree with the models. Body masses of collected birds fit the predictions of the mixed (long-term I) model better than the long-term II model. However, both models underestimated total foraging time often by as much as 50% Long-term foraging optimization strategies apparently are more common in birds than previously thought and are determined by three ecological criteria: (1) degree of foraging specialization, (2) availability of preferred prey, and (3) physiological or behavioral constraints which allow for endogenous fat storage or exogenous caching of food items.

Yellow snow and red deer: Do urinary metabolites reflect anthropogenic influences?

:The effects of nutritional restriction on protein metabolism in non-supplemented alpine red deer (Cervus elaphus hippelaphus) were monitored during winter by snow-urine analysis. Forage was barely restricted in availability, but of low quality. Urinary urea:creatinine ratios (U:C) suggested that in non-supplemented red deer endogenous protein reserves were progressively depleted during the course of the winter and that the animals catabolized body protein to meet N demands already in early winter. However, potassium:creatinine ratios (K:C) reflected that the animals presumably satisfied energy demands by increasing intake. In a supplemented herd studied in comparison, urinary metabolites showed the same seasonal trend, despite constant and unlimited feed supply. Red deer are known to decrease activity, metabolic rate and voluntary feed intake in November or December as an adaptation to reduced forage quality and availability. However, U:C ratios, as an index of protein metabolism, showed a significant decline only in late January in both herds. Intensive hunting pressure may have caused energetically costly predator-avoidance strategies thus extending the period of tissue protein catabolism in non-supplemented red deer and the period of high feed protein intake in supplemented red deer.

Effects of Spring Environment on Nesting Phenology and Clutch Size of Black Brant

We studied the effects of timing of spring snowmelt on nesting phenology, nest site selection, and clutch size of Black Brant (Branta bernicla nigricans) breeding at the Tutakoke River colony, Yukon-Kuskokwim Delta, Alaska. In late springs, brant nested later; however, time between peak arrival at Tutakoke and nest initiation (6 to 12 days) was similar in early and late springs. Nest initiation was more synchronized in late springs than early springs. Height of nests relative to spring meltwater levels was lower in late springs than early springs, indicating that the interval between snowmelt and nest initiation was shorter. Reduced availability of nest sites and increased nesting synchrony in late years may result in greater competition for available nest sites and reduced site fidelity. Clutch size was greater in late springs than in early springs. This increase in clutch size may result from greater accumulation of endogenous reserves on spring staging areas in late springs, or from demographic changes in the breeding population.

Sources of Energy for Increased Metabolic Demand During Metamorphosis of the Abalone Haliotis rufescens (Mollusca).

Pelagic, lecithotrophic (nonfeeding) larvae of the red abalone (Haliotis rufescens) settle and subsequently metamorphose into benthic juveniles capable of feeding on particulate food. Thus, metamorphosis must be fueled by either endogenous reserves or a nonparticulate food source such as dissolved organic material (DOM) in seawater. The metabolic rates (measured as oxygen consumption) of abalone larvae were found to increase by an average of 3- to 5-fold from the larva to early juvenile stage. The total cost of development from embryo to juvenile measured for three cultures ranged from 41.6 mJ to 55.0 mJ. Meeting this cost would require 1.3 to 1.7 {mu}g of biomass (ash-free dry mass), which is similar to the initial biomass of the spawned oocyte at 1.36 +/- 0.04 {mu}g (mean of four cultures). However, there was no net loss of biomass during development from the oocyte to the juvenile. The uptake of alanine and glucose from seawater by larvae and juveniles could provide one-third of the organic material required to supply metabolism, even if the transporters were only operating at 20% of their maximum capacity throughout development. For larvae undergoing metamorphosis (between 6- and 9-days-old) the proportion of total metabolic demand supplied using aerobically catabolized biomass was only 39%. The higher metabolic rates of metamorphosis are met only in part by consuming stored endogenous reserves. Concomitant with an increase in mass-specific metabolic rate during metamorphosis, the maximal capacity (Jmax) for the transport of dissolved alanine from seawater increased 3-fold, from 61.2 +/- 1.9 (SE) to 182.0 +/- 49 pmol alanine individual-1 h-1. The majority (range: 61% to 100%) of the energy requirements of larval and early juvenile development of H. rufescens could be supplied by input of DOM from the environment. Measurements of transport rates of amino acids and sugars by these animals, and calculations of the energy input from these substrates, indicate that the cumulative transport of DOM from seawater during development to the early juvenile stage could supply an amount of energy equivalent to the initial maternal endowment of energy reserves to the oocyte of this lecithotrophic species.

Variation in Reproductive Effort in Female Zebra Finches (Taeniopygia guttata) in Relation to Nutrient-Specific Dietary Supplements during Egg Laying

Although dietary intake is thought to be more important than endogenous reserves for egg production in small, altricial birds (such as passerines), few experimental data are available to address this question. I investigated the reproductive responses of female zebra finches, Taeniopygia guttata, to enhanced dietary intake of macronutrients during the period of egg formation. Lipid supplementation had no effect on egg or clutch size. In contrast, proteino-supplemented females laid larger eggs (10%-12%) than controls, both immediately (i.e., first clutch) and in the longer term (second and third clutches up to 21 d after cessation of protein feeding). Interindividual egg size variation was maintained on the enhanced protein diet. The effect ofprotein on clutch size was equivocal, with some evidence for a longer-term increase in size of second (replacement) clutches 10-14 d after protein feeding. Increased egg size involved an increase in both yolk protein and albumen content but not yolk lipid content. These data suggest that zebra finches are protein limited during egg production. Body mass decreased 2.4 g (15% of initial mass) during the laying cycle in control and lipid-fed females but did not change significantly in protein-fed birds. These mass changes are consistent with the idea that females use stored, endogenous protein for egg production. However, mass loss was reduced or nonsignificant during laying of second (replacement) clutches with the same number and size of eggs. Mass loss during egg laying may thus have an alternate, more complex, and individually variable physiological basis rather than simply reflect a negative energy or nutrient balance.

Energetics of metamorphosis in bonefish (Albula sp.) leptocephali: Role of keratan sulfate glycosaminoglycan

Energy budget calculations, based on published values for changes in biochemical composition and oxygen consumption, have confirmed that metamorphosing bonefish (Albula sp.) larvae from the Gulf of California receive all of their metabolic energy requirements from the breakdown of endogenous reserves. The calculations showed that during metamorphosis, about 80% of the energy was supplied by lipid, and most of the remainder was provided by keratan sulfate glycosaminoglycan. These results support the suggestion that keratan sulfate can function as a storage polysaccharide, a novel function for glycosaminoglycans in vertebrates.

Bacterial defense against aging: role of the Escherichia coli ArcA regulator in gene expression, readjusted energy flux and survival during stasis.

Using two-dimensional gel electrophoresis and N-terminal amino acid sequencing analysis, we demonstrate that a mutant of the global regulatory protein ArcA fails to decrease the synthesis of the TCA cycle enzymes malate dehydrogenase, isocitrate dehydrogenase, lipoamide dehydrogenase E3 and succinate dehydrogenase in response to stasis, while the increased production of the glycolysis enzymes phosphoglycerate mutase and pyruvate kinase is unaffected. Microcalorimetric and respiratory measurements show that the continued production of TCA cycle enzymes in the (delta)arcA mutant is manifested as an elevated rate of respiration and total metabolic activity during starvation. The (delta)arcA mutant is severely impaired in surviving prolonged periods of exogenous carbon starvation, a phenotype that can be alleviated by overproducing the superoxide dismutase SodA. In addition, flow cytometry demonstrates that starving (delta)arcA mutant cells, in contrast to wild-type cells, fail to perform reductive division, remain large and contain multiple chromosomal copies. We suggest that the ArcA-dependent reduced production of electron donors and the decreased level and activity of the aerobic respiratory apparatus during growth arrest is an integral part of a defense system aimed at avoiding the damaging effects of oxygen radicals and controlling the rate of utilization of endogenous reserves.

Egg Size, Temperature and Laying Sequence: Why do Snow Geese Lay Big Eggs When it's Cold?

1. Several studies of altricial passerines ('income breeders') have shown that females lay smaller eggs when they experience low temperatures during egg formation. This is usually explained in terms of a 'physiological trade-off' : birds having to divert more of their finite resources to maintenance and away from reproduction in cold weather, although little is known about the proximate mechanism(s) underlying this phenomenon. 2. We investigated the relationship between egg size and ambient temperature during the egg formation period in the Lesser Snow Goose (Anser caerulescens caerulescens), a precocial, 'capital-breeding' species, using 10 years of data derived from a long-term population study of this species at La Perouse Bay, Man., Canada. 3. Egg size was negatively correlated with ambient temperature in the Snow Goose, i.e. females laid larger eggs when temperatures were lower during egg formation, contrasting markedly with the positive correlation reported in altricial, income-breeders. 4. The effect of temperature on egg size was most marked for last-laid eggs within a clutch (b = -0.675 g °C -1 ), and for temperatures during the last half of the rapid yolk development (RYD) period (rather than for the whole or the middle of the RYD period), as predicted by an exponential growth curve for yolk development. 5. The relationship between egg mass and temperature was time- and laying-sequence specific : for first and middle eggs the correlation was positive early in the period of RYD and negative closer to ovulation. For last-laid eggs the correlation between egg mass and temperature was negative throughout the 10 day RYD period. 6. We suggest that the different relationship between egg size and temperature in the Snow Goose, compared to passerine species, may reflect different contributions of exogenous vs endogenous reserves, and different opportunities to increase energy availability through dietary intake. 7. Although statistically significant, temperature has only a small effect on egg size in the Lesser Snow Goose : the average range of temperatures encountered would only lead to a 3-5% difference in mean egg mass. This is consistent with high heritability of egg size.

Energetics of reproduction in female and male greater snow geese.

Arctic-nesting geese are classified as "capital" breeders (i.e., birds that rely largely on endogenous reserves to meet the high nutrient requirement of clutch formation) as opposed to "income" breeders (those that rely directly on ingested food). However, some evidence has suggested that energy reserves of greater snow geese (Chen caerulescens atlantica) are not sufficient to meet these costs. We tested whether greater snow geese were capital breeders and examined the consequences on their reproductive strategy. We collected 48 females and 47 males from arrival at the breeding colony on Bylot Island (NWT) to the postlaying stage, and determined fat and protein content in somatic and reproductive tissues. Rapid follicular growth was initiated only after arrival on the breeding ground. Somatic fat of females tended to increase during the prelaying and laying stages at the same time that most of the fat was deposited in developing follicles. Decrease in somatic fat in postlaying females was mostly related to its use for meeting metabolic requirements during early incubation. Hence, almost all fat invested in the clutch came from food intake, not endogenous reserves. Somatic protein was maintained during prelaying but decreased during laying, suggesting that some protein reserves were deposited in the eggs. There was no relationship between somatic fat and the number of developing follicles (incubating females excluded) but a relationship was found with somatic protein. Clutch size was not related to body size. In males, somatic fat, which was similar to females at arrival, was almost completely depleted by the postlaying stage. Male somatic protein remained stable. Male somatic reserves were not related to the somatic reserves, clutch size or nutrient investment in reproduction of their mate. We conclude that, in female greater snow geese, little fat reserves (if any) were used for egg formation though some protein reserves were used, whereas males relied heavily on their fat reserves during the same period. This is probably a consequence of the long and costly migration between the last staging area and the breeding grounds.

Reconstructing Avian Diets Using Stable-Carbon and Nitrogen Isotope Analysis of Egg Components: Patterns of Isotopic Fractionation and Turnover

Because eggs are composed of nutrients that are ultimately derived from the diet of adult females, the relative abundance of naturally-occurring stable isotopes of carbon and nitrogen in eggs should be related to those in their diet and this may form the basis of a method for tracing diets. Before such dietary reconstructions can be established, however, it is necessary to know how isotopic signatures change (or fractionate) from the diet during the synthesis of various egg components. In this study, stable-carbon and nitrogen isotopic fractionation factors between diet and whole yolk, lipid-removed yolk, albumen, and shell membranes of eggs of captively-raised Mallards (Anas platyrhynchos), Japanese Quail (Coturnix japonica), Prairie Falcons (Falco mexicanus), Peregrine Falcons (Falco peregrinus), and Gyrfalcons (Falco rusticolis) were established. In addition, carbon isotope fractionation patterns between diet and eggshell carbonate and yolk lipid were determined for quail, Mallards and falcons. On average, yolk, albumen and membranes were enriched in 15 N relative to diet for all birds by 3.4‰, a value typical of processes associated with protein synthesis. For quail and Mallards, albumen, membranes, and shell carbonate were enriched in 13 C relative to diet by 1.5, 3.6, and 14.9‰, respectively, and whole yolk was depleted in 13 C by 2.6‰ due to the presence of yolk lipids. Falcons showed lower carbon diet-tissue fractionation for all tissues (albumen: +0.9, whole yolk: -1.9, membranes: +2.7, carbonate: +11.2‰) and this may be due to a greater reliance on dietary lipids vs. carbohydrates for the synthesis of egg components or on fractionation differences associated with fermentation of carbohydrates. Patterns of isotopic fractionation between diet and Mallard eggs were not influenced by clutch order. A diet-switch experiment using quail indicated that albumen, shell membrane and shell carbonate values reflect diet integrated over 3-5 days and yolk over eight days prior to laying. Because birds were fed ad libitum, these data provide baseline data on fractionation patterns for birds optimally mobilizing nutrients from diet to egg components. These values may differ for those wild birds that rely more heavily on endogenous reserves.