Mary E. Murphy

Energy and nutrient use during moult by White-crowned Sparrows Zonotrichia leucophrys gambelii

The apparent nutrient and energy costs of moult in Gambels Sparrows estimated from the materials deposited in the integument are relatively mild compared with the maintenance requirements (5.3% of BMR, and 45% of the minimum maintenance requirement for protein (MMRP)) and with those of reproduction (34% BMR and 165% MMRP), except perhaps for cystine. Measures of the actual costs of moult indicate that processes in addition to plumage synthesis combine to create daily energy costs for peak moult equaling 58% BMR. These processes include (1) recrudescence of the integument, (2) a cyclic osteoporosis, and (3) a large diel cycling in body protein content (as much as 8%). The main adjustments in nutritional requirements during moult are greater needs for protein to supply substrate and for energy. Also, the needs for iron for erythrocyte production (item 1 above) and for calcium for bone formation (item 2 above) presumably increase. Analyses of several food groups reveal that the energy and essential amino acid (EAA) needs for moult can likely be met by a wide variety of food types. When the total daily EAA needs of moulting birds are taken together the profile of the EAA demands is realigned so that the disproportionately high demand for cystine for keratin synthesis is obscured. Consequently, dietary protein can be used more efficiently for whole-body protein synthesis.

Sparrows increase their rates of tissue and whole-body protein synthesis during the annual molt

Abstract Avian molt is a period of adult growth involving mainly the deposition of keratins. The energy contained in newly synthesized plumage is small compared with the energy expended for molt, resulting in a low energetic efficiency for keratin deposition (as low as 3%). We measured the fractional synthesis rates (FSR) of tissue and whole-body protein in molting and non-molting sparrows using the “flooding dose” method to determine if part of the energetic cost of avian molt might be accounted for by an accelerated rate of whole-body protein turnover. Molting sparrows had significantly higher FSR of protein in liver, muscle, and whole-body (excluding the integument) throughtout the 24 hr cycle compared with values for non-molting sparrows. In absolute terms, molting sparrows synthesized daily 260 mg of body protein (excluding keratins) above that synthesized by non-molting sparrows. The daily increase in whole-body protein synthesis in molting birds equaled at least 3.5-fold the amount of protein synthesized and deposited as keratin per day (75 mg) during the most intensive phase of molt. This accelerated rate of whole-body protein synthesis undoubtedly contributes significantly to the energetic costs of molt.

Ptilochronology : a critical evaluation of assumptions and utility

ABsTRAcr.-Ptilochronology has been proposed as a method that will open up many new lines of investigation in nutritional ecology, in foraging behavior, and of life-history variables that are affected by (or affect) a birds nutritional status. The method depends on measurements of a series of daily growth bars to estimate a feathers growth rate, and thereby to quantitate a birds nutritional status while the feather was growing. The reliability of the method as proposed depends on the fulfillment of several previously unstated assumptions. We identified seven key assumptions and, in experiments with captive White-crowned Sparrows (Zonotrichia leucophrys gambelii), examined the likelihood that six of the assumptions could be fulfilled. The seventh assumption, no less crucial than the others, could not be tested empirically. None of the six tested assumptions were consistently fulfilled. Only lethal kinds or levels of nutritional privation consistently slowed feather growth. Moderate or even severe sublethal privation did not produce consistent effects on feather growth. In short, ptilochronology as originally conceived is fraught with uncertainty. It may yield reliable results in very limited, carefully controlled conditions, but this remains to be proved. Received 23 August 1990, accepted 20 December 1990.

Diurnal Changes in Tissue Glutathione and Protein Pools of Molting White-crowned Sparrows: The Influence of Photoperiod and Feeding Schedule

In molting birds keratin synthesis is intense and continuous through day and night. Keratins are much richer in cystine than are most tissue proteins. We hypothesized that glutathione (γ-glutamylcysteinylglycine) helps to sustain feather synthesis and spare bodyprotein during overnight fasting by serving as a cysteine reservoir. To test this hypothesis, we measured the responses of liver and muscle glutathione and protein pools to various feeding schedules (cysteine supply) andperiods of overnight fasting (cysteine demand) in molting white-crowned sparrows. Our main purpose was to ascertain whether these pools change passively or are instead regulated in relation to cysteine need in the postabsorptive state. During molt, significantly more liver glutathione and pectoralis protein were stored by day and utilized overnight than in postmolt. Liver glutathione and pectoralis protein were stored and utilized diurnally during molt in proportion to the duration of the overnight fast (12 h > 8 h > 4 h). Diurnal changes in these pools resulted from significantly larger evening pools, not from significantly smaller morning pools. Liver glutathione and pectoralis protein pools appeared to be specifically regulated to support the demands of overnight feather synthesis. In contrast, changes in liver protein pools during molt were smaller than in postmolt and were unrelated to the duration of the overnight fast. The sizes of liver protein pools in evening were nearly the same in molting and nonmolting birds. Similarly, the size of pectoralis glutathione pools in evening was nearly the same in molting and nonmolting birds, butpectoralis glutathione was utilized overnight in molt in relation to the duration of the overnight fast. Liver protein pools and possibly other tissue protein pools appeared to be spared by storage of glutathione in the liver. Pectoralis glutathione pools appeared to be passively emptied according to overnight cysteine demand. Overnight force-feeding of chick starter mash or serial injection of cysteine (im) attenuated overnight utilization of liver and muscle glutathione, indicating a specific role for GSH as a cysteine reservoir. The dynamics of tissue glutathione and protein pools during molt in relation to photoperiod may have important consequences for the energetic and amino acid costs of molt.

Amino acid composition of feather barbs and rachises in three species of pygoscelid penguins : nutritional implications

To evaluate the nutritional challenge faced by molting penguins we studied the composition of contour feathers of three species of penguins, Pygoscelis adeliae, P. antarctica, and P. papua. The feathers of these species are nearly identical in structure and chemical composition. They have a unique broad, flat rachis that accounts for 60 to 70% of the total feather mass. Their barbules are pennaceous and able to interlock tightly, which probably accounts for the shedding of plumage in sheets rather than as individual feathers. Compositionally, the penguin feathers are remarkably similar to feathers of other species of birds representing six different orders and varied life-styles. Whole penguin feathers averaged 8-10% water. Ash contents of P. adeliae and P. antarctica feathers averaged less than 1%, but P. papua averaged 2.6%. The nitrogen contents of the barbs were nearly identical in the three species and averaged 16.4%. The nitrogen content of the rachises of P. adeliae and P. antarctica feathers averaged 16.4%, but was slightly less in P. papua (15.5%), probably due to the higher ash content and slightly higher pigment content in this species. The most abundant amino acids in barbs and rachises were gly, pro, ser, cys/2, val, and leu. Six nonessential amino acids (ala, asp, glu, gly, pro, ser) made up 52.5 and 54.3% of the barbs and rachises, respectively. The basic amino acids (lys, his, arg) were among the least concentrated amino acids. This amino acid profile is typical of mixed feather keratins. The high cys/2 contents of feather proteins results in a large mismatch between nonkeratinous mixed tissue proteins and feathers that could result in highly inefficient reutilization of tissue amino acids in feather synthesis during the molt fast. Some compensatory mechanisms that penguins might use to minimize this inefficiency are discussed.

Dietary complementation by wild birds: Considerations for field studies

Free-living birds must satisfy fluctuating nutrient requirements in diverse and varying environments. Ingesting nutritionally complementary foods may be the most effective means by which wild birds match nutrient ingestion and nutrient needs. Dietary complementation may occur fortuitously when foods chosen in response to non-nutritive factors (e.g. competition, predation risk, food colour), or on the basis of energy density, also fulfill specific nutrient needs (passive dietary complementation). In some environments, especially during productive phases (e.g. reproduction), free-living birds may rely on nutrient appetites to ensure their choice of foods satisfies their nutrient needs (active dietary complementation). Meeting nutrient needs through dietary complementation can be facilitated, complicated, or impeded by any of several environmental or organism determinants of food choice. Nutrient appetites, exogenous food stores, and endogenous nutrient stores are three organismal determinants that are probably the most important in facilitating dietary complementation.

Dietary amino acid complementation as a foraging strategy for wild birds

Foraging birds finding foods containing protein of various quality could satisfy their amino acid needs by either 1) choosing only those foods that contain a suitable array of essential amino acids, or 2) choosing foods in amounts that permit complementation of constituent amino acids. We studied the abilities of sparrows (Zonotrichia leuchophrys gambelii) to use dietary amino acid complementation as a foraging strategy. We conducted two series of tests: 1) to determine if sparrows could select adequate portions from food pairs in order to compensate for reciprocal dietary deficiencies of either valine and lysine or lysine and threonine, and 2) to evaluate to what extent fortuitous (passive) complementation of dietary amino acids was constrained in sparrows by the magnitude of the dietary amino acid deficiency and the schedule of daily intakes of complementary foods. Small birds appear to have limited abilities to actively exploit dietary amino acid complementation. Birds offered a choice of two foods deficient in either lysine, valine, or threonine but of complementary compositions, reduced their daily intakes of food and body masses, but to a lesser extent (ca. one-half to one-third, and ca. one-quarter as much, respectively) than when either of the deficient foods were offered alone. Even passive complementation of dietary amino acids was severely constrained by both the magnitude of the dietary amino acid deficiency and the time course of feeding. The greater the amino acid deficiency, the less effective the complementation of dietary amino acids. The time course for effective and efficient complementation of dietary essential amino acids in these small, metabolically active animals was less than 2 h.

Sparrows discriminate between diets differing in valine or lysine concentrations.

White-crowned Sparrows (WCS) were given free access to pairs of semisynthetic diets that were either adequate or subadequate (25% of requirement) in valine or lysine. Within 2 to 4 days WCS chose a ratio of the paired diets that allowed them to maintain body mass or restore any losses quickly. On the initial choice days the birds transiently reduced total daily food intake (TDFI) roughly in proportion to their intake of the subadequate diet. The initial decrease of TDFI was greater and the latency in choosing an effective ratio of the paired diets was 2-3 days longer with valine than with lysine diets in well-nourished test birds. In malnourished birds fed only the subadequate test diet for 3 days, valine-deficient birds increased TDFI and body mass more promptly than did lysine-deficient birds when offered a choice of adequate and subadequate diets. The form of the test amino acid (CAA = crystalline, PB = protein-bound) had little effect on choice behavior, but sudden transfer of WCS from a PB acclimation diet to test diets with a large total CAA concentration increased the latency of effective choice by 2-3 days. A brief acclimation (2-3 days) to a CAA diet precludes any bias between nutritionally equivalent CAA and PB diets. The small differences in choice dynamics between valine and lysine and between dietary forms may help to identify mechanisms involved in food choice but are probably ecologically insignificant to free-living WCS. These birds are very adept at selecting diets that satisfy their amino acid requirements.

Diurnal variation in oxygen consumption by molting and nonmolting sparrows

Abstract To evaluate the effects of time of measurement on estimates of daily energetic costs of avian molt, oxygen (O 2 ) consumption was measured for molting and wintering sparrows ( Zonotrichia leucophrys gambelii ) at 6-hr intervals through the 24-hr cycle and continuously overnight for wintering sparrows exposed to long nights (9L:15D, 23°C). A significant diurnal cycle in O 2 consumption was evident in all birds. In molting birds (16L:8D, 23°C), O 2 consumption during midday was significantly higher than at all other times, and O 2 consumption towards the end of the night was higher than at its beginning. O 2 consumption by wintering birds was significantly higher towards the end of the night than during midnight and was typically higher towards the end of the night than during midday, though not always significantly so. Overnight, O 2 consumption by wintering birds (9L:15D) initially decreased, then remained stable, and finally increased towards the end of the night. Daily O 2 consumption was higher for molting birds than for wintering birds, but the increase in metabolism of molting birds compared with that of wintering birds varied through the diurnal cycle. Based on daily measures of O 2 consumption, peak energetic costs of molt in sparrows were estimated as 10.0 to 19.1 kJ/d.

Estimates of the mass of structures other than plumage produced during molt by white-crowned sparrows

Analysis of the caloric or nutritional demands of molt requires a thorough inventory of the mass and composition of all molted structures and of the ephemeral nonmolted structures (e.g., feather pulp) that accompany the process. Only plumage mass and composition are adequately known in a selection of species. We reported previously that the air-dried plumage mass of a 27-g White-crowned Sparrow (Zonotrichia leucophrys gambelii) is about 2,000 mg at the end of the postnuptial (PN) molt, during which about 400 mg of feather sheaths were grown and shed. In this report we show that the stratum corneum (air-dried mass = 88 mg) of captive Z. 1. gambelii is totally shed and replaced during the PN molt, and that the podotheca (19 mg, both legs) is molted about 10 weeks later, in November. The rhamphotheca is not shed during feather molt, but appears to be renewed continuously in response to wear of the tomia. It is unlikely that the molt of the podotheca is delayed because of nutritional stringency during the PN molt, since its mass is only about 1% of the combined mass of feathers, sheaths, and stratum corneum. Very little is known in other species about the renovation of corneous structures other than feathers. It is thought that skin, beak, and claws grow continuously in response to wear, and that the skin also molts totally during feather molt. In some species, claws and parts of the beak may also be shed episodically during or near the time of feather molt. The podotheca is probably shed annually in all species, often during feather molt but sometimes earlier or later.