Catabolic capacity of the muscles of shorebird chicks: maturation of function in relation to body size

Newly hatched precocial chicks of arctic shorebirds are able to walk and regulate their body temperatures to a limited extent. Yet, they must also grow rapidly to achieve independence before the end of the short arctic growing season. A rapid growth rate may conflict with development of mature function, and because of the allometric scaling of thermal relationships, this trade-off might be resolved differently in large and small species. We assessed growth (mass) and functional maturity (catabolic enzyme activity) in leg and pectoral muscles of chicks aged 1-16 d and adults of two scolopacid shorebirds, the smaller dunlin (Calidris alpina: neonate mass 8 g, adult mass 50 g) and larger whimbrel (Numenius phaeopus; neonate mass 34 g, adult mass 380 g). Enzyme activity indicates maximum catabolic capacity, which is one aspect of the development of functional maturity of muscle. The growth rate-maturity hypothesis predicts that the development of catabolic capacity should be delayed in faster-growing muscle masses. Leg muscles of both species were a larger proportion of adult size at hatching and grew faster than pectoral muscles. Pectoral muscles grew more rapidly in the dunlin than in the whimbrel, whereas leg muscles grew more rapidly in the whimbrel. In both species and in both leg and pectoral muscles, enzyme activities generally increased with age, suggesting increasing functional maturity. Levels of citrate synthase activity were similar to those reported for other species, but l-3-hydroxyacyl-CoA-dehydrogenase and pyruvate kinase (PK) activities were comparatively high. Catabolic capacities of leg muscles were initially high compared to those of pectoral muscles, but with the exception of glycolytic (PK) capacities, these subsequently increased only modestly or even decreased as chicks grew. The earlier functional maturity of the more rapidly growing leg muscles, as well as the generally higher functional maturity in muscles of the more rapidly growing dunlin chicks, contradicts the growth rate-maturity function trade-off and suggests that birds have considerable latitude to modify this relationship. Whimbrel chicks, apparently, can rely on allometric scaling of power requirements for locomotion and the thermal inertia of their larger mass to reduce demands on their muscles, whereas dunlin chicks require muscles with higher metabolic capacity from an earlier age. Thus, larger and smaller species may adopt different strategies of growth and tissue maturation.     

Influence of body composition on the metabolic rate of nestling European shags (Phalacrocorax aristotelis)

During the early development of avian nestlings, their mass-specific resting metabolic rate (RMR) changes in a biphasic pattern with the peak value often being much higher than that expected for an adult bird of similar body mass. In the present study we examined the possible influence of variations in the size of internal organs in “setting” the high RMR and peak metabolic rate (PMR) during development in a large altricial species, the European shag (Phalacrocorax aristotelis). Thermoneutral RMR and cold-exposure induced PMR were measured in nestlings 15 days old, the age at which the highest RMR occurred during development. Body mass averaged 414 g. Mean values of RMR and PMR were 5.75 W and 9.08 W, respectively; the RMR value corresponds to approximately 250% of the expected value for an adult non-passerine bird of similar body mass. The masses of all the organs measured (breast and leg muscles, heart, liver, intestine, and kidney) varied isometrically with total body mass. However, large chicks had a significantly lower fractional water content than small chicks, suggesting that the former had achieved a higher level of functional maturity. In contrast to what has been suggested for adult birds in general, the heart and kidney masses of shag nestlings were not significantly correlated with the metabolic rates. The intestine length, in contrast, was highly and positively correlated with both the RMR and the PMR, i.e. intestine length was a better predictor of RMR and PMR than was total body mass. In addition, liver mass was positively correlated with RMR. The results of the present study suggest that the liver in particular may play a key role in establishing the high, mass-specific RMR which is attained during development in bird chicks. Our results also support previous suggestions that early in their development, altricial chicks mainly allocate energy to the growth of `energy-processing' organs (such as the intestine and liver) rather than to `energy-consuming' organs. Accepted: 3 March 1999     

Chick metabolic rate and growth in three species of albatross: a comparative study

The relative importance of genetic vs. environmental factors in determining the pattern of avian post-embryonic development is much debated. Previous cross-fostering of albatrosses suggested that although inter-specific variation in growth rate was determined primarily by differences in dietary energy content, species-specific constraints might have evolved that could limit maximal growth, even in chicks fed at similar rates and on similar diets. This study aimed to determine whether intrinsic differences in resting metabolic rate were apparent during the linear phase of growth in chicks of three species (black-browed, grey-headed and light-mantled sooty albatrosses). There was a gradual increase in absolute, and a reduction in mass-specific metabolic rate from 5.0 W kg(-1) during the earliest part of linear growth, to 3.5 W kg(-1) by the time chicks reached peak mass. These values are considerably higher than in resting adults of comparable or lower mass, presumably reflecting the large size and high metabolic demand of organs involved in rapid nutrient processing and tissue synthesis by chicks. The lack of any detectable inter-specific variation in the pattern of metabolic rate changes casts some doubt on the existence of fundamental differences in growth rate that cannot be attributed simply to differences in dietary energy or nutrient delivery rate.     

Growth and energy expenditure of Wandering Albatross Diomedea exulans chicks

Wandering Albatross Diomedea exulans chicks require 9–10 months to achieve adult body size at fledging, at which time they are also sexually size dimorphic. Because the developmental period spans the winter season, chicks must endure severe winter conditions and variability in provisioning effort by their parents. Thus chicks may adjust their rate of energy utilization to accommodate variations in provisioning, but this has not previously been studied. We followed longitudinally the changes in growth, body composition and oxygen consumption of 10 chicks from the end of the brooding period until fledging on the Crozet Islands. Body mass, culmen length and wing length were measured every 10 days and total body water (TBW) and resting metabolic rate (RMR) were measured monthly. Overall growth followed a logistic curve for all chicks, and sexual dimorphism in body mass appeared as early as the second month of measurements (males being heavier than females). Absolute TBW followed a logistic increase like that of body mass and was significantly higher in males owing to the difference in body mass. Conversely, mass-specific TBW (i.e. the proportion of body mass made up of water) did not differ significantly between male and female chicks. Absolute RMR peaked at 1.5 × adult basal metabolism in midwinter when chicks achieved maximum body mass, but decreased to adult levels by the time chicks fledged. The decrease in absolute RMR following attainment of peak mass is atypical of most seabird chicks (Procellariiformes) and may be explained partly by a reduction in size of the gut when parents reduce provisioning effort. The changes in mass-specific RMR did not differ between sexes but male chicks, being heavier, had higher absolute oxygen consumption and therefore greater energy requirements.     

Lipid reserves,fasting capability and the evolution of nestling obesity in procellariiform seabirds

Several alternative explanations have been proposed to account for the evolution of nestling obesity in a variety of avian groups. These predict quite different patterns of fat accumulation, storage and use by chicks of different ages. Yet surprisingly few studies have measured changes in body composition during chick development. We tested the applicability of these hypotheses for fulmars, Fulmarus glacialis, by direct measurement of changes in water, lipid and lean dry mass in growing chicks. Lipid and lean dry mass increased until ca. 70% of the way through chick rearing, but then levelled off. Total body water also increased until the same stage, but gradually declined thereafter, and it was this change rather than fat metabolism that resulted in mass recession. The observed pattern of a continued increase in stored lipid, and most importantly, its maintenance all the way through the mass-recession phase until chicks reach fledging, is incompatible with many of the proposed hypotheses. We suggest that the most likely ultimate explanation for large fat deposits is to fuel chicks during the initial critical period away from the nest site while they learn to forage     

The effect of egg size on post-hatching development in the Razorbill: an experimental study

A recent experimental study reported that Thick-billed Murre Uria lomvia chicks that hatched from large eggs grew their wing feathers more quickly than did small-egg chicks. There is little evidence of this (or any other) egg-size effect on post-hatching development in other birds. Thick-billed Murres are marine birds of the family Alcidae that employ the unique "intermediate" developmental strategy: chicks go to sea after 15-30 days at the nest site, at <30% of adult mass, accompanied by their male parent. Rapid feather growth during the brief nestling period is critical to enable chicks to make the transition from life at the nest site to life at sea quickly and safely. At the Gannet Islands, Labrador, Canada, in 1996 and 1997, I tested whether egg size has the same effect on wing-feather growth in the Razorbill Alca torda , another of the intermediate auks. To control for underlying correlations between egg size and other parental attributes, eggs were switched randomly among pairs. As in other birds, egg size strongly predicted hatchling mass, and to less extent hatchling size (tarsus length), but had no effect on the rate at which nestlings gained mass. However, egg size had the same effect on wing growth in Razorbills as in Thick-billed Murres: the wings of large-egg chicks began rapid, linear growth sooner, indicating that early development of wing feathers was enhanced in large-egg chicks. Differences in wing length established in this manner persisted through the nestling period. Egg-size effects on feather growth have not been detected in experimental studies on other birds, suggesting that effects of the magnitude seen in Razorbills and Thick-billed Murres might reflect evolutionary priorities in the post-hatching development of intermediate auks.     

Does growth rate determine the rate of metabolism in shorebird chicks living in the Arctic?

We measured resting and peak metabolic rates (RMR and PMR, respectively) during development of chicks of seven species of shorebirds: least sandpiper (Calidris minutilla; adult mass 20-22 g), dunlin (Calidris alpina; 56-62 g), lesser yellowlegs (Tringa flavipes; 88-92 g), short-billed dowitcher (Limnodromus griseus; 85-112 g), lesser golden plover (Pluvialis dominicana; 150-156 g), Hudsonian godwit (Limosa haemastica; 205-274 g), and whimbrel (Numenius phaeopus; 380 g). We tested two opposing hypotheses: the growth rate-maturity hypothesis, which posits that growth rate in chicks is inversely related to functional maturity of tissues, and the fast growth rate-high metabolism hypothesis, which suggests that rapid growth is possible only with a concomitant increase in either RMR or PMR. We have found no evidence that chicks of shorebirds with fast growth rates have lower RMRs or lower PMRs, as would be predicted by the growth rate-maturity hypothesis, but our data suggested that faster-growing chest muscles resulted in increased thermogenic capacity, consistent with the fast growth-high metabolism hypothesis. The development of homeothermy in smaller species is a consequence primarily of greater metabolic intensities of heat-generating tissues. The maximum temperature gradient between a chick's body and environment that can be maintained in the absence of a net radiative load increased rapidly with body mass during development and was highest in least sandpipers and lowest among godwits. Chicks of smaller species could maintain a greater temperature gradient at a particular body mass because of their higher mass-specific maximum metabolic rates.     

The growth of the skull and jaw muscles and its functional consequences in the New Zealand rabbit (Oryctolagus cuniculus)

Between weaning and adulthood, the length and height of the facial skull of the New Zealand rabbit (Oryctolagus cuniculus) double, whereas much less growth occurs in the width of the face and in the neurocranium. There is a five-fold increase in mass of the masticatory muscles, caused mainly by growth in cross-sectional area. The share of the superficial masseter in the total mass increases at the cost of the jaw openers. There are changes in the direction of the working lines of a few muscles. A 3-dimensional mechanical model was used to predict bite forces at different mandibular positions. It shows that young rabbits are able to generate large bite forces at a wider range of mandibular positions than adults and that the forces are directed more vertically. In young and adult animals, the masticatory muscles differ from each other with respect to the degree of gape at which optimum sarcomere length is reached. Consequently, bite force can be maintained over a range of gapes, larger than predicted on basis of individual length-tension curves. Despite the considerable changes in skull shape and concurrent changes in the jaw muscles, the direction of the resultant force of the closing muscles and its mechanical advantage remain stable during growth. Observed phenomena suggest that during development the possibilities for generation of large bite forces are increased at the cost of a restriction of the range of jaw excursion.     

Foraging and provisioning strategies of black-browed albatrosses in relation to the requirements of the chick: natural variation and experimental study

We studied regulation of the food supply to black-browed albatrosschicks at Kerguelen by simultaneously recording the provisioningrates achieved by individual parents and satellite trackingforaging birds during two seasons, by studying changes in adultmass, and by experimentally manipulating the food requirementof chicks. In 1994 black-browed albatrosses had a higher breedingsuccess and produced heavier chicks that grew faster than in1995. They spent a similar time foraging but brought heaviermeals to their chick in 1994. Satellite tracking indicated thatin both seasons birds foraged in the same oceanographic area,250 km from the colony. Travel times to and from this area remainedunchanged, and similar times were spent foraging there. In ourstudy area, black-browed albatrosses appear to rely on a foodresource that is predictable in location, but whose availabilityvaries from one year to the next. The principal difference betweenyears of differing food availability was that birds broughtlarger meals when food was more abundant Costs of commutingto nearby feeding areas are probably low and allow the deliveryof energy to the chick at a high rate. A study carried out in1991 indicated that there was no relationship between the changesin adult mass from one trip to the next and the duration offoraging trips or feed mass, suggesting that adult body conditionhad little influence on the provisioning strategy of this species.An experiment whereby some chicks were deprived of food andothers received supplementary food showed that parents of underfedchicks spent the same time foraging and brought slightly largeramounts of food to their chicks as control parents. We suggestthat parents are searching for food to the maximum limits oftheir ability and thus cannot reduce further foraging time,but underfed chicks can swallow more food. Parents of overfedchicks delivered less food and increased the time between feeds.The reduction in provisioning frequency is interpreted as thecapacity of parents to modify their foraging behavior accordingto the nutritional status of the chick, but the reduction offeed mass is probably the result of chicks being close to theirmaximum assimilatory capacity. Comparison between Procellariiformspecies indicates extensive differences in the degree to whichparents can regulate the supply of food to their chicks. Neriticspecies like black-browed albatrosses appear to have a reducedability to regulate, and especially to increase provisioningrates, whereas more pelagic species may have a greater regulationability     

Energetics of growth in semi-precocial shorebird chicks in a warm environment: the African black oystercatcher, Haematopus moquini

We studied prefledging growth, energy expenditure and time budgets of African Black Oystercatcher, Haematopus moquini, chicks on Robben Island, Western Cape, South Africa. The aim of the study was to investigate the effect of parental feeding on the growth and energetics of semi-precocial shorebird chicks. Chicks reached mean fledging mass, 463 g, in 40 days. The growth rate coefficient of African Black Oystercatcher chicks was 2% below the predicted value for a shorebird species of their body mass, but it was smaller than that of other precocial and semi-precocial shorebirds to date. Resting metabolic rate (RMR, measured through respirometry), daily metabolisable energy (DME), defined as daily energy expenditure (DEE, measured with doubly labelled water) plus energy deposited into tissue (E(tis)), and total metabolisable energy (TME) of African Black Oystercatcher chicks were similar to those expected for a species of their body size. DEE was not influenced by weather (ambient temperature, operative temperature and wind speed), therefore, variations in DEE may be explained by body mass alone. The relative RMR of the African Black Oystercatcher was greater, their TME was approximately the same, their average daily metabolisable energy (ADME) was less, and they spent less time foraging (short periods of parental feeding) and more time inactive than three precocial species in the Western Cape. Therefore, the semi-precocial mode of development of African Black Oystercatcher chicks reduced energy costs from thermoregulation and activity, and they were able to grow relatively faster than precocial, self-feeding shorebird species in similar climatic conditions. The growth rate coefficient of African Black Oystercatcher chicks was smaller than that of Eurasian Oystercatcher, Haematopus ostralegus, chicks, which may be a consequence of differences in body size and latitudinal effects.     

The effect of food restriction on morphological and metabolic development in two lines of growing Japanese quail chicks

To investigate whether there is a relationship between the inherent maximum growth rate of a chick and its degree of developmental plasticity, we studied the effects of food restriction on morphological and physiological development in P-line (selected for high growth rates) and C-line (nonselected) chicks of the Japanese quail between 2 and 64 d of age. In each line, three groups were created; one group in which the chicks were fed ad lib. and two other groups in which the chicks received 70% and 40% of the line-specific ad lib. feeding levels, respectively. In all three groups, chick survival rates were very high, and no relationship was detected between feeding level and chick mortality. The experimental feeding levels strongly affected the chicks' attainment of body mass at all ages. In addition, at most ages the growth of the structural components (wing, tarsus, and head) were also significantly affected by the feeding experiment but to a much smaller extent than the body mass. The feeding levels also affected the achievement of female sexual maturity such that, at the end of the experiment, most of the ad lib.-fed females and none of the females that received 40% of the ad lib. feeding level were laying eggs. In chicks of both lines that were fed ad lib., homeothermy was achieved at 7 d of age, but in chicks that received 40% of the line-specific ad lib. levels, homeothermy was achieved after 15-22 d of age. Poikilothermic chicks (P- and C-line) that were relatively heavy for their age exhibited relatively high resting metabolic rates (RMRs) and peak metabolic rates (PMRs) for their age. In addition, a positive relationship was found between the chicks' relative mass and RMR (based on mass-based predictive equations). No relationship was detected between the chicks' relative body mass and their relative PMR (relative to mass-based predictive equations). With respect to the metabolic scope (i.e., PMR-RMR), Japanese quail chicks exhibited remarkable developmental plasticity: chicks with body masses that were 50% lower than the normal growing chicks did exhibit a normal capacity of thermogenic heat production for their mass. Because no differences were found with respect to the level of plasticity of morphological and physiological development between the two strains, we conclude that the selection for high postnatal growth rates in P-strain chicks has not resulted in a in a higher vulnerability of these chicks to food restrictions.     

Variations in growth of Cape petrel Daption capense chicks

This study reports on the growth of Cape petrel chicks at Nelson Island, South Shetland Islands, Antarctica, during the breeding seasons 1990/91 and 1991/92. Parameters of logistic growth model fitted to mass, wing, culmen and tarsus measurements were compared between available composite data sets. Differential growth rate of morphometric characters and their proportional development at hatching and fledging conform to the pattern observed in other fulmarine petrels, overall growth rate being among the fastest found in Procellariiformes. Composite growth curves varied significantly between populations, but few annual, seasonal, and intercolony differences were found within the Nelson Island population. As the differences between chicks from equally disturbed colonies were less marked than in comparison with the control colony, regular handling most probably reduced the growth in this study. Larger eggs produced heavier rather than structurally larger hatchlings, which attained higher peak and fledging mass and size. Strength of the relationship between egg-size and chick measurements initially declined with chick age but, in contrast with results of earlier studies, increased again after around the middle of the chick-rearing period. This suggests that pre-hatching maternal factors probably influenced initial and fledging (peak) size and mass of chicks via egg-size, while intermediate stages of growth were less affected. A difference in mass between chicks from small and large eggs was maintained until fledging and increased gradually until peak mass was reached.     

A junk-food hypothesis for gannets feeding on fishery waste

Worldwide fisheries generate large volumes of fishery waste and it is often assumed that this additional food is beneficial to populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannets Morus capensis and of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fishes) is depleted and birds now feed extensively on fishery wastes. These are beneficial to non-breeding birds, which show reduced feeding effort and high survival. By contrast, breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fishes. Owing to a scarcity of this resource, they fail and most chicks die. Our study supports the junk-food hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery wastes on the growth patterns of gannet chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds and that an abundance of this artificial resource will automatically inflate their populations.     

Mechanisms promoting higher growth rate in arctic than in temperate shorebirds

We compared prefledging growth, energy expenditure, and time budgets in the arctic-breeding red knot (Calidris canutus) to those in temperate shorebirds, to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate. Growth rate of knot chicks was very high compared to other, mainly temperate, shorebirds of their size, but strongly correlated with weather-induced and seasonal variation in availability of invertebrate prey. Red knot chicks sought less parental brooding and foraged more at the same mass and temperature than chicks of three temperate shorebird species studied in The Netherlands. Fast growth and high muscular activity in the cold tundra environment led to high energy expenditure, as measured using doubly labelled water: total metabolised energy over the 18-day prefledging period was 89% above an allometric prediction, and among the highest values reported for birds. A comparative simulation model based on our observations and data for temperate shorebird chicks showed that several factors combine to enable red knots to meet these high energy requirements: (1) the greater cold-hardiness of red knot chicks increases time available for foraging; (2) their fast growth further shortens the period in which chicks depend on brooding; and (3) the 24-h daylight increases potential foraging time, though knots apparently did not make full use of this. These mechanisms buffer the loss of foraging time due to increased need for brooding at arctic temperatures, but not enough to satisfy the high energy requirements without invoking (4) a higher foraging intake rate as an explanation. Since surface-active arthropods were not more abundant in our arctic study site than in a temperate grassland, this may be due to easier detection or capture of prey in the tundra. The model also suggested that the cold-hardiness of red knot chicks is critical in allowing them sufficient feeding time during the first week of life. Chicks hatched just after the peak of prey abundance in mid-July, but their food requirements were maximal at older ages, when arthropods were already declining. Snow cover early in the season prevented a better temporal match between chick energy requirements and food availability, and this may enforce selection for rapid growth.     

Timing of fledging is influenced by glucocorticoid physiology in Laysan Albatross chicks

Fledging is a major life transition for birds, when juveniles move from the safety of a nest into an environment where they must find food and avoid predators. The timing of fledging within a season can have significant effects on future survival and breeding success. Proximate triggers of fledging are unknown: though wing development is likely a primary factor, other physiological changes, such as elevated plasma corticosterone (CORT), may affect fledging behavior. Laysan Albatross (Phoebastria immutabilis) chicks have an extended post−hatching period during which they reach 150% of adult mass. However, approaching fledging, chicks fast for days to weeks and lose mass while still putting energy into feather growth. We evaluated chick morphology and physiology to elucidate proximate triggers of fledging. As in some other species, CORT increased as chicks fasted and lost body mass. At the same time, corticosteroid binding globulin (CBG) declined, thus amplifying free CORT prior to fledging. Once chicks reached a morphological threshold, free CORT levels predicted how long they stayed at the colony: chicks with higher free CORT fledged sooner. To perturb the relationship between body condition, endocrine physiology, and fledging behavior, we supplementally fed chicks for the month before fledging. Fed birds had a slower decrease in body mass, slower decrease in CBG, slower increase in free CORT, and stayed at the colony longer after reaching a morphological threshold. Our study suggests that as chicks lose mass, free CORT acts as a signal of energetic or nutritional state to adjust the timing of fledging.     

Factors affecting chick growth in the South Polar Skua (Catharacta maccormicki): food supply, weather and hatching date

This study investigated chick growth in a pelagic Antarctic seabird, the South Polar Skua (Catharacta maccormicki). The factors food supply, weather and hatching date were analysed in a population of 54 breeding pairs at King George Island/South Shetland Islands. Food supply was manipulated by offering fish corresponding to 20% of daily energy demand of chicks to half of the breeding pairs every second day. Growth of mass, head, wing and tarsus was followed and related to the treatment, weather conditions, hatching date and interactive effects. Food supply did not limit chick growth in the studied season. Parents seemed to try to feed their chicks at a maximum rate and succeeded in the studied season because the general food supply was very good. Low temperatures and strong winds depressed chick growth. A growth advantage of food-supplemented chicks could be observed when the natural conditions for chick growth were sub-optimal. Chick growth rate was strongly negatively associated with hatching date and worsening weather during the reproductive season could be excluded as explanatory variable for this finding.     

Embryonic osmoregulation: consequences of high and low water loss during incubation of the chicken egg

The rates of water loss of domestic chicken eggs were varied during incubation to measure the osmoregulatory ability of the avian embryo. Egg water loss was increased by drilling holes in the eggshell over the airspace on day 13 (I = 21 days) and then placing these eggs in a low relative humidity (r.h.: 0-10%) incubator until hatch. Egg water loss was decreased by placing other eggs in a high-r.h. (85-90%) incubator on day 0. Eggs with low water loss (approximately 6% of initial fresh mass [IFM]) produced embryos and yolks that were not different in wet or dry mass when compared to control eggs that lost approximately 12% of IFM. However, 1-4 gm of excess albumen were left in low-water-loss eggs on day 21. Hatching success was 71% and 89% for low and control eggs, respectively. Low egg water loss did not appear to disturb embryonic growth. The allantoic fluid volume and millimolar allantoic Na+ and Cl- ions declined faster with high and slower with low rates of water loss. Thus, excess water was lost as a result of increased movement of water out of allantoic fluid, which was due to increased active transport of Na+ ions by the chorioallantoic membrane (CAM). Eggs with high water loss had elevated Cl- levels after day 17 in plasma and amniotic fluid, which indicated a period of osmotic stress after depletion of allantoic fluid between day 18 and hatch. The decrease in wet embryo mass measured in embryos from high-water-loss eggs was due principally to dehydration of skin. Embryonic skin may serve as an emergency water reservoir during osmotic stress. Dehydrated chicks produced from high-water-loss eggs were 6 gm less in wet mass at hatch compared to controls. However, these chicks regained the water deficit 7 days after hatch and grew at a rate not different from control chicks through 6 weeks of age. Total egg water loss of 12% of IFM results in highest hatching success. However, water losses between 6% and 20% of IFM do not appear to affect adversely the growth or water content of the chick. Water losses above 20% of IFM cause early depletion of allantoic fluid, prolong the period of osmotic stress, and result in subsequent dehydration of blood, amniotic fluid, and embryonic skin.(ABSTRACT TRUNCATED AT 400 WORDS)     

Sex-specific growth patterns and effects of hatching condition on growth in the reversed sexually size-dimorphic great skua Stercorarius skua

In many sexually size-dimorphic species of birds and mammals, the larger sex, often the males, show increased environmental sensitivity during ontogeny. This is generally assumed to be due to higher energy requirements, reflected in higher absolute growth rates of the larger sex. Poor early conditions often increase the sex differences in vulnerability. However, it is not clear whether these patterns are equally pervasive in species where females are larger, as males face an additional early disadvantage due to high levels of testosterone. We investigated sex-specific growth patterns of mass, tarsus and wing of the great skua Stercorarius skua , a seabird with reversed size dimorphism. We were particularly interested in sex-specific effects of early conditions on growth. Beside data from unmanipulated nests, we present results from an egg removal experiment, which caused chicks to hatch from smaller eggs and in poorer body condition. Half of the experimental chicks were raised by pairs in which mothers were in poor body condition. At the end of the nesting period, great skua chicks exhibited a comparable degree of size dimorphism as is found in adults, although neither sex had reached final adult size. Despite females reaching larger asymptotic values of mass and tarsus, timing of growth was not different between the sexes. Absolute growth was higher for females around the time of maximum growth, which suggests that daughters face higher energetic demands. We found sex-specific effects of poor early conditions on growth patterns, although not to the extent which we had predicted. Hatching in poor body condition was related to slowed growth in females but not males. However, our experimental manipulations had no additional negative effect on growth. Our results indicate that daughters in the great skua face higher demands during growth than sons, and that early conditions are more important for the development of the larger sex in this reversed dimorphic species.     

Seasonal changes in the provisioning behaviour and mass of male and female wandering albatrosses in relation to the growth of their chick

Procellariiform seabirds have a number of extreme life-history characteristics in common, in particular low reproductive rates and slow postnatal development, which are generally assumed to reflect the difficulty in acquiring energy in the marine environment. The wandering albatross (Diomedea exulans) is a sexually dimorphic species with the longest postnatal growth found in any bird, suggesting severe constraints on provisioning and possible sex-specific strategies of provisioning. We studied the provisioning behaviour and mass changes of male and female parent wandering albatross throughout the 9-months rearing period to examine how each sex adjusts its foraging effort in relation to the needs of the chicks and the seasonal changes in food availability. The study was carried out on the Crozet Islands, using an automated system recording continuously the attendance pattern of parents between March and December 1994. During the brooding period when energy requirements are highest, parents only perform trips of short duration to sea, and their body condition deteriorates. When the chick is old enough to be left alone, the parents mix short and long foraging trips. The proportion of short trips is very high until July, allowing high rate of food delivery and rapid growth, and at the same time the body condition of adults improves. From August this proportion declines until fledging in December. As a result, the feeding rate decreases from August and adult condition declines, suggesting that feeding conditions at sea are better during the first part of the chick-rearing period, i.e. in autumn and winter. Male parents perform more short trips of shorter duration and provide larger meals than females, delivering an estimated total after brooding of 110 kg of food, compared to 70–80 kg delivered by females. Meal size is inversely related to the body condition of male chicks but not to that of female chicks, suggesting that food delivery is regulated by the adults in response to the condition of the male chick. Male chicks received larger meals and more food every month than female chicks, and overall it was estimated that they receive, after brooding, 195 kg of food compared to 180 kg for the female. As a result, male chicks have a higher growth rate, attain a higher asymptotic mass, and are larger and heavier at fledging than female chicks. However, the differences are relatively small between the chicks of each sex and suggest that energy may be used differently between the sexes to maximise fitness. The results of the study suggest that provisioning effort of wandering albatrosses is adjusted by parents in relation to the availability of food, to the energetic needs of the chick and to the sex of the chick. The adult body mass is likely to play an important role in the long term for the regulation of provisioning, deficits in body mass probably providing the buffer in high power-requirement periods. Accepted: 20 March 2000     

Ontogenetic changes in enzyme activities associated with energy production in the spiny lobster, Jasus edwardsii

The larval life of the spiny lobster Jasus edwardsii is one of the longest and most complex of any marine organism and is poorly understood due to the difficulty of studying cryptic, pelagic organisms. Hence, the capacity for active swimming in the phyllosoma, puerulus and juvenile stages and the use of possible metabolic fuel reserves was inferred from a number of enzyme activities, including citrate synthase, lactate dehydrogenase, and HOAD. High activities of CS and LDH in abdominal tissues of Stage 11 phyllosoma and pueruli are consistent with a capacity to commence active on-shore movement. The activities of LDH and HOAD showed positive allometry while CS was independent of body mass. The body mass dependence of LDH activity may reflect the developing ability of the lobster to initiate brief escape manoeuvres, and the scaling of HOAD reflects an increased use of lipid fuel reserves. Aerobic enzyme activities were higher in abdominal tissues than in cephalic tissues of pelagic pueruli, but high activities appear in the cephalic tissues of juveniles. These changes mirror a developmental shift in activity from pelagic oceanic swimming to a benthic existence on the seabed of the near shore. The low LDH activity in pueruli confirmed previous findings that they have limited feeding capacity, with carbohydrate contributing little towards the major energy reserves. The highest LDH activities occur in the abdominal muscles of juveniles and correlate with rapid tail-flicking escape behaviour. The activities of HOAD increased throughout development, and in the abdominal tissues of juveniles, may reflect lipid transformation and accumulation as an energy reserve. Enzyme activities, therefore, provide useful information concerning migratory behaviour that is presently unavailable from ecological studies.