Large Chicks Research Articles

Storlommens Gavia arctica häckningsframgång innanför och utanför fågelskyddsområden i sjöarna Fegen och Sottern

We compared the breeding success of Black-throated Divers Gavia arctica inside and outside bird sanctuaries with restricted public access during the incubation period in Lake Fegen-Svansjöarna and Lake Sottern, South Sweden. Both lakes held populations of approximately 15–20 pairs. At Fegen-Svansjöarna, average breeding success was 0.51 large chicks per pair and year inside and 0.27 outside the sanctuaries (field surveys in 1983—1984 and 1997—2000). The difference was not statistically significant, however, and in two out of the six study years breeding success was higher outside the bird sanctuaries. At Sottern, breeding success was 0.39 and 0.25 large chicks per pair and year inside and outside the bird sanctuary, but breeding success was higher inside the sanctuary only in four out of nine years, 1997—2005. The results from the two lakes together indicated an overall positive effect (P = 0.08). We recommend keeping a constant water-level during incubation to be the primary measure to enhance breeding success. Sanctuaries with limited access may be an additional benefit at lakes highly frequented for out-door recreation.

The Diet of the Glossy Ibis During the Breeding Season in Doñana, Southwest Spain

We present the first detailed study of the diet of Glossy Ibis (Plegadis falcinellus) in Europe, from an expanding breeding colony in Doñana, southwest Spain. In 2000, fecal samples, mainly from adults, were collected from 15 nests. In 2001, 36 regurgitates were collected, mainly from large chicks. Fecal contents were dominated by aquatic beetles (Coleoptera) and dragonfly (Odonata) larvae, which were present in 100% and 93% of samples respectively. Regurgitates contained mainly aquatic beetles (41% by aggregate percent, mainly Cybister spp.), dragonfly larvae (29%, mainly Sympetrum fonscolombei, Aeshna mixta and Anax imperator), Sharp-ribbed Salamanders (Pleurodeles waltl, 12%) and Carp (Cyprinus carpio, 7%). The absence of vertebrate and other hard remains from feces was presumably due to their excretion in pellets. Thus fecal analysis is not a suitable method to investigate the food of the Glossy Ibis. The results suggest that there may be no major difference in the diet of breeding adults and their chicks, and that the recent increase in numbers of this ibis in Doñana is not explained by the abundance of introduced Red-swamp Crayfish (Procambarus clarkii) in the breeding area.

Brood sex ratio in the Kentish plover

How and why do the mating opportunities of males and females differ in natural population of animals? Previously we showed that females have higher mating opportunities than males in the Kentish plover Charadrius alexandrinus. Both parents incubate the eggs, and males provide more brood care than females; thus it is not obvious why the females find new mates sooner than the males. In this study we investigated whether the sex-biased mating opportunities stem from biased offspring sex ratios. We determined the sex of newly hatched, precocial chicks using CHD gene markers. Among fully sexed broods, 0.461 6 0.024 (SE) of chicks (454 chicks in 158 broods) were male, and this sex ratio was not significantly different from unity. The proportion of males at hatching decreased significantly over the breeding season, which occurred consistently in all 3 years of the study. Large chicks were more likely to be males than females. Neither parental age nor body size of male and female parents was related to brood sex ratio. We also sexed a number of chicks that were caught after they left their nest (range of estimated ages 0–17 days) and found that the proportion of males increased with brood age. This relationship remained highly significant when controlling statistically for hatching date. As brood size decreased due to mortality after the chicks left their nest, these results suggest that the mortality of daughters was higher than that of the sons shortly after hatching. Taken together, our results show that the female-biased mating opportunities in the Kentish plover are not due to biased brood sex ratio at hatching but, at least in part, are due to female-biased chick mortality soon after hatching. Key words: Charadrius alexandrinus, Kentish plover, mating opportunities, parental care, seasonal trends, sex allocation, sex ratio. [Behav Ecol 15:58–62 (2004)]

Heavier chicks at hatch improves marketing body weight by enhancing skeletal muscle growth

This study examined some of the factors connected with the greater marketing weight observed in chicks hatching with higher BW. Examination of chicks hatching from maternal flocks of different ages indicated that BW at hatch increased quadratically and yolk sac weight linearly with age, whereas components of the gastrointestinal tract showed no significant trend. Growth of pectoralis muscles and gastrointestinal tract were compared in chicks hatching at the same weight from maternal flocks of 28 and 64 wk of age and in chicks from the same maternal flock (44 wk old) hatching at different weights. The results indicated that no differences were found among chicks hatching with the same weight from maternal flocks of different ages. In contrast, in chicks from the same maternal flock hatching at different weights the gastrointestinal tract tended to compose a smaller proportion of BW in large chicks, and its growth was not correlated with performance. Liver proportions were greater in heavier chicks. Pectoralis growth and satellite cell numbers and activity were greater in heavier chicks through 5 d posthatch, and pectoralis muscles were heavier at marketing. Examination of some of the growth factors involved suggested that in heavier chicks satellite cells underwent higher proliferation and earlier differentiation during their critical period of activity in the immediate posthatch days. To determine when these differences in activity were established, examination of 15-d embryonic myoblast activity indicated that at this stage activity was already greater in the heavier eggs. This finding suggests that programming of muscle growth may be completed in late embryonic stages. This study suggests that enhanced satellite cell activity is involved in increased growth of chicks hatching with higher BW.

Demography and conservation of the Tristan albatross Diomedea [exulans] dabbenena

The Tristan albatross Diomedea [exulans] dabbenena is the third rarest albatross species, with a breeding population of around 1500 pairs almost totally restricted to Gough Island in the Tristan da Cunha group, central South Atlantic. During January 2000, the entire breeding population of Gough was surveyed for the first time since 1956, and 2400 incubating pairs were counted. An analysis of the areas that are likely to have been surveyed most accurately in the past suggests that the population has decreased by around 28% over 46 years. The number of large chicks counted over three successive seasons (1999–2001) was highly variable (range 318–1129). The average count over this period (705 chicks) is less than counts made in 1979 (792) and 1982 (798). A total of 656 chicks were counted in September 2001, giving an island breeding success of just 27.3%. However, breeding success varied considerably in different areas of the island, ranging from 17.6 to 68.0%. During the 2001 season most breeding failures were of large chicks, and over 4 years where data were available, 75% of breeding failures occurred during the chick period. Predation by introduced house mice Mus musculus is the most likely cause of chick mortality. In a small study population, birds began breeding at an average age of 9.7 years and annual adult survival from 1985 to 2001 was 92.6% (SE=1.6%). Both breeding success and adult survival estimates are low in comparison with other Diomedea species and population modelling predicts a population decreasing at an annual rate of 2.9–5.3%. Further research is needed urgently to assess whether breeding success is typical, and to confirm that mouse predation is the cause of chick mortality. The low productivity of this species will compound the negative impacts of longline fishing mortality, which are likely to be reducing adult and juvenile survival.

Reproductive Success of Shiny Cowbird (Molothrus Bonariensis) Parasitizing the Larger Brown-and-Yellow Marshbird (Pseudoleistes Virescens) in Argentina

Abstract Shiny Cowbirds (Molothrus bonariensis) often parasitize larger hosts. It has been proposed that larger hosts are preferred by that parasite because they provide higher reproductive success, but available data are quite variable. We studied the reproductive success of Shiny Cowbirds in nests of Brown-and-yellow Marshbirds (Pseudoleistes virescens), a larger and often multiply parasitized host. To estimate the extent of interspecific competition, we compared the hatching success of parasite eggs in nests with and without reduction of the clutch size of the host as a result of egg punctures inflicted by the parasite, and the survival and growth of parasite chicks reared with and without host chicks. To estimate the extent of intraspecific competition, we compared Shiny Cowbird egg losses, hatching success, and chick survival in singly versus multiply parasitized nests. Reproductive success of Shiny Cowbirds was 8% with depredation causing 80% of losses. Clutch reduction due to egg punctures were higher in multiply than in singly parasitized nests, but it did not improve hatching success of parasite eggs. Neither survival nor growth of parasite chicks was affected by the presence of host chicks. Shiny Cowbird hatching success and chick survival did not differ between singly and multiply parasitized nests. Parasite chicks were smaller than same-age Brown-and-yellow Marshbird chicks. However, because parasite chicks hatched one or two days before host chicks and had a higher growth rate, they were the larger chicks in the nest. Overall Shiny Cowbird reproductive success in Brown-and-yellow Marshbird nests was apparently higher than that reported in other smaller or similar-sized hosts. We think that host life-history traits like large clutch size, a longer incubation period, and slower growth rate of chicks are responsible for the high reproductive success of Shiny Cowbirds with Brown-and-yellow Marshbirds.

Use of the Nest Site as a Rendezvous in Penguins

For most birds, it is difficult to study what life would be like without nest sites. In penguins, however, nesting and non-nesting species can be compared. We contrasted the King Penguin (Aptenodytes patagonicus), which has no nest and carries its chick on its feet, with the Macaroni Penguin (Eudyptes chrysolophus), which has a nest similar to other birds. We investigated the use of the nest site when it ceased to be necessary, that is, after chick emancipation during the crèche period. When adults return to their crowded colony from foraging at sea, both penguin species exhibit individual recognition between parents and chicks via calls. Observations were made on how parents find and feed large chicks. We examined whether the use of the empty nest as a geographical meeting place was advantageous to Macaroni Penguin parents looking for their chicks, and whether the more sophisticated recognition of calls aided King Penguin parents in searching for their chicks. Macaroni Penguin parents found their chicks in about half a minute, giving two or three calls to bring chicks to the site of their previous nest. In contrast, King Penguin parents took longer (about three minutes) to find their chicks, and gave four or five calls to attract chicks. In addition, about a quarter of King Penguin parents had to walk an average of 11-12 m through the crèche in order to find a chick to feed. For Macaroni chicks and their parents, the nest was used as a “rendezvous” location that facilitated reunion.

Feeding experience and relative size modify the begging strategies of nestlings

The offspring of birds and mammals use a combination of movements and vocalizations, known as begging, to solicit food from their parents. A widespread interpretation of begging is that it constitutes an honest signal of offspring need. But we know that in the house sparrow (Passer domesticus) the intensity of begging calls reflects the past experience of offspring in addition to their need. Here we show that this result generalizes to other species. An experiment with hand-reared magpies (Pica pica) and great spotted cuckoos (Clamator glandarius) indicates that the begging strategies depend on the past experience of chicks and the composition of their brood. In asynchronous two-magpie broods, both chicks begged at the same intensity when the large chick obtained food more easily than its sibling, but the large chick begged at higher intensity when it was easier for the smaller chick to obtain food. Cuckoo chicks begged at higher intensity than magpies.

Early social influence on nestling development in Waldrapp ibis (Geronticus eremita)

AbstractThe Waldrapp ibis is critically endangered; hence specific knowledge is needed to support the management of the last birds in the wild, and to prepare for reintroduction projects. In this study we attempted to test the effects of raising an ibis as a single chick from hatching to the age of 3 weeks, as compared to raising it together with nestmates, on development and juvenile socialization. In times of food shortage, interference competition between nestlings may cause quick starvation of all but the largest chick. In the context of establishing a free‐flying, semi‐tame colony of Waldrapp ibis at the Konrad Lorenz Research Station in Grünau, Austria, 12 zoo‐bred hatchlings were experimentally hand‐raised under ad libitum food conditions. Seven individuals were placed into three nests in visual and acoustical contact with each other to mimic a colony situation. Five others were raised in isolation their first 21 days after hatching and then were united with the sibling‐raised individuals in a colony‐like situation. After hatching, isolated chicks showed high frequencies of distress calls; they begged and ate less, put on less weight, and were less active than the socially‐housed chicks, and fledged an average of 6 days later. As the groups did not significantly differ in excreted corticosterone metabolites, we assume that the lack of social stimulation, rather than stress, caused the observed effects in the single‐raised chicks. After unification, individuals of both groups tended to stay apart from each other. Formerly single‐housed birds mainly interacted dyadically among themselves, whereas the sibling‐raised birds tended to have more varied contacts with colony members of different ages. The potential applications of these results to conservation and management are discussed. Zoo Biol 21:467–480, 2002. © 2002 Wiley‐Liss, Inc.

Kinetics, dose‐response, excretion, and toxicity of methylmercury in free‐living Cory's shearwater chicks

Methylmercury (MHg) kinetics, dose-response, excretion, and toxicity were experimentally evaluated and compared between small (one to two weeks old) and large (six to seven weeks old), free-living Cory's shearwater chicks. The half-time for the terminal elimination phase of MHg in blood (5.7 d) and the average percentage of ingested MHg deposited in the blood volume (12%) were independent of the age at exposure. Therefore, these data were employed to derive a relationship between steady-state blood concentrations and dietary intake of MHg in bird chicks. Plumage:blood ratios were independent of dose and could be used as partition coefficients. Dose-response relationships in plumage and blood were linear over the wide range of exposures employed. Blood dose-responses of MHg in small and large chicks were similar. Excretion percentages into the final plumage varied between 42 and 60% of intake. The body condition of experimental chicks did not indicate sublethal toxicity of the doses administered; hence, the exposure levels provide maximum avian no-observed-adverse-effect levels for external symptoms in wild seabird chicks.

Determining food requirements in marine top predators: a comparison of three independent techniques in Great Cormorants,Phalacrocorax carbocarbo

Assessment of food requirements is a key feature in the evaluation of the ecological status of the marine megafauna. However, this remains technically difficult because prey intake by marine top predators occurs mainly under water, out of sight. In this paper, we compare three independent methods currently available for use in quantitative dietary studies: (1) time-energy budget; (2) stomach-temperature measurements; and (3) automatic weighing. To this end, concurrent measurements were performed on Great Cormorants (Phalacrocorax carbo carbo) breeding in Normandy. According to the time-energy budget method, breeding males required 690 g of fish while incubating, 1050 g when rearing small chicks, and 1350 g when rearing large chicks; corresponding values for breeding females were 500, 760, and 970 g. These measurements are similar to estimates derived from automatic weighing data, which gave a mean food intake of 540 and 390 g for incubating males and females, 1150 and 830 g for those tending small chicks, and 1410 and 1010 g for those tending large ones, respectively. Stomach-temperature measurements, which can only be performed for birds raising small chicks, were lower (640 g fish in males and 450 g in females) than those obtained using the other two methods. We compare these results with former estimates obtained at the same study site and for other Great Cormorant subspecies and discuss the relative accuracies of the three techniques. Finally, we stress that better assessment of the ecological status of marine top predators requires further technical improvements and additional investigations outside of the reproductive phase.

Behavioral Domination of Food Delivery by Tree Swallow Nestlings

In altricial birds, scramble competition for favorable feeding positions in the nest may cause younger chicks to starve. We studied nestling survival in a population of Tree Swallows (Tachycineta bicolor) breeding in nestboxes near Seattle, Washington, in a year of bad weather. Only a mean of 0.5 chicks fledged per nest (range 0–2, 22 nests). Nestling mortality appeared to be caused by starvation. Video filming showed that when chicks were old enough (largest chick within the brood had reached a wing length of about 55–60 mm), they spent much time in the nestbox opening, calling loudly. This behavior seemed to be driven by hunger because it occurred mainly in broods where chicks had low body masses. Parents fed the chick in the opening and did not try to push it back into the nest cavity or go around it. We suspect that blocking of the nestbox opening accelerated mortality of other young in the nest. Such behavior by dominant chicks may be more readily achieved in hole nesting birds with narrow entrances to their nest site than by open nesting birds.

Factors affecting ostrich egg hatchability

Ostrich eggs often have low hatchability (HATCH) rates because they do not lose sufficient weight during incubation. Because egg size, eggshell porosity and thickness (THICK), and length of preincubation egg storage are known to affect egg weight loss during incubation (EWL) and HATCH of chicken eggs, these factors were examined using ostrich eggs. The effects of eggshell porosity (number of large pores per cm2 of shell; LP); and THICK on EWL and HATCH were assessed by categorizing the eggs as having either low, intermediate, or high LP or low, intermediate, or high THICK. Mean EWL was higher (P<0.05) in eggs of the high LP group when compared with eggs in either the low or intermediate LP groups that lost similar amounts of weight during incubation. Mean HATCH was also higher (more than 25%; P<0.10) in eggs with high LP when compared with the HATCH found in eggs having low LP. Eggs from the intermediate LP group had an intermediate HATCH response. Moreover, numbers of LP were positively correlated to both EWL (r2 = 0.64; P<0.0001) and HATCH (r2 = 0.25; P<0.03). Inverse relationships existed between THICK and EWL and between THICK and HATCH according to the order (P< 0.05): eggs of low THICK, highest mean EWL and HATCH > eggs of intermediate THICK, intermediate mean EWL and HATCH > eggs of highest THICK, lowest mean EWL and HATCH. Shell thickness was not correlated to either EWL or HATCH. The influence of egg size on mean LP, THICK, EWL, HATCH, and chick weight (CWT) was assessed. Although THICK was unaffected by egg size, higher LP (P<0.10), EWL (P<0.05), and HATCH (P<0.10) were found in medium-sized eggs when compared with either small or large eggs. The CWT was associated with egg size (P<0.05) according to the order: large eggs, highest CWT > medium eggs, intermediate CWT > small eggs, lowest CWT. Neither EWL nor HATCH was affected by length of preincubation egg storage. Collectively, our findings suggest that 1) ostrich eggs that possess low LP and increased THICK hatched poorly, 2) intermediate-sized eggs hatch best, 3) large eggs produced large chicks, and 4) ostrich eggs can be stored under conditions typically used in the poultry industry for a minimum of 10 d without negatively impacting HATCH.

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.

Regulation of food provisioning in the Antarctic petrel; the importance of parental body condition and chick body mass

1. Two hypotheses may explain how long‐lived seabirds regulate the food provisioning to their chick. The fixed level of investment hypothesis states that the parents provide food for their chick according to an intrinsic rhythm, independent of their chick's need. The flexible investment hypothesis states that the parents adjust their food provisioning both according to their chick's and their own need. 2. We tested how the Antarctic petrels adjust the food‐provisioning according to their own body condition or to their chick's need. First, we selected parents in poor and good body condition. Then we gave all parents randomly a chick of different body mass, but of the same age. We then measured the chicks daily until they were fed for the first time after swapping. 3. Parents in good body condition at hatching were more likely to produce a chick that was still alive 9 days after hatching than parents in poor body condition. Chick body mass at day 9 and at the end of the guarding period was positively related to the mean body condition of the parents at hatching. 4. The meal size provided by parents in good body condition was larger than that provided by parents in poor body condition. Parents in good body condition delivered more food to small than to large chicks, whereas no such relationship was found among parents in poor body condition. 5. Our results suggest that the Antarctic petrel parents adjust the amount of food delivered to their chick according to both the chick's need and their own body condition, and that the ability to respond to the chick's need is dependent upon their own body condition.

Brood division in birds in relation to offspring size: sibling rivalry and parental control

In some altricial birds with biparental care, it is the female, and in others the male, that provides more food to the smallest offspring within the brood. Many hypotheses have been proposed to account for such puzzling patterns of parental care. A parsimonious explanation is that no difference exists between the parents in priority of care but that differences arise simply from sibling rivalry, with dominant chicks trying to position themselves closest to the parent that provides most care (the sibling rivalry hypothesis). A refinement of the idea is that parents use the way they approach the chicks to counter selfish offspring and in this way control allocation of care (the parental approaching hypothesis). A comparison across species suggested that female care of the smallest chick within a brood is the ancestral and most common pattern. However, strong variation exists within single populations. In one species, the American robin,Turdus migratoriusthe sibling rivalry hypothesis and the parental approaching hypothesis were both supported because in broods where males provided more care than females, the largest chick was predominantly fed by the male whereas the smallest chick was predominantly fed by the female. When the male provided less care than the female, an opposite result was found. The same patterns of allocation of care also seemed to exist when chicks were quite immobile just after having left the nest and when their positions were experimentally controlled, suggesting parental control.

Osmoregulation by Adélie Penguin Chicks on the Antarctic Peninsula

-Physiologists have long contended that consumption of a diet of marine invertebrates imposes a high salt load on animals. I measured water and salt contents in the food, excreta, and body fluids of Ad6lie Penguin (Pygoscelis adeliae) chicks to determine patterns of osmoregulation in a bird that eats almost exclusively marine invertebrates. Adelie Penguins eat krill (Euphausia spp.) and feed the same to their chicks by regurgitation. Adelie chicks sometimes receive food that is significantly saltier than their body fluids, but on average the food has salt concentrations similar to those in their plasma. Adelie chicks excrete excess solutes via the salt glands, which are fully functional at hatching, and via the kidneys, which produce urine that is more concentrated relative to urine of other bird species. Larger chicks receive food that is drier than that eaten by smaller chicks, and larger chicks may compensate by excreting more of a given salt load via the salt glands, thus conserving water. Regurgitated food has significantly less Na+ than Cl-, but the salt glands secrete equal amounts of these two ions. Consequently, in larger chicks Na+ may be shunted from the urine to be excreted via the salt glands. The loss of this cation in the urine is compensated for by addition of NH4+. Received 26 July 1996, accepted 1 February 1997. ADPLIE PENGUINS (Pygoscelis adeliae) live in an osmotically challenging marine environment. Adelie Penguins have little or no access to fresh water, and up to 99% of their diet is marine invertebrates, usually krill (mostly Euphausia superba; Volkman et al. 1980). Adelie chicks potentially face the same osmotic challenges as the adults, because the only food they receive is that regurgitated by their parents. Unless adults modify the composition of krill fed to chicks, then the chicks' osmoregulatory physiology must be sufficiently developed to handle potentially high salt loads delivered in the food within hours after hatching (Douglas 1963, 1968). The purpose of this study was to determine the magnitude of salt loads received by chicks, determine if adults alter the salt composition of food given to chicks, and measure the salt concentrations of chick excretions (e.g. urine and salt-gland secretion) to determine salt-output capability. Adelie Penguins are good subjects for physiological studies of osmoregulation for four important reasons. First, their large size (adults weigh 4 to 5 kg) allows collection of relatively large samples of tissues and body fluids, which facilitates ion analyses. Second, Adelie Penguins are found in dense colonies near research 1 E-mail: donjanes@ucracl.ucr.edu stations in Antarctica, and this abundance combined with their relative tameness permits acquisition of large sample sizes. Third, their life history is well known (Ainley et al. 1983). Fourth, all of the material input into chicks is regurgitated by the parents, simplifying measurements of water and salt influx.

Physiological characteristics of arctic tern Sterna paradisaea chicks in relation to egg volume

The effect of egg volume on body mass, body composition and growth rate in Arctic tern Sterna paradisaea chicks was studied at Ny-Alesund, on Svalbard (78°55'N, 12°00'E), in order to investigate whether differences in egg size influence the physiological characteristics of the hatchlings. The relative content of yolk and albumen in eggs did not vary in proportion to egg volume. Hatchlings from large eggs had larger body masses than hatchlings from small eggs, with 71% of the overall variation in body mass accounted for egg volume. In newly-hatched chicks, water content, lean body and total lipid mass, as well as both leg and pectoral muscles, changed isometrically in proportion to egg volume. Hatchlings from large eggs, however, had disproportionately larger yolk sacs. The leg muscles of small chicks contained a lower proportion of water than the leg muscles of large chicks, indicating that the leg muscles of small hatchlings were functionally more mature. There was a weak, but significant, correlation between egg volume and growth rate. However, a residual analysis made to eliminate the effect of egg volume showed no correlation between hatchling body mass and growth rate. The results of the present study show that Arctic tern hatchlings from large eggs emerge with more yolk sac reserves, enabling them to better withstand periods of food-scarcity. During embryonic growth in small eggs, however, there seems to be a greater relative usage of yolk, resulting in a more developed leg musculature. This may partly compensate for the higher mass-specific heat loss in small hatchlings.

Energetics, growth, and body composition of Adélie penguin chicks, Pygoscelis adeliae.

Adélie penguins are very abundant in Antarctica and constitute a large biomass of predatory consumers in the Antarctic ecosystem. Adélies eat almost exclusively krill (Euphausia spp.), and to determine krill requirements by Adélies, information on energetics is needed, including energy intake of the chicks. I measured energy use and growth in Adélie penguin chicks, using both field and laboratory techniques. Field metabolic rate was quite variable, but mass-specific rates were not correlated with body mass. Growth followed the logistic equation: the growth constant was 0.143 d-1, and the asymptote for growth to fledging was 3,200 g. Different body organs had similar energy densities (in kilojoules per gram of dry mass), and total body energy density did not vary with chick mass. However, proportional mass of the skin increased rapidly as chicks grew, making the skin an important energy store in larger chicks. Metabolic efficiency measured in the laboratory averaged 69% and did not vary with chick mass. Total energy ingested over the 50-d development period was 162 MJ, which corresponds to approximately 33.6 kg of fresh krill. Previous studies of Adélie energetics have focused on adult energy balance and have calculated chick energy requirements indirectly on the basis of adults' stomach loads of krill and frequency of feeding chicks. Values from previous studies do not agree with those from the present study. The method used in the present study is more informative and accurate for measuring energy use by chicks, since measurements are made directly from chicks.

Physiological characteristics of Arctic ternSterna paradisaeachicks in relation to egg volume

The effect of egg volume on body mass, body composition and growth rate in Arctic tern Sterna paradisaea chicks was studied at Ny-&Aring;lesund, on Svalbard (78&deg;55'N, 12&deg;00'E), in order to investigate whether differences in egg size influence the physiological characteristics of the hatchlings. The relative content of yolk and albumen in eggs did not vary in proportion to egg volume. Hatchlings from large eggs had larger body masses than hatchlings from small eggs, with 71% of the overall variation in body mass accounted for egg volume. In newly-hatched chicks, water content, lean body and total lipid mass, as well as both leg and pectoral muscles, changed isometrically in proportion to egg volume. Hatchlings from large eggs, however, had disproportionately larger yolk sacs. The leg muscles of small chicks contained a lower proportion of water than the leg muscles of large chicks, indicating that the leg muscles of small hatchlings were functionally more mature. There was a weak, but significant, correlation between egg volume and growth rate. However, a residual analysis made to eliminate the effect of egg volume showed no correlation between hatchling body mass and growth rate. The results of the present study show that Arctic tern hatchlings from large eggs emerge with more yolk sac reserves, enabling them to better withstand periods of food-scarcity. During embryonic growth in small eggs, however, there seems to be a greater relative usage of yolk, resulting in a more developed leg musculature. This may partly compensate for the higher mass-specific heat loss in small hatchlings.