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.     

Accelerated growth rates in late‐hatched Rhinoceros Auklet Cerorhinca monocerata chicks depend on food conditions and growth stage: an experimental approach

In some bird species, the survival of chicks hatching later in the season is lower than those hatched earlier due to increased risk of predation and a seasonal decline in feeding conditions. To reduce these risks, it might be advantageous for late‐hatched chicks to grow faster and hence fledge at younger age. In this experimental study, the growth rates of early‐ and late‐hatched Rhinoceros Auklet Cerorhinca monocerata chicks were compared under average and poor food supplies in captivity. Controlling for potentially confounding effects of chick mass at 10 days old, chick age and nest‐chamber temperature, late‐hatched chicks had higher wing growth rate than early‐hatched chicks before attaining the minimum wing length required for fledgling under both average and poor food supplies. After attaining the minimum wing length, however, late‐hatched chicks had a lower fledging mass, indicating a potential cost that could diminish the early advantage of fast wing growth.     

Fly or die: the role of fat stores in the growth and development of Grey-headed Albatross Diomedea chrysostoma chicks

Chicks of albatrosses, like other Procellariiformes, become independent at a mass similar to their parents but during growth attain a peak mass some 30% or more greater, before losing mass prior to fledging. The current views are that this high peak mass represents chicks storing fat reserves as an energy sink, or as an insurance against periodic food scarcity, or as a Consequence of natural stochastic variation in provisioning rate. We analysed growth and body composition of Grey‐headed Albatross Diomedea chrysostoma chicks at Bird Island, South Georgia in 1984 and 1986, two years of very different food availability. In 1984 when overall breeding success was only 28% (the lowest in 20 years and less than halt that in 1986), chicks were significantly smaller in terms of peak mass (by 37%), primary length (by 25%), liver, lung, heart and kidney size (by 18–34%) and fat (by 75–80%) but not significantly different in terms of skeletal (tarsus, culmen, ulna, sternum) or muscle (pectoral, leg) size. Despite these differences, there were some important similarities in the patterns of growth in both years. Up to the attainment of peak mass, most of the growth of organs and of skeletal structures was completed and little fat was deposited. In the remaining part of the chick‐rearing period, feather growth and acquisition of fat stores were undertaken. Thus Grey‐headed Albatross chicks begin to acquire substantial fat stores only during the later part of the development period; this is contrary to the predictions of any of the existing hypotheses concerning provisioning patterns and the role of fat stores in Procellariiformes. We propose that the deposition of fat in the later stages of chick growth is an adaptation to: (a) ensure against energy demands and/or nutritional stress affecting the quality of flight feathers (many of which are not renewed for up to three years after fledging); and (b) provide an energy reserve for chicks to use in the critical period immediately after independence.     

All you can eat: is food supply unlimited in a colonially breeding bird?

Food availability is generally considered to determine breeding site selection and therefore plays an important role in hypotheses explaining the evolution of colony formation. Hypotheses trying to explain why birds join a colony usually assume that food is not limited, whereas those explaining variation in colony size suggest that food is under constraint. In this study, we investigate the composition and amount of food items not eaten by the nestlings and found in nest burrows of colonially nesting European bee‐eaters (Merops apiaster). We aimed to determine whether this unconsumed food is an indicator of unlimited food supply, the result of mistakes during food transfer between parents and chicks or foraging selectivity of chicks. Therefore, we investigated the amount of dropped food for each nest in relation to reproductive performance and parameters reflecting parental quality. Our data suggest that parents carry more food to the nest than chicks can eat and, hence, food is not limited. This assumption is supported by the facts that there is a positive relationship between dropped food found in a nest and the number of fledglings, nestling age, and chick health condition and that the amount of dropped food is independent of colony size. There is variation in the amount of dropped food within colonies, suggesting that parent foraging efficiency may also be an important determinant. Pairs nesting in the center of a colony performed better than those nesting on the edge, which supports the assumption that quality differences between parents are important as well. However, dropped food cannot be used as an indicator of local food availability as (1) within‐colony variation in dropped food is larger than between colony variation and, (2) the average amount of dropped food is not related to colony size.     

Parent-offspring interactions in food provisioning of Manx shearwaters: implications for nestling obesity

Procellariiform seabirds such as the Manx shearwater Puffinus puffinus, rear only one chick at a time but may breed many times in their lives; parents should thus limit food delivery to the chick in keeping with the balance between current and future reproductive output. Yet procellariiform chicks accumulate large quantities of lipid, which may provide a buffer against pronounced and unpredictable variation in food provisioning, resulting in part from an inability of parents to regulate food supply to the nest. We switched chicks between nests to examine the roles of parents and offspring in controlling food delivery. The serial autocorrelation in age-specific body masses for unmanipulated chicks decreased from 0.61 (P< 0.01) to 0.35 (NS) over a period of 15 days and remained nonsignificant thereafter. By contrast, the serial autocorrelation for switched chicks increased from 0.64 (P< 0.01) to 0.83 (P< 0.001) and the serial cross-correlation rose from 0.23 (NS) to 0.50 (P< 0.05). These results supported both chick determination and parental determination models of food provisioning, indicating that chicks conveyed information about their nutritional status, which parents acted upon by adjusting their rate of food delivery. We discuss these results in relation to the optimization of nestling lipid reserves and parental foraging effort. We suggest that information conveyed by the chick's begging intensity serves to reduce the provisioning rate to well-fed chicks, but parents cannot or do not increase food provisioning to poorly fed chicks. Such adjustment of food provisioning does not refute the hypothesis that nestling obesity provides a buffer against highly variable food delivery. Copyright 1999 The Association for the Study of Animal Behaviour.     

On the importance of fat reserves for the little auk (Alle alle) chicks

Summary The pattern of fat deposition and inter-year variation in the amount of deposited fat, lean dry mass (LDM) and water were studied in the chicks of little auk (Alle alle), an arctic alcid, at Spitsbergen in the 1984, 1986 and 1987 breeding seasons. The lipid index (lipid mass/LDM) rose from 0.29 at hatching to about 0.70 at the age of maximum body mass attained in the nest, the highest yet recorded for seabirds except procellariiforms. Just before fledging the index dropped to 0.38. Fat mass in 1984 chicks and also fresh body mass of older 1984 chicks was significantly lower than in the other two seasons, but there were no statistical year-to-year differences in LDM's of chicks. The amount of fat in chicks was significantly correlated with certain weather parameters. Fasting capability (FC) of the chicks (the time that chicks could survive when using only their lipid stores) was calculated from fat mass and previous data on metabolic rates of chicks. The FC's of all 108 chicks collected in three seasons were greater than maximum interval between two consecutive feeds to chicks reported in the study colony. Also the estimated fat reserves of 99.7% of chicks weighed in 1984 were sufficient to support them for longer than the maximum recorded intervals between feeds. In relation to death by starvation, little auk chicks, at least up to the age of maximum body mass, have a substantial surplus of fat. This is contrary to the hypothesis that fat depots in seabird chicks assist survival during the periodic fasts resulting from unpredictable feeding conditions.     

Seasonal cycles of reserves in relation to reproduction inSebastes

Synopsis Seasonal cycles of reserve deposition and utilization in many fishes, amphibians and reptiles alleviate temporal mismatches of energy supply and demand. Utilization of reserves can be related to maintenance during periods of reduced food supply, to reproduction, particularly during periods of poor food availability, and to migration. Published data on the seasonal cycles of reserves and reproduction inSebastes suggest that reserves are important for maintenance during wintertime periods of low food availability. Unlike many other ectothermic vertebrates, some species ofSebastes deposit fat reserves at the same time as gametogenesis, a pattern consistent with the longevity and iteroparity evident in the genus. Other species ofSebastes have similar seasonal timing of fat cycles, but since reproduction takes place later in the year, the decline in reserves during winter coincides with the main period of reproductive activity. The significance of this is not clear. Interspecific differences in amounts of reserves may be related to geographical differences in the seasonality or abundance of food. Intraspecific variation in reserves, marked most strongly by allometry of reserves with regard to fish legth, bears further study, since it may link the proces of sexual maturation and the responses of repeat spawners to variability in food supply and other environmental factors.     

Possible roles for corticosterone and critical size in the fledging of nestling pied flycatchers

Our study was designed to see whether corticosterone (B) rises abruptly in the blood of nestling pied flycatchers (Ficedula hypoleuca) at the time they fledge, as reported recently for kestrels, and if so, why. We measured the growth and blood levels of B and selected nutrients of nestlings in broods of five, seven, and nine chicks during 1998 and 1999. In half of the broods, we clipped selected wing and tail feathers of both parents with the intention of making it more difficult for them to provide their chicks with food. We collected blood samples when the chicks were six to 10 d old (period of rapid growth) and 15 d of age or older (0-5 d before fledging). B increased substantially several days before the chicks left the nest and then declined somewhat. We found no differences in rates of growth or blood levels of B, nutrients, and hematocrit as a function of either brood size or parental handicapping. Nestlings within a day of fledging appear to have been food deprived in 1998; their glucose was significantly reduced, and B, free fatty acids, and glycerol were significantly elevated compared to levels in chicks 1-4 d younger. Such changes did not occur in 1999. Blood levels of B were significantly correlated with brood size near the day of fledging, but not earlier, in both years of the study. It was possible to predict the day on which chicks would leave the nest, using their wing length when 12 d old. These results suggest that high blood levels of B associated with food restriction and sibling competition induce chicks to fledge, provided they have reached a critical size, and that the importance of fasting, sibling competition, and B may vary from year to year.     

On the optimal growth of the alimentary tract in avian postembryonic development

It was shown in the mathematical model described elsewhere that when growth rate of the chicks is maximized and not constrained by the food availability, the optimal relationship between body mass and alimentary tract mass should conform to a single straight line, or two-, or three-segmented straight lines. Here, we present the data on growth of 11 bird species, and we test the model using the mass of intestines as an indicator of growth of the alimentary tract. The results support the predictions of the model for altricial species and contradict them for precocials. Since precocial species examined here were not food-limited, we suggest that the lack of optimal growth of their alimentary tract is inherent to their mode of development. This may account for their lower growth rate, as compared to altricials. The existence of the optimal growth of the alimentary tract in altricial nestlings suggests that under natural conditions the food is much more abundant than it is generally assumed.     

Developmental plasticity in a passerine bird: an experiment with collared flycatchers Ficedula albicollis

Young birds often face poor food supply, which reduces their growth and development. However, if the shortage of resources is only temporary, there is a possibility to adjust the growth trajectory of morphological traits after the end of the short-term limitation period. The two main ways of compensatory growth are delayed development (parallel growth) and growth acceleration (catch-up growth). Parallel growth has been widely demonstrated in birds, but the presence of catch-up growth in altricial species has been questioned. However, most experiments have been conducted in laboratory conditions. We manipulated the food supply of nestling collared flycatchers Ficedula albicollis in the wild by removing the male parent for three days at 4–7 days of chick age. We performed early partial swapping to control for origin effects on growth, and total swapping after the period of food limitation to ensure similar late growth environment for deprived and control chicks. Both body mass and tarsus length of deprived chicks was negatively affected by the food scarcity. Body mass showed efficient catch-up growth, but this compensation was absent in skeletal size. Body mass is an important determinant of postfledging survival in this long-distance migrant. Further studies are needed in a variety of species to examine developmental plasticity in relation to age at food scarcity and the allocation hierarchy of various morphological traits.     

Variability and stochasticity of meal size and feeding frequency in the Little Sheanvater Puffinus assimilis

The pattern of chick feeding in Little Shearwater Puffinus assimilis on Selvagem Grande was examined by weighing chicks at 4–h intervals throughout eight successive nights and daily for a further 11 days (19 days in all). Individual meals fed to chicks averaged 23.2 g (s.d. ±4.7) or 13.6% of adult mass. Mass increments over 24 h (NET) were linearly related to the sum of positive mass increments over 4–h intervals during the night (SUM) by the equation NET = 0.36SUM - 5.89 (r²= 0.60). Using this relationship, I estimated that over a period of 18 nights, a mean of 95% of chicks were fed each night, and the mean interval between feeds was 1.05 nights, with a maximum of three nights. There was no significant day-to-day variation in feeding rate. These results were not compatible with the prevalent idea that the purpose of large fat deposits in Procellariiformes is to tide chicks over periodic fasts resulting from poor feeding conditions. On average, chicks required 16 g of food per day to maintain constant mass and converted 33% of their intake of food above this requirement into biomass. Meal size and feeding frequency were independent of chick size and body condition (body-mass corrected for body-size), and the masses of food received by individual chicks each night varied in direct proportion to previous values. These results suggest that the rate of food supply to chicks was not regulated by adjustment according to chicks' nutritional requirements. To some extent, this supports the hypothesis that lipid accumulation among Procellariiformes is related to stochastic variation in food supply rate, resulting from an absence of regulation of feeding. However, feeding was not stochastic, in that adults tended to deliver consistent amounts of food to their chicks, and the pattern of feeding among even the worst-fed chicks was inconsistent with a need for large lipid stores based upon chance variation in food delivery.     

Predicting animal performance through climatic and plant phenology variables: The case of an omnivore hibernating species in Finland

Annual variation in the environment is expected to influence individual performance, e.g. measured as body condition, such as body mass or fat deposition, through its direct or indirect effects on food abundance and availability. Such environmental variation is traditionally measured by climatic observation, but recently, measures of environmental phenology obtained from satellite images have been successfully used. We examined the performance of climatic and plant phenology variables in explaining body condition of an invasive omnivore species: the raccoon dog Nyctereutes procyonoides. We collected data on fat deposition of juveniles in southern Finland from the end of June to the beginning of November. A four-parametric logistic model was fitted separately for each province to the data by non-linear regression procedure and the residuals were compared to the expected average as measure of individual performance. These values were then analysed with respect to the environmental variables. Climatic variables describing spring conditions performed better than plant phenology variables in explaining the variation in fat deposition. Harsh spring conditions negatively affected the amount of fat deposed during the growing season. Plant phenology variables, effective in explaining life history traits in herbivores, might not reflect variation in food abundance and quality for omnivore species. We propose that in Europe raccoon dogs will benefit from climate warming, because of a longer growing season, but increased spring precipitation in the form of snow at higher latitudes might compensate for the effect of greater primary productivity and outline the border of their expansion towards harsher environments.     

Food supplementation and predation risk in harsh climate: interactive effects on abundance and body condition of tit species

Food availability and predation risk can have drastic impacts on animal behaviour and populations. The tradeoff between foraging and predator avoidance is crucial for animal survival and will strongly affect individual body mass, since large fat reserves are beneficial to reduce starvation but may increase predation risk. However, two‐factor experiments simultaneously investigating the interactive effects of food and predation risk, are still rare. We studied the effects of food supplementation and natural predation risk imposed by pygmy owls Glaucidium passerinum on the abundance and fat reserves of tit species in boreal forests of north Europe, from January to March in 2012 and in 2013. Food supplementation increased the number of individuals present in a given forest patch, whereas the level of predation risk had no clear impact on the abundance of tit species. The stronger impact of food supply respect to predation risk could be the consequence of the harsh winter conditions in north Europe, with constant below‐zero temperatures and only few (5–7 h) daylight hours available for foraging. Predation risk did not have obvious effects on tit abundance but influenced food consumption and, together with food supplementation, affected the deposition of subcutaneous fat in great tits Parus major. High owl predation risk had detrimental effects on body fat reserves, which may reduce over‐winter survival, but the costs imposed by pygmy owl risk were compensated when food was supplemented. The starvation–predation tradeoff faced by great tits in winter may thus be mediated through variation in body fat reserves. In small species living in harsh environment, this tradeoff appeared thus to be biased towards avoidance of starvation, at the cost of increasing predation risk.     

Relative importance off environmental variables in determining the growth off nestling Tree Swallows Tachycineta bicolor

Unpredictable, short-term changes in environmental conditions associated with weather patterns have severe impacts on the reproductive success of Tree Swallows Tachycineta bicolor , as well as other aerial insectivores. We examined the effects of day-to-day environmental variation on the growth of nestling Tree Swallows. Using path analysis, we compared the relative importance of changes in food availability, ambient temperature and wind speed on changes in mass and feather length over four years at our study site near Ithaca, New York. Changes in environmental conditions explained a significant amount of the variation in nestling growth, with daily high temperature having the greatest influence for nestlings younger than five days. Both food supply and temperature had significant direct effects on growth of nestlings older than nine days, with temperature also having a significant indirect effect through its influence on food availability. For both young and old chicks, mass gains were smaller for chicks hatched later in the season. Environmental conditions also explained a significant amount of the linear growth of the ninth primary feather in one of two years, with food supply showing the most consistent positive effect. Environmental conditions several days prior to the measurements significantly influenced feather growth, indicating that the effects of adverse conditions are spread out over several days of feather growth, but this effect was not seen for change in mass.     

Growth and energetics of a small shorebird species in a cold environment: the little stint Calidris minuta on the Taimyr Peninsula, Siberia

The little stint Calidris minuta is one of the smallest shorebird species breeding in the Arctic (weighing 4.3  g on hatching). Their chicks are small and have a high surface area-to-volume ratio. We determined prefledging growth, energy expenditure and time budgets for little stint chicks in northwestern Taimyr, Siberia. A modified power curve was introduced to model the relationship between daily energy expenditure and body mass. Total metabolisable energy, TME, over the 15-d prefledging period was 107% greater than the allometric prediction for a bird the size of a little stint. Their growth rate coefficient was 14% greater than the prediction for a bird their size. The growth of young chicks was reduced in cool weather, possibly due to a reduction in foraging time in order to be brooded and reduced food availability which impact foraging efficiency. We did not detect weather effects on energy expenditure of chicks, but lack of temperature variation during energy expenditure measurements may have prevented this. In sum, both growth rate coefficient and energy expenditure of little stint chicks were greater than predicted and this is similar to that observed in other arctic shorebird species.     

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.     

Validating growth and development of a seabird as an indicator of food availability: captive‐reared Caspian Tern chicks fed ad libitum and restricted diets

ABSTRACT For seabirds raising young under conditions of limited food availability, reducing chick provisioning and chick growth rates are the primary means available to avoid abandonment of a breeding effort. For most seabirds, however, baseline data characterizing chick growth and development under known feeding conditions are unavailable, so it is difficult to evaluate chick nutritional status as it relates to foraging conditions near breeding colonies. To address this need, we examined the growth and development of young Caspian Terns (Hydroprogne caspia), a cosmopolitan, generalist piscivore, reared in captivity and fed ad libitum and restricted (ca. one‐third lower caloric intake) diets. Ad libitum‐fed chicks grew at similar rates and achieved a similar size at fledging as previously documented for chicks in the wild and had energetic demands that closely matched allometric predictions. We identified three general characteristics of food‐restricted Caspian Tern chicks compared to ad libitum chicks: (1) lower age‐specific body mass, (2) lower age‐specific skeletal and feather size, such as wing chord length, and (3) heightened levels of corticosterone in blood, both for baseline levels and in response to acute stress. Effects of diet restriction on feather growth (10–11% slower growth in diet‐restricted chicks) were less pronounced than effects on structural growth (37–52% slower growth) and body mass (24% lower at fledging age), apparently due to preferential allocation of food resources to maintain plumage growth. Our results suggest that measurements of chick body mass and feather development (e.g., wing chord or primary length) or measurement of corticosterone levels in the blood would allow useful evaluation of the nutritional status of chicks reared in the wild and of food availability in the foraging range of adults. Such evaluations could also inform demography studies (e.g., predict future recruitment) and assist in evaluating designated piscivorous waterbird conservation (colony) sites.     

The effect of food restriction on circulating insulin-like growth factor-I in mice divergently selected for high or low protein or fat to body mass ratios

1. Plasma insulin-like growth factor-I (IGF-I) was measured in mice divergently selected for high and low lean tissue gain or high and low fat to body weight ratio, both before and after fasting and refeeding. 2. Selection for high lean tissue resulted in increased body weight and a higher basal IGF-I concentration at 10 weeks of age. 3. Selection resulting in a difference in fatness had no effect on IGF-I concentration. 4. Circulating IGF-I decreased more rapidly in response to 24 hr food withdrawal in growing (5-week-old) than in almost fully grown (10-week-old) animals from all lines.     

Genetics of lipid deposition in the Japanese quail

Summary The research presented here was designed to investigate the mode of inheritance of fat and lean tissue deposition, and the relationship between them and body weight in Japanese quail. Heterotic effects were found for weight, size, and number of adipocytes in the abdominal fat depots, weight of the sartorial fat depot and percentage carcass fat with means for the hybrids being lower than those for the parental lines. General inferences concerning the importance of nonadditive genetic variation for lean and body weight were precluded due to inconsistencies observed among mating combinations. Thus, although heterosis and recombination effects were general for characteristics associated with fat deposition, the situation for body weight and lean was unique to the populations involved. It may be hypothesized that heterosis in the efficiency of feed utilization is reflected by the heterosis for fat deposition which explains why hybrids utilize feed better than their parental lines.     

Annual variation in fat storage by a migrant warbler overwintering in the Indian tropics

1. We studied fat storage in a population of greenish leaf warblers ( Phylloscopus trochiloides ) in southern India over four winters (1993–97). This species breeds in temperate regions and overwinters in India from October to April.
2. Diurnal variation in fat scores was comparable to that seen among temperate wintering passerines. Seasonal variation was slight, except for premigratory fattening. There was significant annual variation: in drier winters, which were also winters of low food supplies, fat scores were higher.
3. Energy metabolized overnight is unlikely to vary across winters, and annual variation in fat scores is considered a response to uncertainty of food intake on a given day. Fat scores varied inversely with short-term rainfall, which drives the abundance of arthropod prey.
4. Annual variation in fat scores was not accompanied by changes in total body mass. This suggests that protein reserves were being compromised by increased fat deposition in dry years and offers an explanation for the observed delay in moult during drier winters. These results suggest that strategies for maximizing short-term probability of survival translate into future fitness costs, and may shape long-term life-history strategies through simple physiological processes.