Nest and foraging‐site selection in Yellowhammers Emberiza citrinella: implications for chick provisioning

Capsule Vegetation structure and invertebrate abundance interact to influence both foraging sites and nestling provisioning rate; when invertebrate availability is low, adults may take greater risks to provide food for their young.

Aims To investigate nesting and foraging ecology in a declining farmland bird whose fledging success is influenced by the availability of invertebrate prey suitable for feeding to offspring, and where perceived predation risk during foraging can be mediated by vegetation structure.

Methods Provisioning rates of adult Yellowhammers feeding nestlings were measured at nests on arable farmland. Foraging sites were compared with control sites of both the same and different microhabitats; provisioning rate was related to habitat features of foraging‐sites.

Results Foraging sites had low vegetation density, probably enhancing detection of predators, or high invertebrate abundance at high vegetation density. Parental provisioning rate decreased with increasing vegetation cover at foraging sites with high invertebrate abundance; conversely, where invertebrate abundance was low, provisioning rate increased with increasing vegetation cover.

Conclusions Vegetation structure at foraging sites suggests that a trade‐off between predator detection and prey availability influences foraging site selection in Yellowhammers. Associations between parental provisioning rate and vegetation variables suggest that where invertebrate abundance is high birds increase time spent scanning for predators at higher vegetation densities; however, when prey are scarce, adults may take more risks to provide food for their young.     

Importance of feeding ecology to the reproductive success of Blackbirds Turdus merula nesting in rural habitats

The feeding ecology of Blackbirds Turdus merula breeding in contiguous woodland and farmland habitats was studied over three years. The aim of the study was to investigate how reproductive success was influenced by nestling diet and the provisioning rates of parents feeding nestlings. Parental provisioning rates increased with brood size, and consequently individual nestlings were no lighter in larger broods. None of the environmental factors measured had strong effects on parental provisioning rate. The nestling diet was dominated by caterpillars and earthworms, the former occurring in a short period in the middle of the breeding season. The availability of earthworms was higher in woodland and was dependent on rainfall in farmland. Nestling mass and provisioning rates were marginally higher under predominantly earthworm diets. Nestling mass increased with rainfall in farmland only, and was higher in farmland than in woodland or woodland-edge, although it is doubtful whether this result is of any significance for fledgling survival. Overall, Blackbirds were able to provision their nestlings adequately throughout the breeding season across a range of conditions. There was no evidence to suggest that reproductive success was constrained by aspects of feeding ecology within the natural range of brood size.     

Is Mate Provisioning Predicted by Ornamentation? A Test with Northern Cardinals (Cardinalis cardinalis)

Male birds of many species feed their mates during courtship and incubation. The amount of food provided can be substantial and even essential for successful reproduction in some species, and can influence female nest attentiveness in many others. Additionally, mate provisioning may predict later nestling feeding rates. Females may thus benefit from being able to determine male provisioning effort. We assessed the expression of several ornaments, known to indicate condition in male northern cardinals (Cardinalis cardinalis), and compared these with mate provisioning rates, nestling feeding rates, and nest attentiveness. We found that male ornamentation may not be indicative of mate provisioning rates. Mate provisioning rate did not co‐vary with reproductive success, male feedings to nestlings, or nest attentiveness of females. However, females which were fed more often during incubation tended to provision nestlings less. Reduced female parental effort following extensive incubation feeding may be indicative of females using incubation feeding to assess future male parental effort. Male hormonal condition that favors high rates of nestling provisioning may be a proximate cause of mate provisioning during incubation, even in the absence of selection, favoring high rates of mate provisioning. Both sexes may have capitalized on this unselected behavior.     

Seasonal variation in food availability influences the breeding strategy of White‐collared Blackbirds Turdus albocinctus on the Tibetan Plateau

Parent birds show a continuous spectrum of breeding strategies, ranging from a low‐fecundity and high‐survival pattern to a high‐fecundity, low‐survival pattern. Investigations of parental breeding strategies under variable environmental conditions can illustrate how parents trade‐off the benefits and costs of these two extreme strategies. White‐collared Blackbirds Turdus albocinctus can breed twice a year on the Tibetan Plateau. We show that both life‐history traits and parental feeding behaviour differ between these two breeding attempts. In the first attempt, the birds produced small clutches and fledged a small number of nestlings of high body condition. In the second attempt, they produced larger clutches and fledged more nestlings of lower body condition. Males made greater contributions to brood provisioning compared with females in the first attempt but there was no sex difference in brood provisioning in the second attempt. In the first attempt, producing smaller clutches can shorten the nestling period, and the increased male contribution to brood provisioning can protect the energy reserves of females. Thus, females can begin a second attempt sooner and produce larger clutches. During the second nesting attempt, when conditions are warmer and wetter, parents rely on a broader array of food types (both invertebrates and plant material, primarily berries) than during the first attempt, which includes only animal food such as arthropods and annelids. We suggest that this difference in breeding strategies between nesting attempts and sexes is in part influenced by marked seasonal variation in food availability.     

Living with Aliens: Effects of Invasive Shrub Honeysuckles on Avian Nesting

Invasive species have come to the forefront of conservation biology as a major threat to native biodiversity. Habitats dominated by shrub honeysuckles (Lonicera spp.) in the United States have been characterized as “ecological traps” by ecologists. Here we tested this hypothesis by investigating the effects of shrub honeysuckles on the nesting ecology of native birds in seven study sites in central Pennsylvania, USA. We examined how the abundance of shrub honeysuckles influenced the selection of nesting substrates and habitat for a community of common songbirds, and the parental-care behavior and nestling development of gray catbirds (Dumetella carolinensis). We found that birds had a strong bias towards nesting in honeysuckle shrubs, but not necessarily for nesting in honeysuckle-dominated habitats. Nest predation rates were affected by the density of nests in a habitat, but not by the overall abundance of honeysuckles in such habitats. Honeysuckle abundance in the habitat did show significant effects on some parental-care behavioral parameters: catbirds had higher nest visitation rates and shorter visit lengths in areas of high honeysuckle density. On average, Gray catbirds fed fruit 12%±0.31 s.e. of their nestling-feeding bouts, mostly fruits of shrub honeysuckles. Nestlings in sites with high honeysuckle density also showed higher mass:tarsus ratios, suggesting a good (possibly better) physiological condition of catbird nestlings at the time of fledging. Our study shows that honeysuckle-dominated habitats could have equivocal effects on nesting parameters of common species of native birds. We advise more caution in the widespread denomination of novel plant communities with high densities of honeysuckle as “ecological traps” as effects can be null or positive on native birds in certain localities.     

Habitat quality, nestling diet, and provisioning behaviour in great tits Parus major

Variation in early nutrition is often a strong predictor of offspring condition and fitness. In the case of woodland passerine birds, nestling diet is determined by the spatiotemporal distribution of prey items such as caterpillars during the nestling period, and is usually quantified as differences in provisioning behaviour between habitats. However, the habitat level does not account for variation between individual territories, the level at which competition and selection are assumed to operate. Here we use nestbox cameras and Radio Frequency Identification technology (RFID) to simultaneously assess variation in both nestling diet (components) and provisioning rates (quantity) among a sample (n=22) of different quality great tit Parus major territories selected from a larger breeding population (n=310 fledged broods) in a single year. Caterpillars were by far the most numerous item provisioned to nestlings (mean=75% of prey items), as expected given the known importance of this food source for this species. Broods raised close to an oak tree, or far from the woodland edge, were provisioned the highest proportion of caterpillars. Provisioning rates declined seasonally and there was a weak association between low provisioning rates and caterpillar rich diets. During the first week of the nestling stage, nestling condition was unrelated to the proportion of caterpillars in the diet, provisioning rates and oak proximity. Condition at fledging was slightly improved in broods fed a higher proportion of caterpillars in the diet and in broods raised close to an oak tree. However, in our data early breeding was the only predictor of recruitment success, although power was low for this test. Analyses of long‐term data (41 years) from the same population confirmed a relationship between oak proximity and fledgling mass, but not recruitment success. Our results suggest that territory level environmental variation can affect offspring condition, probably through observed changes in nestling diet, but that such variation does not necessarily produce discernable effects on offspring fitness.     

Nest success of Lapwings Vanellus vanellus on organic and conventional arable farms in the Netherlands

Increasing agricultural intensification has put farmland bird populations under great stress. Although organically managed farms tend to have higher densities of farmland birds than conventionally managed holdings, differences in crop management may also lead to differences in breeding success. With the use of agrochemicals prohibited on organic farms, weeds are controlled using mechanical methods that may pose a threat to ground-nesting birds. This study compares the territory densities and nesting success of the Lapwing Vanellus vanellus on organic and conventional arable farms in the Netherlands. Territory densities were generally higher on organic farms, although in one year nesting success was lower on organic than on conventional farms. This was caused by higher nest loss resulting from farming activities on organic farms. There were no differences in predation rates. The results of this study show that breeding Lapwings may face potential threats on organic farms. To sustain or enhance Lapwing populations on these farms, additional conservation measures should be implemented.     

Corticosterone manipulations alter morph-specific nestling provisioning behavior in male white-throated sparrows,Zonotrichia albicollis

In the polymorphic white-throated sparrow (Zonotrichia albicollis), tan-striped males provision nestlings at higher rates than do white-striped males. In a previous study, we found that tan-striped males had lower baseline corticosterone levels than white-striped males during the nestling stage. To determine if this variation in corticosterone influences morph-specific differences in nestling provisioning behavior, we used intraperitoneal osmotic pumps to increase baseline corticosterone levels in tan-striped males (TS CORT) and administer RU486, a glucocorticoid receptor antagonist, in white-striped males (WS RU486). These manipulations essentially reversed morph-specific nestling provisioning behavior in males. TS CORT males fed nestlings at lower rates than TS controls (vehicle-only implant), and at similar rates to WS controls (vehicle-only implant), while WS RU486 males fed nestlings at higher rates than WS controls, and at similar rates to TS controls. These results demonstrate that (1) increases in baseline corticosterone (i.e., below concentrations associated with the adrenocortical response to stress) can directly or indirectly inhibit nestling provisioning behavior, and (2) corticosterone influences morph-specific variation in parental behavior in male white-throated sparrows. This study contributes to the growing evidence that modulating baseline CORT mediates parental care and self-maintenance activities in birds, and thus may serve as a mechanism for balancing current reproductive success with survival.     

Behavioural responses to ectoparasites in pied flycatchers Ficedula hypoleuca: an experimental study

Nests of cavity‐nesting birds usually harbor some species of haematophagous ectoparasites that feed on the incubating adults and nestlings. Given the negative impact of ectoparasites on nestlings there will be selection on hosts to reduce parasite infestations through behavioural means. We have experimentally reduced the abundance of all ectoparasites in nests of pied flycatchers Ficedula hypoleuca to explore both whether there are changes in the frequency and duration of putative anti‐parasite behaviours by tending adults, as well as whether such anti‐parasite behaviours are able to compensate for the deleterious effects that parasites may have on nestlings. Heat treatment of nests substantially decreased the density of ectoparasites, and thereby positively affected nestling growth. The frequency and intensity of female grooming and nest sanitation behaviours during the incubation and nestling periods decreased as a consequence of the experimental reduction of ectoparasite infestation. Although nestlings begged more intensely in infested nests, the experiment had no significant effect on parental provisioning effort. Reduction of parasites resulted in larger nestlings shortly before fledging and increased fledging success. This study shows a clear effect of a complete natural nest ectoparasite fauna on parental behaviour at the nest and nestling growth in a cavity‐nesting bird. Although ectoparasites induce anti‐parasite behaviours in females, these behaviours are not able to fully remove parasite's deleterious effects on nestling growth and survival.     

Corticosterone manipulations alter morph-specific nestling provisioning behavior in male white-throated sparrows, Zonotrichia albicollis

In the polymorphic white-throated sparrow (Zonotrichia albicollis), tan-striped males provision nestlings at higher rates than do white-striped males. In a previous study, we found that tan-striped males had lower baseline corticosterone levels than white-striped males during the nestling stage. To determine if this variation in corticosterone influences morph-specific differences in nestling provisioning behavior, we used intraperitoneal osmotic pumps to increase baseline corticosterone levels in tan-striped males (TS CORT) and administer RU486, a glucocorticoid receptor antagonist, in white-striped males (WS RU486). These manipulations essentially reversed morph-specific nestling provisioning behavior in males. TS CORT males fed nestlings at lower rates than TS controls (vehicle-only implant), and at similar rates to WS controls (vehicle-only implant), while WS RU486 males fed nestlings at higher rates than WS controls, and at similar rates to TS controls. These results demonstrate that (1) increases in baseline corticosterone (i.e., below concentrations associated with the adrenocortical response to stress) can directly or indirectly inhibit nestling provisioning behavior, and (2) corticosterone influences morph-specific variation in parental behavior in male white-throated sparrows. This study contributes to the growing evidence that modulating baseline CORT mediates parental care and self-maintenance activities in birds, and thus may serve as a mechanism for balancing current reproductive success with survival.     

Carotenoid-based nestling colouration and parental favouritism in the great tit

While elaborate carotenoid-based traits in adult birds may have evolved as honest signals of individual quality in the context of sexual selection or other social interactions, the function of carotenoid-based colours in juveniles is less well understood. We investigated the hypothesis that carotenoid-based nestling colouration has evolved in response to parental preference of intensely coloured offspring during food provisioning. In a field experiment, we manipulated nestling plumage colouration by a carotenoid-supplementation and analysed the parental food provisioning behaviour before feather appearance and at the end of the nestling stage. Carotenoids per se did not influence the nestlings begging behaviour or parental feeding decisions and we found no evidence that carotenoid-based colouration in nestling great tits has a signalling function in parent-offspring interactions. Parents did not discriminate between intensely coloured and control offspring in their food provisioning and in accordance with this finding intensely coloured nestlings were not heavier or larger at the end of the nestling stage. Alternative explanations for the evolution of carotenoid-based colours in nestling birds are discussed.     

Habitat associations and breeding success of the Chaffinch Fringilla coelebs

Capsule Population trends for Chaffinch on farmland are unlikely to be explained by their preference for non-crop habitats alone.

Aims To investigate the importance of non-cropped habitats for Chaffinch territory distribution, breeding success and foraging habitat selection in Scottish farmland.

Methods Territory distribution, nesting success and foraging behaviour of adults feeding chicks at the nest were recorded and related to habitat composition on two Scottish lowland farms.

Results Higher Chaffinch territory densities were associated with the presence of hedgerows, trees and grass leys, whereas lower densities were found adjacent to winter Barley. Nests were predominantly located in conifer trees and hedgerows. Trees were selected preferentially for foraging. Poor breeding success was detected in nests associated with cereal crops and wider field margins. Farmland in Scotland supported much lower territory densities than in England.

Conclusion Chaffinches rely predominantly on non-cropped habitats for territory establishment, nesting and foraging habitats. Differences in habitat composition between England and Scotland may explain differences in territory densities. However, the Chaffinch's preference for non-crop habitats is unlikely to explain its population trends alone. Immigration from other habitats and/or a decrease in inter-specific competition for resources may also have contributed to the increase in the national farmland Chaffinch population.     

Experimental food supplementation affects the physical development,behaviour and survival of Little Owl Athene noctua nestlings

In birds, energy supply during growth is a major predictor of the fledglings' physical condition and survival prospects. Differential quantity and quality of fledglings produced under varying nestling food supplies are likely to affect the number of offspring that recruit into the breeding population. However, the underlying mechanisms and associated consequences are still poorly known. Using a partial cross‐fostering and food supplementation experiment, we estimated the effect of variation in food supply during growth on nestling survival and fledgling phenotypic traits of Little Owls Athene noctua. Survival to fledging was much higher in food‐supplemented nestlings (98.6%) than in control nestlings (82.4%). Furthermore, supplemented nestlings were on average 8.9 g heavier and were more likely to develop subcutaneous fat deposits (99.4 vs. 73.7% of treatment and control nestlings, respectively). Supplemented nestlings also had on average longer wings than control nestlings, but tarsi and culmen did not differ significantly. Furthermore, experimentally supplemented fledglings struggled more when handled and emerged sooner from tonic immobility than control fledglings. The irises of supplemented fledglings were less intensely coloured. The experimentally induced changes in nestling development probably affect individual performance beyond fledging. Nestlings from orchard‐dominated habitats were larger than those from habitats dominated by arable land. As nestling food supply is largely determined by natural food availability, we conclude that habitat quality affects Little Owl productivity and offspring quality, and ultimately, population dynamics.     

Relative performance of hybrid nestlings in Ficedula flycatchers: a translocation experiment

Ecological speciation predicts that hybrids should experience relatively low fitness in the local environments of their parental species. In this study, we performed a translocation experiment of nestling hybrids between collared and pied flycatchers into the nests of conspecific pairs of their parental species. Our aim was to compare the performance of hybrids with purebred nestlings. Nestling collared flycatchers are known to beg and grow faster than nestling pied flycatchers under favorable conditions, but to experience higher mortality than nestling pied flycatchers under food limitation. The experiment was performed relatively late in the breeding season when food is limited. If hybrid nestlings have an intermediate growth potential and begging intensity, we expected them to beg and grow faster, but also to experience lower survival than pied flycatchers. In comparison with nestling collared flycatchers, we expected them to beg and grow slower, but to survive better. We found that nestling collared flycatchers indeed begged significantly faster and experienced higher mortality than nestling hybrids. Moreover, nestling hybrids had higher weight and tended to beg faster than nestling pied flycatchers, but we did not detect a difference in survival between the latter two groups of nestlings. We conclude that hybrid Ficedula nestlings appear to have a better intrinsic adaptation to food limitation late in the breeding season compared with nestling collared flycatchers. We discuss possible implications for gene flow between the two species.     

Forest fragmentation is associated with primary brood sex ratio in the treecreeper (Certhia familiaris)

We studied the primary brood sex ratio of an old-growth forest passerine, the Eurasian treecreeper (Certhia familiaris), along a gradient of forest fragmentation. We found evidence that male nestlings were more costly to produce, since they suffered twofold higher nestling mortality and were larger in body size than females. Furthermore, the proportion of males in the brood was positively associated with the provisioning rate and the amount of food delivered to the nestlings. During the first broods, a high edge density and a high proportion of pine forests around the nests were related to a decreased production of males. The densities of spiders, the main food of the treecreeper, were 38% higher on spruce trunks than on pine trunks. This suggests that pine-dominated territories with female-biased broods may have contained less food during the first broods. The observation was further supported by the fact that the feeding frequencies were lower in territories with high proportions of pines. In the second broods, territories with a high forest patch density produced female-biased broods, whereas high-quality territories with a large amount of deciduous trees and mixed forests produced male-biased broods. Our results suggest that habitat quality as measured by habitat characteristics is associated with sex allocation in free-living birds.     

Behavioural responses to ectoparasites: time-budget adjustments and what matters to Blue Tits Parus caeruleus infested by fleas

Blue Tit nests are often heavily infested by fleas, which feed on the incubating female and the nestlings. Depending on habitat quality, the drawing of blood by fleas reduces offspring quality, or it is compensated by an increase in food provisioning by the adults and may reduce their future reproduction. Given these fitness costs, tits are expected to have evolved behavioural responses enabling them to remove, destroy or minimize the contact with fleas. To identify these traits, we video-recorded the changes in frequency and duration of the hosts' potential anti-flea behavioural defences in nests experimentally infested with low and high flea densities. We also investigated whether flea load affected the number of male feeds delivered to incubating females, and whether the parents increased their rate of food provisioning to the nestlings equally at high flea density. Flea density significantly affected the nest sanitation and sleeping behaviour of Blue Tit females but had no significant effect on grooming. Female Blue Tits increased the frequency but decreased the duration of bouts of these behavioural traits, and hence their time-budgets, based on per hour duration of behaviour, were not significantly affected by flea density. High flea density reduced nestling weight at the early nestling stage but these costs were fully compensated by an increase in female feeding effort. Males did not increase their frequency of food provisioning to incubating females nor to nestlings in heavily infested nests. The results are discussed in the light of parasite-mediated selection on host behaviour and the reciprocal host selection on flea life-history and behavioural traits.     

Life-history variation of a neotropical thrush challenges food limitation theory

Since David Lack first proposed that birds rear as many young as they can nourish, food limitation has been accepted as the primary explanation for variation in clutch size and other life-history traits in birds. The importance of food limitation in life-history variation, however, was recently questioned on theoretical grounds. Here, we show that clutch size differences between two populations of a neotropical thrush were contrary to expectations under Lack's food limitation hypothesis. Larger clutch sizes were found in a population with higher nestling starvation rate (i.e. greater food limitation). We experimentally equalized clutches between populations to verify this difference in food limitation. Our experiment confirmed greater food limitation in the population with larger mean clutch size. In addition, incubation bout length and nestling growth rate were also contrary to predictions of food limitation theory. Our results demonstrate the inability of food limitation to explain differences in several life-history traits: clutch size, incubation behaviour, parental feeding rate and nestling growth rate. These life-history traits were better explained by inter-population differences in nest predation rates. Food limitation may be less important to life history evolution in birds than suggested by traditional theory.     

Azure‐winged Magpies Cyanopica cyanus trade off reproductive success and parental care by establishing a size hierarchy among nestlings

It is common in birds that the sizes of nestlings vary greatly when multiple young are produced in one nest. However, the methods used by parents to establish size hierarchy among nestlings and their effect on parental provisioning pattern may differ between species. In the Azure‐winged Magpie Cyanopica cyanus, we explored how and why parents controlled the sizes of nestlings. Asynchronous hatching was the main cause of size hierarchy within the brood, although the laying of larger eggs later in the laying sequence reduced this effect. Parents with asynchronous broods produced more eggs and fledged more nestlings than those with synchronous broods but their brood provisioning rates, food delivery per feeding bout and feeding efficiency did not differ. We performed a cross‐fostering experiment to synchronize some asynchronous broods. Provisioning rates of asynchronous broods were lower than those of synchronized broods, but the daily growth rates and fledging body mass of their nestlings were not different. Our findings indicate that parents of asynchronous broods can achieve higher reproductive success than those of synchronous broods based on the same parental care, and the same reproductive success as those of synchronized broods based on less parental care. It appears that parent birds can better trade off reproductive success and parental care by establishing a size hierarchy among nestlings.     

Facultative adjustment of pre‐fledging mass recession by nestling chimney swifts Chaetura pelagica

In species susceptible to mass‐dependent flight costs, mass recession prior to fledging may ensure that fledglings have appropriate wing loading. Our objectives were to determine if mass recession by chimney swift Chaetura pelagica nestlings is intrinsically controlled or facultatively adjusted by nestlings, and if mass recession is driven by changes in parental (i.e. reduced provisioning rates) or nestling (i.e. reduced begging) behavior. Nestling swifts (n = 50 in 17 broods) were divided into three treatment groups: controls, half‐weighted, or weighted. Half‐weighted and weighted nestlings had 0.6–0.7 or 1.2–1.3‐g lead weights, respectively, glued to body feathers on their backs during the period from 16 to 26 d post‐hatching. Weighted nestlings lost more mass than control and half‐weighted nestlings. After accounting for the added weights, control nestlings also had a higher wing loading than weighted nestlings. Video recordings revealed that provisioning rates of adult swifts did not vary throughout the nestling period, but the percent time nestlings spent begging increased slightly with age. Differences in mass recession among nestlings in different treatment groups resulted in convergence toward similar wing loading values likely optimal for flight efficiency. Mechanism(s) involved in this process remain unclear because provisioning rates were similar (from day 12 to 26 post‐hatching) whereas percent begging time by nestlings tended to increase with nestling age. However, weighted nestlings may have lost more mass than control nestlings by soliciting less food from adults than siblings, being more active, losing more water due to tissue maturation, or through some combination of two or more of these factors.     

Intensity of mouth coloration in Blackcap Sylvia atricapilla nestlings affects food distribution among siblings but not provisioning of the whole brood

Among various begging stimuli, mouth coloration has received increasing attention in recent years, and previous research has demonstrated that mouths of nestling Canaries Serinus canaria get redder with the extent of food deprivation and that parents preferentially feed nestlings of redder gapes. This study assesses whether the intensity of red mouth colour in nestling Blackcaps Sylvia atricapilla is a signal in parent–offspring communication. This is one of the few species with a naturally red gape in which the function of mouth redness has been tested. Three predictions were experimentally tested: (1) reddening the gape of a single nestling within a brood increases its provisioning in relation to other siblings; (2) reddening the gapes of all nestlings within a brood increases parental feeding rate; and (3) food deprivation increases nestling mouth redness. The effect of nestling quality on mouth redness was also assessed. The intensity of gape coloration affected food distribution, but in a way opposite to that expected: an increase in mouth redness of the nestling caused reduced feeding by parents. However, reddening the gapes of all nestlings had no effect on provisioning of the whole brood, suggesting that Blackcap parents use different cues for provisioning particular nestlings and the whole brood. Intensity of mouth redness in Blackcap nestlings was not affected either by food deprivation or by nestling quality in terms of mass and rank in the nest.