Effect Of Brood Size Research Articles

Early developmental carry-over effects on exploratory behaviour and DNA methylation in wild great tits (Parus major).

Adverse, postnatal conditions experienced during development are known to induce lingering effects on morphology, behaviour, reproduction and survival. Despite the importance of early developmental stress for shaping the adult phenotype, it is largely unknown which molecular mechanisms allow for the induction and maintenance of such phenotypic effects once the early environmental conditions are released. Here we aimed to investigate whether lasting early developmental phenotypic changes are associated with post-developmental DNA methylation changes. We used a cross-foster and brood size experiment in great tit (Parus major) nestlings, which induced post-fledging effects on biometric measures and exploratory behaviour, a validated personality trait. We investigated whether these post-fledging effects are associated with DNA methylation levels of CpG sites in erythrocyte DNA. Individuals raised in enlarged broods caught up on their developmental delay after reaching independence and became more explorative as days since fledging passed, while the exploratory scores of individuals that were raised in reduced broods remained stable. Although we previously found that brood enlargement hardly affected the pre-fledging methylation levels, we found 420 CpG sites that were differentially methylated between fledged individuals that were raised in small versus large sized broods. A considerable number of the affected CpG sites were located in or near genes involved in metabolism, growth, behaviour and cognition. Since the biological functions of these genes line up with the observed post-fledging phenotypic effects of brood size, our results suggest that DNA methylation provides organisms the opportunity to modulate their condition once the environmental conditions allow it. In conclusion, this study shows that nutritional stress imposed by enlarged brood size during early development associates with variation in DNA methylation later in life. We propose that treatment-associated DNA methylation differences may arise in relation to pre- or post-fledging phenotypic changes, rather than that they are directly induced by the environment during early development.

Early-life environmental effects on mitochondrial aerobic metabolism: a brood size manipulation in wild great tits.

In avian species, the number of chicks in the nest and subsequent sibling competition for food are major components of the offspring's early-life environment. A large brood size is known to affect chick's growth, leading in some cases to long-lasting effects for the offspring, such as a decrease in size at fledgling and in survival after fledging. An important pathway underlying different growth patterns could be the variation in offspring mitochondrial metabolism through its central role in converting energy. Here, we performed a brood size manipulation in great tits (Parus major) to unravel its impact on offspring's mitochondrial metabolism and reactive oxygen species (ROS) production in red blood cells. We investigated the effects of brood size on chicks' growth and survival, and tested for long-lasting effects on juvenile mitochondrial metabolism and phenotype. As expected, chicks raised in reduced broods had a higher body mass compared to enlarged and control groups. However, mitochondrial metabolism and ROS production were not significantly affected by the treatment either at chick or juvenile stages. Interestingly, chicks raised in very small broods were smaller in size and had higher mitochondrial metabolic rates. The nest of rearing had a significant effect on nestling mitochondrial metabolism. The contribution of the rearing environment in determining offspring mitochondrial metabolism emphasizes the plasticity of mitochondrial metabolism in regards to the nest environment. This study opens new avenues regarding the implication of postnatal environmental conditions in shaping the offspring's early-life mitochondrial metabolism.

Brood size, food availability, and body size affects male care decisions and offspring performance.

Parental care strategies do not only vary greatly across species, but also within species there can be substantial between- and within-individual variation in parental care behavior. To better understand the evolution of care strategies, it is crucial to determine how and when parents modify their behavior in response to internal as well as environmental factors. Here, we investigated the effect of brood size, resource size and an individual's quality on care strategies of uniparental males and examined the downstream consequences on offspring performance in the burying beetle Nicrophorus vespilloides. Burying beetles breed on small vertebrate cadavers and, on average, males invest much less in care than females. Nevertheless, we found that uniparentally caring males were responsive to their social and non-social environment and adjusted the amount as well as the type of care to the size of the brood, the size of the cadaver and their own body size. Additionally, we show that the care strategies affected offspring performance. Specifically, males that cared longer had larger and more surviving larvae. Our results add to our understanding of plastic parenting strategies by showing that even the sex that provides less care can evolve a very flexible care behavior.

Developmental stress does not induce genome-wide DNA methylation changes in wild great tit (Parus major) nestlings.

The environment experienced during early life is a crucial factor in the life of many organisms. This early life environment has been shown to have profound effects on morphology, physiology and fitness. However, the molecular mechanisms that mediate these effects are largely unknown, even though they are essential for our understanding of the processes that induce phenotypic variation in natural populations. DNA methylation is an epigenetic mechanism that has been suggested to explain such environmentally induced phenotypic changes early in life. To investigate whether DNA methylation changes are associated with experimentally induced early developmental effects, we cross-fostered great tit (Parus major) nestlings and manipulated their brood sizes in a natural study population. We assessed experimental brood size effects on pre-fledging biometry and behaviour. We linked this to genome-wide DNA methylation levels of CpG sites in erythrocyte DNA, using 122 individuals and an improved epiGBS2 laboratory protocol. Brood enlargement caused developmental stress and negatively affected nestling condition, predominantly during the second half of the breeding season, when conditions are harsher. Brood enlargement, however, affected nestling DNA methylation in only one CpG site and only if the hatch date was taken into account. In conclusion, this study shows that nutritional stress in enlarged broods does not associate with direct effects on genome-wide DNA methylation. Future studies should assess whether genome-wide DNA methylation variation may arise later in life as a consequence of phenotypic changes during early development.

No evidence for associations between brood size, gut microbiome diversity and survival in great tit (Parus major) nestlings

BackgroundThe gut microbiome forms at an early stage, yet data on the environmental factors influencing the development of wild avian microbiomes is limited. As the gut microbiome is a vital part of organismal health, it is important to understand how it may connect to host performance. The early studies with wild gut microbiome have shown that the rearing environment may be of importance in gut microbiome formation, yet the results vary across taxa, and the effects of specific environmental factors have not been characterized. Here, wild great tit (Parus major) broods were manipulated to either reduce or enlarge the original brood soon after hatching. We investigated if brood size was associated with nestling bacterial gut microbiome, and whether gut microbiome diversity predicted survival. Fecal samples were collected at mid-nestling stage and sequenced with the 16S rRNA gene amplicon sequencing, and nestling growth and survival were measured.ResultsGut microbiome diversity showed high variation between individuals, but this variation was not significantly explained by brood size or body mass. Additionally, we did not find a significant effect of brood size on body mass or gut microbiome composition. We also demonstrated that early handling had no impact on nestling performance or gut microbiome. Furthermore, we found no significant association between gut microbiome diversity and short-term (survival to fledging) or mid-term (apparent juvenile) survival.ConclusionsWe found no clear association between early-life environment, offspring condition and gut microbiome. This suggests that brood size is not a significantly contributing factor to great tit nestling condition, and that other environmental and genetic factors may be more strongly linked to offspring condition and gut microbiome. Future studies should expand into other early-life environmental factors e.g., diet composition and quality, and parental influences.

Epigenetics and Early Life Stress: Experimental Brood Size Affects DNA Methylation in Great Tits (Parus major)

Early developmental conditions are known to have life-long effects on an individual’s behavior, physiology and fitness. In altricial birds, a majority of these conditions, such as the number of siblings and the amount of food provisioned, are controlled by the parents. This opens up the potential for parents to adjust the behavior and physiology of their offspring according to local post-natal circumstances. However, the mechanisms underlying such intergenerational regulation remain largely unknown. A mechanism often proposed to possibly explain how parental effects mediate consistent phenotypic change is DNA methylation. To investigate whether early life effects on offspring phenotypes are mediated by DNA methylation, we cross-fostered great tit (Parus major) nestlings and manipulated their brood size in a natural study population. We assessed genome-wide DNA methylation levels of CpG sites in erythrocyte DNA, using Reduced Representation Bisulfite Sequencing (RRBS). By comparing DNA methylation levels between biological siblings raised in enlarged and reduced broods and between biological siblings of control broods, we assessed which CpG sites were differentially methylated due to brood size. We found 32 differentially methylated sites (DMS) between siblings from enlarged and reduced broods, a larger number than in the comparison between siblings from control broods. A considerable number of these DMS were located in or near genes involved in development, growth, metabolism, behavior and cognition. Since the biological functions of these genes line up with previously found effects of brood size and food availability, it is likely that the nestlings in the enlarged broods suffered from nutritional stress. We therefore conclude that early life stress might directly affect epigenetic regulation of genes related to early life conditions. Future studies should link such experimentally induced DNA methylation changes to expression of phenotypic traits and assess whether these effects affect parental fitness to determine if such changes are also adaptive.

Similarities and differences in the biotransformation and transcriptomic responses of Caenorhabditis elegans and Haemonchus contortus to five different benzimidazole drugs

We have undertaken a detailed analysis of the biotransformation of five of the most therapeutically important benzimidazole anthelmintics - albendazole (ABZ), mebendazole (MBZ), thiabendazole (TBZ), oxfendazole (OxBZ) and fenbendazole (FBZ) - in Caenorhabditis elegans and the ruminant parasite Haemonchus contortus. Drug metabolites were detected by LC-MS/MS analysis in supernatants of C. elegans cultures with a hexose conjugate, most likely glucose, dominating for all five drugs. This work adds to a growing body of evidence that glucose conjugation is a major pathway of xenobiotic metabolism in nematodes and may be a target for enhancement of anthelmintic potency. Consistent with this, we found that biotransformation of albendazole by C. elegans reduced drug potency. Glucose metabolite production by C. elegans was reduced in the presence of the pharmacological inhibitor chrysin suggesting that UDP-glucuronosyl/glucosyl transferase (UGT) enzymes may catalyze benzimidazole glucosidation. Similar glucoside metabolites were detected following ex vivo culture of adult Haemonchus contortus. As a step towards identifying nematode enzymes potentially responsible for benzimidazole biotransformation, we characterised the transcriptomic response to each of the benzimidazole drugs using the C. elegans resistant strain CB3474 ben-1(e1880)III. In the case of albendazole, mebendazole, thiabendazole, and oxfendazole the shared transcriptomic response was dominated by the up-regulation of classical xenobiotic response genes including a shared group of UGT enzymes (ugt-14/25/33/34/37/41/8/9). In the case of fenbendazole, a much greater number of genes were up-regulated, as well as developmental and brood size effects suggesting the presence of secondary drug targets in addition to BEN-1. The transcriptional xenobiotic response of a multiply resistant H. contortus strain UGA/2004 was essentially undetectable in the adult stage but present in the L3 infective stage, albeit more muted than C. elegans. This suggests that xenobiotic responses may be less efficient in stages of parasitic nematodes that reside in the host compared with the free-living stages.

Body condition of Little Egret Egretta garzetta nestlings in relation to hatching order in a southern Tunisian breeding colony

The effect of asynchronous hatching on nestling health and condition in ardeids is still in need of empirical evidence from populations living in different environmental conditions. Using morphometric and hematologic data from Little Egret Egretta garzetta nestlings in a Tunisian breeding colony, we assessed the relationship between hatching order and nestling condition, while accounting for the effects of brood size, age and hatching date. Our results showed that the youngest nestlings had lower values of hematocrit and body condition index but higher levels of fluctuating asymmetry compared with their older siblings. These trends seem to stem from increased nutritional stress experienced by younger nestlings who would have received less food from their parents than their siblings due to their less competitive nature. Additional constraints during the rearing period, such as possible injuries resulting from conflicts with siblings and the energy cost of thermoregulation, may also have contributed to the deterioration of the condition of last nestlings. Overall, our findings provide empirical evidence of the short-term repercussions of asynchronous hatching in a North African population of Little Egrets. They also highlight the great complexity of mechanisms by which asynchronous hatching may affect body condition and health of bird nestlings.

Carry-over effects of brood size on morphology, reproduction, and lifespan in barn swallows

Early life ecological conditions have well-documented short-term effects on offspring phenotype and survival, but the extent to which these effect carry-over into adulthood is much less known. Yet, unveiling such carry-over effects is essential to understand the evolution of parental life-history strategies. In altricial birds, the number of brood mates can affect competition regime and other nest ecological conditions, whose effects may be at least partly expressed in adulthood. We either increased or decreased the size of barn swallow (Hirundo rustica) broods and analyzed the consequences of brood size manipulation on morphological feather traits, breeding performance, and lifespan of the offspring when adult. Upon recruitment (age 1 year), individuals from enlarged broods had shorter wings, later reproduction, and lower breeding output than those from reduced broods. The negative effect of brood enlargement on wing length persisted at age 2 years. Recruits from enlarged broods had longer lifespan but the proportion of nestlings that were recruited tended to be smaller for enlarged compared to reduced broods. Hence, large brood size had negative phenotypic effects in adulthood. Our results also suggest that stronger viability selection on offspring from enlarged broods results in differential survival of highly viable offspring that express longer life expectancy when adult and/or that smaller reproductive effort of 1-year-old offspring from enlarged broods boosts their life expectancy, potentially compensating for reduced annual fecundity. Number of brood mates can thus have carry-over effects on fitness components, including lifespan, which should be incorporated in the analysis of complex reproductive trade-offs. Ecological conditions in early life can affect survival and physical conditions but the extent to which these effects extend into adulthood is largely unknown. In this experiment, we altered the size of barn swallow broods and monitored the consequences of the change in competition regime in the brood of rearing in adulthood. When adult, individuals that had been reared in an enlarged brood had shorter wings and decreased breeding success. However, individuals from enlarged broods lived longer, possibly because only high-quality individuals from such broods survived through the first year of life. Thus, rearing conditions have important long-term effects, implying that parents have to optimize the number of offspring they decide to produce.

Joint effects of brood size and resource availability on sibling competition

The evolution of sibling competition is promoted when the brood's demand for resources (brood size) exceeds the parents' supply of resources (resource availability). However, little is known about the joint effects of brood size and resource availability and whether these effects are independent of each other. We conducted a study on the burying beetle Nicrophorus vespilloides, in which we manipulated both brood size and resource availability. We manipulated brood size by providing parents with 5, 10 or 20 larvae and resource availability by providing parents with a 5, 10 or 20 g mouse carcass. We found that resource availability had positive effects on parental care, larval body mass and larval survival, while brood size had a negative effect on larval body mass and larval survival. There were positive effects of the interaction between brood size and resource availability on larval begging and larval body mass, suggesting that the slopes describing the effect of brood size on larval begging and larval body mass became less negative as carcass size increased. When we repeated the analysis using larval density (i.e. brood size/resource availability) as a proxy for the shortage of resources, there were negative effects on parental care, larval body mass and larval survival. Our results have important implications by showing that there were main effects of both brood size and resource availability, and that their effects were not always independent of each other. Thus, treating brood size and resource availability as independent factors is preferential to using offspring density.

An experimental test of the effect of brood size on glucocorticoid responses, parental investment, and offspring phenotype

Because elevated glucocorticoid levels can impair reproduction, populations or species that engage in particularly valuable reproductive attempts may down-regulate the glucocorticoid stress response during reproduction (the brood value hypothesis). It is not clear, however, whether individuals rapidly modulate glucocorticoid responses based on shifting cues about the likelihood of reproductive success. By manipulating brood size to create broods that differed in potential value, we tested whether female barn swallows (Hirundo rustica) rapidly modulated the glucocorticoid stress response to promote investment in high-value broods, and whether nestling phenotype was influenced by treatment. Within-individual changes in female corticosterone, body mass, and measures of oxidative stress were unrelated to brood size treatment. Standard offspring provisioning rate did not differ across treatments; however, in the presence of a model predator, females raising enlarged broods maintained higher offspring feeding rates relative to control broods. Brood size did influence nestling phenotype. Nestlings from enlarged broods had lower body mass and higher baseline corticosterone than those from reduced broods. Finally, in adult females both baseline and stress-induced corticosterone were individually repeatable. Thus, while under moderately challenging environmental conditions brood size manipulations had context-dependent effects on parental investment, and influenced nestling phenotype, maternal glucocorticoid levels were not modulated based on brood value but were individually consistent features of phenotype during breeding.

Evolution of nestling faeces removal in avian phylogeny

Nest sanitation-related traits have often been explained at the intraspecific level as reducing the probability of infection or detection by predators and parasites, but its evolution within the avian phylogeny is still poorly understood. We compiled detailed information of such traits for more than 400 bird species and, by means of modern comparative methodologies, we reconstructed the evolution of adults' contribution to removing their offspring's faeces and the production of faecal sacs by nestlings. Furthermore, because the functional hypotheses used to explain nest sanitation behaviour assume potential effects of brood size, body mass, nestling period and diet, we explored the association between these traits and those related to nest sanitation in a phylogenetically controlled framework. Our results suggest that parental removal of nestling faeces has driven the evolution of faecal sacs, while the ancestral states involved birds with faecal sacs removed by parents. These results support the long-held idea that faecal sacs facilitate the removal of faeces by parents. Moreover, we found that animal diets and small body sizes have favoured the evolution of faecal sacs suggesting the existence of some chemical and physical constraints in relation to the evolution of the mucous covering. Our results highlight the importance of nest sanitation in the evolution of birds and their life history characteristics.

Effect of natural brood size variability on growth and survival of thornbird nestlings

AbstractFor many bird species, brood size is a highly variable trait. Several aspects of the development and survival of nestlings are affected by brood size. Most scientific evidence comes from brood manipulation experiments, and the complementary information offered by studies of natural variability has received little attention in tropical and subtropical species. Here, we provide data on the effect of brood size on the development and survival of two furnariid species under natural conditions. Weekly during two breeding seasons, two forest patches (40 ha. each) from central Argentina, were exhaustively examined for active nests. Nestlings were monitored repeatedly from hatching to fledging. Factors that were considered potential confounders or effect modifiers were also recorded and included in the statistical analysis. We found a positive effect of brood size on growth, and a negative effect on survival. The first effect was only observed when preceding weeks were not rainy, and the latter was present in only one breeding season, so both effects appeared to depend on environmental conditions. Our results suggest that the benefit of a large or small brood size is dependent on context. In the studied populations, plasticity in or within‐population genetic diversity in brood size may be advantageous in the light of the unpredictable circumstances that will prevail during the breeding season.

Brood size constrains the development of endothermy in blue tits.

Altricial birds are unable to maintain body temperature when exposed to low ambient temperatures during the first days after hatching. Thermoregulatory capacity begins to form as postnatal development progresses, and eventually nestlings become homeothermic. Several factors may influence this development at both the level of the individual and the level of the whole brood, but to our knowledge no studies have focused on the effect of brood size per se on the development of endothermy in individual nestlings. We performed cooling experiments on blue tit (Cyanistes caeruleus) nestlings in the field, to study how different experimental brood sizes affected the development of endothermy in individual nestlings and the thermal environment experienced by the whole brood in the nest. Nestlings from all experimental brood sizes showed a decrease in cooling rate as they grew older, but birds from reduced broods showed an earlier onset of endothermy compared with nestlings from enlarged and control broods. This difference manifested during early development and gradually disappeared as nestlings grew older. The thermal environment in the nests differed between treatments during nestling development, such that nest temperature in reduced broods was lower than that in enlarged broods during all days and during nights at the end of the experimental period. We suggest that the development of endothermy in blue tit nestlings is not ontogenetically fixed, but instead may vary according to differences in developmental, nutritional and thermal conditions as determined by brood size.

The effects of quantitative fecundity in the haploid stage on reproductive success and diploid fitness in the aquatic peat moss Sphagnum macrophyllum.

A major question in evolutionary biology is how mating patterns affect the fitness of offspring. However, in animals and seed plants it is virtually impossible to investigate the effects of specific gamete genotypes. In bryophytes, haploid gametophytes grow via clonal propagation and produce millions of genetically identical gametes throughout a population. The main goal of this research was to test whether gamete identity has an effect on the fitness of their diploid offspring in a population of the aquatic peat moss Sphagnum macrophyllum. We observed a heavily male-biased sex ratio in gametophyte plants (ramets) and in multilocus microsatellite genotypes (genets). There was a steeper relationship between mating success (number of different haploid mates) and fecundity (number of diploid offspring) for male genets compared with female genets. At the sporophyte level, we observed a weak effect of inbreeding on offspring fitness, but no effect of brood size (number of sporophytes per maternal ramet). Instead, the identities of the haploid male and haploid female parents were significant contributors to variance in fitness of sporophyte offspring in the population. Our results suggest that intrasexual gametophyte/gamete competition may play a role in determining mating success in this population.

Sibling competition does not exacerbate inbreeding depression in the burying beetle Nicrophorus vespilloides.

Inbreeding results from matings between relatives and can cause a reduction in offspring fitness, known as inbreeding depression. Previous work has shown that a wide range of environmental stresses, such as extreme temperatures, starvation and parasitism, can exacerbate inbreeding depression. It has recently been argued that stresses due to intraspecific competition should have a stronger effect on the severity of inbreeding depression than stresses due to harsh physical conditions. Here, we tested whether an increase in the intensity of sibling competition can exacerbate inbreeding depression in the burying beetle Nicrophorus vespilloides. We used a 2 × 3 factorial design with offspring inbreeding status (outbred or inbred) and brood size (5, 20, or 40 larvae) as the two factors. We found a main effect of inbreeding status, as inbred larvae had lower survival than outbred larvae, and a main effect of brood size, as larvae in large broods had lower survival and mass than larvae in medium-sized broods. However, there was no effect of the interaction between inbreeding status and brood size, suggesting that sibling competition did not influence the severity of inbreeding depression. Since we focused on sibling competition within homogeneous broods of either inbred or outbred larvae, we cannot rule out possible effects of sibling competition on inbreeding depression in mixed paternity broods comprising of both inbred and outbred offspring. More information on whether and when sibling competition might influence inbreeding depression can help advance our understanding of the causes underlying variation in the severity of inbreeding depression.

Filial cannibalism in a nest-guarding fish: females prefer to spawn in nests with few eggs over many

In fish, fecundity correlates with female body size and egg-tending males often eat small broods. Therefore, small females may prefer to spawn in nests that already contain many eggs, to ensure the brood is as large as possible. In contrast, large females may prefer nests with few eggs, if high egg number or density has a negative effect on egg survival, or if there are drawbacks of spawning last in a nest. To test the hypothesis that female body size affects nest (and male mate) choice, using the sand goby (Pomatoschistus minutus), we allowed small and large females to choose between two males that were matched in size — one guarding a small clutch and the other a large clutch, respectively. We recorded where females spawned (measure of female preference), the combined brood size, male courtship, egg care and nest building. We also quantified the effect of brood size and egg density on egg survival in a separate data set. Although the combined broods did not exceed the small brood sizes that are at risk of being eaten, both small and large females preferred to spawn in nests with smaller clutch sizes. This preference could not be explained by more courtship or male parental effort, nor by reduced survival of larger or denser broods. Instead, our result might be explained by females avoiding the danger of cannibalism of young eggs by males or the risk of reduced egg health associated with being near the nest periphery.

Does Nest Predation Risk Induce Parent Birds to Eat Nestlings' Fecal Sacs? An Experimental Study

Adult birds are frequently observed consuming nestling feces. However, fecal sac ingestion has received little attention, including a lack of experimental tests to understand such behavior. Traditionally, it has been explained by the “parental nutrition hypothesis” (parents acquire nutrients and energy) or the “economic disposal hypothesis” (parents save time to do other tasks). Here, we propose a third explanation, the “nest predation hypothesis”: parents ingest fecal sacs to reduce nest detectability in the presence of a nest predator. We experimentally manipulated the nest-predation risk perceived by adult common blackbirds (Turdus merula). We detected an effect of brood size in the removed and ingested feces while our experiment did not increase fecal sac comsumption. However, we found other evidences supporting that nest predation could play a more subtle role in this parental care behavior: (1) both sexes contributed equally to fecal ingestion; (2) adults ingested more feces in the population with the highest nest-predation risk; and (3) parents that ate fecal sacs increased their permanence at the nest.

Maternal provisioning and possible joint breeding in the burrower bugAdomerus triguttulus(Heteroptera:Cydnidae)

AbstractSubsocial burrower bugs (Heteroptera:Cydnidae) provide unique opportunities to investigate evolutionary ecological questions regarding parental provisioning and family dynamics. Observations and marked nutlet‐setting experiments in the field showed thatAdomerus triguttulusfemales progressively delivered mint nutlets into nests harbouring nymphs under the litter. More than one female often attended nymphs, but not eggs, in a nest in the field. The number of nymphs aggregating in a nest with a single female was usually smaller than that in a nest with two females, suggesting the joining of different families and facultative joint parental care. There was a positive correlation between the number of nutlets delivered and the number of nymphs in a nest. The number of attendant females also affected the amount of provisioning; more nutlets were found for second‐instar broods with more females. The effect of brood size on provisioning was confirmed for families under laboratory rearing. Maternal provisioning also varied with the developmental stage of offspring; second‐instar broods received more nutlets than first‐instar broods, with a temporal decrease in provisioning during the moulting of nymphs. Considering the growing evidence of food solicitation signals of young in subsocial insects, the observed finely tuned supply of food by the female could be induced by begging signals from the nymphs.

In the BlackcapSylvia atricapillaLast-Hatched Nestlings Can Catch up with Older Siblings

Development during the relatively short time that young spend in the nest is crucial in a bird's life history. The rate of nestling growth strongly depends on numerous environmental and social factors, even within the same species or population. In the present study I examine the relative contributions of brood size, hatching asynchrony, hatching date and feeding rate in determining intraspecific variation in the growth of Eurasian Blackcap Sylvia atricapilla nestlings. I found a significant effect of brood size, hatching order and date on nestling development. However, the effect of hatching order and date was significant only for young nestlings and it gradually disappeared with nestling age. The only factor significantly affecting nestling development just before fledging was brood size. Nests of four siblings produced the heaviest young with the longest tarsi. This probably resulted from the highest feeding rate per nestling observed in broods of four nestlings. The study shows that for Blackcaps bree...