Impact of weather variation on feeding behaviour, nestling growth and brood survival in Wrynecks Jynx torquilla

While habitat destruction is thought to be the most important reason for the decline of the Wryneck Jynx torquilla throughout Europe, it has been hypothesised that weather factors may also play a crucial role. We studied the impact of variations in ambient temperature and rainfall on feeding behaviour, nestling growth and daily brood survival probabilities in a population from the Swiss Alps. We recorded the frequency of food provisioning and measured nestlings’ growth on 6 days at 17 nests, and monitored the success of 181 broods from 2002 to 2006. The mean feeding frequency was 7.9 feedings per hour, and increased with temperature and with nestling age. Changes of body mass, tarsus length and of the 8th primary feather were not strongly influenced by temperature and rainfall. Body growth was negatively influenced by the initial size of the different body measures towards the end of the growing phase of the corresponding body measure, pointing towards compensatory growth. Daily brood survival probabilities declined in the course of the season and with increasing rainfall, and they increased with increasing temperature and with increasing nestling age. Our findings highlight that the effects of adverse weather on feeding behaviour, nestling growth and nest survival in Wrynecks are complex, as they alter with the age of the nestlings and possibly with the duration of the adverse weather events. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Allometric relations in three species of finches (Aves: Fringillidae)

Static nestling, adult and ontogenetic allometry were analysed in three species of finches. Static nestling allometry was very similar across age in early ontogeny and among species and could be approximated by a single matrix of phenotypic variances and covariances. The first eigenvector of this matrix showed negative allometry of bill and tarsus to mass, but positive for wing length to mass. Adult static allometry was also very similar among species, but differed from nestling pattern. In adults the bill had a positive allometry in relation to tarsus and wing, but negative to mass, while tarsus and wing were unrelated to mass. The ontogenetic allometry in each species was very similar to nestling static allometry. Viewed in relation to final size, bill characters grew more slowly than body characters, but for a longer time, which created the difference between adult and nestling allometric patterns. There were differences among species both with regard to elevation and slope of allometric coefficients, suggesting that the differences among species came about by changes in the three fundamental ontogenetic parameters namely growth rate, onset of growth and offset of growth.     

Growth of yellow-headed blackbird Xanthocephalus xanthocephalus nestlings in relation to maternal body condition, egg mass, and yolk carotenoids concentrations

Condition‐dependent resource allocation to eggs can affect offspring growth and survival, with potentially different effects on male and female offspring, particularly in sexually dimorphic species. We investigated the influence of maternal body condition (i.e., mass‐tarsus residuals) and two measures of female resource allocation (i.e., egg mass, yolk carotenoid concentrations) on nestling mass and growth rates in the polygynous and highly size dimorphic yellow‐headed blackbird Xanthocephalus xanthocephalus. Egg characteristics and carotenoid concentrations were obtained from the third‐laid egg of each clutch and were correlated with the mass and growth rates of the first two asynchronously hatched nestlings. Maternal body condition was associated with the growth of first‐hatched, but not second‐hatched nestlings. Specifically, females in better body condition produced larger and faster growing first‐hatched nestlings than females in poorer body condition. As predicted for a polygynous, size‐dimorphic species, females that fledged first‐hatched sons were in better body condition than females that fledged first‐hatched daughters. Associations between egg mass, yolk carotenoid content, and nestling growth were also specific to hatching‐order. Egg mass was positively correlated with the mass and growth rates of second‐hatched nestlings, and yolk concentrations of β‐carotene were positively correlated with second‐hatched nestling mass. Surprisingly, the relationship between yolk lutein and hatchling growth differed between the sexes. Females with high concentrations of yolk lutein produced larger and faster growing first‐hatched sons, but smaller first‐hatched daughters than females with lower lutein concentrations. Mass and growth rates did not differ between first‐ and second‐hatched nestlings of the same sex, despite asynchronous hatching in the species. Results from this study suggest that maternal body condition and the allocation of resources to eggs have carotenoid‐, sex‐, and/or hatch‐order‐specific effects on yellow‐headed blackbird nestlings.     

Offspring number and quality in the blue tit: a quantitative genetic approach

The effect of natural brood size variation on offspring quality was studied in a blue tit ( Parus caeruleus ) population on the island of Gotland in the Baltic Sea. Offspring quality, measured as nestling body mass at day 13 post-hatch, declined significantly with increasing brood size, as did offspring structural body size (tarsus length). A quantitative genetic analysis revealed a high heritability of tarsus length, but also that the shorter tarsi of young from larger broods represented a negative environmental deviation from the genotypic values of their parents. Similarly, positive environmental deviations in tarsus length were found in small broods. Nestling mortality increased with increasing brood size, and smaller and lighter nestlings suffered higher mortality between day 13 and 20 post-hatch. These findings, together with those of previous studies showing that the survival prospects of malnutritioned passerine young are greatly reduced, provide evidence for a trade-off between the quantity and quality of young under non-manipulative conditions.     

Do climatic conditions affect host and parasite phenotypes differentially? A case study of magpies and great spotted cuckoos

Climatic conditions, through their effects on resource availability, may affect important life history strategies and trade-offs in animals, as well as their interactions with other organisms such as parasites. This impact may depend on species-specific pathways of development that differ even among species with similar resource requirements (e.g., avian brood parasites and their hosts). Here we explore the degree of covariation between environmental-climatic conditions and nestling phenotypes (i.e., tarsus length, body mass, immune response to phytohemagglutinin injection) and ectoparasite loads of great spotted cuckoos (Clamator glandarius) and those of their magpie (Pica pica) hosts, both within and among 11 study years (1997–2011). Our main results were that (1) nestling phenotypes differed among years, but differently for great spotted cuckoos and magpies; (2) nestling phenotypes showed significant among-year covariation with breeding climatic conditions (temperature and precipitation); and (3) these associations differed for cuckoos and magpies for some phenotypic traits. As the average temperature at the beginning of the breeding season (April) increased, body mass and tarsus length increased only for cuckoos, but not for magpie hosts, while immune response decreased in both species. Finally, (4) the strength of the within-year relationships between the probability of ectoparasitism by Carnus hemapterus flies and laying date (used as an estimate of the within-year variation in climatic conditions) was negatively affected by the annual accumulated precipitation in April. These results strongly suggest that variation in climatic conditions would result in asymmetric effects on different species with respect to the probability of ectoparasitism, immunity and body size. Such asymmetric effects may affect animal interactions in general and those of brood parasites and their hosts in particular.     

Genetic and environmental components of growth in nestling blue tits (Parus caeruleus)

We investigated the effect of brood‐size mediated food availability on the genetic and environmental components of nestling growth in the blue tit (Parus caeruleus), using a cross‐fostering technique. We found genetic variation for body size at most nestling ages, and for duration of mass increase, but not of tarsus growth. Hence, nestling growth in our study population seems to have the potential to evolve further. Furthermore, significant genotype–environment interactions indicated heritable variation in reaction norms of growth rates and growth periods, i.e. that our study population had a heritable plasticity in the growth response to environmental conditions. The decreasing phenotypic variance with nestling age indicated compensatory growth in all body traits. Furthermore, the period of weight increase was longer for nestlings growing up in enlarged broods, while there was no difference to reduced broods in the period of tarsus growth. At fledging, birds in enlarged broods had shorter tarsi and lower weights than birds in reduced broods, but there was no difference in wing length or body condition between the two experimental groups. The observed flexibility in nestling growth suggests that growing nestlings are able to respond adaptively to food constraint by protecting the growth of ecologically important traits.     

Mild stress during development affects the phenotype of great tit Parus major nestlings: a challenge experiment

Conditions experienced during early development may affect both adult phenotype and performance later during life. Phenotypic traits may hence be used to indicate past growing conditions and predict future survival probabilities. Relationships between phenotypic markers and future survival are, however, highly heterogeneous, possibly because poor‐ and high‐quality individuals cannot be morphologically discriminated when developing under good environmental conditions. Sub‐optimal breeding conditions, in contrast, may unmask poor‐quality individuals in a measurable way at the morphological level. We thus predict stronger associations between phenotype and performance under stress. In this field study, we test this hypothesis, experimentally challenging the homeostasis of great tit (Parus major) nestlings by short‐term deprivation of parental care, which had no immediate effect on nestling fitness. The experiment was replicated during two subsequent breeding seasons with contrasting ambient weather conditions. Experimental (short‐term) stress affected tarsus growth but not residual mass at fledging, whereas ambient (continuous) stress affected residual mass but not tarsus growth. Short‐term stress effects on tarsus length and tarsus fluctuating asymmetry were only apparent when ambient conditions were unfavourable. Residual mass and hatching date, but none of the other phenotypic traits, predicted local survival, whereby the strength of the relationship did not vary between both years. Because effects of stress on developmental homeostasis are likely to be trait‐specific and condition‐dependent, studies on the use of phenotypic markers for individual fitness should integrate multiple traits comprising different levels of developmental complexity. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 103–110.     

Body component growth and composition of the magpie Pica pica

Magpie nestling growth is documented as increments in body mass, tarsus length, and tenth primary length. A sample of 41 nestlings and eight adults was used to provide comparative data on changes in water content, lean dry mass, and fat content for 14 body components.
Changes in the composition of various components implicate water index (water content/ lean dry mass) as an indicator of tissue and nestling maturity. Lipid index (fat content/lean dry mass) for the whole body exhibited a sustained linear increase during the first two-thirds of the nestling period. About 80% of nestling body fat was located in the skin, body shell, and alimentary canal.
The state of development of particular components appeared to be related to the current functional requirements of the nestling. Thus the food processing components assumed an early significance, while the development of insulative and locomotory components was somewhat curtailed by comparison.     

Contrasting sensitivity of nestling and fledgling Barn Swallow Hirundo rustica body mass to local weather conditions

Local weather can influence the growth and development of young birds either indirectly, by modifying prey availability, or directly, by affecting energetic trade-offs. Such effects can have lasting implications for life history traits, but the nature of these effets may vary with the developmental stage of the birds, and over timescales from days to weeks. We examined the interactive effects of temperature, rainfall and wind speed on the mass of nestling and fledgling Barn Swallows Hirundo rustica both on the day of capture and averaging weather across the time since hatching. At the daily timescale, nestling mass was negatively correlated with temperature, but the strength of this association depended on the level of rainfall and wind speed; nestlings were typically heavier on dry or windy days, and the negative effect of temperature was strongest under calm or wet conditions. At the early lifetime timescale (i.e. from hatching to pre-fledging), nestling mass was negatively correlated with temperature at low wind speed. Fledgling body mass was less sensitive to weather; the only weather effect evident was a negative correlation with temperature at the daily scale under high rainfall that became slightly positive under low rainfall. These changes are consistent with weather effects on the availability and distribution of insects within the landscape (e.g. causing high concentrations of flying insects) and with the effects of weather variation on nest microclimate. These results together demonstrate the impacts of weather on chick growth, over immediate (daily) and longer term (nestling/fledgling lifetime) timescales. This shows that sensitivity to local weather conditions varies across the early lifetime of young birds (nestling–fledgling stages) and illustrates the mechanisms by which larger scale (climate) variations influence the body condition of individuals.     

Egg size and offspring performance in the collared flycatcher (<Emphasis Type="Italic">Ficedula albicollis</Emphasis>): a within-clutch approach

Adaptive within-clutch allocation of resources by laying females is an important focus of evolutionary studies. However, the critical assumption of these studies, namely that within-clutch egg-size deviations affect offspring performance, has been properly tested only rarely. In this study, we investigated effects of within-clutch deviations in egg size on nestling survival, weight, fledgling condition, structural size and offspring recruitment to the breeding population in the collared flycatcher (Ficedula albicollis). Besides egg-size effects, we also followed effects of hatching asynchrony, laying sequence, offspring sex and paternity. There was no influence of egg size on nestling survival, tarsus length, condition or recruitment. Initially significant effect on nestling mass disappeared as nestlings approached fledging. Thus, there seems to be limited potential for a laying female to exploit within-clutch egg-size variation adaptively in the collared flycatcher, which agrees with the majority of earlier studies on other bird species. Instead, we suggest that within-clutch egg-size variation originates from the effects of proximate constraints on laying females. If true, adaptive explanations for within-clutch patterns in egg size should be invoked with caution.     

Change in body mass in relation to breeding phase in bull-headed shrikes

Changes in body mass of both sexes of the bull-headed shrike, Lanius bucephalus, were investigated over the six breeding phases of this species. Standardized body mass (SBM), which was defined as body mass divided by the length of the tarsus, of the males was relatively constant over the phrases, while the SBM of the females changed drastically. In the females, the SBM during egg-laying was higher than the SBM in all the other breeding phases. The SBM of the females did not differ between the incubation and early-nestling phases, and was lowest during the fledgling phase. Mass loss in bull-headed shrikes did not correspond to an adaptive adjustment of body mass to permit a reduction in the power required for flight in the nestling period. It is likely that incubating females constantly maintain their body mass to invest in parental efforts from the incubating to nestling periods.     

Body mass changes in female tawny pipits Anthus campestris during the nesting stage

We analysed female body mass change, corrected by tarsus length (body condition) in tawny pipits Anthus campestris during the nesting period in a population subject to high nest predation rates (between 70 and 85%), which leads to the need for replacement clutches. Decrease in female body condition over the nesting stage (6.8 g, around 27% of the initial mass during the whole nesting process) was related to laying date, clutch size and nesting period (incubation and nestling phases). Data from recaptured females indicated a decrease during each of the three nesting phases considered (the last days of incubation and first and last days of the nestling phase), with body mass always being higher in the first of the two measurements taken in each of these phases. The observation of a continuous decrease in body condition during the last days of incubation and first and last days of the nestling phase does not support the programmed anorexia hypothesis, but adjusts well to predictions of the stress hypothesis. These results suggest that the costs accumulated during the entire nesting stage in ground passerines subjected to high nest predation rates are linked to a superimposed effect of the cost of replacement clutches.     

Offspring sex ratio is related to male body size in the great tit (Parus major)

Sex allocation theory predicts that the allocation of resourcesto male and female function should depend on potential fitnessgain realized through investment in either sex. In the greattit (Parus major), a monogamous passerine bird, male resourceholdingpotential (RHP) and fertilization success both depend on malebody size (e.g., tarsus length) and plumage traits (e.g., breaststripe size). It is predicted that the proportion of sons ina brood should increase both with male body size and plumage traits,assuming that these traits show a father—offspring correlation. Thiswas confirmed in our study: the proportion of sons in the brood increasedsignificantly with male tarsus length and also, though not significantly,with the size of the breast stripe. A sex ratio bias in relationto male tarsus length was already present in the eggs because(1) the bias was similar among broods with and without mortalitybefore the nestlings' sex was determined, and (2) the bias remainedsignificant when the proportion of sons in the clutch was conservativelyestimated, assuming that differential mortality before sex determinationcaused the bias. The bias was still present among recruits.The assumption of a father—offspring correlation was confirmedfor tarsus length. Given that both RHP and fertilization successof male great tits depend on body size, and size of father andoffspring is correlated, the sex ratio bias may be adaptive.     

Sexual size dimorphism and positive assortative mating in red-backed shrike Lanius collurio: an adaptive value?

During field studies in 1997–1999 in South Bohemia (Czech Republic), we found significant differences in size between the sexes in a local breeding population of red-backed shrike Lanius collurio. Males were significantly larger than females for wing length and tarsus length, but had smaller body mass than females. However, there was considerable overlap in the ranges of these parameters between the sexes. Interestingly, pairs were formed at random with respect to wing length and tarsus length, but assortative mating was significant for body mass/body condition. Among tested variables, only male wing length correlated significantly with nestling body mass at day 7. However, clutch size and the number of fledglings strongly depended on differences in tarsus length between mates, but not on body size of mates. Individual improvements in foraging skills and/or courtship feeding rates are proposed as possible explanations for these findings.     

Effects of temperature and nest heat exposure on nestling growth,dehydration and survival in a Mediterranean hole‐nesting passerine

Variable environments impose constraints on adaptation by modifying selection gradients unpredictably. Optimal bird development requires an adequate thermal range, outside which temperatures can alter nestling physiology, condition and survival. We studied the effect of temperature and nest heat exposure on the reproductive success of a population of double‐brooded Spotless Starlings Sturnus unicolor breeding in a nestbox colony in central Spain with a marked intra‐seasonal variation in temperature. We assessed whether the effect of temperature differed between first and second broods, thus constraining optimal nest‐site choice. Ambient temperature changed greatly during the chick‐rearing period and had a strong influence on nestling mass and all body size measures we recorded, although patterns of clutch size or nestling mortality were not influenced. This effect differed between first and second broods: nestlings were found to have longer wings and bills with increasing temperature in first broods, whereas the effect was the opposite in second broods. Ambient temperature was not related to nestling body mass or tarsus‐length in first broods, but in second broods, nestlings were lighter and had smaller tarsi with higher ambient temperatures. The exposure of nestboxes to heat influenced nestling morphology: heat exposure index was negatively related to nestling body mass and wing‐length in second broods, but not in first broods. Furthermore, there was a positive relationship between nest heat exposure and nestling dehydration. Our results suggest that optimal nest choice is constrained by varying environmental conditions in birds breeding over prolonged periods, and that there should be selection for parents to switch from sun‐exposed to sun‐protected nest‐sites as the season progresses. However, nest‐site availability and competition for sites are likely to impose constraints on this choice.     

Vitamin E improves growth of collared flycatcher Ficedula albicollis young: a supplementation experiment

In altricial birds, the quantity and quality of food provided by parents is a crucial determinant of nestling performance. Vitamin E is an important micronutrient with various physiological functions, including a positive role in the antioxidant system. Sufficient intake of vitamin E has been shown to condition normal avian development in poultry, yet, our knowledge of the role of vitamin E in free‐living birds is limited. Thus, we experimentally examined the effects of vitamin E on nestling development in the collared flycatcher Ficedula albicollis. We supplemented nestlings with vitamin E and evaluated their growth and survival till fledging. Increased availability of vitamin E did not affect body mass, wing length or survival, but improved tarsus growth. The effect of supplementation on tarsus length changed over season and with initial body mass. Supplemented nestlings that were smaller at hatching and those that hatched later in the season grew longer tarsi compared to the control. Our results suggest that 1) vitamin E may be limiting for the development of collared flycatcher nestlings, 2) seasonal changes of vitamin E availability may affect breeding success of collared flycatchers, and 3) increased income of vitamin E may improve growth of nestlings with bad start in life.     

Sympatric and allopatric combinations of hen fleas and great tits: a test of the local adaptation hypothesis

To test whether allopatric nest parasites differ from sympatric ones in their effect on various life history traits of their avian host, I designed a cross-transfer experiment in which hen fleas (Ceratophyllus gallinae) were exchanged between great tit (Parus major) nests in two geographically widely separated areas. In neither of the areas did allopatric fleas influence body mass, tarsus length, wing length, duration of nestling period or mortality in great tit nestlings more severely than did sympatric fleas. Duration of incubation was also similar among females independent of experimental treatment. This lack of difference between allopatric and sympatric fleas is hypothesized to reflect the comparative harmlessness of hen fleas for their hosts.     

Prudent investment in rearing nestlings in bull-headed shrikes

I investigated seasonal changes in the relationships between brood size, body mass of nestlings and body mass of parents of the bull-headed shrike, Lanius bucephalus, in Ishikari, northern Japan. When the broods were 12days old, the body mass of the heaviest nestling in a brood did not differ among brood sizes, or throughout the season. However, the body mass of the lightest nestlings in a brood was different among brood sizes. The body mass of the lightest nestling in five- and six-nestling broods decreased throughout the season. The lightest nestling in four-nestling broods, and the lightest and the second lightest nestlings in five-nestling broods, were significantly lighter than the heaviest nestling in broods of this size. It is likely that pairs with six nestlings at 12days old can feed at least five of these nestlings enough to ensure their survival . The standardized body mass of parents (SBM), which was defined as the body mass divided by the length of the tarsus, did not differ among brood sizes, or throughout the season. It is possible that the relationship between the constancy of the SBM and the seasonal decline in the body mass of nestlings indicates that bull-headed shrikes have a limit to their parental efforts.     

Manipulation of hunger levels affects great spotted cuckoo and magpie host nestlings differently

Brood parasitic nestlings usually exhibit an exaggerated begging behaviour, which is mainly attributed to reduced inclusive fitness costs since they typically share the nest with unrelated individuals. However, energetic costs also constrain begging expression and accordingly a relation between food requirements and intensity of begging behaviour could also exist in brood parasites, just as in nesting bird species. Here, we tested this hypothesis in the great spotted cuckoo Clamator glandarius and its main host, the magpie Pica pica, by studying the effect of an appetite enhancer, cyproheptadine hydrochloride, on nestling provisioning and development (size, body mass and cell‐mediated immune response). To study nestling provisioning, neck‐collars were meticulously placed around nestling necks allowing normal respiration but avoiding the ingestion of food delivered by adult magpies during ca 2.5 h. Loss in body mass during neck‐collar trials was used as a proxy for energetic begging costs, while the amount of food received during these trials and growth during the whole nestling period were used as variables reflecting short‐ and long‐term effects of the experimental treatment. During neck‐collar trials, we found that experimental nestlings of both species received more food than control nestlings. However, experimental magpies, but not cuckoos, lost more body mass than control nestlings. These results suggest a short‐term beneficial effect of an escalated begging behaviour in both species that would be energetically cheaper for cuckoos than for magpies. We found positive long‐term effects of the appetite enhancer only in magpies (in terms of tarsus and wing length at fledging, but not in terms of immune response and body mass); suggesting that exaggerated begging would be beneficial for hosts only. We discuss the possible effect of begging behaviour on the risk of predation and on inclusive fitness, but also the possibility that our results may be explained by some kind of limitation in the capability of food assimilation by parasitic species.     

Variation in the magnitude of sexual size dimorphism in nestling Coal Tits (Periparus ater)

The magnitude of sexual size dimorphism can be affected by sex differences in environmental sensitivity early in ontogeny that result in differential growth rates of male and female nestlings. Here, the larger sex might either be more sensitive because of higher food demands or less sensitive due to greater competitive ability. When environmental conditions deteriorate during the breeding season, this “environmental stress” hypothesis predicts differential seasonal declines in the performance of male and female offspring. Based on a sample of molecularly sexed Coal Tit (Periparus ater) nestlings from 2 years, we investigated sexual size dimorphism in body mass, condition (i.e. size-corrected mass), tarsus and wing length and whether its magnitude changed from early to late broods. Male offspring were heavier, larger (in terms of tarsus and wing length) and had higher size-corrected mass than their female nest mates (the same was evident in adult breeders). In 2002 (the year with the longer effective breeding season), body mass and condition declined with progressing hatching date and this effect was significantly more pronounced in male than in female nestlings. There was also a seasonal decline in male wing length, while female wing length remained relatively constant, which resulted in males having shorter wings than females in late broods. Tarsus length was unaffected by time of breeding, except that the difference between males and females was relatively smaller in late (i.e. second) broods in 2002. While these results are in accordance with the idea of an increased environmental sensitivity of the larger males, confounding effects of sex-differential hatching order cannot be ruled out. Dedicated to Doris Winkel.