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It is widely assumed that female birds use nonphotic supplemental cues, including social factors, to fine-tune timing of egg-laying to local conditions, but our knowledge of the nature of these social cues and how they operate remains limited. We analyzed the relationship between a female's social environment (nearest neighbor distances, residency, female -and- network familiarity, synchrony) and variation in timing of egg-laying in European starlings (Sturnus vulgaris) using individual, residual laying date (controlling for annual variation) and temperature-independent residual laying date (accounting for the effect of ambient temperature on laying date). Female social environment varied systematically with overall spatial distribution of nest-boxes (linear vs clumped boxes) but this was not associated with spatial variation in laying date or temperature-independent residual laying date. We found no evidence for any relationships between individual variation in social environment and individual, residual laying date and only weak evidence for any association with individual, temperature-independent residual laying date. The latter was associated with (1) nearest neighbor distances in the linear habitat, with females nesting closer to neighbors laying earlier than predicted by temperature, but not in the two clumped habitats, and (2) neighbor familiarity: females with an intermediate number of returning females (3/8) laid closest to the predicted date. Finally, despite the fact that synchrony was not associated with other social environment metrics, females with lower laying synchrony among neighbors laid earlier than predicted by temperature. This suggests that some components of the female-female social environment could act as supplemental cues for timing of egg-laying. [ABSTRACT FROM AUTHOR]

It has long been recognized that mass loss during breeding could be adaptive (e.g., by ameliorating the costs of increased parental activity). However, many studies still commonly interpret mass loss as evidence of "stress" or a cost of reproduction (i.e., a negative effect of high workload during chick provisioning). Despite several studies reporting evidence in support of both hypotheses, the ecological and/or life‐history contexts under which mass loss may be viewed as a "cost" or an adaptive strategy are still unclear. Here, we used a long‐term dataset from a breeding population of European starlings (Sturnus vulgaris) to investigate natural annual and individual variation in body mass and mass loss and to test whether mass loss during chick rearing represents a phenotypically plastic trait that varies predictably in relation to ecological context and individual quality. While there was significant annual variation in incubation mass, chick‐rearing mass, and mass change, there were no systematic relationships between mass loss and current breeding success or future fecundity and survival. In addition, we found no evidence of intra‐annual repeatability of mass loss between first and second broods (=.00) but moderate interannual repeatability of mass loss (R =.61) during first broods, suggesting differences in mass loss under different selective pressures. However, we found no covariation between residual intra‐individual variation in mass loss for first broods and other reproductive or life‐history traits. We therefore found no support for the idea that mass loss reflects "reproductive stress" in our system: there were no negative relationships between mass loss and either current or future reproduction and survival (local return rate). Our results are consistent with mass loss being an individually plastic trait, with individuals using mass loss to "level the playing field" and individually optimize reproductive effort and fitness within their specific ecological context and relative to their individual quality for a given breeding attempt. [ABSTRACT FROM AUTHOR]

It is generally assumed that larger juveniles are more physiologically mature, hence their overall condition and subsequent performance are higher.Some taxa face extreme workload transitions during development (e.g. nest departure in birds), which may select for non‐linear growth profiles that decouple relationships between body size and physiological state, making the links between metrics of development (e.g. body mass) and juvenile performance uncertain.We manipulated perceived mass in European starlings approaching fledging using 4.0 g weighted backpacks, measuring subsequent growth trajectories (mass, wing length) and physiological state (aerobic capacity, energy state, oxidative status) to test whether body size and physiology are coupled during a non‐linear developmental phase (pre‐fledging mass recession). Nanotag radio transmitters were then used to track post‐fledging performance (activity, activity‐slope, dispersal).Weighted nestlings had greater pre‐fledging mass recession and marginally reduced wing growth when compared to controls. Consequently, weighted birds had lower body mass at fledging, while also displaying markers of oxidative stress (increased reactive oxygen metabolites), yet aerobic capacity and energy state were equal between treatment groups.Previously weighted birds showed no correlation between fledgling state (body size, physiology) and subsequent performance. However, control fledglings that had decreased mass recession and greater wing growth prior to fledging dispersed earlier, while longer wings at fledging were associated with more rapid increases in post‐fledging activity (activity‐slope). In addition, control fledglings with lower haemoglobin also dispersed earlier, while increased reactive oxygen metabolites were associated with decreased activity levels. Body mass and energy state were unrelated to any metric of post‐fledging performance.Our data suggest mass‐independent development of some physiological traits in species with non‐linear growth profiles, potentially with a context‐dependent oxidative cost, and that physiology may predict some measures of post‐fledging performance not captured by body size. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Temperature, particularly within ~1 month of egg laying, is thought to be an important, short-term cue used by female birds to calibrate timing of breeding to local conditions. Here, we show that a relatively broad, long-term, temperature window (January 2 to April 4, 92 days; r2 = 0.73) best predicted timing of egg laying in European Starlings (Sturnus vulgaris). A “mid-winter” temperature window was also strongly correlated with laying date (r² = 0.58), but we found no support for an influence of short-term temperatures immediately before egg laying. We assessed the relationship between ambient temperature and timing of egg laying using three complimentary approaches: (1) an “unconstrained,” exploratory analysis; (2) a traditional sliding window approach; and (3) specific, biologically informed temperature windows. Our results contrast with the widely held view that short-term, prebreeding temperatures best predict variation in laying because they allow birds to adjust timing of breeding to local conditions around the time of egg laying. This means that mechanisms that allow integration of long-term temperature information must exist in birds—perhaps most parsimoniously involving indirect effects of temperature on growth of the bird’s ectothermic insect prey—even though these are currently poorly characterized. [ABSTRACT FROM AUTHOR]

Sexual conflict occurs in biparental species because working together provides shared benefits while incurring individual costs. In birds, coordination of provisioning visits via turn taking has been proposed as a strategy to mitigate this conflict. However, alternation of visits requires that birds have access to reliable information on their partner's behaviour, e.g. through high synchrony of nest visits or short foraging distances (allowing for direct observation of partners). Here we investigated parental coordination in the European starling, a species that forages at considerable distances from the nest (200–1600 m), where there is no evidence that pairs forage together, and where synchrony at the nest appears to be low, so that direct access to information on partners will be variable and limited. There was some evidence that individuals were 'paying attention' to their partner's provisioning rate, adjusting their behaviour in response to their partner's behaviour. In first broods, female intervisit intervals that were preceded by a male visit (order of visits: male, female, female) were longer than those that were preceded by a female visit (order of visits: female, female, female). Females and males both responded to mate removal by decreasing their provisioning rates though these returned to preremoval levels the day after removal. This is consistent with 'matching' of parental workload not 'partial compensation'. These results suggest that birds do adjust their behaviour in relation to information about their partner's behaviour or absence/presence. However, despite this, there was no evidence of true coordination via alternation or synchrony (i.e. this was not different from random) in European starlings. • Parental coordination requires information on the partner's provisioning behaviour. • Starlings have long foraging distances and low synchrony at the nest. • Individuals appeared to 'pay attention' to their partner's provisioning rate. • Individuals appeared to adjust their behaviour relative to their partner's behaviour. • However, alternation and synchrony were not different from random. [ABSTRACT FROM AUTHOR]

Parental care is widely assumed to be costly, and life-history theory predicts that individuals that invest more in parental care should benefit in terms of number of offspring produced but that increased parental care might come at a cost in terms of decreased future fecundity and/or survival. However, the notion that parents that work 'harder', commonly measured by the rate at which parents visit the nestbox to provision their chicks, produce more, fitter chicks is surprisingly poorly supported. One potential reason for this apparent lack of relationship between measured workload during parental care and breeding productivity is that nest visit rate does not provide a good measure of foraging effort. Here, we used an automated radiotelemetry system to measure activity of individual female European starlings, Sturnus vulgaris , during breeding, combined with a handicapping experiment (combination of radiotransmitters and wing clipping) and measures of foraging metrics, current breeding productivity, future fecundity and return rate. Handicapping decreased current breeding success due to higher abandonment and nest failure, but among successful birds (fledging ≥ 1 chick) there was no effect of handicapping on brood size at fledging for the current breeding attempt. Handicapping decreased future fecundity, the probability of initiating a second brood, and return rate, but there was no evidence for additive costs of reproduction in wing-clipped females. Handicapping had no effect on provisioning rate but automated tracking data showed that, during chick rearing, wing-clipped females had 22% lower activity compared to females with radios only. Our data provide an explanation for the often contradictory effects of handicapping reported on reproductive effort and costs of reproduction: individuals can use behavioural flexibility – decreasing overall activity while maintaining provisioning rate – along with changes in mass and nestling diet to mitigate putative effects of increased workload imposed by handicapping. Highlights • We studied effects of wing clipping on breeding female starlings. • Handicapping decreased current and future breeding success. • There was no evidence for an additive cost of reproduction between handicapped groups. • Wing-clipped females had 22% lower activity than females with radios only. • Wing-clipped females adjusted activity and foraging behaviour to mitigate effects. [ABSTRACT FROM AUTHOR]

Costs of reproduction are an integral and long-standing component of life-history theory, but we still know relatively little about the specific physiological mechanisms underlying these tradeoffs. We experimentally manipulated workload during parental care in female European starlings (Sturnus vulgaris) using attachment of radios and/or wing clipping and assessed measures of workload, current breeding productivity, future fecundity, and survival (local return rate) in relation to treatment. Females with wing clipping and radio attachment paid a clear cost of reproduction compared with all other treatment groups: they had lower future fecundity and lower return rates despite having lower current breeding productivity. We then measured 13 physiological traits, including measures of aerobic/metabolic capacity, oxidative stress and muscle damage, intermediary metabolism and energy supply, and immune function. Our results show that the cost of reproduction in females with wing clipping and radio attachment was associated with lower oxygen-carrying capacity (lower hematocrit and hemoglobin levels), lower energy reserves (plasma non-esterified fatty acid and triglyceride levels), decreased immune function (lower haptoglobin levels), and elevated levels of oxidative stress (higher levels of dROMs [reactive oxygen metabolites] and lower levels of the endogenous antioxidant uric acid). Our study provides evidence that costs of reproduction involve a widespread decline in physiological function across multiple physiological systems consistent with longstanding ideas of cumulative "wear and tear" and allostatic load. [ABSTRACT FROM AUTHOR]

In avian species, little is known about the development of physiological traits in the days preceding fledging, a critical life history transition marked by a high mortality rate. Developmental trajectory during this period may be flexible based on ecological context or hardwired, with potential costs for variation in growth in the form of oxidative stress. Patterns in development are likely to relate to variation in life history, for which seabirds and aerial insectivores have been well studied, while our focal species is a grassland ground forager, the European starling (Sturnus vulgaris). We show that changes in haematocrit, body mass and wing length are independent of year and brood quality, while changes in haemoglobin concentration are higher in low-quality broods. Moreover, we also identify higher oxidative stress in low-quality year and second broods, a potential cost for maintaining a hardwired developmental trajectory in a lower quality environment. Finally, we experimentally test the effects of food supplementation on development and maturity of chicks at fledging to show that although food increases body mass early in development, it does not change the trajectory or final maturity of chicks at fledging. Collectively this study demonstrates that some developmental changes prior to fledging may be hardwired, but may have long-term oxidative costs in low-quality environments. [ABSTRACT FROM AUTHOR]

Given the function of haemoglobin and observed increases in haematocrit during periods of increased energetic demands, haematocrit and haemoglobin are assumed to be related to aerobic capacity. Reductions in haematocrit and haemoglobin during reproduction are similar in magnitude to increases associated with aerobically demanding activities, and therefore, we sought to investigate whether these reductions in haematology have consequences for reproductive performance., We analysed associations between natural variation in haematology in free-living European starlings ( Sturnus vulgaris) and reproductive performance. To test whether transient reductions in haematology during different stages of reproduction (egg production and late incubation/early chick rearing) affected measures of reproductive performance, we also manipulated haematology using phenylhydrazine ( PHZ), which lyses red blood cells., To investigate effects of reductions of haematology during egg-laying, we treated females with PHZ or saline (control) upon completion of their unmanipulated first clutch and removed eggs to induce the production and rearing of a replacement clutch. To investigate effects of reductions of haematology during chick rearing, we treated females during incubation of the unmanipulated first clutch and then monitored the subsequent hatching and rearing of the clutch., Individuals with higher haematocrit and haemoglobin initiated nesting earlier. Furthermore, higher haemoglobin levels during incubation were associated with a greater number of chicks fledged., PHZ treatment prior to egg production resulted in a significant delay in the laying of replacement clutches, but had no effect on provisioning rate or the size or number of chicks fledged. PHZ treatment during incubation and early chick rearing resulted in decreased hatchling mass in all years and a decrease in the size and number of fledglings in one of 2 years. The year that the effect of PHZ was observed appeared to be a particularly difficult year, as hatchling mass, brood size at hatching and at fledging were low among control females compared to other years., Our results suggest that a reduction in haematology during reproduction can be functionally significant, but that these costs are context-dependent. [ABSTRACT FROM AUTHOR]

Abstract: European starlings (Sturnus vulgaris) are a valuable model species for the assessment of concentrations and effects of environmental contaminants in terrestrial birds. Polybrominated diphenyl ethers (PBDEs) are found in birds throughout the world, but relatively little is known of their concentrations or effects in free-living terrestrial passerines. We used a nest box population of European starlings to 1) measure the variation in egg concentrations of persistent organohalogen contaminants at an agricultural site, and 2) assess whether individual variation in PBDE concentrations in eggs was related to reproductive parameters, as well as maternal or nestling characteristics including body condition, thyroid hormones, oxidative stress, and hematocrit. As PBDEs were the main contaminant class of interest, we only assessed a subset of eggs for other organohalogen contaminants to establish background concentrations. Exposure to organohalogen contaminants was extremely variable over this relatively small study area. Geometric mean wet weight concentrations (range in brackets) of the major contaminants were 36.5 (12–174) ng/g ΣDDT (n=6 eggs) and 10.9 (2–307) ng/g ΣPBDEs (n=14). ΣPCBs at 3.58 (1.5–6.4) ng/g (n=6) were lower and less variable. There were low levels of other organochlorine (OC) pesticides such as dieldrin (2.02ng/g), chlordanes (1.11ng/g) and chlorobenzenes (0.23ng/g). The only form of DDT detected was p,p′-DDE. The congener profiles of PBDEs and PCBs reflect those of industrial mixtures (i.e. DE-71, Aroclors 1254, 1260 and 1262). For all of the contaminant classes, concentrations detected in eggs at our study site were below levels previously reported to cause effects. Due to small sample sizes, we did not assess the relationship between ΣPCBs or ΣOCs and adult or chick condition. We observed no correlative relationships between individual variation in PBDE concentrations in starling eggs and reproductive success, maternal condition, or nestling condition in the corresponding nests. [Copyright &y& Elsevier]

The levels of haematocrit (Hct) and plasma haemoglobin (Hb) vary markedly through the annual cycle of birds, as well as among individuals at all life-stages (embryos, chicks, adults). It is thus surprising that the functional, fitness-related consequences of this variation are poorly understood. Putative 'adaptive' variation in these haematological traits has been associated with varying demands for aerobic capacity and oxygen transport, for example during migration, winter acclimatization, with increasing altitude, or during parental care. It has also been proposed that changes in Hct might reflect 'costs' of parental investment, for example during 'reproductive anaemia'. However, almost all studies to date have been correlative. Here we describe a series of experiments that validate the use of phenylhydrazine hydrochloride (PHZ) for the transient, reversible experimental manipulation of Hct and Hb in birds. A single bolus injection (12.5 μg PHZ/g body weight delivered via intra-muscular injection) caused a rapid decrease in Hct and plasma Hb within 24 h, from pretreatment values of 50-54% to 40-44% in non-breeding Zebra Finches Taenipoygia guttata and European Starlings Sturnus vulgaris, and to 35% in breeding female Zebra Finches, changes within the normal physiological range. Hct and Hb returned to pre-injection levels within 5-10 days of treatment. Changes in plasma Hb paralleled those for Hct. We suggest that PHZ treatment provides a widely applicable technique for use in experimental work to establish relationships between haematological status, aerobic capacity, workload (e.g. migration, parental care, thermoregulation), individual quality (of both adults and chicks) and trade-offs such as costs of reproduction. [ABSTRACT FROM AUTHOR]

The question of why maternal stress influences offspring phenotype is of significant interest to evolutionary physiologists. Although embryonic exposure to maternally derived glucocorticoids (i.e., corticosterone) generally reduces offspring quality, effects may adaptively match maternal quality with offspring demand. We present results from an interannual field experiment in European starlings (Sturnus vulgaris) designed explicitly to examine the fitness consequences of exposing offspring to maternally derived stress hormones. We combined a manipulation of yolk corticosterone (yolk injections) with a manipulation of maternal chick-rearing ability (feather clipping of mothers) to quantify the adaptive value of corticosterone-induced offspring phenotypes in relation to maternal quality. We then examined how corticosterone-induced "matching" within this current reproductive attempt affected future fecundity and maternal survival. First, our results provide support that low-quality mothers transferring elevated corticosterone to eggs invest in daughters as predicted by sex allocation theory. Second, corticosterone-mediated sex-biased investment resulted in rapid male-biased mortality resulting in brood reduction, which provided a better match between maternal quality and brood demand. Third, corticosterone-mediated matching reduced investment in current reproduction for low-quality mothers, resulting in fitness gains through increased survival and future fecundity. Results indicate that the transfer of stress hormones to eggs by low-quality mothers can be adaptive since corticosterone-mediated sex-biased investment matches the quality of a mother to offspring demand, ultimately increasing maternal fitness. Our results also indicate that the branding of the proximate effects of maternal glucocorticoids on offspring as negative ignores the possibility that short-term phenotypic changes may actually increase maternal fitness. [ABSTRACT FROM AUTHOR]

Traditionally, studies of sexually size-dimorphic birds and mammals report that the larger sex is more sensitive to adverse environmental conditions during ontogeny. However, recent studies in avian species that exhibit moderate size-dimorphism indicate that the smaller sex may be more sensitive to poor rearing conditions. To better understand sex-specific sensitivity in a passerine exhibiting moderate size-dimorphism, we examined growth, cell-mediated immunity (CMI) and survival of European starling Sturnus vulgaris nestlings following an experimental reduction of maternal rearing ability (via a feather-clipping manipulation). Contrary to conventional theory, daughters showed reduced growth in both body mass and measures of structural size in response to the maternal treatment. In contrast, sons showed no reductions in any of these traits in relation to the treatment. No sex-specific differences in nestling CMI were found for either group, although CMI of nestlings raised by manipulated mothers were higher than those of control nestlings. Finally, fledging sex ratios did not change from those at hatching indicating that neither sex appeared differentially sensitive to the maternal treatment in terms of mortality. These results reveal that variation in the quality of the rearing environment can have significant effects on the smaller sex of a passerine exhibiting moderate dimorphism and as such support recent studies of species with small-moderate sexual size-dimorphism. Combined results suggest that sex-specific effects of environmental variation on nestling development may be both context- (i.e., brood size, resource level, hatching order) and temporally- (when during development they occur) specific. Furthermore, more studies are needed that examine multiple traits at several developmental stages and then follow the sexes over the longer-term to examine potential effects on fitness. [ABSTRACT FROM AUTHOR]

In sexually size-dimorphic species, the larger sex can be more sensitive to stressful environmental conditions, often resulting in reduced growth and elevated mortality rates. Development of the immune system is regarded as highly resource dependent, and recent data suggest that nestling passerines experience a possible resource-based trade-off between growth and immunity. Given the hypothesized importance of maximizing growth for the larger sex, the corresponding immune system may also exhibit similar sensitivity to limited resources. To better understand how natural variation in brood size and resources might differentially affect growth and immune function in nestlings of a sexually size-dimorphic species, we examined the relationship between brood size and inter-sexual differences in cell-mediated immunity (CMI) and survival in European starling Sturnus vulgaris nestlings where males are larger in both mass and structural size. We hypothesized that male CMI response should be negatively impacted by increasing sibling competition (brood size), especially during periods of low resource availability. In a year of reduced parental provisioning rates and reduced chick growth rates, male offspring exhibited the predicted negative relationship, whereas female CMI response was unaffected. However, in a year of improved provisioning rates and chick growth, neither sex exhibited a negative relationship between immune response and brood size. Thus, natural variation in brood size can affect sex-specific immunity differently in offspring of a sexually size-dimorphic passerine. However, this relationship appears resource-dependent, suggesting that the hypothesized resource-based trade-off may be compensated for in years of adequate resource abundance. [ABSTRACT FROM AUTHOR]

Body composition in vertebrates is known to show phenotypic plasticity, and changes in organ masses are usually rapid and reversible. One of the most rapid and reversible changes is the transformation of the female avian reproductive organs before breeding. This provides an excellent system to investigate the effects of plasticity in organ size on basal metabolic rate (BMR) through relationships between organ masses and BMR. We compared body composition of female European starlings (Sturnus vulgaris) during various reproductive stages over 3 yr and investigated the pattern of changes in reproductive and nonreproductive organ mass during follicular development and ovulation. Furthermore, we analyzed the relationship between organ mass and resting metabolic rate (RMR) in nonbreeding, laying, and chick-rearing females. Our analysis revealed marked variation in organ masses between breeding stages but no consistent pattern among years except for kidney and pectoralis muscle. Furthermore, changes in nonreproductive organs did not parallel the cycle of growth and regression of the reproductive organs. The oviduct gained 62% of its 22-fold increase in mass in only 3 d, and oviduct regression was just as rapid and began even before the final egg of the clutch was laid, with 42% of the oviduct mass lost before laying of the final egg. In laying females, 18% of variation in mass-corrected RMR was explained by the mass of the oviduct (r⊃2 = 0.18, n = 80, P < 0.0005), while pectoralis muscle mass in nonbreeding individuals and liver and gizzard mass in chick-rearing females were the only organs significantly related to RMR (r⊃2 = 0.31-0.44). We suggest that the nonreproductive organs are affected more by changes in local ecological conditions than the reproductive state itself and that the activity and maintenance cost of the oviduct is high enough that selection has led to a very tight size-function relationship for this organ. [ABSTRACT FROM AUTHOR]

The energy cost of egg production in passerine birds has typically been estimated to be 45%-60% of basal metabolic rate (BMR), but this is based on theoretical models using data on energy content of eggs and reproductive tissue; there are still very few empirical data on egg production costs. In this study, we directly measured resting metabolic rate (RMR) in egg-laying female European starlings (Sturnus vulgaris) over 3 yr. We compared these data with RMR of nonbreeding and chick-rearing birds and with estimated energy expenditure generated from a typical energy content model by using empirically derived data from body composition analysis for this species. We found marked variation in RMR between years and between reproductive stages, which complicates comparisons among breeding stages for the assessment of relative egg production costs. On the basis of this method, RMR during egg laying varied from +74% to -13% of nonbreeding RMR and from +20% to -7% of chick-rearing RMR. We therefore used an alternate approach: measuring changes in RMR through the complete cycle of follicle development and ovulation. The increase in RMR from the beginning of prelaying to the six-follicle stage (before first ovulation) when birds have a complete developing follicle hierarchy was 22.4%. This value is still much lower than that estimated from our energy content model. We discuss conceptual problems associated with the theoretical energy content approach but also suggest, on the basis of earlier work done in our lab, that the measured increase in RMR might still underestimate the actual cost of egg production if birds reallocate energy between different physiological systems. [ABSTRACT FROM AUTHOR]

Investigates the quantitative matching of plasma yolk precursor supply to follicle demand during yolk formation in the European starling Sturnus vulgaris. Variation in follicular growth and plasma yolk concentrations throughout the laying cycle; Evidence for follicular atresia; Diurnal variations in yolk precursor concentrations.

Focuses on intraspecific variation in the reproductive physiology and egg quality of European starling or Sturnus vulgaris. Mechanisms underlying the intraspecific variation in egg mass; Relationship between albumen protein and oviduct mass.

Focuses on a study which investigated the role of estradiol in the determination of primary reproductive effort in a free-living, nest box population of European starlings. Information on related studies; Materials and methods; Results and conclusions.

Background: It is widely assumed that variation in fitness components has a physiological basis that might underlie selection on trade-offs, but the mechanisms driving decreased survival and future fecundity remain elusive. Here, we assessed whether physiological variables are related to workload ability or immediate fitness consequences and if they mediate future survival or reproductive success. We used data on 13 physiological variables measured in 93 female European starlings (Sturnus vulgaris) at two breeding stages (incubation, chick-rearing), for first-and second-broods over two years (152 observations). Results: There was little co-variation among the physiological variables, either in incubating or chick-rearing birds, but some systematic physiological differences between the two stages. Chick-rearing birds had lower hematocrit and plasma creatine kinase but higher hemoglobin, triglyceride and uric acid levels. Only plasma corticosterone was repeatable between incubation and chick-rearing. We assessed relationships between incubation or chick-rearing physiology and measures of workload, current productivity, future fecundity or survival in a univariate manner, and found very few significant relationships. Thus, we next explored the utility of multivariate analysis (principal components analysis, Mahalanobis distance) to account for potentially complex physiological integration, but still found no clear associations. Conclusions: This implies either that a) birds maintained physiological variables within a homeostatic range that did not affect their performance, b) there are relatively few links between physiology and performance, or, more likely, c) that the complexity of these relationships exceeds our ability to measure it. Variability in ecological context may complicate the relationship between physiology and behavior. We thus urge caution regarding the over-interpretation of isolated significant findings, based on single traits in single years, in the literature. [ABSTRACT FROM AUTHOR]

In the context of breeding phenology, social behaviour (especially song) has long been considered an important ‘supplemental cue’ that females integrate with other environmental information to determine timing of egg laying. However, to our knowledge, no studies have experimentally manipulated song in the wild in the context of female breeding phenology and performance. We studied natural variation in, and response to experimental manipulation of, prebreeding song and social behaviour in European starlings, Sturnus vulgaris , to determine whether male behaviour acts as a phenological cue determining female timing of egg laying and subsequent, postlaying breeding performance. In our highly synchronous system, natural variation in prebreeding male song quality and singing effort was surprisingly high, and singing increased slightly closer to egg-laying date. There was a strong prebreeding response of both males and females to the playback treatment, but no effect on female breeding phenology (egg-laying date) or performance (nestbox occupancy, egg size, clutch size, total chicks hatched, total chicks fledged or double-brooding behaviour). Our 3-year study finds no evidence that male prebreeding song is a cue determining female breeding phenology or performance in starlings. [ABSTRACT FROM AUTHOR]

Abstract: Leptin, a protein hormone secreted by fat cells, is best known for its role as an adiposity signal; however, leptin has diverse physiological roles ranging from regulation of feeding behavior and body weight, to effects on reproduction and immune function. Although leptin has been extensively studied in mammals, the identification and function of leptin in birds remains controversial, and studies have focused on captive or domesticated species. Here, we describe changes in plasma leptin-like immunoreactivity during the reproductive and non-reproductive seasons in free-living female European starlings (Sturnus vulgaris). Plasma leptin-like immunoreactivity was high during egg-laying (27.8±2.4ng/mL) and clutch completion (23.8±1.6ng/mL), decreased during incubation (13.0±1.6ng/mL) and chick-rearing (12.0±1.3ng/mL), but was elevated again in non-breeders in November (23.7±1.1ng/mL). Although there was marked and consistent variation in total body mass and body composition with breeding stage and season in this population, plasma leptin-like immunoreactivity did not parallel changes in body mass or body composition. These data suggest that the strong positive relationship between plasma leptin-like immunoreactivity and body mass reported for captive birds and mammals does not hold for free-living birds. Rather, among free-living female European starlings, variation in plasma leptin-like immunoreactivity is associated with breeding stage or seasonal variation per se, and we discuss possible mechanisms underlying this variation, focusing on ovarian function and egg production. [Copyright &y& Elsevier]

Current research in birds suggests that a conflict should exist during reproduction for the role of the glucocorticoid corticosterone (CORT). While elevated levels have been correlated with the increased energetic demand of raising offspring, elevated CORT levels have traditionally been implicated in reproductive abandonment. We examined the relationship between CORT and nest desertion in breeding wild female European starlings (Sturnus vulgaris) incorporating analyses of both total circulating levels and ‘free’, unbound CORT through analysis of corticosteroid-binding globulin (CBG). Free baseline CORT levels of nest-abandoning birds were significantly higher than nonabandoning birds within each stage, with chick-rearing birds exhibiting the highest free baseline CORT levels, while concurrently remaining the most resistant stage to nest desertion. Elevated free baseline CORT levels in chick-rearing birds were not due to increased total CORT secretion, but rather to a decrease in CBG levels. Overall, our results suggest that CORT and CBG interact to play a role in mediating the increased energetic demand of offspring, while minimizing the chances of nest desertion, thereby alleviating any potential behavioral conflict for CORT during reproduction. Furthermore, these results demonstrate that the traditional view of the role of CORT during reproduction is much more complex than previously appreciated. Together with mounting evidence, we suggest that elevated corticosteroid levels are an inherent and necessary part of reproduction in nonmammalian tetrapods. [Copyright &y& Elsevier]

Biota samples from the Vancouver municipal landfill located in Delta, BC, Canada, have some of the highest polybrominated diphenyl ether (PBDE) levels reported from North America. We followed a population of European starlings (Sturnus vulgaris) breeding in a remediated area in the landfill to identify exposure routes and bioaccumulation of PBDEs in a simple terrestrial food chain. This population was compared to a reference farm site located 40 km east in Glen Valley. We analyzed samples of European starling eggs and nestling livers as well as invertebrate prey species consumed by starlings for PBDE concentrations. We also collected soil samples from starling foraging areas. All samples from the Delta landfill had higher PBDE congener concentrations compared to the Glen Valley reference site and were dominated by BDE-99 and BDE-47. Stable nitrogen (δ N15) and carbon (δ C13) isotope analysis of starling blood samples and provisioned invertebrates revealed that stable δ C 13 signatures differed between the sites indicating that the diet of starlings in the Delta landfill included a component of human refuse. Biota-soil accumulation factors (BSAFs) > 1 demonstrated that PBDEs were bioaccumulating in soil invertebrates, particularly earthworms, which were readily accessible to foraging starlings in the landfill. Biomagnification factors (BMFs) calculated from foraged food items and starling egg and liver samples were >1, indicating that a diet of soil invertebrates and refuse contributed substantially to the PBDE exposure of local starlings. • BDE concentrations were higher in starling eggs and chicks from an urban landfill than a rural farm. • Human refuse and soil invertebrates were dominant dietary sources of BDE exposure to starlings at the landfill. • BSAFs for BDE-47, -99, −100, and −154 were >1 indicating bioaccumulation in earthworms and refuse at the landfill. • BMFs for BDE-47, -99, −100, −153, and −154 were >1 indicating biomagnification in starlings from their diet. [ABSTRACT FROM AUTHOR]