High levels of liver antioxidants are associated with life-history strategies characteristic of slow growth and high survival rates in birds

Antioxidants have a large potential to coevolve with life-histories because of their capacity to counteract the negative effects of free radicals on fitness. However, only a few studies have explored the association between antioxidant levels and life-history strategies comparing a large number of species. Here we used an extensive dataset of 125 species of birds to investigate the association between concentrations of antioxidants (carotenoids and vitamin E) in the liver, which is the main storage organ for fat-soluble antioxidants, and life-history and morphology. We found that high liver antioxidant concentrations were associated with life-history strategies characterized by "live slow, die old", in clear contrast to previous studies reporting a relationship between high plasma antioxidants and life-histories characterized by "live fast, die young". Thus, high carotenoid concentrations were present in species with large body, brain and egg sizes, high absolute metabolic rate and a resident lifestyle, while high vitamin E concentrations were present in species with large brain size and long life span and incubation period. Our results indicate that antioxidants and life-histories coevolve, and that this may be mediated by positive fitness consequences of the accumulation of liver antioxidants, as species with higher antioxidant levels live longer.     

Fat soluble antioxidants in brood-rearing great tits Parus major: relations to health and appearance

The concept of parasite-mediated sexual selection assumes that females may improve offspring fitness by selecting mates on the basis of sexual ornaments that honestly reveal the health state of a partner. Expression of such signals may be particularly sensitive to oxidative damage caused by excess production of oxidative metabolites and free radicals. To control and neutralise free radicals, animals rely heavily on dietary fat-soluble antioxidants such as vitamin E and A, and carotenoids. However, the organism's need for free radical scavenging may interfere with the opposite need to generate oxidative stress for fighting parasitic infections. We investigated plasma concentrations of carotenoids and vitamin A and E in brood-rearing great tits Parus major in relation to carotenoid-based plumage coloration, sex, habitat, leukocyte hemoconcentrations and infection status with Haemoproteus blood parasites. Rural great tits differed from urban ones and males from females with respect to the hue of the yellow ventral feathers. However, plasma antioxidant concentrations were not related to sex, habitat or plumage coloration. Plasma carotenoid concentration correlated positively with indices of immune system activation as measured by blood counts of lymphocytes and eosinophils. Birds with gametocytes of Haemoproteus in their blood had higher plasma concentrations of carotenoids and vitamin E than unparasitized individuals. These results are consistent with the idea that maintenance of high blood antioxidant levels might conflict with individual needs to rely on oxidative stress for fighting infections.     

High urban population density of birds reflects their timing of urbanization

Living organisms generally occur at the highest population density in the most suitable habitat. Therefore, invasion of and adaptation to novel habitats imply a gradual increase in population density, from that at or below what was found in the ancestral habitat to a density that may reach higher levels in the novel habitat following adaptation to that habitat. We tested this prediction of invasion biology by analyzing data on population density of breeding birds in their ancestral rural habitats and in matched nearby urban habitats that have been colonized recently across a continental latitudinal gradient. We estimated population density in the two types of habitats using extensive point census bird counts, and we obtained information on the year of urbanization when population density in urban habitats reached levels higher than that of the ancestral rural habitat from published records and estimates by experienced ornithologists. Both the difference in population density between urban and rural habitats and the year of urbanization were significantly repeatable when analyzing multiple populations of the same species across Europe. Population density was on average 30 % higher in urban than in rural habitats, although density reached as much as 100-fold higher in urban habitats in some species. Invasive urban bird species that colonized urban environments over a long period achieved the largest increases in population density compared to their ancestral rural habitats. This was independent of whether species were anciently or recently urbanized, providing a unique cross-validation of timing of urban invasions. These results suggest that successful invasion of urban habitats was associated with gradual adaptation to these habitats as shown by a significant increase in population density in urban habitats over time.     

Interspecific variation in avian blood parasites and haematology associated with urbanization in a desert habitat

Many avian species are negatively impacted by urbanization, but other species survive and prosper in urbanized areas. One factor potentially contributing to the success of some species in urban areas is the reduced presence of predators or parasite vectors in urban compared to rural areas. In addition, urban areas may provide increased food and water resources, which can enhance immune capacity to resist infection and the ability to eliminate parasites. We determined patterns of blood parasitism, body condition, and immune cell profiles in urban and rural populations of five adult male songbird species that vary in their relative abundance within urban areas. Urban birds generally exhibited less blood parasitism than rural birds. This difference was particularly evident for the urban-adaptable Abert's towhee Pipilo aberti . In contrast, no difference in haemoparasitism was seen between urban and rural populations of the curve-billed thrasher Toxostoma curvirostre , a less-urban adaptable species. In two closely related species, the curve-billed thrasher and the northern mockingbird Mimus polyglottos , urban birds had a higher leukocyte count and a higher heterophil to lymphocyte ratio, which is often associated with chronic stress or current infection, than rural birds. Urban northern mockingbirds were in better condition than rural counterparts, but no habitat-related differences in condition were detected for other species. Parasitic infection was correlated with body condition in only one species, the canyon towhee Pipilo fuscus . Parasitic infection in most species was correlated with changes in leukocyte abundance and profile. The findings suggest that interspecific differences in parasitic infection cannot be attributed entirely to differences in vector abundance or body condition. Interactions between immune function, parasite infection risk, and resource availability may contribute to determining the relative ability of certain species to adapt to cities.     

Do dietary antioxidants alleviate the cost of immune activation? An experiment with greenfinches

Reactive oxygen and nitrogen species produced by metabolism and immune defenses can cause extensive damage to biomolecules. To counteract this damage, organisms rely on exogenous and endogenous antioxidants, although their relative importance in maintaining redox balance is unclear. We supplemented captive greenfinches with dietary antioxidants--carotenoids and vitamin E--and injected them with an inflammatory agent, phytohemagglutinin. Compared to controls, immune-challenged birds circulated more lipid peroxidation products but also increased total plasma antioxidativity. Carotenoid (but not vitamin E) supplementation generally reduced lipid peroxidation, but this did not compensate for the effects of immune activation. Levels of an endogenous antioxidant--uric acid--strongly contributed to plasma antioxidativity. We found no evidence that dietary antioxidants are immunostimulatory. These results demonstrate the antioxidant function of carotenoids in birds and show that simultaneous assessment of oxidative stress-driven damage, antioxidant barrier, and individual antioxidants is critical for explaining the potential costs of immune system activation.     

Effect of Urbanization and Seasonality in Bird Communities of Kathmandu Valley,Nepal

Kathmandu Valley, Nepal is undergoing rapid urbanization but its effects on the bird communities have not been reported till date. Kathmandu Valley was categorized into urban, sub-urban and rural to study the impact of urbanization in bird communities. By mobilizing volunteers, we monitored 24 transects each with one km long in summer and winter seasons of 2016. A total of 13,749 individuals of birds belonging to 102 species were recorded. Species richness and diversity of all birds declined from rural to urban areas and showed significant variation along urban–rural gradients. Insectivore was the most species-rich guild while nectarivore the least. The richness of insectivore, frugivore and carnivore guilds showed significant variations along the urban–rural gradients and higher preference towards the rural areas. Similarly, species richness of all birds and richness of insectivore and carnivore guilds showed significant seasonal variation and were higher in the winter season. Our results indicate that richness, diversity and feeding guilds of birds show different response towards the urbanization gradients and seasons. Sub-urban areas can function as bird refugia, however, habitat enrichments (like increasing green spaces, setting up new parks and gardens, plantation of native fruiting trees etc.) are utmost necessary to support the bird communities in urban areas of Kathmandu Valley.     

Circulating carotenoid concentrations are positively correlated with later clutch initiation in Florida Scrub-Jays (Aphelocoma coerulescens)

Antioxidants play key roles in preventing free radical damage to various molecules, cells, and tissues, but it is not well understood how variation in antioxidant levels may relate to the reproductive success or health of wild animals. We explored the relationship between circulating antioxidant concentrations and both body condition and timing of reproduction in male and female Florida Scrub-Jays (Aphelocoma coerulescens), a cooperatively breeding passerine bird. We examined whether levels of uric acid, vitamin E, and carotenoids (all potentially important antioxidants) were linked to body condition and timing of reproduction, two measures that are directly related to reproductive success. Antioxidant concentrations were not correlated with body condition, but they were related to timing of first clutch initiation, though not always in the predicted direction. Elevated circulating levels of carotenoids were associated with delayed clutch initiation in female breeders. Relatively higher vitamin E levels in control birds were associated with earlier clutch initiation, whereas male breeders that received long-term food supplementation had elevated levels of vitamin E and delayed reproduction. Several potential explanations for the link between elevated levels of antioxidants and delayed clutch initiation are discussed. Separate explanations for each sex include, but are not limited to, oxidative stress as a result of territory defense efforts in males, different dietary regimes due to supplementation, and mobilized plasma antioxidants in females that were coping with a stressor.     

Independent colonization of multiple urban centres by a formerly forest specialist bird species

Urban areas are expanding rapidly, but a few native species have successfully colonized them. The processes underlying such colonization events are poorly understood. Using the blackbird Turdus merula, a former forest specialist that is now one of the most common urban birds in its range, we provide the first assessment of two contrasting urban colonization models. First, that urbanization occurred independently. Second, that following initial urbanization, urban-adapted individuals colonized other urban areas in a leapfrog manner. Previous analyses of spatial patterns in the timing of blackbird urbanization, and experimental introductions of urban and rural blackbirds to uncolonized cities, suggest that the leapfrog model is likely to apply. We found that, across the western Palaearctic, urban blackbird populations contain less genetic diversity than rural ones, urban populations are more strongly differentiated from each other than from rural populations and assignment tests support a rural source population for most urban individuals. In combination, these results provide much stronger support for the independent urbanization model than the leapfrog one. If the former model predominates, colonization of multiple urban centres will be particularly difficult when urbanization requires genetic adaptations, having implications for urban species diversity.     

Egg yolk carotenoids in relation to habitat and reproductive investment in the great tit Parus major

Maternal allocation of antioxidants to egg yolk has been shown to affect early embryonic development and nestling survival. In environments with high levels of anthropogenic pollution, antioxidants (such as carotenoids) are important to protect the body from elevated oxidative stress. Thus, female allocation of antioxidants to yolk may be traded off against self-maintenance. Here we investigate maternal reproductive investment with respect to yolk carotenoid content and composition in relation to subsequent female condition and carotenoid status in urban and rural great tits Parus major. We found no differences between the urban and rural populations in total yolk carotenoids, egg mass, clutch size, hatching success, or female carotenoid status. Interestingly, however, rural eggs contained more zeaxanthin, a more potent antioxidant than lutein, which suggests that rural embryos have better antioxidant protection than urban embryos. Whether rural females actively transfer more zeaxanthin to the yolk or whether it passively reflects differences in dietary access or uptake needs to be further investigated. This highlights the importance of carotenoid identity and composition in future studies of carotenoid physiology, ecology, and signaling.     

北京市麻雀体质水平沿城市化梯度的变化

麻雀是城市和乡村均有分布的鸟类物种.快速的城市化正在使城市麻雀的栖息地和食物资源大量减少.以北京市为例,研究了麻雀的体质水平沿城市化梯度的变化,以期为我国城市化过程中的鸟类保护提供参考.研究结果表明城市高层楼房居民区、低层楼房居民区以及大学校园中麻雀的体质指数显著低于郊区环境,而城市公园和平房居民区麻雀的体质水平则与郊区环境的差异较小.随采样点城市化水平的增加,麻雀的体质水平呈下降趋势,高度城市化的环境导致麻雀的体质水平下降.在城市化过程中,增加城市公园的数量及居民区的植被覆盖量可为麻雀等鸟类提供必要的生活资源,从而实现城市化过程中的生物多样性保护.     

Fat soluble antioxidants in brood‐rearing great tits Parus major: relations to health and appearance

The concept of parasite‐mediated sexual selection assumes that females may improve offspring fitness by selecting mates on the basis of sexual ornaments that honestly reveal the health state of a partner. Expression of such signals may be particularly sensitive to oxidative damage caused by excess production of oxidative metabolites and free radicals. To control and neutralise free radicals, animals rely heavily on dietary fat‐soluble antioxidants such as vitamin E and A, and carotenoids. However, the organism's need for free radical scavenging may interfere with the opposite need to generate oxidative stress for fighting parasitic infections. We investigated plasma concentrations of carotenoids and vitamin A and E in brood‐rearing great tits Parus major in relation to carotenoid‐based plumage coloration, sex, habitat, leukocyte hemoconcentrations and infection status with Haemoproteus blood parasites. Rural great tits differed from urban ones and males from females with respect to the hue of the yellow ventral feathers. However, plasma antioxidant concentrations were not related to sex, habitat or plumage coloration. Plasma carotenoid concentration correlated positively with indices of immune system activation as measured by blood counts of lymphocytes and eosinophils. Birds with gametocytes of Haemoproteus in their blood had higher plasma concentrations of carotenoids and vitamin E than unparasitized individuals. These results are consistent with the idea that maintenance of high blood antioxidant levels might conflict with individual needs to rely on oxidative stress for fighting infections.     

Yolk antioxidants vary with male attractiveness and female condition in the house finch (Carpodacus mexicanus)

The manipulation of egg content is one of the few ways by which female birds can alter offspring quality before hatch. Lipid-soluble vitamins and carotenoids are potent antioxidants. Female birds deposit these antioxidants into eggs in variable amounts according to environmental and social conditions, and the quantities deposited into eggs can have effects on offspring health and immunological condition. Allocation theory posits that females will alter the distribution of resources according to mate quality, sometimes allocating resources according to the differential allocation hypothesis (DAH), investing more in offspring sired by better-quality males, and other times allocating resources according to a compensatory strategy, enhancing the quality of offspring sired by lower-quality males. It is unknown, however, whether antioxidants are deposited into eggs according to the DAH or a compensatory strategy. We examined deposition patterns of yolk antioxidants (including vitamin E and three carotenoids) in relation to laying order, mate attractiveness, female condition, and yolk androgen content in the house finch (Carpodacus mexicanus). Female house finches deposited significantly more total antioxidants into eggs sired by less attractive males. Additionally, yolk antioxidant content was significantly positively correlated with female condition, which suggests a cost associated with the deposition of antioxidants into eggs. Finally, concentrations of antioxidants in egg yolks were positively correlated with total yolk androgen content. We suggest that yolk antioxidants are deposited according to a compensatory deposition strategy, enabling females to improve the quality of young produced with less attractive males. Additionally, yolk antioxidants may act to counter some of the detrimental effects associated with high levels of yolk androgens in eggs and, thus, may exert a complementary effect to yolk androgens.     

Antioxidants in eggs of great tits <Emphasis Type="Italic">Parus major</Emphasis> from Chernobyl and hatching success

Antioxidants are powerful protectors against the damaging effects of free radicals that constitute the inevitable by-products of aerobic metabolism. Growing embryos are particularly susceptible to the damaging effects of free radicals produced during rapid growth, and mothers of many species provide protection against such damage by allocating antioxidants to their eggs. Birds living in radioactively contaminated areas use dietary antioxidants to cope with the damaging effects of radiation, but females also allocate dietary antioxidants to eggs, potentially enforcing a physiological trade-off between self-maintenance and reproductive investment. Here we tested whether female great tits Parus major breeding in radioactively contaminated study areas near Chernobyl allocated less dietary antioxidants to eggs, and whether such reduced allocation of dietary antioxidants to eggs had fitness consequences. Concentrations of total yolk carotenoids and vitamins A and E were depressed near Chernobyl compared to concentrations in a less contaminated Ukrainian study area and a French control study area, and all antioxidants showed dose-dependent relationships with all three dietary antioxidants decreasing with increasing level of radiation at nest boxes. These effects held even when controlling statistically for potentially confounding habitat variables and covariation among antioxidants. Laying date was advanced and clutch size increased at nest boxes with high dose rates. Hatching success increased with increasing concentration of vitamin E, implying that hatching success decreased at boxes with high levels of radiation, eventually eliminating and even reversing the higher potential reproductive output associated with early reproduction and large clutch size. These findings are consistent with the hypothesis that radioactive contamination reduced levels of dietary antioxidants in yolks, with negative consequences for hatching success and reproductive success.     

Non‐linearities in bird responses across urbanization gradients: A meta‐analysis

Urbanization is one of the most extreme forms of environmental alteration, posing a major threat to biodiversity. We studied the effects of urbanization on avian communities via a systematic review using hierarchical and categorical meta‐analyses. Altogether, we found 42 observations from 37 case studies for species richness and 23 observations from 20 case studies for abundance. Urbanization had an overall strong negative effect on bird species richness, whereas abundance increased marginally with urbanization. There was no evidence that city size played a role in influencing the relationship between urbanization and either species richness or abundance. Studies that examined long gradients (i.e. from urban to rural) were more likely to detect negative urbanization effects on species richness than studies that considered short gradients (i.e. urban vs. suburban or urban vs. rural areas). In contrast, we found little evidence that the effect of urbanization on abundance was influenced by gradient length. Effects of urbanization on species richness were more negative for studies including public green spaces (parks and other amenity areas) in the sampled landscapes. In contrast, studies performed solely in the urban matrix (i.e. no green spaces) revealed a strong positive effect on bird abundance. When performing subset analyses on urban–suburban, suburban–rural and suburban–natural comparisons, species richness decreased from natural to urban areas, but with a stronger decrease at the urban–suburban interface, whereas bird abundance showed a clear intermediate peak along the urban–rural gradient although abundance in natural areas was comparable to that in suburban areas. This suggests that species loss happens especially at the urban–suburban interface, and that the highest abundances occur in suburban areas compared to urban or rural areas. Thus, our study shows the importance of suburban areas, where the majority of birds occur with fairly high species richness.     

How birds colonize cities: genetic evidence from a common waterbird,the Eurasian coot

Much effort has been devoted to identify ecological and life‐history traits which facilitate urban colonization by wild avian species, but surprisingly little is known about the population‐level mechanisms of urbanization processes. In general, two different patterns of urban colonization have been proposed: 1) the model of independent colonization predicts that birds colonize cities independently in different geographical regions; 2) the model of leapfrog colonization assumes a single colonization event, while additional urban populations are established from the initial urban populations. The aim of this paper was to determine the pattern of urban colonization in a common waterbird, the Eurasian coot Fulica atra. For this purpose, we analysed microsatellite variation in three pairs of urban and rural coot populations from central Poland. We found that a newly‐established urban population was genetically more similar to neighbouring rural populations than to long‐established urban populations, as indicated by the analysis of fixation index, genetic distance and Bayesian assignment of individuals to genetic clusters. These results are consistent with the model of independent colonization, where neighbouring rural populations are a source of individuals that colonize new urban areas. However, our analysis also showed significant differentiation between long‐established urban populations and adjacent rural populations, suggesting that genetic connectivity between two types of habitat decreases with increasing time since urbanization. Our study shows high complexity of urbanization processes in wild animal populations, as well as it underpins utility of molecular tools in studying population‐level mechanisms of urbanization.     

Blue‐green eggshell coloration reflects yolk antioxidant content in spotless starlings Sturnus unicolor

The hypothesis that eggshell colouration is a sexually selected trait of female birds is based on the fact that biliverdin, the pigment responsible for blue‐green colours of the eggshell, is a potent antioxidant and that only females with high antioxidant capacity can deposit higher concentrations of biliverdin as eggshell pigment. Antioxidants (e.g. carotenoids, vitamins) are also abundant in the egg yolk, which serve as nutrient reserves for the developing embryo, and eggshell colour intensity may reflect maternal investment in yolk antioxidants. Here, we test the relationship between blue‐green eggshell colour intensity and concentration and amount of carotenoids, vitamin A, and vitamin E in the egg yolk of spotless starling Sturnus unicolor, a species for which we have previously shown good evidence of sexual selection driving egg coloration. As could be extrapolated from the hypothesis of sexual selection driving the evolution of blue‐green eggshells, we found that eggshell colour intensity was positively related to the concentration and amount of carotenoids and vitamin E in the yolk. Thus, mothers may use egg colour intensity to signal to fathers the antioxidant status of their offspring. Moreover, we provide evidence suggesting that maternal yolk investment in more coloured eggs can also explain the detected association between feeding decisions of males and egg colour intensity that we have found previously in this species.     

Song Post Height in Relation to Predator Diversity and Urbanization

Birds may sing from positions in the vegetation (song posts) to allow efficient transmission of sexual and territorial vocal displays while simultaneously minimizing the risk of predation because of avian and mammalian predators. Because urban areas are deficient in specialized avian predators, but have many cats while the opposite is the case for nearby rural areas, urban birds should display higher in the vegetation. In a comparison of the abundance of predators in three cities (Oslo, Brønderslev, Orsay), I show that avian predators are more common in rural areas, while mammalian predators are more common in urban areas. Singing birds sang from higher positions in the vegetation of urban than nearby rural areas. Differences in song post heights between urban and rural areas were consistent among cities, suggesting inherent specific difference in microhabitat choice. Bird species that have become urbanized recently had similar song post heights in urban and rural habitats, while species that have been urbanized for a long time sang from relatively higher song posts in urban areas. These findings suggest that urban and rural birds differ in habitat use when singing. These differences in song post choice between urban and rural habitats may have a number of consequences for vocal displays in the two different habitats.     

Plasma Glutathione and Carotenoid Coloration as Potential Biomarkers of Environmental Stress in Great Tits

Measures of oxidative stress in animals may be useful biomarkers of environmental stressors, such as anthropogenic pollution. In birds, studies of oxidative stress have focused on dietary antioxidants, primarily carotenoids, which are interesting due to their multiple physiological and pigmentary functions but therefore also unspecifically related to oxidative stress. A useful complementary biomarker may be the glutathione system, commonly used in human medicine, but rarely applied to wild, terrestrial vertebrates. In this study of urban versus rural adult and nestling great tits Parus major, we investigated both the carotenoid-based yellow plumage (by reflectance spectrometry) and the plasma levels of glutathione, the latter measured as total glutathione (tGSH) and as the ratio between oxidized and reduced glutathione (GSSG:GSH), respectively. We found that urban adults had higher current oxidative stress (GSSG:GSH) and paler yellow plumage compared to rural adults, suggesting elevated stress in the urban environment. Total glutathione levels (tGSH), however, which may indicate long-term up-regulation of the GSH reservoir, did not differ between the environments. Nestlings did not show any consistent pattern between environments in either tGSH or GSSG:GSH and, among individuals, glutathione levels were uncorrelated with carotenoid coloration. The results thus suggest some population-level correspondence between the two stress biomarkers in adult birds, but more work is obviously needed to understand how the two antioxidant systems interact in different individuals and in response to different environmental disturbances.     

Serum antioxidant levels in wild birds vary in relation to diet, season, life history strategy, and species

Micronutrient antioxidants are thought to be generally important for health in many animals, but factors determining levels in individuals and species are not well understood. Diet and season are obvious environmental variables that might predict the degree to which species can accumulate such nutrients. We analyzed antioxidant levels [Trolox-equivalent antioxidant capacity (TEAC), uric acid (UA), vitamin E, and four carotenoids] in 95 bird species and compared these to species-level data on diet from the literature. Using compositional principal components analysis, we identified two main axes of diet variation: invertebrate consumption and seed-to-fruit ratio. We then examined associations between diet axes and antioxidant measures, with and without control for life-history variation and phylogeny. We also analyzed a subset of 13 species for which we had data on seasonality of antioxidant levels and diet, assessing the variance in antioxidant levels explained by seasonality, diet, and species. Unsurprisingly, there were strong associations between antioxidant levels and diet. TEAC and UA concentration were consistently positively associated with invertebrate consumption and seed-to-fruit ratio, and carotenoid concentrations (e.g. zeaxanthin and β-carotene) were negatively associated with invertebrate consumption. However, vitamin E was not associated with diet as measured here. Importantly, there is much variation in antioxidants that is not explained by diet, and we are able to identify diet-independent effects of species, season/breeding stage, and life history on antioxidant levels. Circulating antioxidant concentrations within and across species can therefore be viewed as a function of multiple factors, including but not limited to diet, and antioxidant metabolism appears to differ across species and seasons irrespective of diet.     

Antioxidants in the egg yolk of a wild passerine: differences between breeding seasons

Carotenoids and fat-soluble vitamins play crucial roles in several physiological processes. Yolk carotenoid composition may be influenced by the bird's dietary intake and by the possible discrimination during carotenoid metabolism. Information regarding the pigment composition of passerine eggs is very limited. In the present 2-year study, we determined the carotenoid and vitamin concentrations and the percentage profile of carotenoid components in collared flycatcher (Ficedula albicollis) eggs. The major carotenoid was lutein in both years, followed by cis-lutein, zeaxanthin and beta-carotene as other significant components. Carotenoid concentration was higher in 2000 than in 2001. As caterpillar abundance and ambient temperature was lower in 2001 than in 2000, we suggest that the decreased availability of carotenoid-rich resources and the elevated antioxidant demand of the female restricted the carotenoid allocation to the eggs. Our study is the first to indicate that the concentration and profile of yolk carotenoids may considerably vary in the same wild bird population between breeding seasons with different environmental conditions. Compared to other birds, the yolk of this species was relatively rich in vitamins A and E. Vitamin E concentration was positively correlated with total carotenoid concentration, which may be beneficial for the nestlings as these antioxidants synergistically provide better protection.