Bird Eggshells Research Articles

Surface texture heterogeneity in maculated bird eggshells.

Many of the world's 10 000 bird species lay coloured or patterned eggs. The large diversity of eggshell patterning among birds, achieved through pigment, has been attributed to a few selective agents such as crypsis, thermoregulation, egg recognition, mate signalling, egg strength and protecting the embryo from UV. Pigmentation may influence the texture of eggshells, which in turn may be important for dealing with water and microbes. We measured surface roughness (Sa, nm), surface skewness (Ssk) and surface kurtosis (Sku), which describe different aspects of surface texture, across 204 bird species with maculated (patterned) eggs and 166 species with immaculate (non-patterned) eggs. Using phylogenetically controlled analyses, we tested whether maculated eggshells have different surface topography between the foreground colour and background colour, and between the background colour of maculated eggshells and the surface of immaculate eggshells. Secondly, we determined to what extent variation in eggshell pigmentation of the foreground and background colour is determined by phylogenetic relatedness, and whether certain life-history traits are important predictors of eggshell surface structure. We show that the surface of maculated eggs consists of a rougher foreground pigment compared to the background pigment across 71% of the 204 bird species (54 families) investigated. Species that lay immaculate eggs showed no difference in surface roughness, kurtosis or skewness compared to background pigment of maculated eggs. The difference in eggshell surface roughness between foreground and background pigmentation was greater among species that occupied dense habitats, such as forests with closed canopies, compared to those that nest in open and semi-open habitats (e.g. cities, deserts, grasslands, open shrubland and seashores). Among maculated eggs, foreground texture was correlated with habitat, parental care, diet, nest location, avian group and nest type, while background texture was correlated with clutch size, annual temperature, development mode and annual precipitation. Surface roughness among immaculate eggs was greatest for herbivores, and species that have larger clutch sizes. Together, this suggests that multiple life-history traits have influenced the evolution of eggshell surface textures in modern birds.

Nesting Behaviour and Calcium Carbonate Content in Eggshells of Different Birds: A Review

Nesting Behaviour and Calcium Carbonate Content in Eggshells of Different Birds: A Review

Egg Incubation Mechanics of Giant Birds

Simple SummaryExtinct giant birds have been a source of imagination, and knowledge of their incubation mechanics is crucial to our understanding of the evolution of avian reproduction. Despite the extensive studies on avian eggs, our understanding of the eggshell mechanics of giant birds, particularly the extinct ones, remains incomplete—most of these prior works were based on empirical or allometric relationships with limited quantitative analysis. In the present study, with the help of advanced three-dimensional computer simulation using data from published fossil records, we obtain more comprehensive quantitative analysis to answer important questions related to contact incubation of giant birds. Specifically, how much safety margin does the reversed sexual size dimorphism (RSSD) of moas provide? What is the theoretical upper limit of body mass for contact incubation? Is the Williams’ egg, or the putative Genyornis oological material (PGOM), really the egg of the extinct giant bird Genyornis newtoni, as commonly accepted since its discovery in 1981?Finite element analysis (FEA) was used to conduct mechanical analyses on eggshells of giant birds, and relate this to the evolution and reproductive behavior of avian species. We aim to (1) investigate mechanical characteristics of eggshell structures of various ratite species, enabling comparisons between species with or without reversed sexual size dimorphism (RSSD); (2) quantify the safety margin provided by RSSD; (3) determine whether the Williams’ egg can have been incubated by an extinct giant bird Genyornis newtoni; (4) determine the theoretical maximum body mass for contact incubation. We use a dimensionless number C to quantify relative shell stiffness with respect to the egg size, allowing for comparison across wide body masses. We find that RSSD in moas significantly increases the safety margin of contact incubation by the lighter males. However, their safety margins are still smaller than those of the moa species without RSSD. Two different strategies were adopted by giant birds—one is RSSD and thinner shells, represented by some moa species; the other is no RSSD and regular shells, represented by the giant elephant bird. Finally, we predicted that the upper limit of body mass for contact incubation was 2000 kg.

ASSESSING MERCURY POLLUTION USING BLACK STORK EGGSHELLS

Female birds whose bodies contain environmental contaminants produce eggs with shells that are likewise contaminated, making bird eggshells appropriate indicators for monitoring environmental toxins. Common contaminants include organic mercury compounds, especially methylmercury, which are known to bioaccumulate and biomagnify in the food chain. Black storks (Ciconia nigra) predominantly consume fish and are thus at risk for high mercury intake. In this study, we used eggshells of black storks as a proxy to reconstruct the concentration levels and distribution of mercury, a well-known toxic element, in various parts of Latvia. Preliminary analyses have shown that deposition levels of mercury vary in different parts of the eggshell. Specifically, the shell and shell membrane differ in their level of mercury contamination by an average factor of nine; therefore, we measured the mercury content in these components separately whenever possible. We analysed 34 eggshell samples from nesting sites in Latvia using an atomic absorption spectrometer with Zeeman correction Lumex RA-915M and its attachment for pyrolytic combustion. We found that mercury concentrations varied from 5 to 22 ng/g in eggshells and from 42 to 293 ng/g in shell membranes. We discuss possible contamination sources and reasons behind this disparity.

Structure and Composition of the Eggshell of a Passerine Bird, Setophaga ruticilla (Linnaeus, 1758).

The mineral composition of eggshells is assumed to be a conserved phylogenetic feature. Avian eggshells are composed of calcite, whereas those of taxa within Chelonia are aragonitic. Yet, the eggshells of a passerine bird were reported to be made of aragonite. Here, we report a new study of the same bird eggshells using a combination of in situ microscopy and chemical techniques. A microstructural analysis finds a similar arrangement to other avian eggshells, despite their very thin and fragile nature. Fourier transform infrared spectrometry (FTIR) and electron backscatter diffraction (EBSD) results also confirm that the eggshells are entirely composed of calcite. Our findings demonstrate that passerine eggshells are not an exception and similar to other birds and reinforce the phylogenetic placement of this bird species.

Great spotted cuckoo eggshell microstructure characteristics can make eggs stronger

Obligate avian brood parasites lay stronger eggs than their hosts or non‐parasitic relatives because they are rounder and have a thicker eggshell. Additionally, some other characteristics of the brood parasitic eggshells related to their microstructure such as size and orientation of calcite crystal units could also contribute to generating even stronger shells. An eggshell microstructure formed by small randomly oriented calcite crystal units can increase the robustness of the eggshells of birds. Here, the eggshell microstructure of avian brood parasites as well as their hosts have been characterized in detail, using X‐ray diffraction analyses to estimate the size and degree of orientation of calcite crystal units making the eggshell. Specifically, the brood parasitic great spotted cuckoo Clamator glandarius and two hosts (jackdaws Corvus monedula and magpie Pica pica) and one non‐host species (the pigeon, Columba livia domestica) were considered. Calcite crystal of the eggshell of the brood parasitic species was smaller and more randomly oriented than those of the eggshells of non‐parasitic species, which suggest that eggshell microstructure would contribute to explain why parasitic eggs are more resistant to breakage than those of their hosts.

Antimicrobial activity of nest-lining feathers is enhanced by breeding activity in avian nests.

The use of feathers as nest material has been proposed as a kind of self-medication strategy because antimicrobial-producing microorganisms living on feathers may defend offspring against pathogenic infections. In this case, it is expected that density of antimicrobial-producing bacteria, and their antimicrobial effects, are higher in feathers that line the nests than in eggshells. Moreover, we know that feather pigmentation and breeding activity may influence density and antimicrobial production of bacteria. To test these predictions, we analyzed bacterial densities and antimicrobial activity of bacterial colonies isolated from bird eggshells and nest-lining feathers against bacterial strains comprising potential pathogens. Samples were collected from spotless starling (Sturnus unicolor) nests, and from artificial nests to isolate the effects of breeding activity on bacterial communities. The composition of feathers lining the nests was experimentally manipulated to create groups of nests with pigmented feathers, with unpigmented feathers, with both types of feathers or without feathers. Although we did not detect an effect of experimental feather treatments, we found that bacterial colonies isolated from feathers were more active against the tested bacterial strains than those isolated from eggshells. Moreover, bacterial density on feathers, keratinolytic bacteria on eggshells and antimicrobial activity of colonies isolated were higher in starling nests than in artificial nests. These results suggest that antimicrobial activity of bacteria growing on nest-lining feathers would be one of the mechanisms explaining the previously detected antimicrobial effects of this material in avian nests, and that breeding activity results in nest bacterial communities with higher antimicrobial activity.

Eggshell resorption, and embryonic mobilization and accumulation of calcium and metals in eggs of wild and captive Capercaillies Tetrao urogallus

Although it is fairly well known that eggshells are the major source of Ca and other micronutrients for developing avian embryos, potential anatomical and/or ecological correlates explaining the variation in embryo-induced depletion of micronutrients from eggshells remain to be addressed. Using unhatched eggs at various developmental stages and post-hatched eggshells of wild and captive-bred birds of a large precocial species, the Capercaillie Tetrao urogallus, we explored two major questions. (i) Do egg size, regional eggshell thickness as well as levels of two major micronutrients (Ca and Mg) and eight trace elements (Cr, Cu, Mn, Fe, Co, Cd, Pb and Zn) measured in egg shells and contents vary with embryonic age within and between wild and captive-bred bird eggs? (ii) How the proportions of eggshell elements become depleted during the entire process of embryogenesis? The eggshells of wild Capercaillies were thinner at the equator and the sharp pole, and contained more Mg and Ca, while in their contents there was more Cu, Cd and Pb compared with captive birds. All ten metal concentrations measured in the egg contents increased (from 15% to 285% more) with the age of embryos. The concentrations of six elements measured in eggshells (Cu, Mn, Fe, Co, Cd and Zn) decreased consistently (from 15 to 70% less) during embryogenesis. This suggests the presence of these elements in the innermost decalcified shell layer and their further mobilization into the embryos/egg contents. Our results strongly imply that most trace elements present in the egg contents/developing embryos are mobilized from the eggshells. We highlight the fact that knowledge of the magnitude of embryogenesis-related functional changes in the physical (such as shell thickness) and chemical traits of the eggs and eggshells of oviparous vertebrates is fundamental for drawing correct inferences regarding the response of an individual to variable environmental conditions.

Calcium Carbonate Crystal Shapes Mediated by Intramineral Proteins from Eggshells of Ratite Birds and Crocodiles. Implications to the Eggshell’s Formation of a Dinosaur of 70 Million Years Old

In this contribution we want to show how the intramineral proteins affect the crystal morphology of calcite crystals grown in vitro. Intramineral proteins from emu eggshells and two crocodile species were isolated, purified by ultrafast liquid chromatography, and characterized by biochemical and biophysical methods. We saw that the crystal habit of calcite was modified when intramineral proteins were present at certain concentration. Therefore, all crystal species were individually characterized by scanning electron microscopy (SEM) and by electron diffraction with an electron-reduced dosage in transmission electron microscopy. Additionally, transversal SEM micrographs of eggshells of four types of species, namely, emu, crocodile, hen, and dinosaur (70 million years old), were compared to track the changes produced by the interacting intramineral proteins. Finally, the organic sulfur content analysis of these eggshells was performed by using X-ray absorption techniques like X-ray fluorescence and X-ray absorption near-edge structure. From the analyses of the dinosaur eggshells, these X-ray absorption data showed a very characteristic organic sulfur bonding similar to that semiessential proteogenic amino acid l-cysteine, which implies that there is a possibility of having a very old intramineral protein similar to those found in emu and crocodiles.

Oxygen isotope fractionation between bird eggshell calcite and body water: application to fossil eggs from Lanzarote (Canary Islands).

Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ(18)Ocalc and δ(13)Ccalc) are regularly used to reconstruct paleoenvironmental conditions. However, the interpretation of δ(18)Ocalc values of fossil eggshells has been limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids, and drinking water have not been determined yet. For this purpose, eggshell, albumen water, and drinking water of extant birds have been analyzed for their oxygen and carbon isotope compositions. Relative enrichments in (18)O relative to (16)O between body fluids and drinking water of +1.6±0.9‰ for semi-aquatic birds and of +4.4±1.9‰ for terrestrial birds are observed. Surprisingly, no significant dependence to body temperature on the oxygen isotope fractionation between eggshell calcite and body fluids is observed, suggesting that bird eggshells precipitate out of equilibrium. Two empirical equations relating the δ(18)Ocalc value of eggshell calcite to the δ(18)Ow value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to fossil eggshells from Lanzarote in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene. Both δ(13)Ccalc and δ(18)Ocalc values of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater, whereas low δ(13)Ccalc and high δ(18)Ocalc values of eggshells from the Pliocene giant bird suggest a terrestrial lifestyle. This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental or climatic conditions.

Environmental Bioindication Studies by Bayesian Network with Use of Grey Heron as Model Species

The article presents a procedure for assessing the quality of the environment, using eggshells of birds as a biomarker implemented into a Bayesian network. An environmental quality index (EQI) was proposed and calculated on the basis of local quality indicators. Experimental data on concentrations of toxic elements in grey heron (Ardea cinerea) eggshells (biomarker of river valleys) were used to determine the empirical variables (nodes) and the probability distributions on the set of these variables. A probabilistic graphical model represents a multitude of relationships between variables in a system that enables the prediction of EQI. The model presented is a useful tool for environmental quality management.

Shedding Light on Bird Egg Color: Pigment as Parasol and the Dark Car Effect.

The vibrant colors of many birds' eggs, particularly those that are blue to blue-green, are extraordinary in that they are striking traits present in hundreds of species that have nevertheless eluded evolutionary functional explanation. We propose that egg pigmentation mediates a trade-off between two routes by which solar radiation can harm bird embryos: transmittance through the eggshell and overheating through absorbance. We quantitatively test four components of this hypothesis on variably colored eggs of the village weaverbird (Ploceus cucullatus) in a controlled light environment: (1) damaging ultraviolet radiation can transmit through bird eggshells, (2) infrared radiation at natural intensities can heat the interior of eggs, (3) more intense egg coloration decreases light transmittance ("pigment as parasol"), and (4) more intense egg coloration increases absorbance of light by the eggshell and heats the egg interior ("dark car effect"). Results support all of these predictions. Thus, in sunlit nesting environments, less pigmentation will increase the detrimental effect of transmittance, but more pigmentation will increase the detrimental effect of absorbance. The optimal pigmentation level for a bird egg in a given light environment, all other things being equal, will depend on the balance between light transmittance and absorbance in relation to embryo fitness.

The cuticle modulates ultraviolet reflectance of avian eggshells.

ABSTRACTAvian eggshells are variedly coloured, yet only two pigments, biliverdin and protoporphyrin IX, are known to contribute to the dramatic diversity of their colours. By contrast, the contributions of structural or other chemical components of the eggshell are poorly understood. For example, unpigmented eggshells, which appear white to the human eye, vary in their ultraviolet (UV) reflectance, which may be detectable by birds. We investigated the proximate mechanisms for the variation in UV-reflectance of unpigmented bird eggshells using spectrophotometry, electron microscopy, chemical analyses, and experimental manipulations. We specifically tested how UV-reflectance is affected by the eggshell cuticle, the outermost layer of most avian eggshells. The chemical dissolution of the outer eggshell layers, including the cuticle, increased UV-reflectance for only eggshells that contained a cuticle. Our findings demonstrate that the outer eggshell layers, including the cuticle, absorb UV-light, probably because they contain higher levels of organic components and other chemicals, such as calcium phosphates, compared to the predominantly calcite-based eggshell matrix. These data highlight the need to examine factors other than the known pigments in studies of avian eggshell colour.

Laying date, incubation and egg breakage as determinants of bacterial load on bird eggshells: experimental evidence.

Exploring factors guiding interactions of bacterial communities with animals has become of primary importance for ecologists and evolutionary biologists during the last years because of their likely central role in the evolution of animal life history traits. We explored the association between laying date and eggshell bacterial load (mesophilic bacteria, Enterobacteriaceae, Staphylococci, and Enterococci) in natural and artificial magpie (Pica pica) nests containing fresh commercial quail (Coturnix coturnix) eggs. We manipulated hygiene conditions by spilling egg contents on magpie and artificial nests and explored experimental effects during the breeding season. Egg breakage is a common outcome of brood parasitism by great spotted cuckoos (Clamator glandarius) on the nests of magpie, one of its main hosts. We found that the treatment increased eggshell bacterial load in artificial nests, but not in magpie nests with incubating females, which suggests that parental activity prevents the proliferation of bacteria on the eggshells in relation to egg breakage. Moreover, laying date was positively related to eggshell bacterial load in active magpie nests, but negatively in artificial nests. The results suggest that variation in parental characteristics of magpies rather than climatic variation during the breeding season explained the detected positive association. Because the eggshell bacterial load is a proxy of hatching success, the detected positive association between eggshell bacterial loads and laying date in natural, but not in artificial nests, suggests that the generalized negative association between laying date and avian breeding success can be, at least partially, explained by differential bacterial effects.

Visualisation of Latent Fingerprint on Wild Bird Eggshells by Alternate Light Sources Following Superglue Fuming

The theft of the eggs of endangered or protected species of bird, and subsequent reduction in wildlife population, is a significant problem worldwide. Detection rates are comparatively low towards this type of crime and fingerprinting of egg shells is infrequently utilised due to the technical barrier. This paper explores a novel technique using cyanoacrylate (superglue) fuming in conjunction with fluorescent dye to visualise latent fingerprints upon avian eggshells assisted with alternate light sources. A systematic investigation of experimental parameters has also been carried out to optimise the condition for the fingerprint visualisation. This research project has successfully developed latent fingerprints upon smooth wild bird eggshells but was less successful on developing prints on more textured, porous eggshells.

The stable isotopic composition of carbonate (C & O) and the organic matrix (C & N) in waterbird eggshells from South Florida: insights into feeding ecology, timing of egg formation, and geographic range

In order to better understand the feeding ecology and timing of egg formation and regional geographic range of wading birds from South Florida, the δ13C and δ18O values of eggshells and the δ13C and δ15N values of the organic matrix, were measured in ~400 samples, representing nine species of waterbirds. Results reveal major differences between the eggshells of birds nesting in the Everglades versus Florida Bay, with the samples from the Everglades having lower δ13C, and more positive δ18O values, compared to specimens from Florida Bay. The differences in the δ13C values represent a fundamental difference in the δ13C of the organic material at the base of the food chains in the two areas. In the Everglades, the δ13C values are controlled by particulate organic material derived from terrestrial vegetation, while in Florida Bay δ13C values are controlled by seagrasses and other marine plants. The positive δ18O values from the Everglades reflect enrichment in 18O of the water as a result of evaporation in the Everglades compared to Florida Bay during the period of egg formation. All of the samples exhibited similar δ15N values and the absence of positive correlation between δ13C and δ15N suggests that either the birds are feeding at generally similar trophic levels, or that the δ13C and δ15N of the organic material in the eggshell are not an effective trophic indicator in these environments.

First light for avian embryos: eggshell thickness and pigmentation mediate variation in development and UV exposure in wild bird eggs

Summary The avian embryo's development is influenced by both the amount and the wavelength of the light that passes through the eggshell. Commercial poultry breeders use light of specific wavelengths to accelerate embryonic growth, yet the effects of the variably patterned eggshells of wild bird species on light transmission and embryonic development remain largely unexplored. Here, we provide the first comparative phylogenetic analysis of light transmission, through a diverse range of bird eggshells (74 British breeding species), in relation to the eggshell's thickness, permeability, pigment concentration and surface reflectance spectrum (colour). The percentage of light transmitted through the eggshell was measured in the spectral range 250–700 nm. Our quantitative analyses confirm anecdotal reports that eggshells filter the light of the externally coloured shell. Specifically, we detected a positive relationship between surface eggshell reflectance (‘brightness’) and the percentage of light transmitted through the eggshell, and this relationship was strongest at wavelengths in the human‐visible blue‐green region of the spectra (c. 435 nm). We show that less light passes through thicker eggshells with greater total pigment concentrations. By contrast, permeability (measured as water vapour conductance) did not covary significantly with light transmission. Eggs of closed‐nesting species let more light pass through, compared with open nesters. We postulate that greater light transmission is required to assist embryonic development under low light exposure. Importantly, this result provides an ecological explanation for the repeated evolution of immaculate, white‐ or pale‐coloured eggshells in species nesting in enclosed spaces. Finally, we detected correlative support for the solar radiation hypothesis, in that eggshells of bird species with a longer incubation period let significantly less of the potentially harmful, ultraviolet (UV) light pass through the eggshell. In summary, we demonstrate suites of avian eggshell properties, including eggshell structure and pigmentation, which are consistent with an evolutionary pressure to both enhance and protect embryonic development.

Trace elements in eggshells of the Grey Heron (Ardea cinerea) from the colony in the Roztocze Hills (South East Poland)

Concentrations of 14 trace elements (Sr, B, Al, Zn, Cu, Li, Se, Mn, Cr, As, Ni, Pb, V, Cd) in eggshells of the Grey Heron Ardea cinerea collected from the colony located in the Roztocze Hills (East Poland) were determined. The concentrations of strontium (geometric mean, 153.88mm/kg dry weight [dw]) proved to be the highest. However, they were lower than those found in eggshells of other birds. The following sequence of concentrations of four important elements was obtained in this study: Cu > Ni > Pb > Cd. This sequence of concentrations is substantially different from the one reported by other authors based on experiments on other Heron species. Interestingly, the concentrations of heavy metals obtained in this study, those of lead and copper in particular, were a dozen or so times lower than those determined in other Heron species. The only exception was the concentration of Ni. Zn concentrations (8.26 mg/kg dw) determined in this study correspond with the results obtained in other eggshell studies.

Why are birds' eggs colourful? Eggshell pigments co-vary with life-history and nesting ecology among British breeding non-passerine birds

The colourful appearance of bird eggshells has long fascinated biologists and considerable research effort has focused on the structure and biochemistry of the avian eggshell matrix. The presence of tetrapyrrole pigments was identified nearly a century ago. Surprisingly, how the concentrations of avian eggshell pigments vary among related species, and whether this variability is associated with either eggshell appearance and/or species life-history traits, remains poorly understood. We quantified the concentrations of the two key eggshell pigments, protoporphyrin IX and biliverdin, from a diverse sample of eggshells stored at the Natural History Museum, Tring, UK. We explicitly tested how these two pigments are associated with physical measures of eggshell coloration and whether the pigment concentrations and colour diversity co-vary with phylogenetic affiliations among species. We also tested a series of comparative hypotheses regarding the association between the concentrations of the two pigments and specific life-history and breeding ecology traits. Across species, the average concentrations of protoporphyrin and biliverdin were positively correlated, and both strongly co-varied with phylogenetic relatedness. Controlling for phylogeny, protoporphyrin concentration was associated with a higher likelihood of cavity nesting and ground nesting, whereas biliverdin concentration was associated with a higher likelihood of non-cavity nesting habit and bi-parental provisioning. Although unlikely to be explained by a single function, the breeding ecology and life history-dependence of eggshell pigment concentrations in these comparative analyses implies that related species share pigment strategies, and that those strategies relate to broad adaptive roles in the evolution of variation in avian eggshell coloration and its underlying mechanisms.

Attractive blue-green egg coloration and cuckoo−host coevolution

Recent evidence suggests that blue-green coloration of bird eggshells may be related to female and/or egg phenotypic quality, and that such colour may affect parental effort and therefore the nutritional environment of developing nestlings. Here we suggest that these relationships and the signal function of eggshell coloration would affect the outcome of coevolution between avian brood parasites and their hosts in at least three different non-exclusive evolutionary pathways. First, by laying blue-green coloured eggs, cuckoo females may exploit possible sensory biases of their hosts, constraining the evolution of parasitic egg recognition, and thus avoid rejection. Second, because of the relatively high costs of laying blue eggs, cuckoo females may be limited in their ability to mimic costly blue-green eggs of their hosts because cuckoo females lay many more eggs than their hosts. Furthermore, costs associated with foreign egg recognition errors would be relatively higher for hosts laying blue eggs. Third, cuckoos may use coloration of host eggs for selecting individuals or specific hosts of appropriate phenotypic quality (i.e. parental abilities). We here explored some predictions emerging from the above scenarios and found partial support for two of them by studying egg coloration of European cuckoos (Cuculus canorus) and that of their 25 main hosts, as well as parasitism and rejection rate of hosts. Cuckoo hosts parasitized with more blue, green, and ultraviolet cuckoo eggs, or those laying more blue-green eggs, were more prone to accept experimental parasitism with artificial cuckoo eggs. In addition, coloration of cuckoo eggs is more variable when parasitizing hosts laying bluer-greener eggs, even after controlling for the effect of host egg coloration (i.e. degree of egg matching). Globally, our results are consistent with the proposed hypothesis that host egg traits that are related to phenotypic quality of hosts, such as egg coloration, may have important implications for the coevolutionary interaction between hosts and brood parasites. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 154–168.