Red Chroma Research Articles

Vision Experiments on Chroma-Related Preference for Color Quality of Lighting

ABSTRACT Two vision experiments were conducted to quantify the chroma-related preference in color quality of lighting in a real room-size cubicle simulating interior lighting environment with spectrally tunable light sources. The first experiment used 9 different lights with increased or decreased chroma in nine levels in red-green directions. The second experiment used 11 different lights with increased or decreased chroma in three hue directions, for red, green, and yellow, controlled as independently as possible. About 20 subjects participated in these two experiments evaluating the appearance of various fruits and vegetables as well as skin tone under these test lights by numerous pair comparisons. The results of the first experiment showed that chroma increase in ΔC*ab ≈ 4 to 8 from the reference light was most preferred for all target objects, and desaturated lights were disliked in all cases. The second experiment showed that chroma change in red is significantly important for the preference, green was second, and yellow had the least effect on preference. The results of the second experiment suggested that preference increases with increasing red chroma in light, and after a peak in preference (between ΔC*ab ≈ 5 to 10), preference starts decreasing, which is consistent with findings from the first experiment. Neither the viewing targets nor the correlated color temperature (CCT) conditions were found to have significant impact on the subjects’ preference.

Effect of light intensity in the nest site on eggshell pigmentation in a hole-nesting passerine

Daylight is an important factor necessary for the proper embryonic development of birds, which raises the question, what happens when birds nest in relatively dim sites? The study experimentally tested whether there is a relationship between light conditions at the nesting site and the protoporphyrin-based pigmentation in the eggshell of the Great Tit (Parus major). We hypothesised that at lower light levels, eggs are less pigmented to increase the amount of light reaching the embryo. Our study system consisted of two types of nest boxes: "dark", in which the only source of light was the entrance hole, and "bright", which had two additional side windows. Photographs of clutches taken during the incubation period were used to quantify eggshell pigmentation. Multispectral image analyses were performed to measure variables correlating with protoporphyrin content, such as spot brightness, average spot size, spotting coverage, and spot red chroma. Repeatability analysis indicated that eggshell colouration characteristics were significantly and moderately repeatable between eggs from a single clutch, which suggests that they are under genetic and environmental control. However, none of the pigmentation traits differed significantly between the two types of nest boxes. We speculate about other ecological aspects that might have influenced the observed variability in eggshell pigmentation.

The signalling function of plumage colour traits in the Chestnut Thrush (Turdus rubrocanus)

Melanin is a common pigment in birds, and several studies have shown that melanin‐based plumage coloration could signal individual body condition, social status and personality traits. However, most of these studies have focused on males, and little is known about the role of plumage coloration in females. Here, we investigated whether body condition and personality traits (activity and exploratory behaviour) were associated with plumage coloration in wild populations of the Chestnut Thrush Turdus rubrocanus, an apparently monochromatic species. We also tested whether the signals of plumage colour traits differed between sexes. In this study, we found that females had better body condition compared with males. Females with lower chroma and brightness of their black wings had better body condition, but no plumage colour measures reflected male body condition. Males with a lower red chroma of their brown back plumage were less active, and females with lower red chroma of the back plumage were more active. However, plumage coloration did not explain variation in exploratory behaviour. Our findings suggest that plumage colour traits may act as sex‐specific signals in Chestnut Thrushes and these traits may play important roles in sexual or conspecific communication in the wild.

Effect of high temperatures on the magnetic susceptibility of loess.

Coal fires refer to fires generated by the self-combustion of coal seams, which have a maximum temperature of 1000 °C. Such fires can significantly alter the properties of surrounding rock and soil. However, in Northern Shaanxi, China, coal resources are abundant, and the buried depth of coal seams is shallow; therefore, coal fires often occur. Because Northern Shaanxi is located in China's Loess Plateau, there is a large amount of loess accumulation on the surface. For this reason, it is imperative to study the effects of high temperatures on loess. In this paper, the loess samples are heat treated at different temperatures (200-1000 °C), and their surface redness (a*) and mass magnetic susceptibility (χ) are measured to simulate the high-temperature effects of coal fires on the loess in northern Shaanxi, and also study its chromaticity changes and abnormal magnetic properties. The results show that (1) the loess χ value is affected by the heat-treatment temperature; at 600 °C, the χ value decreases, increasing rapidly above after 850 °C. Further, the magnetic susceptibility changes significantly. (2) The thermal-induced transformation of ferromagnetic minerals and the buried depth of loess are the main reasons for these changes in magnetic susceptibility and red chroma of loess.

Using a single-board computer as a low-cost instrument for SPAD value estimation through colour images and chlorophyll-related spectral indices

The leaf chlorophyll content is a major indicator of plant stress. Therefore, it is often used for the evaluation of crop status to adjust agricultural management to ensure high quality yield while concurrently applying water and agrochemicals in a sustainable manner. Since laboratory procedures for their assessment are time-consuming and destructive, nondestructive methods have been developed recently based on known vegetation spectral response characteristics. In addition to various vegetation indices derived from remotely sensed data, hand-held sensors such as SPAD-502 are currently widely used for in-field sampling to gain precise information for decision-making in terms of best-fitting agricultural management. However, the costs of such commercial devices can be limiting for farmers. The low-cost alternatives that have been developed recently exploit widely accessible digital cameras with sensors sensitive to the visible region of the electromagnetic spectrum. Digital numbers extracted from colour images in RGB channels serve as the input for broadband “chlorophyll index” calculations. Major constraints regarding digital cameras are, however, the natural light illuminance and the necessity of data postprocessing. In the framework of this study, a novel technological solution was developed to address these issues. A Raspberry Pi single-board computer together with a Pi Camera and a simple LED incorporated in a 3D print case created a prototype called Rasp2SPAD, which was programmed to acquire and analyse a colour image. The prototype and its setup were further tested on the experimental plant material of the winter rapeseed. A set of 22 chlorophyll-related parameters across various colour representation models were generated, from which an SPAD value was modelled using i) a simple linear model, ii) a generalized linear model, and iii) an artificial neural network. The blue (Cb) and red (Cr) chroma components of the YUV colour space were found to be most suitable for SPAD value modelling. Calibration equations were determined, and the results reached relatively high accuracy (mean absolute deviance 1.85 and R-squared 0.81 for simple linear model) while keeping the costs significantly low compared to the most commonly used commercial sensor. In this way, a simple and cheap methodology was introduced to bring the results of research closer to practice, which should help first spread the precision agriculture concept to a wider audience and second allow them to utilize with it.

The reliability of achromatic displays is island‐dependent in nocturnal Storm Petrels

Nocturnal birds rely on achromatic visual signals to assess rivals and potential mates, but variation in the expression of these displays has been understudied. Here we use UV‐visible reflectance spectrometry to study colour variation and the potential signalling function of the dark brown chest and white rump plumage – a colour pattern conspicuously exhibited during twilight courtship displays – in nocturnal Mediterranean Storm Petrels Hydrobates pelagicus melitensis from three islands with different exposures to predation and human disturbance. Human activity may increase perceived predation risk and thus affect activity budgets and the physiological stress response, with possible consequences on the relationship between individual body condition and plumage coloration. We found that chest and especially rump feathers reflected in the ultraviolet (UV) but there was no evidence of sexual dichromatism. However, we found support for a male‐specific signalling role of plumage coloration. Indeed, chest yellow–red chroma and rump UV chroma were positively related to body condition in males, but only in the two islands representing the poorer environmental conditions. Therefore, environmental variability can potentially modify the reliability of achromatic displays, with possible consequences on sexual selection patterns in a nocturnal bird.

Covariation between eggshell colouration and eggshell bacteria abundance and egg characteristics in blackbirds

Several functions have been proposed to explain eggshell colouration in birds. Eggshell colour may, for instance, signal female egg investment and hence the quality of the female and/or the egg. Such a covariation between eggshell colour and egg quality is supported by several studies, but what is related to eggshell colour is not necessarily consistent between populations, species or egg compounds.In this study, we examined several maternally derived egg compounds; namely yolk mass, egg white lysozyme and pH, yolk testosterone, oestrogens and eggshell colour and we determined the abundance of cultivable bacteria on the eggshell surface of blackbirds’ eggs Turdus merula. Based on that, we examined whether there is an association between eggshell colour parameters derived via spectrophotometric analyses and eggshell spot size and any of the investigated egg parameters.Our results suggest that two eggshell colour components derived by a principle component analyses and eggshell spot size covary with different egg parameters. We found that eggs containing more UV, yellow and red chroma in their eggshells contain heavier yolks. In contrast more bluish, greener and brighter eggs have to face higher loads of bacteria i.p. haemolytic bacteria and bacteria originating from the urogenital tract of the female. No other egg compound investigated seemed to be reflected in any eggshell colour parameter. Our data do not support an antibacterial function of eggshell colour as the abundance of bacteria originating from the female urogenital tract is negatively related to eggshell colouration. Furthermore, we found a positive but weak association between egg spot size and egg white lysozyme levels. Possible functional implications of our results are discussed.

The effect of dietary carotenoid increase on painted turtle spot and stripe color.

Determination of how carotenoid-based color patches change with pigmentary access is important to understanding color patch function in animals. We performed a carotenoid addition experiment on male painted turtles (Chrysemys picta) to determine if an increase in dietary carotenoids led to location-specific changes in painted turtle spot and stripe color. Turtles fed large quantities of carotenoids had increased yellow chroma in chin stripes and increased red chroma in the neck and carapace stripes, as well as reduced ultraviolet (UV) chroma in the neck (orange to the human eye) and fore -limb (red to the human eye) stripes. Turtles fed large quantities of carotenoid had reduced brightness (B1) in the hind-limb stripes (red to the human eye) as well as reduced red and UV chroma in the post orbital spot of turtles (yellow to the human eye) compared to turtles fed moderate amounts of carotenoid. These results imply that integumentary spot and stripe colors are dependent upon carotenoid access, and increased lutein access leads to increased yellow and red chroma, as well as reduced ultra-violet chroma and brightness in male painted turtles. These results are discussed with respect to dietary access to carotenoids and color in other model systems, and the possibility that spot and stripe color functions as a visual signal.

Dental properties, ultrastructure, and pulp cells associated with a novel DSPP mutation

To investigate physical characteristics and behaviours of dental pulp cells of teeth isolated from a dentinogenesis imperfecta (DGI) patient with a novel dentin sialophosphoprotein (DSPP) mutation. Whole exome and Sanger sequencing were employed to identify mutations. Physical characteristics of the teeth were examined. Pulp cells' behaviours including cell proliferation, colony-forming unit, osteogenic differentiation, pluripotent markers, and mesenchymal stem cell markers were investigated. The proband had opalescent brown primary teeth with extensive loss of enamel. Mutation analysis revealed a novel heterozygous 4-bp deletion, c.1915_1918delAAGT (p.K639QfsX674), in exon 5 of the DSPP associated with DGI. Analysis of the extracted primary incisor demonstrated a decrease in brightness but an increase in yellow and red chroma. The dentin showed reduced mineral density. The dentinal tubules were present in the predentin, but progressively collapsed in the dentin. The pulp cells exhibited markedly reduced CD105 expression, decreased cell proliferation, and smaller colony-forming units. We identified a novel mutation in the DSPP gene which disturbed dentin characteristics and pulp cells' behaviours. Our study expands the mutation spectrum and understanding of pathologic dentin phenotypes related to the frameshift deletion in the dentin phosphoprotein (DPP) region of the DSPP gene.

Sexual signals reveal males’ oxidative stress defences: Testing this hypothesis in an invertebrate

Abstract The hypothesis that sexual traits reveal the oxidative stress resistance of their bearers has been widely tested in vertebrates but remains unexplored in invertebrates. Here, Hetaerina americana was used to test whether oxidative stress defences are advertised by male wing spot size and colour (a male sexual trait). To this end, we investigated (1) whether oxidative stress reduced survival, (2) whether wing spot size revealed males’ antioxidant defences and (3) how wing spot size and colour were affected by oxidative stress. We elevated oxidative stress by injecting adult males with paraquat (PQ, a compound that favours the production of free radicals) and then examined how this affected male survival and wing spot size. We then related the expression of wing spot size to indicators of oxidative stress—hydrogen peroxide (H2O2) and total antioxidant capacity (TAC), super oxide dismutase (SOD) and catalase (CAT)—in adult males (whose wing spot is fixed) injected with PQ. In teneral males, whose wing spots are still forming, we compared wing spot size, colour (red and yellow chroma) and brightness in individuals injected with PQ or water as a control. Oxidative stress reduced the survival of adult and teneral males. While the H2O2 and TAC markers of antioxidant defences were positively correlated with wing spot size, there was no correlation with CAT and a negative correlation with SOD. In teneral males, PQ increased the yellow chroma and brightness of wing spots, but did not affect spot size or red chroma. Our results highlight the importance of measuring different markers as indicators of male oxidative stress defences, and that the sexual signals of invertebrates may reveal the oxidative stress status of their bearers. A plain language summary is available for this article.

Variation in melanin pigmentation of a sexually selected plumage trait and its adaptive value in the Common SnipeGallinago gallinago

There is increasing evidence that melanin‐based plumage coloration correlates with different components of fitness and that it may act as a social or sexual signal of individual quality. We analysed variation in melanin pigmentation in the outermost tail feathers of the Common SnipeGallinago gallinago. During courtship flights, male Snipe use their outermost tail feathers to generate a drumming sound, which plays a role in territory establishment and mate choice. As the outermost tail feathers are displayed to females during these flights, we predicted that conspicuous variation in their rusty‐brown (pheomelanin‐based) coloration may act as an honest signal of individual quality. To test this prediction, we spectrophotometrically measured brightness (an indicator of total melanin content) and red chroma (an indicator of pheomelanin content) of the outermost tail feathers in 180 juvenile and adult Common Snipe. An age‐related decline in feather brightness was found exclusively in females, suggesting that melanization could have evolved by natural selection to camouflage incubating birds. In both sexes, brightness of the tail feathers was inversely correlated with their structural quality (as measured with mass–length residuals), suggesting that melanization could increase mechanical properties of feathers and, in males, enhance the quality of courtship sonation. Red chroma positively correlated with total plasma protein concentration, supporting our prediction that pheomelanin pigmentation of tail feathers may act as an honest signal of condition. Our study indicated that variation in the melanin‐based coloration of the outermost tail feathers in the Common Snipe could have evolved as a result of several different selection pressures and it emphasizes the complexity of the processes that underlie the evolution of melanin‐based plumage coloration in birds.

Mate choice for major histocompatibility complex complementarity in a strictly monogamous bird, the grey partridge (Perdix perdix)

BackgroundSexual selection has been hypothesised as favouring mate choice resulting in production of viable offspring with genotypes providing high pathogen resistance. Specific pathogen recognition is mediated by genes of the major histocompatibility complex (MHC) encoding proteins fundamental for adaptive immune response in jawed vertebrates. MHC genes may also play a role in odour-based individual recognition and mate choice, aimed at avoiding inbreeding. MHC genes are known to be involved in mate choice in a number of species, with ‘good genes’ (absolute criteria) and ‘complementary genes’ (self-referential criteria) being used to explain MHC-based mating. Here, we focus on the effect of morphological traits and variation and genetic similarity between individuals in MHC class IIB (MHCIIB) exon 2 on mating in a free-living population of a monogamous bird, the grey partridge.ResultsWe found no evidence for absolute mate choice criteria as regards grey partridge MHCIIB genotypes, i.e., number and occurrence of amino acid variants, though red chroma of the spot behind eyes was positively associated with male pairing success. On the other hand, mate choice at MHCIIB was based on relative criteria as females preferentially paired with more dissimilar males having a lower number of shared amino acid variants. This observation supports the ‘inbreeding avoidance’ and ‘complementary genes’ hypotheses.ConclusionsOur study provides one of the first pieces of evidence for MHC-based mate choice for genetic complementarity in a strictly monogamous bird. The statistical approach employed can be recommended for testing mating preferences in cases where availability of potential mates (recorded with an appropriate method such as radio-tracking) shows considerable temporal variation. Additional genetic analyses using neutral markers may detect whether MHC-based mate choice for complementarity emerges as a by-product of general inbreeding avoidance in grey partridges.

Human perceptions of colour rendition vary with average fidelity, average gamut, and gamut shape

An experiment was conducted to evaluate how subjective impressions of a light source’s colour quality depend upon the details of the shifts it causes in the colour appearance of illuminated objects. Twenty-eight participants each evaluated 26 lighting conditions in a 3.1 m by 3.7 m room filled with objects selected to cover a range of hue, saturation, and lightness. IES TM-30-15 Fidelity Index ( Rf) values ranged from 64 to 93, IES TM-30 Gamut Index ( Rg) values ranging from 79 to 117, and IES TM-30 red chroma shift ( Rcs,h1) values ranging from −19% to 26%. All lighting conditions had the same nominal illuminance and chromaticity. Participants were asked to rate each condition on eight point scales for saturated–dull, normal–shifted, and like–dislike, as well as classifying the condition as one of saturated, dull, normal, or shifted. The findings suggest that gamut shape is more important than average gamut area for modeling human preference, with red playing a more important role than other hues. Average fidelity alone is a weak predictor of human perception, especially CIE Ra. Nine of the top 12 rated products had a CIE Ra value of 73 or less, which indicates that the criteria of CIE Ra ≥ 80 may be excluding many preferred light sources.

식이습관 및 구강보건 행태와 상악 전치부 색조 관련 특성 비교

Purpose: This study was conducted to find oral health and eating attributes relating to the maxillary anterior teeth color and examine the meaning. Methods: This study aims to prepare the basic data of the teeth color by measuring analyze mode using the color of the maxillary anterior teeth(maxillary central incisor, lateral incisor, canine) of the dental patients as the dental colorimeter. Also, This researcher explained the purpose of this study to dental patients and got agreement of 111 patients(50 men and 61 women). We conducted the survey from 2 March to 25 May, 2015. So the color of total 333 teeth was examined, and eating habit attributes and oral health behaviors were researched. Results: Lightness(L) was significantly high in female compared to male(12, p<0.05), the more often intake of red pepper paste decreased(11, 13) lightness. and the brightness of the 31-40 age group was significantly higher(12, p<0.05) than the group under the age of 20. Red chroma(a) was significantly low in over 50 age group compared to the group under the age of 20(12, p<0.05), and the red chroma(a) of the “received periodic scaling” group was significantly lower(13, p<0.01) than the other group. [Abstract]

Maximum likelihood conjoint measurement of lightness and chroma.

Color varies along dimensions of lightness, hue, and chroma. We used maximum likelihood conjoint measurement to investigate how lightness and chroma influence color judgments. Observers judged lightness and chroma of stimuli that varied in both dimensions in a paired-comparison task. We modeled how changes in one dimension influenced judgment of the other. An additive model best fit the data in all conditions except for judgment of red chroma where there was a small but significant interaction. Lightness negatively contributed to perception of chroma for red, blue, and green hues but not for yellow. The method permits quantification of lightness and chroma contributions to color appearance.

Dedivost sfarbenia slovensk�ho pinzgausk�ho dobytka

The objective of the work was analysis of chestnut coat colour inheritance of Slovak Pinzgau cattle in accordance to age and farming system. In 304 cows of breeding groups P0,P1,P2 and R3 born between 2000 to 2010 from four breeding herds (4 agricultural cooperatives and JSC: PD Smrecany – farm Veterna Poruba, PD Spisske Bystre – farm Kvetnica, Agria Liptovský Ondrej JSC – farm Liptovska Porubka, PD LCV Cimhova) was measured intensity of coat colour. For objective measurement of coat colour the handheld Minolta Chromameter CM-2600d was applied using the CIE L*a*b* colour space. The instrument recorded the values L*, a* and b*. The L* value shows the lightness of the colour, a* value indicates the red/green, while the b* value indicates the yellow/blue chromaticity of the colour. The values C* (Chroma/saturation) and h (hue) were derived from the values a* and b*. Average lightness in observed animals was 22.60; average of the red chroma was 8.84 resp. 13.32 for the yellow chroma. Saturation of coat colour was 16.19 resp. 0.97 for hue.

Age-related change in carotenoid-based plumage of the American Redstart (Setophaga ruticilla)

Plumage colouration serves a variety of functions for birds, including conspecific signalling, crypsis, and predator–prey interactions. Though much research has been conducted on colour changes in species with delayed plumage maturation, where birds do not exhibit definitive adult plumage until their second breeding season or later, relatively few studies have examined how plumage colour changes once definitive adult plumage has been attained. In this study on male and female American Redstarts (Setophaga ruticilla), which exhibit male delayed plumage maturation, we used reflectance spectrometry to evaluate carotenoid-based tail colour changes over 11 breeding seasons, examining both within-individual and population-level changes. At a population level, males in their first breeding season in definitive adult plumage had a feather hue that was more orange-shifted than birds in their second year in adult plumage, and marginally, but not significantly, more orange-shifted than birds in their third year in adult plumage. Within-individual analysis of males recaptured in subsequent seasons also revealed a shift away from orange towards a more yellow feather hue as individuals aged. Within individuals, red chroma was highest for males in their second year in adult plumage, but it showed no population-level effects. At the population level, female redstarts in their first breeding season displayed plumage with a higher red chroma and a lower brightness than birds in their second breeding season, potentially as a result of differences in the timing and conditions of moult (first-year bird tail feathers were grown in the nest). For adult males and females, there was no difference in plumage colouration between birds that returned to the study site compared to those that failed to return. Together, our results suggest that within-individual change rather than differential survival best explains our findings. We suggest that studies examining age-related colour changes are critical for understanding the evolution of complex signalling systems, such as that of American Redstarts.

Red coloration in juvenile spiny-footed lizards, Acanthodactylus erythrurus, reduces adult aggression

In many animal taxa, coloration is a visual signal used for communication among conspecifics, for example between age classes. Juvenile coloration has been hypothesized to reduce aggression from adults in some species, in what is called the aggression avoidance hypothesis. Spiny-footed lizards are good subjects for testing this hypothesis, as juveniles develop conspicuous red coloration on their hind limbs and tails that fades in adulthood. To test the influence of juvenile coloration on adult aggressiveness, we conducted videotaped encounters in captivity between adults of both sexes and juveniles with their natural red coloration, or experimentally painted either red or white on their natural red parts. Then we recorded the number of times juveniles were bitten and attacked. In unpainted juveniles, no significant relationship was found between juvenile coloration (brightness, red chroma or hue) and adult aggressiveness. However, juveniles painted red were bitten less than those painted white when number of times bitten was controlled for number of times attacked. This result supports the aggression avoidance hypothesis, as an escalation from low-intensity (attacking) to high-intensity aggression (biting) was less probable towards red juveniles. The presence of red coloration in juveniles caused the reduction in adult aggression, while small natural variations in this red colour did not seem to have any further effect. Juvenile red coloration in this species might indicate age or sexual immaturity to adults. © 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Juvenile sexual dimorphism, dichromatism and condition-dependent signaling in a bird species with early pair bonds

AbstractSexual selection in juvenile vertebrates is a rare and seldom studied phenomenon. Bearded Reedlings are passerines that form stable, life-long pair bonds within a few weeks after fledging. We investigated the degree to which juvenile Bearded Reedlings are sexually dimorphic and whether they possess condition-dependent ornaments. We found significant intersexual differences in the bill reflectance, reflectance and size of eumelanin-based plumage traits (lore and back patch) and morphological traits. Females that were in better body condition had longer tails and bills with greater red chroma, and lore size was negatively related to the occurrence of chewing lice. In males, body condition was positively related to melanic back patch length. Moreover, a positive relationship between bill color and feather mite load in males suggests a symbiotic, rather than parasitic, relationship. Our study provides the first evidence that sexually dimorphic traits in immature birds with pair bonds have the potential to signal condition and resistance to parasites.

Inter-annual variation in American redstart (Setophaga ruticilla) plumage colour is associated with rainfall and temperature during moult: an 11-year study.

Carotenoid-based colouration plays an important role in sexual signaling in animals as an honest indicator of individual quality during mate choice and competitive interactions. However, few studies have examined how natural variation in weather conditions influences inter-annual variation in the expression of ornamentation, potentially through affecting the dietary availability of carotenoids. In this study, we examine variation in the expression of carotenoid-based plumage colouration in relation to temperature and rainfall during the pre-moulting and moulting period over 11 years in a population of American redstarts, Setophaga ruticilla, breeding in eastern Canada. We used reflectance spectrometry of tail feathers collected from male and female redstarts to relate feather colour with weather conditions the previous breeding season during the months over which redstarts are likely to moult (June-September). At a population level, birds expressed feathers with higher red chroma and lower brightness in years following high July rainfall and low August temperature. The pattern was stronger in males, but was generally consistent across ages and sexes. Analyses of feathers from repeatedly captured birds indicated that the above patterns could be explained by individual change in feather colour. We suggest that higher rainfall during the moulting period may increase insect abundance and the availability of dietary carotenoids. This is among the first studies to show effects of weather conditions on a sexual signalling trait, which may have important consequences for sexual selection, mate choice, and the reliability of putative signals.