Seasonal Color Change Research Articles

Monitoring of water Quality to assess Seasonal Color Changes of Lunar-Lubha River in East Jaintia Hills, Meghalaya (India)

The Lunar-Lubha River is a significant river in Meghalaya, India, flowing through the Jaintia Hills and eventually reaching Bangladesh’s Surma valley. During winter, the river undergoes a remarkable transformation, changing its color from turquoise to a vibrant sky-blue hue. This study investigated the reason behind this color change by examining the physicochemical characteristics of the river water during pre-monsoon, post monsoon and winter season of the year 2020 to 2022. Chemical properties of the white-powdery sediment (which acts as light reflecting media) found on the riverbed of the color-changing stretches of the river were also investigated. The analysis revealed the presence of high levels of Iron (Fe) and Alumina (Al) in sediments of the Lunar-Lubha River beds. The water quality in stations located at Lunar River can be designated below-E as per Central Pollution Control Board (Govt. of India) guidelines as the water in those stations is not fit for drinking, bathing, propagation of marine life as well as irrigation or agricultural uses. The blue coloration is more prominent in the deeper sections of the river compared to the shallow stretches. This observation aligns with the argument that shorter wavelengths of light scatter more as the depth increases. The presence of light scattering effect due to variation in water depth and the white-colored sediments at the riverbed could explain the intensified blue color in the river. The apparent blue color of the Lukha River is most likely an illusion induced by the scattering effect rather than the genuine blue color of the water.

Unmasking complex migration syndromes and seasonal plumage colouration in the White‐naped Xenopsaris (Xenopsaris albinucha)

The White‐naped Xenopsaris Xenopsaris albinucha is an uncommon suboscine passerine with a disjunct distribution extending from Venezuela to the Southern Cone of South America. The ornithological literature concerning this species contains contradictory claims about potential migratory movements, although most authors consider it to be sedentary. In addition, observations of the species exhibiting a mix of male‐ and female‐like plumage during the non‐breeding season have raised the hypothesis that it may undergo seasonal colour changes – a trait often associated with migratory behaviour and seemingly uncommon in Neotropical birds. Here we use citizen science and museum specimen data to interrogate the hypotheses of migratory behaviour and seasonal phenotypic variation in the species. We found evidence for three disjunct breeding populations, of which one is resident, one is apparently partially migratory and one is fully migratory, with birds from the last two populations coming into contact during the non‐breeding season. We also found evidence for seasonal variation in the species' plumage colouration. Our results suggest that the White‐naped Xenopsaris has both resident and migratory populations and exhibits an eclipse plumage, and highlight the value of citizen science data to study seasonal variation in plumage colouration.

A bird that changes colour without moulting: how the wîskicâhk (Canada Jay, Perisoreus canadensis) tricked the taxonomists

Avian and mammalian colours are thought to be constant in life and in museum specimens, but several early 20th-century taxonomists singled out the Canada Jay (Perisoreus canadensis (Linnaeus, 1766)) as having unstable feather pigments and warned against using old museum specimens for taxonomic purposes. One such error was Brisson’s (1760) original naming of the species as “the Brown Jay of Canada”. Another was Ridgway’s (1899) naming of the “Gray Jay” as a new subspecies, Perisoreus (canadensis) griseus, through inappropriate comparison of fresh grey specimens with old brown ones. We discovered that browning of initially grey plumage also occurs between annual moults in living individuals of the Canada Jay’s Pacific morphotype. We documented this change using photographs and re-sightings of colour-banded individuals and through spectral analysis of year-old (brown) and incoming (grey) rectrices collected from the same moulting individuals. To assess the distribution of this colour change, we compared September vs. May eBird photographs from across North America. We showed that seasonal colour change is normal in the Pacific morphotype but rare in the two other morphotypes. Collectively, these data have important implications for the taxonomy of the Canada Jay and are a cautionary tale for taxonomists studying animal colouration.

Optimal Color Composition Method for Generating High-Quality Daily Photographic Time Series From PhenoCam

Phenology camera (PhenoCam) data and the derived green chromatic coordinate (GCC) time series are commonly used to track seasonal changes in canopy greenness. However, the GCC time series is noisy because color distortion commonly exists in the captured photographs owing to the varying illumination conditions and nonlinear response of the consumer-grade camera to the incoming light. Hence, we proposed an optimal color composition (OCC) method to generate high-quality daily photographic time series by compositing multiple photographs captured in a single day. First, the optimal acquisition time with good illumination conditions and correct exposure settings is determined for each pixel throughout the day based on a comprehensive color index, combining the brightness and saturation. A virtual photograph consisting of the selected digital numbers acquired at the optimal time is then composited for each day. Finally, the daily GCC time series is calculated based on the virtual photographs. By testing the photographs of six forest sites, the proposed method was compared with the commonly used 90th percentile (Per90) filter. The results show that the daily photographs composited using the OCC method were more homogeneous with less shaded areas compared to those selected by the Per90 filter, and the corresponding GCC time series derived from the OCC method is more stable and less influenced by varying atmospheric conditions and solar angles than the Per90 filter. These results indicate that the OCC method can generate high-quality daily photographic time series with the potential to better indicate seasonal color changes in the forest canopy.

Evolution of breeding plumages in birds: A multiple-step pathway to seasonal dichromatism in New World warblers (Aves: Parulidae).

Many species of birds show distinctive seasonal breeding and nonbreeding plumages. A number of hypotheses have been proposed for the evolution of this seasonal dichromatism, specifically related to the idea that birds may experience variable levels of sexual selection relative to natural selection throughout the year. However, these hypotheses have not addressed the selective forces that have shaped molt, the underlying mechanism of plumage change. Here, we examined relationships between life‐history variation, the evolution of a seasonal molt, and seasonal plumage dichromatism in the New World warblers (Aves: Parulidae), a family with a remarkable diversity of plumage, molt, and life‐history strategies. We used phylogenetic comparative methods and path analysis to understand how and why distinctive breeding and nonbreeding plumages evolve in this family. We found that color change alone poorly explains the evolution of patterns of biannual molt evolution in warblers. Instead, molt evolution is better explained by a combination of other life‐history factors, especially migration distance and foraging stratum. We found that the evolution of biannual molt and seasonal dichromatism is decoupled, with a biannual molt appearing earlier on the tree, more dispersed across taxa and body regions, and correlating with separate life‐history factors than seasonal dichromatism. This result helps explain the apparent paradox of birds that molt biannually but show breeding plumages that are identical to the nonbreeding plumage. We find support for a two‐step process for the evolution of distinctive breeding and nonbreeding plumages: That prealternate molt evolves primarily under selection for feather renewal, with seasonal color change sometimes following later. These results reveal how life‐history strategies and a birds' environment act upon multiple and separate feather functions to drive the evolution of feather replacement patterns and bird coloration.

Investigating seasonal color change in the environment by color analysis and information visualization

AbstractColor, as one of the most important dimensions of vision, plays a key role in place identity and people's experience in the environment. This study aims to investigate people's visual experience of seasonal color change in the environment, and proposes an approach for analyzing and communicating environmental colors by combining color analysis and information visualization. Employing crowdsourced Flickr photos, the approach is tested in four gardens: the Humble Administrator's Garden, Ryoanji, the Garden of Versailles, and Central Park in New York. The results show direct comparisons of seasonal color change patterns in different environments, and reflect characteristics of the environments as well as people's experience of color during the four seasons. The primary contribution of this study is to provide a way of communicating colors in landscape design and color research.

Hormonal control of seasonal color change in female spiny-footed lizards: an observational and experimental approach.

Breeding coloration of females often signals aspects of their reproductive status, suggesting a link between color and sex steroid hormones. In this study, we examined the relationships between 2 sex steroid hormones (progesterone and β-estradiol) and reproductive coloration in female spiny-footed lizards Acanthodactylus erythrurus. We first explored natural variation in female plasma hormone levels and coloration during their reproductive cycle. β-estradiol was negatively related to brightness and positively related to red saturation, whereas progesterone was not significantly related to coloration. After identifying key relationships, plasma hormone concentrations were manipulated by creating 3 experimental female groups (β-estradiol-treated, progesterone-treated, and control), and the effects on coloration were monitored. β-estradiol-treated females, in which there was a rise in both β-estradiol and progesterone levels, lost their red coloration earlier than females in the other 2 experimental groups, whereas progesterone treatment had no significant effect on female coloration. Our results suggest that high levels of either β-estradiol alone or β-estradiol together with progesterone trigger the loss of red coloration in female spiny-footed lizards, and that progesterone alone does not affect coloration. We hypothesize that changes in female breeding color might be regulated by β-estradiol in species in which conspicuous coloration is displayed before ovulation, and by progesterone in species in which this color is displayed during gravidity.

Mapping a keystone shrub species, huckleberry (Vaccinium membranaceum), using seasonal colour change in the Rocky Mountains

ABSTRACTBlack huckleberries (Vaccinium membranaceum) provide a critical food resource to many wildlife species, including apex omnivores such as the grizzly bear (Ursus arctos), and play an important socioeconomic role for many communities in western North America, especially indigenous peoples. Remote sensing imagery offers the potential for accurate landscape-level mapping of huckleberries because the shrub changes colour seasonally. We developed two methods, for local and regional scales, to map a shrub species using leaf seasonal colour change from remote sensing imagery. We assessed accuracy with ground-based vegetation surveys. The high-resolution supervised random forest classification from one-meter resolution National Agricultural Imagery Program (NAIP) imagery achieved an overall accuracy of 75.31% (kappa = 0.26). The approach using multi-temporal 30-meter Landsat imagery similarly had an overall accuracy of 79.19% (kappa = .31). We found underprediction error was related to higher forest cover and a lack of visible colour change on the ground in some plots. Where forest cover was low, both models performed better. In areas with <10% forest cover, the high-resolution classification achieved an accuracy of 80.73% (kappa = 0.48), while the Landsat model had an accuracy of 82.55% (kappa = 0.47). Based on the fine-scale predictions, we found that 94% of huckleberry shrubs identified in our study area of Glacier National Park, Montana, USA are over 100 meters from human recreation trails. This information could be combined with productivity and phenology information to estimate the timing and availability of food resources for wildlife and to provide managers with a tool to identify and manage huckleberries. The development of the multi-temporal Landsat models sets the stage for assessment of impacts of disturbance at regional scales on this ecologically, culturally, and economically important shrub species. Our approach to map huckleberries is straightforward, efficient and accessible to wildlife and environmental managers and researchers in diverse fields.

Seasonal pelage color change of two sympatric arboreal squirrel species in the subarctic region

Some mammal species exhibit pelage color change with seasonal molt. Seasonal molt and pelage color change are beneficial to thermoregulation and concealment, associated with seasonal environmental change. The Eurasian red squirrel Sciurus vulgaris Linnaeus, 1758 and the Siberian flying squirrel Pteromys volans (Linnaeus, 1758) are arboreal and sympatrically distributed in the subarctic northern Eurasian Continent and Sakhalin and Hokkaido islands. We expect that diurnal S. vulgaris may demonstrate more conspicuous difference between summer and winter pelages than nocturnal P. volans, because of its protective coloration in each season. To test this conjecture, we investigated their seasonal pelage color change. To diminish the effect of geographic variation in pelage color, we chose S. vulgaris orientis Thomas, 1906 and P. volans orii (Kuroda, 1921), which are endemic subspecies of Hokkaido Island, Japan. We used skin and stuffed specimens and frozen materials and categorized them into two pelage groups (summer and winter pelages) based on collection date. Pelage color characteristics were measured with a spectrophotometer for lightness, redness and yellowness. Countershading was examined by comparing dorsal and ventral lightness. Both subspecies showed lighter winter pelage than summer pelage, suggesting their greyish-white winter pelage was beneficial to concealment from predators during winter. As we expected, seasonal changes of redness and yellowness were more clearly recognized in S. vulgaris than in P. volans. As S. vulgaris is diurnal and vulnerable to attack by diurnal avian predators, reddish and yellowish pelage patterns may be important for concealment. Because it is nocturnal, P. volans may not need this reddish and yellowish pelage. Sciurus vulgaris also had a remarkably counter-shaded body, indicating that its body may reduce predation risk from daytime visual predators. Differences in seasonal pelage color change of these two arboreal squirrels may be caused by their different circadian rhythms.

The impact of seasonal colour change in planting on patients with psychotic disorders using biosensors

The beneficial effect of nature on patients with mental disorders is of particular importance. There has been an increase in mental illnesses in recent years, but research on the design of healing gardens for mental and behavioural disorders remains limited. This paper is part of a wider study that aims to investigate the effect of selected design elements of healing gardens on patients with mental disorders. This study examines the effect of seasonal colour change in plantings in the design of healing gardens on patients suffering from psychotic disorders by using a questionnaire survey and by recording and analysing human behaviour. Images depicting seasonal colour change in different plantings were viewed on a computer monitor by patients. Patients’ behaviour was studied using biosensors for eye-tracking, facial expression analysis and galvanic skin response. The results showed that differences in gender and age between participants did not affect their preferences. However, it appeared to be more difficult to positively affect the emotions of male participants compared to female participants. Seasonal colour change in a tree canopy created positive and intense emotions in the patients. Based on the results, the use of deciduous trees is proposed in the design of healing gardens for patients with psychotic disorders to create seasonal colour change. Further research is necessary to obtain more detailed design recommendations for landscape architects.

Fish Chromatophores--From Molecular Motors to Animal Behavior.

Chromatophores are pigment-bearing cells of lower vertebrates, including fish that cater for the ability of individual animals to shift body coloration and pattern. Color change provides dynamic camouflage and various kinds of communication. It is also a spectacular example of phenotypic plasticity, and of significant importance for adaptation and survival in novel environments. Through different cellular mechanisms, color change can occur within minutes or more slowly over weeks. Chromatophores have different pigment types and are located not only in the skin, but also in the eyes and internally. While morphological color change, including seasonal color change, has received a lot of interest from evolutionary biologists and behavioral ecologists, the more rapid physiological color change has been largely a research subject for cell physiologists. In this cross-disciplinary review, we have highlighted emerging trends in pigment cell research and identified unsolved problems for future research.

Characterizing background heterogeneity in visual communication

How is a visual signal effectively transmitted through an environment triggering a response by a perceiver? Experimental and theoretical works in disparate fields, such as sexual selection and plant–animal interactions, have demonstrated selection based on signal conspicuousness. However, to properly describe the conspicuousness of a signal, it is necessary to quantify the spatial and temporal heterogeneity of background coloration of a signaler. We intend to compare the effectiveness of four methods developed to characterize background heterogeneity. To describe the background in a seasonal vegetation, we collected reflectance data in dry and wet seasons of (i) target leaves (those leaves against which a signal is predominantly displayed); (ii) overall leaves (leaves from the most common plant species in the community); (iii) frames in a limited area in space, by measuring the reflectance of all material found in the background; and (iv) background items from the most common species, based on their abundance along transects. We analyzed seasonal color changes in terms of hue, chroma and brightness and described the conspicuousness of fruit coloration according to avian vision. All methods found significant differences in the background coloration between seasons, with higher reflectance values in the dry season. Hue values were higher in the dry season, and chroma values were higher in the wet season. Only the methods most restricted in space (target leaves and frames) recorded seasonal differences in fruit conspicuousness. The transects and frames methods are useful for describing the backgrounds of non-stationary signals (i.e., those of most animals). For plant signals, which are displayed against a fixed background in space, we recommend specific sampling of target leaves. Our results support the importance of measuring the seasonal heterogeneity of the background but also indicate that a monthly sampling design is not necessary to evaluate the conspicuousness of fruit signals.

Exploring the function of red colouration in female spiny-footed lizards (Acanthodactylus erythrurus): patterns of seasonal colour change

In spiny-footed lizards (Acanthodactylus erythrurus), adult females (but not males) show conspicuous red colouration in the tail and hind legs. To investigate the function of this red colouring and proximal causes of seasonal colour change, we captured adult females before the reproductive season and kept them in captivity in one of the three following situations: with a male and fertilization possible, with a male and fertilization impossible, or with another female (fertilization also impossible). Colour was quantified using spectrophotometry. Red colouration increased shortly before the onset of reproduction, but faded during the breeding season and became whitish (light buff-gray) in all cases. Both fertilized and unfertilized females laid eggs or were gravid after two months of the experiment, but while fertilized females laid mostly fertile eggs, unfertilized females only laid infertile eggs. Both egg formation and colour change might be triggered by abiotic factors, although female characteristics also play a role, since heavier females changed colour and laid eggs earlier. Females interacting freely with a male were darker at the end of the breeding season than females separated from the male, indicating that fertilization or physical contact might also have an effect on colouration. Colour change patterns found in this study suggest that female red colouration might have a mating-related function, but do not support a courtship rejection function for the red colour. However, whitish colouration resulting from red fading might signal gravidity in this species. Future experimental manipulation of female colouration will be needed to test these hypotheses.

Detecting plant seasonality from webcams using Bayesian multiple change point analysis

Phenological observations have a long tradition. By contrast, digital webcam-based phenological research has only developed in recent years, prompted by the development of cheaper user-friendly digital camera systems and by higher staff costs. Webcam photography provides spectral information in red, green and blue (RGB) wavelengths which mirror the seasonal colour changes in trees during bud burst, leaf unfolding, senescence and leaf fall.Recent publications have mainly used two types of image data analysis to define onset dates of certain phenological stages and to compare species and growing seasons. These methods work well, but require high quality of the webcam images. However, changing light and weather conditions complicate data analysis particularly at increasing camera-to-subject distances. We investigated a series of images providing colour information on different tree species, e.g. Fagus sylvatica, Populus tremula, as well as of trees at different altitudes (700–1200m) in the Bavarian Forest National Park, Germany. Webcam images were analysed by the two previously published methods and compared with results derived from a newly developed Bayesian multiple change point analysis. In particular, transition dates of leaf development were identified in the green, as well as the red, colour channel.The Bayesian analysis described phenological transition dates in spring and autumn and specified the uncertainties of the model fit. By contrast, previously employed methods have shortcomings associated with unrealistic asymptotic assumptions in logistic model fits or inability to cope with noise in data series.The change point analysis at different elevations showed how the Bayesian approach coped with increasingly degraded image quality. A delay in green-up of about 2.5 days per 100m of altitude was estimated for Fagus sylvatica in the study area. Autumn phenology at different altitudes did not show clear patterns.The Bayesian model approach allows not only the calculation of phenological change points during the year but also estimates the probability of those changes occurring on a particular day. This method appears to estimate reliably phenological events in the growing season, especially when handling low quality webcam data, either from poor weather conditions or when the subject is at a considerable distance from the camera.

THE EFFECT OF SEASONAL CHANGE OF PLANTS COMPOSITIONS ON VISUAL PERCEPTION / SEZONINIO AUGALIJOS SUDĖTIES POKYČIO ĮTAKA VIZUALIAM SUVOKIMUI

Plants are important elements of open-green areas in the urban space and perception of an environment. Some plants have seasonal colour changes. The identification of these changes and clarification of the effects on people are quite important for landscape architecture. Seasonal changes of plants in some open-green areas in Düzce were examined in order to explain how it affects people regarding changes in perceptional preferences. Delphi Method was used on photographs as a mean of identification of the visual effects of the plant compositions. The plant composition photographs, which had been examined before, were used in the questionnaire to 370 student groups. As a result, the difference was evaluated between the perceiving of different plant compositions. Summer was the most affecting season having the design value and visual quality. Besides, evergreen plants had a positive effect on design power and visual quality of compositions. Furthermore, as another important result, it was found out that socio-economic levels of the people had some important effects on visual preferences. In this study, perceptional differences of the participants on seasonal changes of the plants were identified. Moreover, the form and the texture were evaluated for identifying perceptional effects. Santrauka Reikšmingas urbanizuotos teritorijos elementas yra želdynų augalija. Kai kurios augalų rūšys kintant sezonui keičia spalvas. Suvokiant šių pokyčių poveikį žmogui, svarbu tai pritaikyti kuriant kraštovaizdžio architektūrą. Sezoninių augalijos pokyčių poveikiui tirti pasirinkta ãtviros Düzce apylinkių vietos. Vizualiam augalijos poveikiui nustatyti taikytas Delphi fotonuotraukų metodas. Anksčiau vertintos nuotraukos buvo panaudotos apklausoje, kurioje dalyvavo 370 studentų grupių. Vertinti augalijos skirtingos sudėties suvokimo skirtumai. Nustatyta, kad didžiausią poveikį vizuali želdinių projektavimo kokybė daro vasaros sezoną. Respondentai, vertindami projektavimą ir vizualią augalijos sudėties kokybę, teigiamai pažymėjo visžalius augalus. Iš apklausų nustatyta, kad didelę įtaką vizualiam suvokimui turi socialiniai-ekonominiai žmonių skirtumai. Įvertinta ir projektuojamų želdinių formos bei sandaros reikšmė suvokiant vaizdo efektus.

The Mystery of Seasonal Color Change

The Mystery of Seasonal Color Change

Effect of feather abrasion on structural coloration in male eastern bluebirds Sialia sialis

We used observations of male eastern bluebirds captured twice within a breeding season to test whether changes in structural coloration are related to feather abrasion. Between first and second broods, the UV chroma and brightness of feathers decreased, while hue shifted towards longer wavelengths. Observed changes were greatest for feathers on the head, least for feathers on the rump, and intermediate for feathers on the back. For head feathers, we found a significant correlation between reduction in barb length and UV chroma. Plumage coloration at first capture was correlated with change in UV chroma such that the most ornamented males tended to lose more coloration. Moreover, the magnitude of UV color change was positively related to the number of days between color measurements.To test whether these changes were caused by abrasive properties of the nesting sites, we randomly increased or decreased the abrasiveness of nesting-box entrances by attaching sand paper or smooth plastic tape. The type of box entrance had no signicant effect on either coloration or barb length change. Our results suggest that feather abrasion is a factor in the seasonal color changes of bluebirds.

Ocean colour changes in the North Pacific since 1930

In this paper we present an analysis of historical ocean colour data from the North Pacific Ocean. This colour is described by the Forel-Ule colour index, a sea colour comparator scale that is composed of 21 tube colours that is routinely measured since the year 1890. The main objective of this research is to characterise colour changes of the North Pacific Ocean at a timescale of lustums. Next to the seasonal colour changes, due to the yearly cycle of biological activity, this time series between 1930 and 1999 might contain information on global changes in climate conditions. From seasonal independent analyses of the long-term variations it was found that the greenest values, with mean Forel-Ule scale, FU¯, of 4.1 were reached during the period of 1950–1954, with a second high (FU¯ = 3) in the period 1980–1984. The bluest ocean was encountered during the years 1990–1994. The data indicate that after 1955 a remarkable long bluing took place till 1980.

Behavioral Ecology of Color Patterns in Atka Mackerel

AbstractThe behavioral ecology of seasonal and ephemeral variations in color patterns of Atka mackerel Pleurogrammus monopterygius was investigated and is discussed relative to alternative mating tactics, reproductive condition, social status, and predation risk. Breeding males underwent a conspicuous seasonal color change during the mating and brooding period, resulting in one of two nuptial phenotypes. Type I males held and defended territories inside nesting colonies and had a uniform yellow coloration with a golden hue across the head and dorsum. Type II males were nonterritorial, hovered above the nesting colony, and attempted periodic forays into the nesting colony; their color was plain yellow with irregular dark blotches across the head and dorsum and a light patch on the nape. When displaced from their nests, type I males also showed dark blotches and a light patch on the nape, but these characteristics were less pronounced than those in type II males. The color of females and nonbreeding males was indistinguishable and exhibited little seasonal variation; however, females close to spawning showed an ephemeral darkening of the body with white spots and patches along the dorsum. Nonbreeding males and females undergoing diel migrations also showed the same pattern across the dorsum but without darkening. The overall mean ratio of males to females in the trawl‐sampled population was 1.22:1.00, of which 44.9% were females, 40% were nonbreeding males, 9.8% were intermediate males (with characteristics intermediate between those of breeding and nonbreeding males), and 5.3% were breeding males. The proportion of breeding males was 12 times higher inside nesting colonies than outside the colonies. The mean fork length (FL) of intermediate and breeding males was larger (by ≤1 cm) than that of females or nonbreeding males. Understanding the behavioral ecology of Atka mackerel is important to the development of a comprehensive ecological index for monitoring and assessing the reproductive health of Atka mackerel stocks.

Seasonal colour change by moult or by the abrasion of feather tips: a comparative study

Many birds undergo seasonal changes in plumage coloration by prebreeding moult, abrasion of cryptic feather tips, or both. Seasonal dichromatism is thought to result from optimizing coloration to the conflicting demands of different life-cycle periods, sexual selection for conspicuousness being substantial during the mating season, whereas selection for camouflage and for social signals may act in all seasons. Furthermore, energetic and time demands may constrain the extent of moult, thereby limiting colour change. We investigated the relative importance of several factors in shaping this variation in a songbird clade using phylogenetic comparative methods. We found that prebreeding moult relates most strongly to breeding onset and winter diet, demonstrating that both time and food availability constrain feather replacement. Feather abrasion was best predicted by winter flocking behaviour, and secondarily by open habitats, implying that exposure to predators and the simultaneous need for social signalling may favour the expression of partially obscured ornaments in the non-breeding season. The combined occurrence of prebreeding moult and feather abrasion was associated with the polygynous mating system, suggesting that species under strong sexual selection may employ both strategies of colour change to ensure the full expression of breeding coloration. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 711–721.