Figure 4
2. Forest light environments in both sunny and cloudy weather. Graphs show irradiance ( y-axes) as a function of wavelength (x-axes) in the human-visible range (400-700 nm). Redrawn from Endler (1993).
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... At the same time, non-signaling plumage patches are expected to show reduced contrast against the background and higher crypsis. The light environment hypothesis establishes that plumage coloration characteristics (such as hue and brightness) should match those of the ambient light and differ from those common in the reflectance spectra of the background to increase conspicuousness, and vice versa (Endler 1993(Endler , 2000Zahavi and Zahavi 1997;Théry 2006). Théry (2004, 2007) avian community of the Neotropical rainforest employing avian visual models and a comparative approach and found that canopy and understory function as different selective regimes for color patterns; plumage brightness and hue seem to have evolved for increased crypsis in each light environment, while the proportion of UV in the color signal is probably selected to increase conspicuousness in canopy birds. ...
Animal communication is a key feature of intra- and inter-specific interactions in nature. Vocalizations and plumage coloration are two of the most exploited signaling pathways among birds and they have an important role in sexual selection and reproductive isolation. The evolution of vocal and visual signals and their efficiency to confer information are influenced by many factors, such as the signaler’s morphology, the environment in which these are transmitted, or the sensitivity of either intended or unintended receivers like potential predators. In this chapter we review the diversity of visual and vocal signals among Neotropical birds which have been less studied than their counterparts from other biogeographic realms. The particularities they may present are not “exceptions,” but opportunities to gain a better understanding of avian communication and the factors influencing its evolution.
... Our assumptions are based on the fact that low UV reflectance (< 15%) (Church et al. 1998, Hunt et al. 1998, and even subtle differences (< 5%) in the UV spectral reflectance (Andersson and Amundsen 1997, Bennett et al. 1997, Andersson et al. 1998, Siitari et al. 2002, Woodcock et al. 2005) may influence bird behavior. Nonetheless, avian visual communication and the conspicuousness of visual signals in the field may be affected by ambient light properties and availability (Théry and Vehrencamp 1995, Endler and Théry 1996, Théry 2006, that in turn depend on environmental traits such as forest geometry and weather conditions (Endler 1993). The incident light that reaches the display sites of the white-bearded manakins at the understory may be either reflected from or transmitted through the vegetation (Endler 1993), and this may reduce the perception of colorimetric differences we observed. ...
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Manakins (Pipridae) are neotropical birds that usually exhibit delayed plumage maturation (DPM). Thus, while plumage of most adult male manakins is brightly conspicuous, subadult males and females are basically dull-olive green. Although sexual dichromatism in some bird species may be evident only through UV reflectance, this phenomenon, known as hidden sexual dichromatism, has not been previously studied in manakins to compare subadult males and females. Within this framework, we carried out spectrophotometric analyses in searching for hidden sexual dichromatism in the white-bearded manakin Manacus manacus, through comparison of UV spectra in females and subadult males in green plumage. Our results revealed UV reflectance in both sexes in green plumage. Moreover, we found UV spectral differences in homologous color patches between sexes, particularly at belly. Since the observed differences may allow intraspecific sex recognition of individuals in green plumage, our results do not support the female-mimicry hypothesis to explain delayed plumage maturation in the white-bearded manakin. Although our findings dismiss the female mimicry hypothesis, we cannot state whether these results support the non-mutually exclusive cryptic and status signaling hypotheses. We propose then, that dull coloration of subadult males may serve both as a cryptic trait and to limit the energetic costs of acquiring the adult plumage before sexual maturity. Meanwhile, differential UV color traits between sexes in green plumage may allow adult males to avoid unnecessary energy expenditures in courtship displays in the presence of males near leks, and to selectively focus their the courtship displays on females. In accordance with the signaling status hypothesis, subadult males can be recognized both as males and subordinates and consequently may practice courtship displays without suffering aggressions by adult males. Our results highlight the importance to include a wider range of spectrophotometric information analyses for testing hypotheses regarding delayed plumage maturation.
... Specific measures of avian plumage, such as hue, chroma, or brilliance can be correlated with different environment or life history variables in males and females (Seddon et al. 2013;2016). In addition, several studies have found that measures of color complexity may also evolve under selective pressures associated with light environment (Gomez and Théry 2004;Cuthill 2006;Théry 2006;Shultz and Burns 2013;Hernández-Palma 2016). Analyses of species belonging to infraorder Furnariides demonstrated that tetrahedral color space measurements of plumage complexity generally did not fit a model of light environment, with the exception of average brilliance (Hernández-Palma 2016). ...
Males and females can be under different evolutionary pressures if sexual and natural selection is differentially operating in each sex. As a result, many species have evolved sexual dichromatism, or differences in coloration between sexes. Although sexual dichromatism is often used as an index of the magnitude of sexual selection, sexual dichromatism is a composite trait. Here, we examine the evolution of sexual dichromatism in one of the largest and most ecologically diverse families of birds, the tanagers, using the avian visual perspective and a species-level phylogeny. Our results demonstrate that the evolutionary decreases of sexual dichromatism are more often associated with larger and more frequent changes in male plumage coloration, and evolutionary increases are not more often associated with larger changes in either sex. Furthermore, we show that the crown and ventral plumage regions are correlated with sexual dichromatism in males, and that only male plumage complexity is positively correlated with sexual dichromatism. Finally, we demonstrate that light environment is important in shaping both plumage brilliance and complexity. By conducting a multi-level analysis of plumage evolution in males and females, we show that sexual dichromatism evolves via a mosaic of sexual and natural selection in both sexes. This article is protected by copyright. All rights reserved
... Ambient light, or irradiance, is the light available for vision, which varies in intensity (amount of light) or spectral composition (‗colour' of light) (Endler 1993a;Thery 2006;Johnsen 2012). While animal vision can account for some variation in ambient light, marked changes will affect visual communication, rendering animal colours more or less conspicuous. ...
Anthropogenic environmental impacts can disrupt the sensory environment of animals and affect important processes from mate choice to predator avoidance. Currently these effects are best understood for auditory and chemo-sensory modalities and recent reviews highlight their importance for conservation. Here we summarise how anthropogenic changes to the visual environment (ambient light, transmission, backgrounds) affect visual communication and camouflage, and highlight implications for conservation. These implications are particularly evident for disrupted camouflage due to its tight links with survival while the conservation importance of impaired visual communication is less well-documented. Such effects can be potentially severe when they affect critical processes such as pollination or species recognition. However, when impaired mate choice does not lead to hybridization, the conservation consequences are less clear. We suggest that the demographic effects of human impacts on visual communication and camouflage will be particularly strong when: (a) human-induced modifications to the visual environment are evolutionary novel, that is, very different from natural variation, (b) affected species and populations have low levels of intraspecific (genotypic and phenotypic) variation and low levels of behavioural, sensory or physiological plasticity and (c) the processes affected are directly related to survival (camouflage), species recognition, or number of offspring produced, rather than offspring quality or attractiveness. The evidence summarized here suggests that anthropogenic effects on the visual environment might be of similar conservation concerns as those on other sensory modalities. This article is protected by copyright. All rights reserved
... We had predicted that if plumage colour in the Eastern Yellow Robin is adapted to the visual environment, lighter coloured robins should inhabit darker habitats with dense vegetation (Marchetti, 1993;Théry et al., 2006). At the continental scale, vegetation density was found to correlate significantly with colour variation, but it was also consistently the variable with the lowest explanatory power. ...
A fundamental goal in biological research is to gain deeper understanding of the ecological and evolutionary processes that drive speciation. Speciation occurs through a complex combination of phenomena that act between and within individuals, across time and space, driven by biotic and abiotic factors. Characterising these drivers is a challenging task that requires powerful analytic tools and strong study systems. Incipient species that are yet to become fully independent groups offer valuable opportunities to understand speciation by exploring it as it progresses. The Eastern Yellow Robin, a widespread Australian passerine, has a discordant pattern of genetic and phenotypic variation that makes it an ideal candidate to study speciation in action. On one hand, according to nuclear genetic markers and plumage colouration, the species varies along its range in a north-south direction. On the other hand, according to mitochondrial genetic markers, the species has a major, species-level disjunction in an east-west direction, resulting into two highly divergent mitochondrial lineages (mitolineages). The species presents a notable example of mitochondrial-nuclear (mitonuclear) discordance: a pattern in which mitochondrial gene and nuclear gene variation have discordant patterns of geographic differentiation. By disentangling this complex pattern of variation and testing hypotheses about causation, I revealed significant events during the Eastern Yellow Robins evolutionary history and proposed a mechanism by which the mitolineages are currently undergoing speciation. The Eastern Yellow Robin started to differentiate more than 1.3 million years ago into two geographically northern and southern isolated populations. During this period, much of the nuclear DNA and plumage colouration differentiation accumulated. Subsequently, these two populations came into secondary contact, generating the current pattern of north-south nuclear genetic and colour variation. After secondary contact, two independent events of adaptive mitochondrial introgression generated the current pattern of east-west mitochondrial genetic variation. According to this scenario, northern mitochondria introgressed southwards along the west and southern mitochondria introgressed northwards along the east. Mitochondrial introgression introduced adaptive genetic variation that assisted west and east mitolineages to thrive in their local environments. However, mitolineages are currently undergoing nuclear gene flow (dispersal and mating), therefore, a more complicated mechanism must be in place that prevents the two mitolineages from becoming unified. Mitochondrial and nuclear genes co-evolve to maintain essential cellular functions, such as gene expression, protein-complex assembly, metabolic, and physiological activities. By scanning thousands of genetic markers along the nuclear genome I found evidence that a subset of nuclear genetic variation accompanies the mitochondrial split. This is consistent with natural selection acting to avoid mitonuclear combinations being disrupted in intermediate forms between west and east mitolineages (i.e. hybrids). The great majority of the highly differentiated nuclear genes between mitolineages are clustered in one large genomic region. This region contains closely-linked, putatively co-adapted genes (i.e. it functions as a supergene) that are related to essential metabolic and physiological functions. This thesis contributes to a growing appreciation that interacting mitochondrial and nuclear genes involved in metabolism can influence the pattern and process of species formation.
... Studies on Steller's jay preference for forest edges are lacking, though jays are commonly observed utilizing the tops of trees to view the landscape and call long distances, and may use forest edges as travel and dispersal corridors. In these types of forest canopies, ambient light is rich in blue and UV wavelengths; therefore selection on coloration strongly reflecting UV enhances conspicuousness [76], [77]. In fact, UV reflecting feathers are often associated with body parts actively moved or erected in sexual displays (such is the case with the jay's crest stripes, wings and tail), conceivably to enhance detection [78]. ...
Genetic analysis of avian mating systems has revealed that more than 70% of monogamous species show incidence of offspring parentage that does not match the social partner. Extra-pair parentage (EPP) has been linked to a variety of factors, including size and symmetry of ornamental traits, coloration, resource availability, and local conspecific density. We examined how ornamental plumage traits of individual Steller's jays (Cyanocitta stelleri) and territory characteristics influence genetic fidelity of socially monogamous pairs. We used seven highly polymorphic microsatellite markers to assign paternity to 79 offspring, and identified 12 (15.2%) as extra-pair young (EPY). Steller's jays with extra-pair young had significantly lower values of feather brightness and hue, indicating more ultraviolet-blue shifted coloration, and nested in closer proximity to the forest edge than Steller's jays with no detected EPY. Body size, crest height, asymmetry of ornamental crest stripes, as well as vegetative composition of territories and their proximity to supplemental feeders appeared to have little relationship to EPP. These results indicate that extra-pair parentage plays a role in the evolution of secondary sexual characteristics in both sexes, and suggest local density and availability of resources may influence Steller's jay mating dynamics.
... When acting as signals, colors must be readily detectable by receivers (i.e. signal efficacy; Andersson 2000), but they must also be cryptic enough to provide necessary camouflage from predators or prey (Endler 1992, Théry 2006, Doucet et al. 2007). Thus, variation in light characteristics of different habitats may have marked effects on the evolution of signaling systems and may also create differential costs of displaying certain plumages, particularly when extrinsic costs exist. ...
... Cerulean Warblers are territorial, sexually dimorphic, socially monogamous songbirds that breed in the canopy of mature deciduous forests of the eastern United States . They are an appropriate species for exploring relationships between the plumage and quality or condition of a canopy-dwelling songbird because they spend most of their life in the upper canopy, usually in large forest tracts where light conditions (both background and ambient) and selective pressures differ from those of the forest floor or understory, open fields, or suburban parks (Endler 1993, Théry 2006, where most previous research has been concentrated. In this light environment, Cerulean Warblers have evolved plumage consisting of several distinct patches that may act as reliable signals (Figure 1): They display a black or dark gray breast band, white tail spots (hereafter ''tail white''), and unique blue upper-parts (including a bright sky-blue forecrown and blue-green rump). ...
Colorful plumage traits in birds may convey multiple, redundant, or unreliable messages about an individual. Plumage may reliably convey information about disparate qualities such as age, condition, and parental ability because discrete tracts of feathers may cause individuals to incur different intrinsic or extrinsic costs. Few studies have examined the information content of plumage in a species that inhabits forest canopies, a habitat with unique light environments and selective pressures. We investigated the information content of four plumage patches (blue-green crown and rump, tail white, and black breast band) in a canopy-dwelling species, the Cerulean Warbler (Setophaga cerulea), in relation to age, condition, provisioning, and reproduction. We found that older males displayed wider breast bands, greater tail white, and crown and rump feathers with greater blue-green (435–534 nm) chroma and hue than males in their first potential breeding season. In turn, older birds were in better condition (short and long term) and were reproductively superior to younger birds. We propose that these age-related plumage differences (i.e. delayed plumage maturation) were not a consequence of a life history strategy but instead resulted from constraints during early feather molts. Within age classes, we found evidence to support the multiple messages hypothesis. Birds with greater tail white molted tails in faster, those with more exaggerated rump plumage (lower hue, greater blue-green chroma) provisioned more, and those with lower rump blue-green chroma were in better condition. Despite evidence of reliable signaling in this species, we found no strong relationships between plumage and reproductive performance, potentially because factors other than individual differences more strongly influenced fecundity.
... When acting as signals, colors must be readily detectable by receivers (i.e. signal efficacy; Andersson 2000), but they must also be cryptic enough to provide necessary camouflage from predators or prey (Endler 1992, Théry 2006, Doucet et al. 2007). Thus, variation in light characteristics of different habitats may have marked effects on the evolution of signaling systems and may also create differential costs of displaying certain plumages, particularly when extrinsic costs exist. ...
... Cerulean Warblers are territorial, sexually dimorphic, socially monogamous songbirds that breed in the canopy of mature deciduous forests of the eastern United States . They are an appropriate species for exploring relationships between the plumage and quality or condition of a canopy-dwelling songbird because they spend most of their life in the upper canopy, usually in large forest tracts where light conditions (both background and ambient) and selective pressures differ from those of the forest floor or understory, open fields, or suburban parks (Endler 1993, Théry 2006, where most previous research has been concentrated. In this light environment, Cerulean Warblers have evolved plumage consisting of several distinct patches that may act as reliable signals (Figure 1): They display a black or dark gray breast band, white tail spots (hereafter ''tail white''), and unique blue upper-parts (including a bright sky-blue forecrown and blue-green rump). ...
Colorful plumage traits in birds may convey multiple, redundant, or unreliable messages about an individual. Plumage may reliably convey information about disparate qualities such as age, condition, and parental ability because discrete tracts of feathers may cause individuals to incur different intrinsic or extrinsic costs. Few studies have examined the information content of plumage in a species that inhabits forest canopies, a habitat with unique light environments and selective pressures. We investigated the information content of four plumage patches (blue-green crown and rump, tail white, and black breast band) in a canopy-dwelling species, the Cerulean Warbler (Setophaga cerulea), in relation to age, condition, provisioning, and reproduction. We found that older males displayed wider breast bands, greater tail white, and crown and rump feathers with greater blue-green (435-534 nm) chroma and hue than males in their first potential breeding season. In turn, older birds were in better condition (short and long term) and were reproductively superior to younger birds. We propose that these age-related plumage differences (i.e. delayed plumage maturation) were not a consequence of a life history strategy but instead resulted from constraints during early feather molts. Within age classes, we found evidence to support the multiple messages hypothesis. Birds with greater tail white molted tails in faster, those with more exaggerated rump plumage (lower hue, greater blue-green chroma) provisioned more, and those with lower rump blue-green chroma were in better condition. Despite evidence of reliable signaling in this species, we found no strong relationships between plumage and reproductive performance, potentially because factors other than individual differences more strongly influenced fecundity.
... Hosts should be able to recognize broadly sympatric raptor species, which may not occur in precisely the same habitat on a finer scale (Pfennig & Mullen 2010). However, habitat may select for a similarity in barred plumage patterns (Endler 1993; Endler & Théry 1996; Grim 2005b; Théry 2006). If this occurs, it would be expected that cuckooe raptor pairs with the highest number of overlapping habitat types would be the most similar; however, this was not the case with the exception of Cacomantis sonneratii and A. fasciatus (Fig. 3, Tables 4, 5, Appendix Table A3 ). ...
A fundamental principle of Batesian mimicry is that it pays to look like a local harmful species that is recognizable to other local species (receivers). Mimicking an allopatric species confers no benefit, as it is not recognizable to local species. It is thought that the common cuckoo, Cuculus canorus, is a Batesian mimic of the Eurasian sparrowhawk, Accipiter nisus, predominantly via its barred plumage, which facilitates access to host nests to deposit eggs. Barring is widespread in five genera of Old World cuckoos, unlike nonparasitic cuckoos, and evolved after the evolution of parasitism. Although barred plumage is predominant in parasitic cuckoos, it is unclear whether it may have a widespread function in cuckoo–hawk mimicry. If widespread, there should be a visual similarity between all five genera of Old World parasitic cuckoos and sympatric raptors. In addition, given that it pays to look like a local harmful species, sympatry should predict the degree of similarity. We compared barred plumage from all five genera of parasitic Old World cuckoos and up to eight sympatric raptors using digital image analysis. Cuckoos predominantly matched most raptors for at least one pattern attribute. In addition, three out of five cuckoos closely resembled a sympatric raptor for all barred pattern attributes examined, and potential model species were not confined to sparrowhawks. Habitat did not appear to influence plumage pattern similarity in most species studied. Finally, the barred plumage of sympatric species was more similar in appearance than those in allopatry. Together this demonstrates that cuckoos look like a local harmful species, which is congruous with Batesian mimicry.
... Several aspects of avian plumage coloration are hypothesized to evolve in conjunction with light environment to either increase plumage conspicuousness or crypsis. To increase crypsis, plumage brightness and contrast might evolve to match that of the background (Doucet et al., 2007;Endler and Thery, 1996;Gomez and Théry, 2007;Gomez and Théry, 2004;Heindl and Winkler, 2003a,b;Thery, 2006). Alternatively, plumage brightness might evolve to contrast against the background to increase conspicuousness, resulting in darker birds in brighter habitats, and brighter birds in darker habitats (Gomez and Théry, 2007;Gomez and Théry, 2004;Marchetti, 1993;Thery, 2006); or brighter birds in open habitats, and darker birds in closed habitats (McNaught and Owens, 2002). ...
... To increase crypsis, plumage brightness and contrast might evolve to match that of the background (Doucet et al., 2007;Endler and Thery, 1996;Gomez and Théry, 2007;Gomez and Théry, 2004;Heindl and Winkler, 2003a,b;Thery, 2006). Alternatively, plumage brightness might evolve to contrast against the background to increase conspicuousness, resulting in darker birds in brighter habitats, and brighter birds in darker habitats (Gomez and Théry, 2007;Gomez and Théry, 2004;Marchetti, 1993;Thery, 2006); or brighter birds in open habitats, and darker birds in closed habitats (McNaught and Owens, 2002). Plumage color diversity could also differ between different light environments within habitats. ...
... Plumage color diversity could also differ between different light environments within habitats. For example, the canopy has been shown to exhibit a greater diversity of colors than the understory (Gomez and Théry, 2004;Thery, 2006). Finally, elevation might shape traits that are under sexual selection due to a scarcity of resources at higher elevations (Badyaev, 1997a;Snell-Rood and Badyaev, 2008). ...
