colour in birds The plumage colour represents one of the most striking features of birds and is also one of the most important signs in visual communication between species and coespecific (Zahavi & Zahavi 1997, Hamilton & Zuk 1998; Rowe & Skelhorn 2004). In birds, colorful plumages are one of the most classic examples of secondary sexual characteristics, especially among species with marked sexual dimorphism, indicating strong sexual selection in this phenotypic trait (Darwin 1958 and Henderson et al 2013). Thus, great discussion on how sexual selection has modeled the colour of birds still seems to lack consensus (Prum 2012) and studies on colour diversity offer great opportunities to understand the origins and maintenance of this diversity (Hill & McGraw 2006). Colorful plumages may represent a high cost to produce and maintain, and some hypotheses based on sexual selection mechanisms have sought to explain the evolution of conspicuity in these traits, especially in polygynic clades (eg quality indicator, Fisher's runaway selection, sensory direction; review in Andersson 1994, Prum 1997, Price 2008). Zahavi & Zahavi (1997) predicts that the female's preference for certain conspicuous characteristics of the male is not random, but may indicate individual genetic quality (Zahavi & Zahavi 1997; Taylor & McGraw 2007). The evolution and maintenance of conspicuous colours would depend on the balance between the partner's choice requirements and the survival costs imposed by natural selection through predation. The development of selected characters in this way would work as an effective quality marker, enabling the ability of one sex to detect quality in the opposite sex selected (Zahavi, 1975, 1977; Grafen, 1990).

Plumage colour The plumage colour represents one of the most striking features of birds and is also one of the most important signs in visual communication between species and coespecific (Zahavi & Zahavi 1997, Hamilton & Zuk 1998; Rowe & Skelhorn 2004). In birds, colorful plumages are one of the most classic examples of secondary sexual characteristics, especially among species with marked sexual dimorphism, indicating strong sexual selection in this phenotypic trait (Darwin 1958 and Henderson et al 2013). Thus, great discussion on how sexual selection has modeled the colour of birds still seems to lack consensus (Prum 2012) and studies on colour diversity offer great opportunities to understand the origins and maintenance of this diversity (Hill & McGraw 2006). Colorful plumages may represent a high cost to produce and maintain, and some hypotheses based on sexual selection mechanisms have sought to explain the evolution of conspicuity in these traits, especially in polygynic clades (eg quality indicator, Fisher's runaway selection, sensory direction; review in Andersson 1994, Prum 1997, Price 2008). Zahavi & Zahavi (1997) predicts that the female's preference for certain conspicuous characteristics of the male is not random, but may indicate individual genetic quality (Zahavi & Zahavi 1997; Taylor & McGraw 2007). The evolution and maintenance of conspicuous colours would depend on the balance between the partner's choice requirements and the survival costs imposed by natural selection through predation. The development of selected characters in this way would work as an effective quality marker, enabling the ability of one sex to detect quality in the opposite sex selected (Zahavi, 1975, 1977; Grafen, 1990).

color in birds Our study demonstrate the importance of the method choice to estimate accurately coloration in birds. Although our visual system is very different in relation to bird vision, methods based simply on human vision can be more realistic than other methods based in spectra data and that use bird colour vision space but that superstimate differences in spectral groups. This is not an encouragement to use methods based on human vision, but a highlight that using spectra data and avian color vision models is important but not plenty to estimate differences in color data with precision. Therefore, we encourage researches to use novel and more robust frameworks available for color analysis throughout many other animal groups.

Conclusion of my thesis Our study demonstrate the importance of the method choice to estimate accurately SD in birds. Although our visual system is very different in relation to bird vision, methods based simply on human vision can be more realistic than other methods based in spectra data and that use bird colour vision space but that superstimate differences in spectral groups. This is not an encouragement to use methods based on human vision, but a highlight that using spectra data and avian color vision models is important but not plenty to estimate differences in color data with precision. Therefore, we encourage researches to use novel and more robust frameworks available for color analysis throughout many other animal groups.

e-mail message Hi Andre, Good to listen to you, I am so exciting in finnaly meet you and can talk about our both projects ongoing. In my opinion, you should not to spend so many time collecting spectral data for all distribution of the lineages, considering that your study area is more restrict at Peru. I agree with you that examining the vouchers personaly is important for a background. However, spectra data for few specimens by lineages should be plenty for comparing with your zone of introgression. Moreover, I also hope that the map that i sent you previously and which is part of my doctoral project should help you to have a overview of of the geographic variation in plumage color of this species even if tt is only to compare with your transect. I have studying color analisys since 2012 and i am sure the error measurement is very low for influencing the color analisis. For you have an idea, database of bird plumage color measured with spectrophotometry of different researchers are available today collected with different protocols. For example, see: http://evoldir.tumblr.com/post/165392386711/other-birdcolourbase By the way, i would be happy to can use your spectra data from Peru area and surely we can talk about colaborations in my paper later. Best regards

colour vision Colour vision has evolved many times relatively to a short period of the evolutionary time even in a small taxonomic group such as the vertebrates. In this group, cone cells of the retina are the photoreceptors responsible to discern colours. Basically, what become an eye to be more sensible to particular wavelengths than others is the visual pigments named opsins present in cone cells. Since different viewers have different visual systems, different wavelengths of light can excite differently photoreceptors of humans, avian and other animals taking them to perceive colours differently . For instance, color vision in birds is mediated by four different photoreceptors types (each one presenting a particular photopigment) which allow them to perceive color in red wave, green wave, blue wave and ultraviolet wavelength of light. This one late is absent to human color vision meaning that birds have an extra dimension of color information which is not perceived to us humans

color vision in birds Most cases known and documented of color in birds are based on the human vision which has its sensibility from 400 to 700 nm of wavelength.. However, system of color vision in birds surpasses that of all mammals, including humans since birds have four single cone cells in the retina, instead 3 in primates, that they use for color discrimination. This evolutionary novelty gives birds the ability to see imperceptibly colors in our eyes as violet and ultraviolet and makes them apt to perceive a greater colour combination than humans. Taking into account these differences observed in the bird visual system in relation to other animal groups, the perception of colors by humans should not be used as a framework for estimating color contrast let alone using as a proxy for color perception in other animal groups.

Rebuttal letter Dear Editor, Thank you very much for your correspondence from December 13th 2017 regarding our manuscript EVEC-D-17-00055, entitled “Spatial and environmental correlates of intraspecific morphological variation in three species of passerine birds from the Purus-Madeira interfluvium, Central Amazonia”, authored by Teófilo FHA, Schietti J and Anciaes M. We received your comments and recommendations and have worked to fix the problems you found in our manuscript by incorporating the requests provided by the referees and the Editor handling it, in the present version of the manuscript. Please find below our summarized responses and indications of how, and where in the manuscript, we have addressed each point raised by you. We appreciate your attention in this regard and are willing to provide more information and further revise the manuscript to adequately incorporate what shall still be considered necessary. Sincerely,

Could someone correct this sentence to me, please? Although latitude and geographic distance are not the same metric per si, we used latitude values as proxy to geographic distance since difference in latitude values between two locations result in a value of geographical distance in decimal degree units.