DOI: 10.5061/dryad.4mw6m90hx
title: Viewing conditions predict avian plumage contrast

description: Birds communicate using multiple sensory channels, most commonly through
 vocalisations and colourful plumage patches. Such colourful plumage has
 evolved through a complex interplay of processes, acting not only on the
 ability of a patch to convey information but also in response to
 physiological and environmental factors. Although much research on
 inter-specific variation in bird plumage has concentrated on sexual
 selection, much less work has considered the role of non-sexual selection
 and how it is affected by joint effects of avian viewing conditions and
 receiver vision. Here we combined taxonomically diverse databases of avian
 plumage measurements with habitat use and behavioural data to test the
 effect of three factors which effect viewing conditions - habitat
 openness, migratory preference, and daily phenology - on avian plumage
 contrast, accounting for shared evolutionary history and variation in
 avian visual systems. We find that habitat structure and migratory
 preference predicted plumage visual contrast, especially for females. Our
 study demonstrates the important role of non-sexually selected traits and
 viewing conditions in shaping avian plumage contrast.
description: The database contains taxonomic information on birds, eye-type (U
 or V) and measures of plumage contrast collected using a
 spectrophotometer. The database is compiled from several sources (all
 cited in the accompanying paper), and compiles data used in other
 publications. We accessed reflection data from
 published and unpublished sources (including Fargevieille et al. 2023;
 Doutrelant et al. 2016; Eaton 2005, 2007; Cardoso and Mota 2008; Cardoso
 and Mota 2022; Gomes, Sorenson, and Cardoso 2016; Shultz and Burns 2017;
 Igic, D’Alba, and Shawkey 2018; Dunning et al. 2023; Stoddard and Prum
 2008), which have been compiled into a single database, the ‘Bird Colour
 Base’, by Thanh-Lan Gluckman and Peter Dunn (made available here - https://github.com/BirdColorBase/home).  Spectra were in the form of calibrated reflectance every 2nm from 300 nm to 700nm collected from 2,610 species, using similar methods and equipment, representing 35 orders and 170 families and 984 genera.  On average there were 6.8±2.8 (mean±SD) birds scanned per species and 6.2±2.6 different plumage patches scanned per bird per species. The database contains 352,155 spectra of which 174,794 are from adult males, 161,952 are from adult females, and 15,409 from individuals with unrecorded sex/maturity.  Given the high rates of sexual dichromatism and concomitant separate evolutionary drivers of sex-related plumage in adult birds, we omitted data from specimens of unknown sex or recorded as immature. We did not select any patch type specifically, opting instead to encompass the full spectrum of avian plumage contrast. However, to avoid taxonomic imbalance in our study we omitted a subset of some well-represented taxonomic groups – from studies that collected a large amount of data on a single group, for example the Estrildid finches (Gomes et al. 2016). Note though, that all data in the Bird Colour Base are included in the supplementary spectrophotometry dataset of for future use. Because we were interested in the possible relationships between environment and plumage colour, particularly in visual communication, we measured plumage contrast using two approaches (A) bird vision models including the effects of ambient light, plumage reflectance and bird vision (following Endler & Mielke 2005) when seen under open/cloudy light environments; open/cloudy light environments occur in all habitats, including at night when it is cloudy, or any time that there is no canopy (Endler 1993); and, (B) bird vision models under the most likely light environment (Endler 1993) based on a given bird species' main habitat and diel activity. For both approaches we set the species eye type (Ultraviolet U or Violet V, following Endler & Mielke 2005) based on published data (Bloch 2015; Endler & Mielke 2005; Ödeen & Håstad 2003, 2010, 2013; Lind et al. 2014) and phylogenetic relationships (Endler & Mielke 2005; Olssen et al. 2021) using Jetz et al. (2012).  Eye models follow that of Vorobyev and Osorio (1998) as in Endler & Mielke (2005); see Renoult et al. (2015) for a detailed discussion. we estimated several measures of within-bird contrast using all adult spectra for a given species (i.e. across different studies/patches). all are related to contrast in bird plumages and thus, conspicuousness: Luminance:  maximum (MaxL), minimum (MinL), difference (Diff), geometric mean (gMeanL) and geometric standard deviation (gSDL; luminance is log-normally distributed); Chroma: mean (MeanCr) and SD (SDCr), and hue circular SD (SDHue), see table 1. Following Dunning et al. (2023), we suggest that maxL may be predicted from the environment, but the other measures of within-bird contrast may also be related to the environment if they are important in intraspecific communication.  For example, maxL is one measure of visual contrast.  This contrast can either be within a given bird's plumage or relative to the background or both.  The difference between the lightest ('brighest") and darkest patch (Diff) also affects contrast, and gmeanL and gSDL could also affect conspicuousness.  Chroma and hue also affect conspicuousness and SD is a measure of the variation across the bird. The gmeanL and meanC are potential measures of possible contrast with the background depending upon average background colouration.
description: # Viewing conditions predict avian plumage contrast Jamie Dunning1,2,
 Catherine Sheard3,4 and John A. Endler5,6 1 Department of Life Sciences,
 Imperial College London, Silwood Park, Ascot, United Kingdom 2 Faculty of
 Biological Sciences, University of Leeds, L C Miall Building, Leeds, LS2
 3AA, United Kingdom 3 Palaeobiology Research Group, University of Bristol,
 24 Tyndall Ave., Bristol, BS8 1TQ, United Kingdom 4 School of Biological
 Sciences, University of Aberdeen, Zoology Building, Tillydrone Ave.,
 Aberdeen AB24 2TZ, United Kingdom 5 School of Life and Environmental
 Sciences, Deakin University, Waurn Ponds VIC 3216, Australia 6 Zoology and
 Ecology, Tropical Environments Sciences, James Cook University,
 Smithfield, Cairns QLD 4878 Australia **Acknowledgements:** The Bird Color
 Base was collated by Thanh-Lan Gluckman and JE, later Peter O. Dunn (full
 BCB acknowledgment and raw data published here -
 [https://github.com/BirdColorBase/home](https://github.com/BirdColorBase/home); and, processed data, this study, - [https://doi.org/10.5061/dryad.4mw6m90hx](https://doi.org/10.5061/dryad.4mw6m90hx)). We thank Jessica K. Armenta, Kevin Burns, Gonalo Cardoso, James Dale, Claire Doutrelant, Peter O. Dunn, Muir Eaton, Amlie Fargevieille, Doris Gomez, Rafael Maia, Richard Prum, Allison Shultz, Mary C. Stoddard, Linda A. Whittingham and their various research teams for their contributions to the BCB. GH, CD, ME, DC, AS, MS, Lock Rowe and two anonymous reviewers also made helpful comments on this manuscript, or data files therein. [https://doi.org/10.5061/dryad.4mw6m90hx](https://doi.org/10.5061/dryad.4mw6m90hx) Dataset contains 3208 measurements of plumage contrast from birds. These data are compiled from multiple studies using a spectrophotometry measurements. We also compiled behavioural data from AVONET and, primary collected data on fine-scale phenology. We tested if these behavioural traits predicted avian plumage contrast. Two datafiles contain equivalent data for two light environements (for which the results are scaled), open/cloudy and appropriate (which varied between species) Associated datasets, the BirdColorData and Avonet are given in this Dryad. submission ### Description of the data and file structure Two data files, ScaledStatsNatural and ScaledStatsOpen Cloudy have equivalent structure: col A-F relate to species taxonomy; G is the source of the spectral measurements; H is eye type (U or V), I-R are taken from AVONET or primary data (O) and denote behavioural traits (details can be found in the accompanying paper or, AVONET files), then S-AP denote measurements of contrast (for example, SD, mean, Min and Max, details of all are given in the paper). Specially, Order and Family are taxonomic rankings, likewise JetzNames is the species name as recorded in the Jetz phylogenetoc tree (which we used in the paper). Species is the species name, and columns E and F denote older spellings, to aid alignment of our taxonomy with the data presented here. Eye type denotes (U)ltraviolet or (V)iolet sensitivity. ScHOpen, ScMigrt, ScPheno are scaled ranks taken from raw measures taken from Avonet (not listed here, but available through the AVONET repository). For details on how scales are achieved see the ESM in this upload. PhenologyCd is a code that denotes the Phenology (Nocturnal, Diurnal or Mixed) - phenology is primary data collected for this study, and not taken from Avonnet. ForgareStyle and TrophicLevel are two more phynotypic traits taken from Avonet directly. Column S onward represent measurements calculated using the Bird Colour Base (also see source column, G). nTotal is the total measurements in the database, following by the number of males and females. then, columns V onwards are colour measurements; minimum luminance, minimum luminance males, minimum luminance females, maximum luminance, max luminance males, max luminance females, geometric mean luminance, mean luminance male, mean luminance female, sd of luminance, sd of luminance males, sd of luminance females, mean chroma, mean chroma males, mean chroma females, sd of chroma, sd of chroma males, sd chroma females, sd of Hue, sd hue males and sd hue females. For details on what each measure means see the associated table in the manuscript DunningSheard_Endler_ESM is a copy of the supplementary files referenced in the manuscript. Finally, we have included four raw results outputs, for each model type; Natural Light Males and Female, and Open Cloudy (OC) Male and Female. NA- Not applicable ### Sharing/Access information Data can be accessed and shared with an appropriate reference. ### Code/Software We used R code to run models, using the MCMCglmm package. The complete code can be found in the supp. mat of the accompanying manuscript. MCMCglmm_Open_cloudy_Females-MaxLum-annotated is a R code file, and Modify Programme shows how it can be amended to run equivielane models in our data (we have included this to save space on attaching repetitive code files).