26 Articles from The Auk, The Auk: Ornithological Advances, The Condor, The Condor: Ornithological Applications

The Avian Color Revolution: Perception, Function, and Application

By Thomas Manna and Mark E. Hauber, Department of Psychology, Hunter College, and the Graduate Center, The City University of New York

Figure 1. Plumage ornaments of Cerulean Warblers reliably convey information about age. See Boves et al. (2014).

Birds have always been best-known for color: Whether it is the diversity of their feathers, skin, egg coloration, or the colorful flowers and fruits they feed on, lay people have long admired and scientists have repeatedly wondered about the evolutionary reasons behind such opulent displays. Fortunately, in recent decades, optical technologies (low-cost and portable reflectance spectrometry) and perceptual modeling (generalizable and avian-specific visual algorithms) have allowed for both the precise measurement of colors across diverse avian clades and these colors' sensory interpretation by the birds themselves, clearing the way for both proximate and ultimate comparative studies examining the impact of color on avian biology.

With the revolutions in tools of technology, comparative methods, and next generation neurogenomics, we are well-equipped to empirically access and test in exciting clarity multiple levels of analyses and divergent hypotheses about the role of color in avian function. In this Joint Special Collection, we highlight recent papers (2012 onward) from both The Auk and The Condor that further understanding of avian visual mechanisms and function, and we showcase innovative investigations that relate the role of coloration to both basic function, continuing to be covered in future issues of The Auk: Ornithological Advances, and applied ornithology to be contributed in and by The Condor: Ornithological Applications.

Applied Ornithology: Repellants and Attractants

We start with several studies that address how birds perceive and interact with anthropogenic, manipulated features of their environment. For example, Doppler et al. (2015) proposed a method of reducing bird–object collision accidents by tuning warning lights to be most salient to the visual system of one of the most common North American airport-flocking species', the Brown-headed Cowbird's, visual system. The potentially large number of human lives saved and the vast amounts of equipment damage avoided represent the best types of applied benefits that avian color vision studies produce. In turn, Duan and Quan (2013) demonstrated preference for certain fruit colors of birds in an area where these avian taxa represent the most important seed dispersal system. Knowledge of these feeding preferences in diverse, agriculturally impactful species can then be applied to designing both attractive artificial baits and repellant barriers to protect crops. Finally, Finity and Nocera (2012) suggested that in human-modified habitats, Chimney Swifts use both visual and vocal conspecific cues to aid in selecting a nesting site; the application of different sensory modalities of conspecific attractants can become beneficial for conservation management involving translocations, restorations, and new breeding colony establishments in diverse bird species.

Functional Avian Biology: Intraspecific Communication, Interspecific Signaling, and Ecological Patterns

Among the basic biology of coloration, we here categorize contributions according to functional categories: the role of color in actual or potential communication functions within species (including age-specific displays and sexual selection), the role of color in interspecific signaling, including parasitic egg rejection and predator–prey interactions, and ecological patterns that are correlated with varying levels of pigment deposition in the plumage of birds.

We have selected some of the most cutting-edge investigations into the visual perception role in individual sexual selection systems. Wiebe and Vitousek (2015) showed that size and pigmentation of a sexual ornament in the Northern Flicker woodpecker provide information across several metrics of mate quality in both sexes. Rathbun et al. (2015) quantified the color variation across and within the morphs of a polymorphic sparrow, showing greater ranges in the white morph, which is more sexually aggressive. Rohwer (2012) provided data suggesting that the polymorphic plumage of juvenile Yellow Warblers is not dependent on sex as was theorized. Boves et al. (2014) attempted to elucidate the information present in the differential plumage of the Cerulean Warbler both within and between age classes, finding that several distinct features indicated multiple metrics of fitness (Figure 1). Blanco and Fargallo (2013) demonstrated that the differential size of a white patch on the wings of Black-billed Magpies predicted several fitness metrics in both sexes as well as testes size in males. Leclaire et al. (2013) examined the possible role of symmetry of wing-tip patterns in sexual selection/reproductive success of male Black-legged Kittiwakes, finding that the symmetry predicted clutch/brood size as well as brightness of sexual signals. Quesada et al. (2013) investigated the effect of Blue Grosbeak ornamentation in sexual selection vs. intrasexual status signaling, finding only evidence of the latter. In turn, Beck (2013) examined the relationship between plumage color and intrasexual competition, finding that more brightly colored male Prothonotary Warblers obtained nest boxes in more preferential locations than more dimly colored males did. Clark et al. (2012) and Clark et al. (2013) described the variation in shuttle and dive mating displays and nuptial plumage in a hybrid hummingbird species, and then in 2013 provided a similar analysis of three closely related hummingbirds. Burns and Shultz (2012) measured UV reflectance in the plumage of neotropical songbirds, providing stunning evidence that a much larger portion of them are sexually dichromatic in a manner perceivable only to birds than we thought, commenting on the history of research of avian sexual selection focusing primarily on what is visible to humans.

Color also serves in critical roles for interspecific interactions, including predator–prey dynamics and host–parasite recognition. For example, Bailey et al. (2015) provided the first experimental evidence that birds actively camouflage their nests by choosing nesting material that matches the background color of their nesting site. Mumme (2014) examined the function of the Hooded Warbler's white tail spots to find that birds with experimentally darkened spots experienced reduced foraging success; video evidence implicates that prey were not lured to dive for the spots as they normally are. Pascual et al. (2014) tested the compensation hypothesis, namely that a conspicuously colored individual would need to engage in more rigorous anti-predatory behavior than a plainer individual, by measuring anti-predator behavior between the sexes of the sexual dimorphic Eurasian Siskin, and found that the conspicuous (male) sex exhibited significantly more vigilance. Our collection also covers new insights into the role of visual cues of eggs in the interaction between avian brood parasites and their hosts. Lang et al. (2014) investigated whether American Robins eject Brown-headed Cowbird eggs because the parasitic eggs represent a minority in their nests (discordancy hypothesis) or because they have learned the appearance of their own eggs regardless of population ratio (true egg recognition hypothesis), finding evidence for the latter. Abernathy and Peer (2014) examined the variability in egg appearance of Brown-headed Cowbird hosts to investigate the proposition that mimetic parasitic eggs should select for low variability in the shells of the host clutch, and Guigueno et al. (2014) demonstrated that size of a parasitic egg is a more salient cue for host species using non-ejection rejection strategies than for ejector hosts, which are more sensitive to color cues.

Finally, we highlight some excellent work on ecological patterns and correlates of pigmentation. Accordingly, Roulin and Randin (2015) experimentally demonstrated Gloger's rule (that species with phenotypic pigment variation should exhibit darker color in warmer, more humid environments) in North American Barn Owls. Luttrell et al. (2015) used digital photography to quantify color variation across four subspecies of Song Sparrows to illustrate that the subspecies that are restricted to more saline environments demonstrate salt marsh melanism (darker, grayer pigmentation). Mateos-Gonzalez et al. (2014) measured escape performance in House Finches with differential carotenoid pigmentation (a trait classically positively correlated with sexual fitness) to demonstrate better performance in individuals with higher carotenoid concentrations. Kilgas et al. (2012) provided experimental evidence of the long-held supposition that relative plumage richness is an indicator of microorganism activity, showing that color saturation of Great Tit feathers was negatively correlated with bacteria levels present on the feathers. Aside from just plumage, we also include studies examining visual features of eggs. Wheelwright et al. (2012) showed that egg coloring as well as size and shape showed significant individual consistency over the course of several breeding seasons in the Savannah Sparrow. Bulla et al. (2012) demonstrated that speckles on shorebird eggs represented areas of the eggshell that were thinner/weaker, lending credence to the theory that speckles provide a structural support function to eggshells.

We not only hope that you find this Joint Collection helpful in reviewing recent progress in ornithological works' contribution to color ecology and function, but also consider contributing your own future works on avian coloration to one or both of our Journals as a relevant and suitable home to reach critical portions of the intended audience and readership for your research.

Articles on COLOR

Applied Ornithology: Repellants and Attractants

Cowbird responses to aircraft with lights tuned to their eyes: Implications for bird–aircraft collisions by Megan S. Doppler, Bradley F. Blackwell, Travis L. DeVault, and Esteban Fernández-Juricic. The Condor 117(2):165–177. Published April 8, 2015. OPEN ACCESS

The Effect of Color on Fruit Selection in Six Tropical Asian Birds by Qiong Duan and Rui-Chang Quan. The Condor 115(3):623–629. Published August 2013. OPEN ACCESS

Vocal and Visual Conspecific Cues Influence the Behavior of Chimney Swifts at Provisioned Habitat by Leah Finity and Joseph J. Nocera. The Condor 114(2):323–328. Published May 2012. OPEN ACCESS

Functional Avian Biology: Intraspecific Communication

Melanin plumage ornaments in both sexes of Northern Flicker are associated with body condition and predict reproductive output independent of age by Karen L. Wiebe and Maren N. Vitousek. The Auk 132(2):507–517. Published April 1, 2015. OPEN ACCESS

Quantitative color variation within and across morphs of the polymorphic White-throated Sparrow by Nathan A. Rathbun, Andrea S. Grunst, Melissa L. Grunst, Joanna K. Hubbard, Rebecca J. Safran, Rusty A. Gonser, and Elaina M. Tuttle. The Auk 132(1):92–104. Published November 15, 2014. OPEN ACCESS

Juvenal Plumage Polymorphism in Yellow Warblers is Not Associated with Sex by Vanya G. Rohwer, Frances Bonier, and Paul R. Martin. The Condor 114(2):407–411. Published May 2012. OPEN ACCESS

Multiple plumage traits convey information about age and within-age-class qualities of a canopy-dwelling songbird, the Cerulean Warbler by Than J. Boves, David A. Buehler, Petra B. Wood, Amanda D. Rodewald, Jeffrey L. Larkin, Patrick D. Keyser, and T. Ben Wigley. The Auk 131(1):20–31. Published January 2, 2014.

Wing whiteness as an indicator of age, immunocompetence, and testis size in the Eurasian Black-billed Magpie (Pica pica) by Guillermo Blanco and Juan A. Fargallo. The Auk 130(3):399–407. Published July 2013.

Symmetry of Black Wingtips is related to clutch size and integument coloration in Black-Legged Kittiwakes (Rissa tridactyla) by Sarah Leclaire, Pierrick Blanchard, Joël White, Scott A Hatch, and Étienne Danchin. The Auk 130(3):541–547. Published July 2013.

Plumage coloration of the Blue Grosbeak has no dual function: A test of the armament–ornament model of sexual selection by Javier Quesada, Carlos Alberto Chávez-Zichinelli, Juan Carlos Senar, and Jorge Ernesto Schondube. The Condor 115(4):902–909. Published November 2013.

Nest-box acquisition is related to plumage coloration in male and female Prothonotary Warblers (Protonotaria citrea) by Michelle L. Beck. The Auk 130(2):364–371. Published April 2013. OPEN ACCESS

Courtship Displays and Sonations of a Hybrid Male Broad-Tailed × Black-Chinned Hummingbird by Christopher J. Clark, Teresa J. Feo, and Kelly B. Bryan. The Condor 114(2):329–340. Published May 2012. OPEN ACCESS

Sounds and Courtship Displays of the Peruvian Sheartail, Chilean Woodstar, Oasis Hummingbird, and a Hybrid Male Peruvian Sheartail × Chilean Woodstar by Christopher J. Clark, Teresa J. Feo, and Wouter F. D. Van Dongen. The Condor 115(3)558–575. Published August 2013. OPEN ACCESS

Widespread Cryptic Dichromatism and Ultraviolet Reflectance in the Largest Radiation of Neotropical Songbirds: Implications of Accounting for Avian Vision in the Study of Plumage Evolution by Kevin J. Burns and Allison J. Shultz. The Auk 129(2):211–221. Published April 2012. OPEN ACCESS

Functional Avian Biology: Interspecific Signaling

Birds build camouflaged nests by Ida E. Bailey, Felicity Muth, Kate Morgan, Simone L. Meddle, and Susan D. Healy. The Auk 132(1):11–15. Published October 1, 2014. OPEN ACCESS

White tail spots and tail-flicking behavior enhance foraging performance in the Hooded Warbler by Ronald L. Mumme. The Auk 131(2):141–149. Published February 19, 2014. http://www.aoucospubs.org OPEN ACCESS

Plumage brightness, vigilance, escape potential, and predation risk in male and female Eurasian Siskins (Spinus spinus) by Jordi Pascual, Juan Carlos Senar, and Jordi Domènech. The Auk 131(1):61–72. Published January 15, 2014. OPEN ACCESS

Effect of parasite-to-host egg ratio on egg rejection by a Brown-headed Cowbird host by A. Karlien Lang, Eric K. Bollinger, and Brian D. Peer. The Auk 131(4):694–701. Published September 17, 2014.

Intraclutch variation in egg appearance of Brown-headed Cowbird hosts by Virginia E. Abernathy and Brian D. Peer. The Auk 131(4):467–475. Published July 9, 2014.

Rejection of parasitic eggs in passerine hosts: Size matters more for a non-ejecter by Mélanie F. Guigueno, Spencer G. Sealy, and Ashleigh M. Westphal. The Auk 131(4):583–594. Published August 13, 2014.

Functional Avian Biology: Ecological Patterns

Gloger's rule in North American Barn Owls by Alexandre Roulin and Christophe Randin. The Auk 132(2):321–332. Published January 7, 2015. OPEN ACCESS

Digital photography quantifies plumage variation and salt marsh melanism among Song Sparrow (Melospiza melodia) subspecies of the San Francisco Bay by Sarah A. M. Luttrell, Sara T. Gonzalez, Bernard Lohr, and Russell Greenberg. The Auk 132(1):277–287. Published December 17, 2014. OPEN ACCESS

Carotenoid coloration predicts escape performance in the House Finch (Haemorhous mexicanus) by Fernando Mateos-Gonzalez, Geoffrey Hill, and Wendy Hood. The Auk 131(3):275–281. Published April 16, 2014. OPEN ACCESS

Variation in Assemblages of Feather Bacteria in Relation to Plumage Color in Female Great Tits by Priit Kilgas, Pauli Saag, Marko Mägi, Meeli Edenberg, Vallo Tilgar, and Raivo Mänd. The Condor 114(3):606–611. Published August 2012. OPEN ACCESS

Relative Consistency in Size, Shape, and Coloration of Savannah Sparrow Eggs within and between Breeding Seasons by Nathaniel T. Wheelwright, Evan S. Graff, and D. Ryan Norris. The Condor 114(2):412–420. Published May 2012. OPEN ACCESS

Eggshell Spotting does not Predict Male Incubation but Marks Thinner Areas of a Shorebird's Shells by Martin Bulla, Miroslav Šálek, and Andrew G. Gosler. The Auk 129(1):26–35. Published January 2012. OPEN ACCESS