Ultraviolet Vision in Birds

Cuthill, Innes C.; Partridge, Julian C.; Bennett, Andrew T. D.; Church, Stuart C.; Hart, Nathan S.; Hunt, Sarah

doi:10.1016/s0065-3454(08)60105-9

Cited by 410 publications

(366 citation statements)

References 224 publications

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“…Although the brown card lacked any ultraviolet (UV) reflectance (birds can see UV; e.g. Cuthill et al 2000), so too does lichen-free oak bark, as used in this study (own measurements and Majerus et al 2000). Patterns were digital samples (using PAINTSHOP PRO; JASC Software, Minneapolis, USA) of scanned bark-rubbings from a sample of 60 oak trees in the study site.…”

Section: Methodsmentioning

confidence: 99%

The predation costs of symmetrical cryptic coloration

Cuthill¹,

Hiby²,

Lloyd³

2006

Proc. R. Soc. B.

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In psychological studies of visual perception, symmetry is accepted as a potent cue in visual search for cryptic objects, yet its importance for non-human animals has been assumed rather than tested. Furthermore, while the salience of bilateral symmetry has been established in laboratory-based search tasks using human subjects, its role in more natural settings, closer to those for which such perceptual mechanisms evolved, has not, to our knowledge, been investigated previously. That said, the salience of symmetry in visual search has a plausible adaptive rationale, because biologically important objects, such as prey, predators or conspecifics, usually have a plane of symmetry that is not present in their surroundings. We tested the conspicuousness to avian predators of cryptic artificial, moth-like targets, with or without bilateral symmetry in background-matching coloration, against oak trees in the field. In two independent experiments, symmetrical targets were predated at a higher rate than otherwise identical asymmetrical targets. There was a small, but significant, fitness cost to symmetry in camouflage patterns. Given that birds are the most commonly invoked predators shaping the evolution of defensive coloration in insects, this raises the question of why bilateral asymmetry is not more common in cryptic insects.

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Section: Methodsmentioning

confidence: 99%

The predation costs of symmetrical cryptic coloration

Cuthill¹,

Hiby²,

Lloyd³

2006

Proc. R. Soc. B.

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“…sequences of discrete keratin and melanin layers). Furthermore, the distance between the melanin granules in this outer layer was consistently lower than 300 nm, therefore not allowing individual interaction with light in all avian visible wavelengths (300-700 nm; Cuthill et al 2000) and conferring an organization typical of single-layer thinfilm optical systems.…”

Section: Barbule Microstructurementioning

confidence: 99%

Iridescent structural colour production in male blue-black grassquit feather barbules: the role of keratin and melanin

Maia

Caetano

Báo

et al. 2009

J. R. Soc. Interface.

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Iridescent coloration plays an important role in the visual communication system of many animal taxa. It is known that iridescent structural colours result from layers of materials with different refractive indexes, which in feathers usually are keratin, melanin and air. However, the role of these materials in the production of structural iridescent coloration is still poorly documented. Despite the great interspecific variation in the organization of such structures in bird plumage, melanin layers are usually considered too opaque, suggesting its main role is to delineate the outermost keratin layer and absorb incoherently scattered stray light. We combined spectrometry, electron microscopy and thin-film optical modelling to describe the UV-reflecting iridescent colour of feather barbules of male blue-black grassquits (Volatinia jacarina), characterized by a keratin layer overlying a single melanin layer. Our models indicate that both the keratin and the melanin layers are essential for production of the observed colour, influencing the coherent scattering of light. The melanin layer in some barbules may be thin enough to allow interaction with the underlying keratin; however, individuals usually have, on an average, the minimum number of granules that optimizes absorbance by this layer. Also, we show that altering optical properties of the materials resulted in better-fitting models relative to the empirically measured spectra. These results add to previous findings concerning the influence of melanin in single-layer iridescence, and stress the importance of considering natural variation when characterizing such photonic structures.

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“…UV vision has been confirmed in at least 29 species of birds, spanning a diverse range of taxonomies and ecological habitats, and is thought to be a general property of birds, although it may be absent in some nocturnal species (Bennett and Cuthill, 1994;Cuthill et al, 2000). Birds have a cone receptor type (the double cone) that appears to be dedicated to this function (Bennett and Cuthill, 1994).…”

Section: Aves Compared To Mammaliamentioning

confidence: 99%

Spatial contrast sensitivity of birds

2006

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Contrast sensitivity (CS) is the ability of the observer to discriminate between adjacent stimuli on the basis of their differences in relative luminosity (contrast) rather than their absolute luminances. Prior to this study, birds had been thought to have low contrast detection thresholds relative to mammals and fishes. This was a surprising phenomenon because birds had been traditionally attributed with superior vision. In addition, the low CS of birds could not be explained by retinal or optical factors, or secondary stimulus characteristics. Unfortunately, avian contrast sensitivity functions (CSFs) were sparse in the literature, so it was unknown whether low contrast sensitivity was a general phenomenon in birds. This study measured CS in six species of birds The quail and pigeon data obtained in this experiment fit well with existing CS data for these species. The kestrel data were not similar to kestrel data in the literature; however the data in the literature were collected from a single subject. All of the birds studied had contrast sensitivities that were consistent with their retinal or optical morphologies relative to other birds (in species for which such data exists) and seem well suited for their natural environments. In addition, all of these birds exhibited low CS relative to humans and most mammals, which suggests that low CS is a general phenomenon of birds.Explanations for this avian low CS phenomenon include a possible trade-off between contrast mechanisms and UV mechanisms in cone systems, and lateral inhibitory mechanisms that are perhaps categorically different from mammals. Lateral inhibition affects contrast gain, and has been shown to differ according to ganglion cell types, which in turn will differ in vertebrate species.

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Ultraviolet Vision in Birds

Cited by 410 publications

References 224 publications

The predation costs of symmetrical cryptic coloration

The predation costs of symmetrical cryptic coloration

Iridescent structural colour production in male blue-black grassquit feather barbules: the role of keratin and melanin

Spatial contrast sensitivity of birds

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