The Visual Ecology of Avian Photoreceptors

Hart, Nathan S.

doi:10.1016/s1350-9462(01)00009-x

Cited by 538 publications

(598 citation statements)

References 180 publications

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“…A film of reflective/ transparent (50%/50%) mirror was used to align an infrared light-source with the camera's view, thus converting the system into an ophthalmoscope. Birds are not expected to be able to see the >750-nm wavelength output of the infrared ophthalmoscope, or through the opaque filter, which had a 720-nm cutoff 22 . Three wild-caught NC crows were housed temporarily in a field aviary (3×3×2 m) where they were given the opportunity to use supplied stick tools to extract beef-heart pieces from a horizontal tube, with the ophthalmoscope filming from the distal end (Fig.…”

Section: Measurement Of Hypothetical Tool-projection Anglesmentioning

confidence: 99%

Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows

et al. 2012

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Section: Measurement Of Hypothetical Tool-projection Anglesmentioning

confidence: 99%

Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows

et al. 2012

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“…The results did not differ qualitatively if we used a different illumination such as forest shade for species that grow exclusively within forests (data not shown). In general, the photoreceptors of birds are remarkably similar, with variation occurring mainly in the UV-sensitive (UVS) cone (Hart 2001). We therefore based our model on the well-known spectral sensitivities of a typical passerine bird, the blue tit (Parus caeruleus), with a UVS cone (Hart et al 2000).…”

Section: Eye Modelmentioning

confidence: 99%

Geographic patterns in fruit colour diversity: do leaves constrain the colour of fleshy fruits?

et al. 2008

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We tested for geographic patterns in fruit colour diversity. Fruit colours are thought to promote detection by seed dispersers. Because seed dispersers differ in their spectral sensitivities, we predicted that fruit colour diversity would be higher in regions with higher seed disperser diversity (i.e. the tropics). We collected reflectance data on 232 fruiting plant species and their natural backgrounds in seven localities in Europe, North and South America, and analysed fruit colour diversity according to the visual system of birds-the primary consumer types of these fruits. We found no evidence that fruit colours are either more conspicuous or more diverse in tropical areas characterised by higher seed disperser diversity. Instead, fruit colour diversity was lowest in central Brazil, suggesting that fruit colours may be more diverse in temperate regions. Although we found little evidence for geographic variation in fruit hues, the spectral properties of fruits were positively associated with the spectral properties of backgrounds. This result implies that fruit colours may be influenced by selection on the reflectance properties of leaves, thus constraining the evolution of fruit colour. Overall, the results suggest that fruit colours in the tropics are neither more diverse nor more conspicuous than temperate fruits, and that fruit colours may be influenced by correlated selection on leaf reflectance properties.

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“…Avian oil droplets are the best studied, with all but one spectral type containing high concentrations of diet-derived, short-wavelength-absorbing carotenoid pigments (Goldsmith et al, 1984;Davies, 1985). Birds possess a single type of medium-wavelength-sensitive (MWS) rod, four spectrally distinct types of single cone and a single type of double cone (for reviews, see Hart, 2001;Hart and Hunt, in press). Single cones containing an ultraviolet-(UVS) or violet-sensitive (VS) visual pigment [SWS1 opsin; for terminology see (Yokoyama, 2000)] have a non-pigmented 'T-type' oil droplet, with no significant absorption of wavelengths between at least 330 and 800·nm.…”

Section: Introductionmentioning

confidence: 99%

Cone photoreceptor oil droplet pigmentation is affected by ambient light intensity

Hart

Lisney

Collin

2006

Journal of Experimental Biology

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SUMMARY The cone photoreceptors of many vertebrates contain spherical organelles called oil droplets. In birds, turtles, lizards and some lungfish the oil droplets are heavily pigmented and function to filter the spectrum of light incident upon the visual pigment within the outer segment. Pigmented oil droplets are beneficial for colour discrimination in bright light, but at lower light levels the reduction in sensitivity caused by the pigmentation increasingly outweighs the benefits generated by spectral tuning. Consequently, it is expected that species with pigmented oil droplets should modulate the density of pigment in response to ambient light intensity and thereby regulate the amount of light transmitted to the outer segment. In this study, microspectrophotometry was used to measure the absorption spectra of cone oil droplets in chickens (Gallus gallus domesticus) reared under bright (unfiltered) or dim (filtered) sunlight. Oil droplet pigmentation was found to be dependent on the intensity of the ambient light and the duration of exposure to the different lighting treatments. In adult chickens reared in bright light, the oil droplets of all cone types (except the violet-sensitive single cones, whose oil droplet is always non-pigmented) were more densely pigmented than those in chickens reared in dim light. Calculations show that the reduced levels of oil droplet pigmentation in chickens reared in dim light would increase the sensitivity and spectral bandwidth of the outer segment significantly. The density of pigmentation in the oil droplets presumably represents a trade-off between the need for good colour discrimination and absolute sensitivity. This might also explain why nocturnal animals, or those that underwent a nocturnal phase during their evolution, have evolved oil droplets with low pigment densities or no pigmentation or have lost their oil droplets altogether.

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The Visual Ecology of Avian Photoreceptors

Cited by 538 publications

References 180 publications

Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows

Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows

Geographic patterns in fruit colour diversity: do leaves constrain the colour of fleshy fruits?

Cone photoreceptor oil droplet pigmentation is affected by ambient light intensity

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