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  • 1
    ISSN: 1432-1351
    Keywords: Key words Colour vision ; Microspectrophotometry ; Avian retina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the visual pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (λmax) of long-wavelength-sensitive single and double cone visual pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitivesingle cones of both species cut off wavelengths below 570–573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise λmax of the long-wavelength-sensitive visual pigment is optimised for the visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their visual ecology.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 183 (1998), S. 621-633 
    ISSN: 1432-1351
    Keywords: Key words Bird ; Colour ; Vision ; UV ; Plumage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract There is a growing body of data on avian eyes, including measurements of visual pigment and oil droplet spectral absorption, and of receptor densities and their distributions across the retina. These data are sufficient to predict psychophysical colour discrimination thresholds for light-adapted eyes, and hence provide a basis for relating eye design to visual needs. We examine the advantages of coloured oil droplets, UV vision and tetrachromacy for discriminating a diverse set of avian plumage spectra under natural illumination. Discriminability is enhanced both by tetrachromacy and coloured oil droplets. Oil droplets may also improve colour constancy. Comparison of the performance of a pigeon's eye, where the shortest wavelength receptor peak is at 410 nm, with that of the passerine Leiothrix, where the ultraviolet-sensitive peak is at 365 nm, generally shows a small advantage to the latter, but this advantage depends critically on the noise level in the sensitivity mechanism and on the set of spectra being viewed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 173 (1993), S. 193-207 
    ISSN: 1432-1351
    Keywords: Spatial memory ; Landmarks ; Food storing ; Corvids ; Garrulus glandarius
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This work suggests how food storing corvids use spatial memory to relocate caches, and how they can do this after some landmarks surrounding caches have become hidden due to leaf fall, snow fall or plant growth. Experiments involved training European jays (Garrulus glandarius) to find buried food, the location of which was specified by an array of 12 landmarks. Tests were then performed with the array rotated, or with certain landmarks removed from the array. The main findings were: (1) birds primarily remembered the position of the goal using the near tall landmarks (15–30 cm from the goal and 20 cm high); (2) birds obtained a sense of direction both from the landmark array and something external to the array; (3) birds did not use smell or marks in the surface of the ground to find the goal. Memory of near tall landmarks is likely to be functional for these birds since (a) nearer landmarks provide a more accurate fix, and (b) taller landmarks are less likely to be completely obscured by snow fall, leaf fall or intervening vegetation. The work also demonstrates the use of G.I.S. software for the analysis and representation of animal search patterns.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Chemoecology 7 (1996), S. 189-190 
    ISSN: 1423-0445
    Keywords: chemical defence ; toxicity ; formic acid ; Formica rufa ; Sturnus vulgaris
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1437-9546
    Keywords: Key words Video playback ; Plumage colour ; Colour measurement ; Bird vision
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Video playback potentially allows the presentation, manipulation, and replication of realistic moving visual stimuli, in a way that is impossible with real animals or static dummies, and difficult even with mechanical models. However, there are special problems attached to the use of this technology; this article concentrates on the problem of accurate colour rendition. Video and television simulate the colour of objects rather than reproduce the spectrum of light that they naturally emit, transmit, or reflect. This simulation is achieved by using relatively narrow waveband light to stimulate the cone cells in the retina in a similar pattern to that produced by the natural object. However, species differ in the spectral tuning of their photoreceptors, so a faithful colour rendition for a human is unlikely to be achieved for another species. This problem is discussed with special reference to birds, a taxon renown for its colourfulness and frequent use in behavioural experiments but which has a very different colour vision from that of humans. We stress that the major pitfalls that can arise when using video playback with avian subjects can also occur in ’normal’ behavioural experiments. However, the problems of faithful colour rendition are particularly severe with video, and the major benefits that the technology brings will only be realised under a limited range of circumstances, with careful validation experiments.
    Type of Medium: Electronic Resource
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