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  • 1
    Electronic Resource
    Electronic Resource
    HOW A HARBOR SEAL SEES THE NIGHT SKY (2005)
    Oxford, UK : Blackwell Publishing Ltd
    Marine mammal science 21 (2005), S. 0 
    Details
    ISSN: 1748-7692
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Astronavigation is a possible mechanism of offshore orientation in marine mammals. However, the basic prerequisite for astronavigation is to see enough stars of the night sky. This cannot be taken for granted in seals as, due to adaptations of their dioptric apparatus to the optical properties of water, seals are supposed to be myopic and astigmatic when out of the water under low light conditions. Using various real and artificial stars in a go/no-go response paradigm we therefore determined the minimum brightness at which a harbor seal (Phoca vitulina) can detect stars. The dark-adapted seal was trained to look through an empty tube (“seal telescope”) and to retract its head only when a star appeared at the opposite aperture. The seal reliably detected Venus or Sirius becoming suddenly visible when the telescope was moved across the night sky. Detection thresholds were determined using artificial stars (parallel light identical to starlight coming from the universe) of predefined brightness generated by an optical system installed in front of the seal's telescope. The seal detected artificial stars down to 4.4 stellar magnitudes. Although these results cannot present evidence for astronavigation, they imply that seals should see enough stars to allow such orientation mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1748-7692.2005.tb01257.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Seal whiskers detect water movements (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 394 (1998), S. 235-236 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] How do pinnipeds orientate themselves under water? As most pinniped species feed in conditions under which visibility is drastically reduced, for example at night, at great depths or in murky waters, it has been particularly unclear how they succeed in finding food. Here we show that harbour ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/28303
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Signature whistle variations in a bottlenosed dolphin, Tursiops truncatus (1994)
    Springer
    Behavioral ecology and sociobiology 35 (1994), S. 243-248 
    Details
    ISSN: 1432-0762
    Keywords: Key words Signature whistle ; Vocal communication ; Forced choice procedure ; Tursiops truncatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To examine whether context-specific information is superimposed upon the individual cues present in the whistling of the bottlenosed dolphin, Tursiops truncatus, parameter variations within the two most frequently emitted whistle types of a captive individual were investigated in three different behavioural contexts. The study concentrated on comparing signal features of spontaneously occurring vocalizations in two possible phases following the performance of a trained discrimination task and those occurring during isolation. Phases of the discrimination task differed according to whether the animal showed “correct” (reward given) or “incorrect” performance (no reward). Signature whistles were most common in isolation, but also represented just over half of the whistles following a choice task. Of 14 signature whistle frequency and time parameters measured 9 differed significantly between isolation and at least one of the phases following a choice task (Table 1). Three parameters also varied according to whether performance was correct or incorrect. In contrast, only one out of four parameters (start frequency) measured from the second most frequent whistle type varied significantly between contexts (isolation vs. phase following correct choice). The results indicate that not only identity but also context-related information is available in the whistles of a bottlenosed dolphin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002650050094
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    Paper (German National Licenses)
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