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Morphometrics of the eyes and orbits of the nocturnal Swallow-tailed Gull (Creagrus furcatus)

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Abstract:

The Swallow-tailed Gull (Creagrus furcatus (Neboux, 1846)) is known for its nocturnal feeding habits and apparently large eyes. Despite frequent observations of its large eyes, detailed measurements of its eyes and orbits are wanting. Here, we provide a detailed analysis of the size and shape of the eye and orbits of this unique species in relation to a range of other gull species. Although the C. furcatus does have a slightly enlarged cornea and optical axis, neither the transverse orbit diameter nor the shape of its eye differs significantly from other larids. In addition, we found no significant difference between C. furcatus and other gulls in terms of its orbit dimensions and orbit orientation. We therefore conclude that C. furcatus does not possess a transversely enlarged eye, but rather a slightly larger cornea and longer eye. Our results do not, however, preclude the presence of other changes in the visual system, such as retinal morphology or neurophysiology, that could be adaptive for nocturnal feeding.

La mouette à queue fourchue (Creagrus furcatus (Neboux, 1846)) est connue pour ses habitudes alimentaires nocturnes et pour ses yeux apparemment agrandis. Malgré de fréquentes observations des grands yeux, il n’existe pas de mesures précises des yeux et des orbites. Nous présentons ici une analyse détaillée de la taille et de la forme des yeux et des orbites de cette espèce particulière en comparaison avec une gamme d’autres espèces de mouettes. Bien que C. furcatus possède une cornée et un axe optique légèrement agrandis, ni le diamètre transversal de l’orbite, ni la forme de l’œil ne différent significativement de ceux des autres laridés. De plus, il n’y a pas de différence significative entre C. furcatus et les autres mouettes en ce qui a trait aux dimensions et à l’orientation de l’orbite. Nous concluons donc que C. furcatus ne possède pas un œil agrandi transversalement, mais plutôt une cornée un peu plus grande et un œil allongé. Nos résultats n’écartent pas, toutefois, la présence d’autres modifications dans le système visuel, par exemple dans la morphologie de la rétine ou la neurophysiologie, qui pourraient être des adaptations à l’alimentation nocturne.

Document Type: Research Article

Publication date: September 1, 2010

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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