Visual fields in Flamingos: chick-feeding versus filter-feeding |
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Authors: | Graham R Martin Nigel Jarrett Phillip Tovey Craig R White |
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Institution: | (1) School of Biosciences, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK;(2) Wildfowl and Wetlands Trust, Slimbridge, Gloucestershire, GL2 7BT, UK |
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Abstract: | In birds, the position and extent of the region of binocular vision appears to be determined by feeding ecology. Of prime
importance is the degree to which vision is used for the precise control of bill position when pecking or lunging at prey.
In birds that do not require such precision (probe and filter-feeders), the bill falls outside the binocular field, which
extends above and behind the head, thus providing comprehensive visual coverage. Flamingos Phoenicopteridae are highly specialised
filter-feeders. They employ a unique technique that does not require accurate bill positioning in which the inverted head
is placed between the feet. Feeding flamingos often walk forwards with the head pointing “backwards”. Here we show that in
Lesser Flamingos Phoeniconaias minor visual fields are in fact the same as those of birds that feed by precision pecking and that feeding flamingos are blind
in the direction of their walking. We suggest that this is due to the requirement for accurate bill placement when flamingos
feed their chicks with “crop-milk”, and possibly when building their nest. We propose that chick-feeding may be the ultimate
determinant of visual field topography in birds, not feeding ecology. |
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