Visual fields in Flamingos: chick-feeding versus filter-feeding

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.

Kiwi Forego Vision in the Guidance of Their Nocturnal Activities

“…1) are the smallest yet reported among birds and exhibit features found in birds whose foraging is known to be guided by non-visual cues [21]. In particular, the frontal binocular field is almost non-existent.…”

“…Kiwi visual fields are simply small, and this, coupled with their absolutely small eye-size, indicates that the birds gather information of low spatial detail only from a very restricted area around the head. The control of forward locomotion by visual cues in birds is thought to be primarily a function of the symmetrical optical flow-fields generated in each eye within the forward facing binocular sector [21]. In Kiwi this small binocular field, coupled with low spatial resolution, clearly restricts the amount of flow-field information that is available to guide locomotion.…”

Visual fields and their functions in birds

“…The ophthalmoscopic technique for determining retinal visual fields This technique has been used in a range of birds of different phylogeny, ecology and feeding techniques and readily permits interspecific comparisons (Martin and Coetzee 2004;Martin et al 2005Martin et al , 2004bMartin and Prince 2001). For a detailed description of the apparatus and methods see Martin and Katzir (1994a).…”

The subtlety of simple eyes: the tuning of visual fields to perceptual challenges in birds

“…The differing informational demands of such key behaviours need to be understood as much as the overall parameters of the environment in which an animal exists. Behaviours which are subjected to strong natural selection on a daily basis are likely to include locomotion, foraging and the detection of predators [9][10][11][12], whereas, less frequent, but highly selected behaviours which are likely to have important informational demands can involve reproduction and the care of young [13].…”