Gaze Strategy in the Free Flying Zebra Finch (Taeniopygia guttata)

Fast moving animals depend on cues derived from the optic flow on their retina. Optic flow from translational locomotion includes information about the three-dimensional composition of the environment, while optic flow experienced during a rotational self motion does not. Thus, a saccadic gaze strategy that segregates rotations from translational movements during locomotion will facilitate extraction of spatial information from the visual input. We analysed whether birds use such a strategy by highspeed video recording zebra finches from two directions during an obstacle avoidance task. Each frame of the recording was examined to derive position and orientation of the beak in three-dimensional space. The data show that in all flights the head orientation was shifted in a saccadic fashion and was kept straight between saccades. Therefore, birds use a gaze strategy that actively stabilizes their gaze during translation to simplify optic flow based navigation. This is the first evidence of birds actively optimizing optic flow during flight

Unusual postnatal development of visually evoked potentials in four brain areas of white zebra finches

Bredenkotter M, Bischof H-J. Unusual postnatal development of visually evoked potentials in four brain areas of white zebra finches. BRAIN RESEARCH. 2003;978(1-2):155-161.The central visual system of white zebra finches is physiologically different from normally coloured (wild type) birds, although the eye pigmentation and the retinofugal projection appear to be normal. Ipsilaterally evoked potentials in the white birds are enhanced in comparison to wild type birds, whereas in albino mammals the ipsilateral component of visually evoked potentials is reduced. The present study shows that the enhancement of ipsilateral responses in white zebra finches is detectable in all areas of the tectofugal pathway, and also in the visual wulst, the only station of the thalamofugal pathway examined so far in white zebra finches. In all investigated areas, the enhancement is already obvious at 20 days after hatching, the earliest age that allows reliable recordings. A deficit in inhibition of ipsilateral stimuli, probably combined with a general increase in the number of ipsilateral projections, may cause the observed enhancements of ipsilateral responses in white birds. (C) 2003 Elsevier Science B.V. All rights reserved

Visual system alterations in white zebra finches

Bredenkotter M, Engelage J, Bischof H-J. Visual system alterations in white zebra finches. BRAIN BEHAVIOR AND EVOLUTION. 1996;47(1):23-32.Visual system anomalies in albino mammals are generally seen to be caused by a lack of retinal pigment and misrouting of retinofugal optic fibers. This study shows that the central visual system of white zebra finches is physiologically different from normally colored (wild type) birds, although the eye pigmentation and the retinofugal projection appear to be normal. Ipsilaterally evoked potentials in our white birds are enhanced in comparison to wild type birds, whereas in albino mammals the ipsilateral component of visually evoked potentials is reduced. Picrotoxin-induced blockade of inhibitory synapses in the ectostriatum reveals remarkable differences between wild type and white zebra finches. In wild type zebra finches, a significant shift of ipsilateral to contralateral stimulus response ratios is observed. However, there is no detectable shift in the white morph. The data suggest that inhibition of ipsilateral stimulus processing, as observed in wild type zebra finches, is significantly reduced in the white morph. Our results indicate that the effects observed in white zebra finches cannot be explained by the theories that have been developed for albinotic animals. We assume that in white zebra finches a genetic defect, which causes the white plumage, is coupled with the demonstrated deviations of inhibitory mechanisms in the central visual system