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

Copy when uncertain: lower light levels increase trail pheromone deposition and reliance on pheromone trails in ants

Animals may gather information from multiple sources, and these information sources may conflict. Theory predicts that, all else being equal, reliance on a particular information source will depend on its information content relative to other sources. Information conflicts are a good area in which to test such predictions. Social insects, such as ants, make extensive use of both private information (e.g. visual route memories) and social information (e.g. pheromone trails) when attempting to locate a food source. Importantly, eusocial insects collaborate on food retrieval, so both information use and information provision may be expected to vary with the information content of alternative information sources. Many ants, such as Lasius niger, are active both day and night. Variation in light levels represents an ecologically important change in the information content of visually-acquired route information. Here, we examine information use and information provision under high light levels (3200 lux, equivalent to a bright but overcast day), moderate light levels simulating dusk (10 lux) and darkness (0.007 lux, equivalent to a moonless night). Ants learn poorly, or not at all, in darkness. As light levels decrease, ants show decreasing reliance on private visual information, and a stronger reliance on social information, consistent with a ‘copy when uncertain’ strategy. In moderate light levels and darkness, pheromone deposition increases, presumably to compensate for the low information content of visual information. Varying light levels for cathemeral animals provides a powerful and ecologically meaningful method for examining information use and provision under varying levels of information content

Are colour oil droplets the basis of the pigeon's chromatic space?

Variable proportions of four kinds of cones with different coloured oil droplets, are distributed in all retinal quadrants. Pigeons can learn and generalize colour recognition in any portion of their visual field. Since they possess trichromatic vision, yet only one cone photopigment has yet been described, it was postulated that colour vision must be mediated by the cut-off filter properties of these coloured oil droplets. A study was conducted wherein behavioural data of colour discrimination, obtained in a sort of matching experiment, were compared with the spectral properties of oil droplets measured in the same bird. In the "red" zone of the spectrum, the best colour discrimination of the pigeon was found to coincide with the steepest slope of the absorption spectra of its own red droplets (590-600 nm). Behavioural data in the "blue" zone are not conclusive. Oil droplets absorption spectra in this zone suggest that colour discrimination for shorter wavelengths might be related t

Perception of rotating spiral patterns by pigeons

The ability of pigeons to discriminate indepth moving stimuli was studied with the rotating spiral illusion. Trained with tightly wound spirals, the birds were able to distinguish apparently approaching from apparently retreating spirals. Discrimination also persisted with loosely wound spirals, even though these did not induce an equivalent illusion in humans. Analysis of the optic flow created by the spirals indicates that the relevant cues were local divergent/convergent motion patterns. Global flow patterns, similar to those arising with approaching/retreating scenes, were only generated by tightly wound spirals. An unidimensional parameter τ could be derived that typified each and all the stimuli used. It is equivalent to the τ that has been used to characterize the optic flow of really approaching objects, indicating the time to collision. With a stationary rotating logarithmic spiral, τ is a joint function of winding tightness and rotation velocity. The τs associated with the rotation speeds yielding threshold discrimination gauged the effectiveness of spirals with different winding inclinations. Threshold τs were high with tight spirals and decreased with loose spirals. This indicates that both local and global kinetic cues must contribute to the detection of in-depth movement by pigeons. Even though the cue efficiency of local flow patterns alone is less than that of global flow patterns the former may be of value when they are dealing with scene elements looming at different rates or with looming objects that are partially occluded.publishe

The visual field and visually guided behavior in the zebra finch (Taeniopygia guttata)

Bischof H-J. The visual field and visually guided behavior in the zebra finch (Taeniopygia guttata). Journal of Comparative Physiology, A: Sensory Neural and Behavioral Physiology. 1988;163(3):329-337.Measurements were made of the physical properties of the visual system of the zebra finch, a bird with laterally placed eyes. The use of the visual system in pecking and courtship behavior was examined. It was demonstrated that the optical axis and the fovea of the eye point in a direction about 62.degree. from the sagittal axis of the head. The visual field of each eye covers about 170.degree. in the horizontal plane. In the frontal region there is an overlap of about 30.degree.-40.degree. where the birds can see binocularly; caudally there is a 'gap' in the visual field of 60.degree.. The point of best binocular viewing is in the sagittal plane at 16.5.degree. below the beak. Concerning movement detection, the upper threshold is 540.degree./s for the binocular (frontal) part of the visual field and about 1100.degree./s for the monocular (lateral) part. Most fixations before pecking occur monocularly. A preference for one eye during pecking was not detected. During the courtship song, a male bird directs its head towards the female. The results are discussed in comparison with findings in pigeons and chickens

Ipsilaterally evoked responses of the zebra finch visual wulst are reduced during ontogeny

Bredenkötter M, Bischof H-J. Ipsilaterally evoked responses of the zebra finch visual wulst are reduced during ontogeny. Brain Research. 1990;515(1-2):343-346.Visual wulst responses to ipsi- and contralateral visual stimuli were investigated in young zebra finches (Taeniopygia guttata castanotis Gould) of different ages. Contralateral responses in 20, 40, 60 and 80 day old birds do not differ significantly from those in adults. In contrast, ipsilateral responses decrease substantially during development and become very weak and irregular in adult birds