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Theriault, Jolan

University of British Columbia

Hummingbirds are highly maneuverable animals that rely on vision to guide flight behaviour. When large field stimuli are presented in their frontal visual field, hovering hummingbirds will drift in the corresponding direction, demonstrating that they use visual input to inform positional stability. In most vertebrates studied to date, one of the brain regions that encodes global visual motion, and guides associated motor output, exhibits a response bias for temporal-nasal motion. Homologous hummingbird visual nuclei lack this directional bias in favor of a more uniform response distribution. Hummingbirds also have a nearly 360° visual field, but their fovea is oriented laterally and their area temporalis, which has lower spatial resolution, is oriented forwards. These features led us to ask whether hummingbird optomotor responses vary across different regions of the visual field and whether they exhibit a directional bias during hovering flight. I addressed these questions by creating a square arena with screens on each wall and presenting hovering Anna’s hummingbirds with several different combinations of expanding and contracting spirals, and a grating of black and white vertical bars drifting in both directions in the horizontal plane. Bird head positions and flight trajectories were recorded using a 3D motion capture system. I found that the hummingbird’s optomotor response was strongest to expanding/contracting in the frontal field and waned as it shifted posteriorly. Black and white vertical bars drifting horizontally in a single plane did not elicit any directional preference, however, they elicited a stronger response to nasal-temporal drift when presented in two parallel planes, especially when centered in the lateral visual field. This suggests that visual field coverage influences directional bias and may be positively correlated with response strength for horizontal motion. Combining the vertical gratings with a competing expanding or contracting spiral consistently led to stronger responses to the former, regardless of location in the visual field. Overall, the results suggest that during hovering, the location of motion in the hummingbird’s visual field is of lesser importance that the type of visual signal, and that hummingbirds may have an unexpected directional bias for horizontal visual motion cues in the nasal-temporal direction.

Text

2024-07-24

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88685

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/