UBC Theses and Dissertations
Visual resolution of Anna's hummingbirds (Calypte anna) in space and time Fellows, Tyee Kenneth
The sampling of spatial and temporal visual information for all living organisms is finite. The speed and accuracy of visual systems contributes in part to an animal's sensitivity to visual motion. The ability to see swift motions is a crucial adaptation among bird species, which are high-speed animals that navigate in a three-dimensional world. Hummingbirds are emerging as important models for studying visual guidance in vertebrates. However, their sensitivity to visual motion remains unknown. A method that can be used to identify hummingbirds' sensitivity to visual motion is to characterise the spatial and temporal acuity of their visual system. It is hypothesised that temporal acuity scales positively with mass-specific metabolic rate and negatively with body size, and spatial acuity scales positively with body size. Given hummingbirds possess the highest mass- specific metabolic rates among vertebrates and the smallest body sizes among birds, I predicted that the Anna's hummingbird (Calypte anna) would have high temporal and low spatial acuities among bird species. Using operant conditioning and optocollic reflex experiments, I identified the temporal and spatial acuity thresholds of the Anna's hummingbird's visual system. Training hummingbirds to differentiate flickering from non-flickering lights at different rates and colours measured their temporal acuity for wavelengths of light between 380-750nm. Spatial acuity was measured by subjecting hummingbirds to rotating stimuli that varied in spatial frequency and luminance. The results indicate the hummingbird's temporal acuity is between 70 and 80Hz, and is unaffected by light colour (red, white, and ultraviolet). Spatial resolving capacity is measured to be between 4.95 and 6.18 cycles per degree in light conditions below 1.77 candela/m². Therefore, my measurements of spatial acuity in the Anna's hummingbird provide support for a positive relationship with body size, and my measurements of temporal acuity do not provide support for a positive relationship with mass-specific metabolic rate. This study marks the first time both spatial and temporal acuity is measured in a sustained hovering animal.
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