Available at: https://digitalcommons.calpoly.edu/theses/2700
Date of Award
MS in Biological Sciences
College of Science and Mathematics
College of Science and Mathematics
There is more human-generated noise and light today than ever before, a trend tied to ongoing urbanization and with reverberating impacts on a wide range of organisms. While research on these impacts is mounting and particularly plentiful when it comes to birds, there is still much to explore within its effects on avian behavior, fitness, and evolution. In chapter 1, we investigated how fledgling movement is influenced by noise and light pollution. While adult birds have well-documented species-specific responses to these stimuli, fledglings are sorely understudied in this context. We experimentally manipulated light levels and took advantage of an existing landscape of artificial noise in the gas fields of northwestern New Mexico to radio track fledglings through gradients of noise and light from four species: Western bluebirds (Sialia mexicana), mountain bluebirds (Sialia currucoides), ash-throated flycatchers (Myiarchus cinerascens), and gray flycatchers (Empidonax wrightii). Step-selection functions assessing resource selection and generalized additive models assessing step length, step velocity, and distance from nest showed no influence of noise and light pollution on fledgling movement, but did show that ash-throated flycatchers moved further each day and further from the nest than gray flycatchers. Our results also revealed the novel pattern of fledglings moving away from the nest through day 10 of the radio tracking period, but moving back towards it after day 20. While we did not find positive results for our primary question, these observations of fledgling movement are valuable given how little we know about this vulnerable life stage.
In chapter 2, we investigated whether dim light vision and its corresponding bony structures within the eye could be under selection with the proliferation of artificial light, given that variation in avian responses to light pollution was recently linked to the quality of a bird's dim light vision. We used museum specimens of six urban adapted species collected across 100+ years and light pollution proxies in the form of collection year and urban density to test two alternative hypotheses. Under the protection hypothesis, selection should drive evolution of poorer dim light vision with higher light pollution exposure, decreasing fitness cost borne via the hormone and circadian rhythm dysregulation associated with retinal-received light pollution. Under the temporal niche shift hypothesis, prolonged foraging opportunities made accessible to birds that can better detect light in artificially lit conditions should drive evolution of improved dim light vision with light pollution exposure. We found that dim light vision improved with collection year for great horned owls (Bubo virginianus) while the opposite was true for red-tailed hawks (Buteo jamaicensis); surprisingly, house sparrows (Passer domesticus) and American crows (Corvus brachyrhynchos) showed support for both hypotheses within single species, exhibiting different directionality in dim light vision patterns for different light pollution proxies. Our results suggest that light pollution may represent a contemporary selective agent for avian vision, but that the directionality may depend on ecological context. More broadly, our findings suggest that quantifying animal perceptual abilities may be important for understanding inter-specific responses to an increasingly bright world.
Available for download on Friday, October 11, 2024