The effects of artificial light on bird movement and distribution
Creators: Adams, Caroline Ann
Publisher: name: University of Alberta Library
Year: 2023

<p>Artificial light is one of the fastest growing pollutants worldwide and conveys biological effects from molecular to ecosystem levels on many taxa, including birds. Birds flying at night sometimes collide with illuminated structures, but artificial light can have other effects that are less lethal or even beneficial for birds. I created a systematic map of the evidence that artificial light affects bird movement and distribution. I located evidence through a systematic search and I built a database of studies with metadata about their populations, interventions/exposures, comparators, and outcomes. I identified relevant evidence for four secondary topics: aggregation and mortality during flight, attraction and disorientation as mechanisms for these aggregations, efficacy of light-based deterrents, and habitat selection when not in flight. The search produced 490 studies. I found relevant evidence for each of my secondary topics, though evidence of bird attraction and disorientation was lacking. My database of these studies and their metadata could support several subsequent reviews of research and management questions by others. I identified a particular need for experiments using light sources similar to those that birds encounter in built environments.<br>
I explored species-specific effects of artificial light with two field studies that targeted species in the nightjar (Caprimulgidae) family. These insectivorous birds forage at low light levels. Nightjars may benefit from foraging on insects aggregating at light sources, but may experience higher predation risk if artificial light makes their camouflaged ground nests more visible. I tested these hypotheses using data from the Canadian Nightjar Survey in British Columbia. I modeled the association between artificial light and the relative abundance of Common Nighthawks (Chordeiles minor) and Common Poorwills (Phalaenoptilus nuttallii). The relative abundance of extra-territorial Common Nighthawks, which are likely to be foraging, showed a positive association with artificial light only at low levels of urban land cover. Relative abundance of territorial Common Nighthawks and of Common Poorwills, which nest and foraging within their territories, were both negatively associated with artificial light. These results suggest that Common Nighthawks may benefit from foraging on insects at artificial lights, but only in areas with very little urban development. Breeding nightjars may experience disadvantages in lit environments, perhaps through greater predation at their nests.<br>
A final component of my dissertation was to assess subtle behavioural changes associated with artificial light, which may affect temporal patterns of habitat use across the daily light cycle with effects that differ by latitude. I studied the effects of artificial light on both spatial and temporal habitat use by Common Nighthawks and compared these effects in a northern and southern region of Alberta. I collected acoustic recordings in the southern Grassland region and northern Boreal region and I measured spatial intensity of territorial and extra-territorial habitat use. At sites where I detected Common Nighthawks, I tested for differences in daily patterns of vocal activity between lit and unlit sites. I found a negative association with artificial light for intensity of both territorial and extra-territorial spatial habitat use in the Grassland region and no association in the Boreal region. I found no effect of artificial light on temporal patterns of habitat use. Artificial light may be more likely to affect spatial habitat use by crepuscular birds at lower latitudes where natural illumination is lower during the breeding season. Artificial light does not appear to affect circadian rhythms or extend foraging activity for Common Nighthawks in my study areas.<br>
Taken together, the results of my dissertation increased the available information about the effects of artificial light on birds. The evidence in my systematic map showed diverse and widespread effects of artificial light on bird movement and distribution that are difficult to generalize among species, contexts, and locations. Some topics have enough evidence for quantitative analyses and my systematic map can provide evidence relevant to particular contexts using metadata searches. My research on nightjars showed effects that differed across urban land cover, behavioural context, and region. My research suggests that artificial light is unlikely to provide widespread foraging benefits for these species, and negative effects may be greater at southern latitudes. Both systematic reviews and further taxa-specific research are needed to support broader generalizations about biological consequences and potential mitigation of artificial light for birds.</p>