Migration in the Spotlight: A Comparative Investigation of Behavioural and Energetic Responses to Artificial Light at Night in Nocturnal Migrant and Nonmigrant Songbirds
Artificial light at night (ALAN) is a rapidly growing pollutant as it is currently outpacing the growth of its leading cause, urbanization. Varying levels of light pollution can generate a wide range of responses including physiological or behavioural changes reported in a growing number of species. Nocturnal migratory songbirds may be particularly vulnerable given their long-distance migration, which increases their exposure risk to ALAN during a potentially sensitive window. I hypothesized that increasing levels of ALAN may alter migratory behaviour and energetics of foraging and flight activity in both nocturnal migrant and to a lesser extent in nonmigrant birds. Here, I used a captive experimental study design across three seasons to compare the activity, behaviour, and energetics of two nocturnal migrant species, Gambel’s white-crowned (Zonotrichia leucophrys gambelli) and White-throated sparrows (Z. albicolis), and a nonmigrant species, the House sparrow (Passer domesticus). Birds were video recorded in captive trials conducted in spring, summer, and autumn seasons, testing a range of ALAN intensities (0.15, 0.5, 1.5 and 10 lux) relative to a dark control treatment (< 0.01 lux). ALAN had little impact on house sparrow activity which remained largely dormant at night. In migratory sparrows, I found an increase in nocturnal activity in response to increasing ALAN along with changes in observed patterns of migratory-specific restlessness behaviours (beak up and beak up flight). Migrants had a threshold response in migratory behaviours, where increasing light intensity stimulated migratory behaviour, but the highest intensity diminished it, suggesting 10 lux may be a threshold for behavioural compensation. Additionally, all birds gained mass in all seasons following ALAN exposure, except the migrants at the highest light intensity. Despite an increase in migratory activity and positive relationship between activity and overall energy expenditure measured using respirometry, neither nocturnal metabolic rate nor food consumption appeared affected by ALAN, though this may be due to low sample size. Diurnal behavioural changes or physiological compensation could also be an energy saving technique when exposed to ALAN. I speculate that ALAN may alter the circadian mechanisms that control seasonally appropriate nocturnal and diurnal behavioural patterns, and possibly reflects an acute stress response, producing the observed effects. ALAN-induced changes in behaviour and energetics of migratory species may have unknown consequences on migration success, survival, and fitness in the wild.
ALAN, Nocturnal migrant, Activity, Migratory behaviour, Metabolism
Master of Science (M.Sc.)