![]() These changes are concerning for both individual and population health of wildlife species, especially when considering that recent advances in more efficient lighting technology have enabled municipalities to rapidly switch to light-emitting diodes (LEDs) and deploy more lights: over the last decade ALAN has increased at an annual rate of approximately 2% worldwide ( Kyba et al. 2018), and serve as an endocrine disruptor across wildlife taxa (e.g., reduced melatonin production Russart and Nelson 2018). 2017), alter flight patterns and the use of stopover sites in nocturnally migrating birds ( McLaren et al. For example, ALAN can reduce plant visits by nocturnal pollinators ( Knop et al. ALAN can disrupt the synchrony between behavioral and physiological processes, including the daily and seasonal light and dark cycles across taxa. To date, evidence suggests that the impacts of ALAN may be significant across wildlife taxa ( Rich and Longcore 2013). Much recent research has been done to better understand the effects of light pollution on wildlife. 2016), with even rural areas exposed to lights from agricultural and industrial buildings ( Bennie et al. Indeed, 88% of the land area in Europe and almost half of the land area in the USA experience ALAN ( Falchi et al. Light pollution is relatively novel and not isolated to urban areas: animals living in otherwise undisturbed habitats may be exposed to artificial light at night (hereafter “ALAN”). Humans have altered the majority of the Earth’s surface through abiotic changes, such as increased light pollution ( Grimm et al. Exposure regimes for free-living birds, such as exposure to a combination of anthropogenic disturbances (i.e., ALAN and noise pollution) or direct and indirect effects of ALAN (i.e., effects on physiology due to direct light exposure and alterations in food availability), may produce different results than those found here. Therefore, while it is possible that the behavioral and physiological changes found here result in long-term consequences, our results also suggest that direct ALAN exposure alone may not have substantially large or negative effects on tree swallows. Finally, we found some support for a negative effect of ALAN on the likelihood that all eggs hatched in a given nest, but not the likelihood that all nestlings fledged. We found no support for our prediction that ALAN would reduce nestling body condition. ALAN-exposed nestlings also showed greater negative feedback of circulating corticosterone. ![]() Although relatively weak, our results also suggested that ALAN-exposed nestlings had reduced baseline and increased stress-induced corticosterone compared with control nestlings. Our results showed that ALAN-exposed females provisioned their nestlings at lower rates than control females. We then measured the effects of ALAN compared with control conditions on parental behavior (provisioning rate), nestling physiology (corticosterone levels), and reproductive success (likelihood of all eggs hatching and all nestlings fledging per nest). Here, we experimentally exposed adult female and nestling tree swallows ( Tachycineta bicolor) to ALAN. However, ALAN may alter energy expenditure and/or stress physiology during the breeding period, potentially reducing reproductive success and resulting in conservation implications. To date, there have been few studies that assess the impacts of ALAN on both wildlife behavior and physiology. ![]() Artificial light at night (hereafter “ALAN”) affects 88% of the land area in Europe and almost half of the land area in the USA, with even rural areas exposed to lights from agricultural and industrial buildings. ![]()
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