Artificial Light at Night Impacts Bird Migration and Breeding Cycles
“Light is one of the primary environmental cues birds use to regulate seasonal biology, and artificial light at night can scramble those signals with cascading consequences. ALAN triggers hormonal cascades through the hypothalamic-pituitary-gonadal axis earlier than natural conditions warrant, advancing gonadal development and the onset of breeding. Dominoni et al. (2013) found that individual-level light intensity measurements revealed significant disruptions to the daily rhythms of urban-dwelling songbirds, with birds in brighter environments showing earlier and more fragmented activity patterns. At the individual level, even low levels of nighttime illumination produce fragmented sleep, reduced melatonin secretion, and altered dawn activity timing—with downstream effects on immune function and cognitive performance. Da Silva et al. (2015) documented these timing shifts across multiple common European songbird species, suggesting the effects are widespread rather than limited to a few sensitive taxa. Migratory songbirds face acute risks from ALAN during their biannual journeys. Many species navigate at night using stars and Earth's magnetic field, and bright structures can disorient migrants until they collide or become exhausted. Smith et al. (2020) demonstrated that pre-migration exposure to artificial light advances spring departure dates in a trans-hemispheric migratory songbird, decoupling arrival timing from peak food availability at breeding grounds. Birds departing too early may encounter adverse weather or food-scarce stopover sites, arriving at breeding grounds in compromised condition. The cumulative disruption of ALAN across the full annual cycle—affecting wintering biology, migration timing, and breeding phenology—represents a significant and underappreciated threat to migratory songbird populations.”
Summary
Artificial light at night disrupts
Sources 56 searched
- Artificial light at night is a top predictor of bird migration stopover density | Nature Communications
As billions of nocturnal avian migrants traverse North America, twice a year they must contend with landscape changes driven by natural and anthropogenic forces, including the rapid growth of the artificial glow of the night sky.
- Light pollution is greatest within migration passage areas for nocturnally-migrating birds around the world | Scientific Reports
Excessive or misdirected artificial light at night (ALAN) produces light pollution that influences several aspects of the biology and ecology of birds, including disruption of circadian rhythms and disorientation during flight.
- High-intensity urban light installation dramatically alters nocturnal bird migration - PMC
ALAN may affect a diverse array of nocturnally active animals, and recent studies have highlighted the need for primary research into these potential impacts (2, 3). The biological effects of anthropogenic light pollution may be especially significant for nocturnally migrating birds (2–6). ...
- Endocrine–circadian interactions in birds: implications when nights are no longer dark - PMC
On an annual time scale, ALAN effects on time patterns of reproductive hormones and other reproductive features have been shown in correlational field studies and in experimental laboratory studies [18,126,127]. Overall, these physiological effects aligned well with the observation of advanced ...
- Exposure to artificial light at night accelerates but does not override latitude-dependent seasonal reproductive response in a North American songbird - ScienceDirect
To explore daily variation in circulating T levels, we measured day and night testosterone. Considering the ALAN impact on the daily clock, we predicted that day and night TGnRH levels would differ in comparison to birds exposed to dark nights.
- The effects of light pollution on migratory animal behavior - ScienceDirect
Light pollution acts as an attractant, and in some instances as a repellent, that can negatively affect wildlife migration by disrupting, disorienting, and at times reshaping the timing of their journey – this disruption occurs across multiple spatial scales. For this reason we examine the effects of light pollution on migration at the local, regional, and macroscales (Figure 1). It may seem obvious to focus on nocturnal migratory species when exploring the impacts of ecological light pollution, but recent evidence suggests this may underestimate the growing effects of light pollution.
- Endocrine-circadian interactions in birds: implications when nights are no longer dark - PubMed
Several studies suggest that melatonin is likely a key mediator for a broad range of effects. We encourage further observational and experimental studies of ALAN impact on melatonin, across the full functional range of this versatile signalling molecule, as well as on other candidate compounds at the endocrine-circadian interface.
- Threats to Birds: Collisions (Nighttime Lighting) | U.S. Fish & Wildlife Service
Limit lighting to necessary times only. Birds begin migrating overnight from dusk until dawn and are vulnerable to the negative effects of lighting throughout the night.
- Dim the Lights for Birds at Night! | U.S. Fish & Wildlife Service
As we all know, Florida will have a different peak migration timeframe than Montana, so please use the map in your planning process! Of course, local weather events and other factors might impact the specific dates of peak bird migration, and you can take that into account during your decision-making process of when will work best for you to turn the lights off. ... This map from BirdCast shows the estimated peak migration dates for the lower 48 states. This map is based on this published research: Horton, K.G., Nilsson, C., Van Doren, B.M., La Sorte, F.A., Dokter, A.M.
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