Editorial Feature

How Does Light Pollution Affect Birds?

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Jun 15 2022Reviewed by Laura Thomson

Artificial light at night (ALAN) has become a worldwide concern, with the American Medical Association declaring it a form of pollution. Birds’ daily physiology and behavior are disrupted by ALAN exposure, and nighttime melatonin synthesis is suppressed. This article will summarize a recent study published in the journal Birds looking at this further within songbirds.

earth at night, light pollution

Image Credit: NicoElNino/Shutterstock.com

In both birds and mammals, ALAN exposure has been linked to major ecological and physiological implications, including impairment of immunological, metabolic, reproductive, and cognitive processes.

The presence of ALAN disrupts the natural habitat, with bright intensity of light close to the light source and low intensity of light at long distances at night. Evidence shows that both no-night (24-hour constant light, LL) and dLAN (dim light at night) have comparable effects in laboratory experiments.

ALAN has negative impacts on various territorial behaviors in wild birds, including reproduction, singing, migration, and sleep. ALAN (LL and dLAN) also has detrimental impacts on learning, memory, mood, and exploration in multiple laboratory investigations.

Melatonin and epigenetic alterations may have a role in ALAN-induced reactions, according to the findings. The underlying mechanism(s) are generic and applicable to a wide range of species; nevertheless, for a better understanding of the issue, the study concentrated on bird species and addressed the relevance of the avian system.

Methodology

Google Scholar was used to find research publications and reports from 2006 to 2021. The search keywords “light at night + sleep + cognition + brain function,” as well as terms and phrases linked with “neuron,” such as “light at night + neurogenesis” or “light at night + sleep + cognition + brain function + neurotransmitter,” were utilized.

Adding the phrases “light at night + sleep + cognition + neuron + melatonin + birds” to the search criteria resulted in the discovery of 3420 publications and papers. The abstracts or full texts of these publications were analyzed to find articles or reports from research on bird species.

Papers that offered no new evidence linked to avian behavioral changes under illumination at night or merely presented viewpoints or opinions were excluded.

Results

House Crows subjected to dLAN exhibited depressive-like behaviors such as lower feeding and grooming, as well as increased feather-picking and self-mutilation consistent with sleep deprivation, according to research. dLAN also decreased neurogenesis in the hippocampus and impacted the expression of numerous genes.

In rodents, sleep deprivation is linked to memory loss, impaired attention and decision-making, and mood abnormalities. ALAN-induced sleep impairments and cognitive dysfunctions in House Crows and Zebra Finches have been seen in birds.

Peafowl (Pavo cristatus) and Great Tits exposed to ALAN, on the other hand, demonstrated sleep disturbance but no cognitive impairment. ALAN-induced depressed behavior was seen in nocturnal mice in a few trials, although there were no effects on sleep following ALAN administration.

Table 1 summarizes the findings of current research on several bird species. The extent of the link between sleep and cognitive functioning, on the other hand, is unknown, and further study is needed. However, as previously mentioned, the effects of ALAN on brain functioning may also be mediated through the hormonal system.

Table 1. Summary of the results from recent studies in different avian species highlighting the effects of light at night on behavioral phenotypes and the molecular correlates. Source: Taufique, 2022

Species	Light Environment	Affected Behavioural Phenotype	Molecular Correlates	Study
American Robins (Turdus migratorius)	ALAN	Advances the morning chorus into the night		Miller [23]
European Robin (Erithacus rubecula) Eurasian Blackbird (Turdus merula) Song Thrush (Turdus philomelos) Great Tits (Parus major) Blue Tits (Cyanistes caeruleus) Common Chaffinch (Fringilla coelebs)	dLAN	Alters the phenology of dawn and dusk singing (Earlier in the year than before)		Da Silva et al. [8]
Blackbirds	dLAN (~0.3 lux)	Early-onset of activity and night restlessness		Dominoni and Partecke [22]
Blackbirds	dLAN (~0.3 lux)	Increase in pre-dawn activity	Decreased nocturnal melatonin levels	Dominoni et al. [54]
Blackbirds	dLAN (~0.3 lux)	Advances seasonal testicular growth.		Dominoni et al. [55]
Great Tits	dLAN (~ 1.6 lux)	Sleep deficits		Raap et al. [10]
Great Tits	Different doses of dLAN (~0.05, 0.15, 0.5, 1.5 or 5 lux)	Dose-dependent increase in nocturnal activity	Dose-dependent reduction in nocturnal melatonin levels	deJong et al. [23]
Great Tits	dLAN (~8 lux) of different wavelength	Increase in nocturnal activity Sleep deficits	Decreased plasma oxalic acid Reduced telomere length (cellular aging)	Ouyang et al. [11]
Great Tits	dLAN (~0.1, 0.5, 1.5 and 5 lux)	Advanced wake-up time	Shift in bmal1 expression Shift in metabolite expressions Desynchronization of metabolic and immune genes	Dominoni et al. [25]
Blue Tits (Cyanistes caeruleus)	dLAN (2 lux)		Affects feather glucocorticoid levels	Dominoni et al. [56]
Indian Peafowl (Pavo cristatus)	dLAN (~0.75 lux)	Increased nocturnal vigilance Sleep loss		Yorzinski et al. [33]
European Nightjars (Caprimulgus europaeus)	dLAN	Increased foraging opportunity Changes in habitat selection		Sierro and Erhardt [15]
Burrowing Owl (Athene cunicularia)	dLAN	Increased foraging opportunity Nest habitat selection near light source		Rodríguez et al. [16]
House Crow (Corvus splendens)	LL (~150 lux)	Activity rhythm disruption Learning and memory deficits	Reduced neuronal activity in HP and NC Decreased expression of tyrosine hydroxylase in the mid-brain	Taufique and Kumar [17]
House Crow	LL (~150 lux)	Learning and memory deficits	Decreased neurogenesis and dendritic complexity in HP and NC	Taufique et al. [36]
House Crow	dLAN (~6 lux)	Increase in nocturnal activity Sleep deprivation Depressive-like	Decreased expression of BDNF, IL1β, TNFR1, NR4A2 in HPs Increased HDAC4 expression and histone H3 acetylation of BDNF gene in HP Decreased neurogenesis in HP Decreased levels of nocturnal melatonin	Taufique et al. [18] * Behavioural phenotypes were rescued by elimination of dLAN
House Crow	LL (~150 lux) and dLAN (~6 lux)		Decreased neuronal soma size Reduced glia–neuron ratio	Taufique et al. [42]
Zebra Finch (Taeniopygia guttata)	LL (~5 lux)	Disturbed activity rhythm Learning deficits		Jha and Kumar [19]
Zebra Finch (male)	LL (~150 lux)	Disrupted activity and singing behavior (30% of individuals) Decline in song quality, reduced amplitude and song production	Loss of rhythm in the expression of clock genes in the hypothalamus	Prabhat et al. [27]
Zebra Finch (female)	LL (~150 lux)	Fattening, weight gain, and lipid accumulation in the liver	Loss of rhythm in the expression of clock genes in the hypothalamus and peripheral tissues	Prabhat et al. [28]
Zebra Finch	LL (~400 lux) and dLAN (~3 lux)		Loss of melatonin and corticosterone diurnal pattern Altered diurnal pattern of cytokines in the brain	Mishra et al. [31]
Zebra Finch	dLAN (~5 lux)	Induced night-time feeding and perch-hopping Sleep deprivation Learning and memory deficits Increased neophobia		Prabhat et al. [37]
Zebra Finch	dLAN (~5 lux)	Sleep deficits	Decreased plasma oxalate levels Decreased tlr4, il-b, nos gene expression, and attenuated achm3 mRNA levels Changes in gene expression of Ca²⁺ dependent sleep-inducing pathway	Batra et al. [26]
Zebra Finch	dLAN (~5 lux)	Increased night-time activity Nocturnal feeding Body fattening and weight gain	Increased levels of plasma glucose Decreased levels of thyroxine and triglycerides Altered metabolic genes expression (sirt1, g6pc, and foxo1)	Batra et al. [29]
Zebra Finch	LL (~150 lux) and dLAN (~5 lux)	Body fattening and weight gain Hepatic lipid accumulation	Changes in gut microbiome with a decline in Lactobacillus richness	Malik et al. [30] * Phenotype was rescued by Lactobacillus supplement
Zebra Finch	dLAN		Increased neuronal recruitment reduced neuronal density in the hippocampus Decreased nocturnal melatonin levels	Moaraf et al. [40,41]
Domestic Pigeons (Columba livia domestica) and Australian Magpies (Cracticus tibicen tyrannica)	dLAN (~9.6 and 18.89)	Reduced sleep duration and fragmentation Slow-wave activity during non-REM sleep Reduced REM sleep		Aulsebrook et al. [34]

Melatonin, which is generated by the pineal gland and released into the third ventricle, is involved in a variety of biological activities and communicates ambient light-dark information to the brain. Melatonin modulates memory and cognition via the MT1 and MT2 receptors.

Melatonin is generated in both nocturnal and diurnal animals during the dark period of the night. However, mice strains from the laboratory have no discernible melatonin rhythms. Melatonin synthesis is suppressed in diurnal species, including humans, when they are exposed to low-intensity light.

dLAN circumstances have been shown to decrease melatonin and impact neurogenesis in diurnal birds, according to publications. Tree Sparrows from urban areas have been shown to have lower plasma melatonin levels than those from rural areas. The findings showed that in urban Tree Sparrows, expression of the Aanat, Mel1, and Mel2 genes in the pineal is altered.

The control of different processes, including brain functioning and mental health, is aided by epigenetic alterations of gene expression. Melatonin has been reported to affect epigenetic medicines and gene expressions, suggesting that it might play a key function in epigenetic control.

Conclusion

The extensive use of electrical lighting, as well as the resulting light pollution, is affecting the temporal arrangement of biological activity in animals, such as sleep and cognitive functioning.

Considering the evidence linking disturbed circadian processes to poor cognitive function, ALAN might be contributing to learning and memory problems as well as depression in people via a variety of circadian controlled pathways, as illustrated in Figure 1.

Figure 1. Schematic depicting effect of ALAN exposure, acting on different levels of organization (affecters) via a number of neuronal pathways (mechanisms), those resulting in a series of adverse effects on brain functions (affected functions). This model may help us to understand the complexity of the relationships among exposure components in a systematic manner and may help in assessing the impact on brain functions of ALAN exposure outcomes and their underlying mechanisms (red and green arrows indicate decreased and increased functions, respectively). BDNF: Brain-derived neurotropic factor. Image Credit: Taufique, 2022

Melatonin may serve as a connection between environmental disturbance of biological cycles and epigenetic changes in genes involved in brain function control.

Zebra Finches would be a good model for these objectives since they reproduce in labs and have been utilized in numerous researches to better understand avian biology, despite being an oddity among passerine birds.

Zebra finch. Image Credit: Wang LiQiang/Shutterstock.com

Despite the substantial prevalence of artificial light at night across the world, it is critical to understand the impacts of ALAN on bird physiologies and behaviors, as well as to identify a safe distance from light sources to reduce the concerns.

Due to the small number of research that has been undertaken, which is also confined to a few species and/or short-term trials, determining the influence on a population is challenging. Understanding the long-term processes that alter communities and ecosystems is crucial to predicting the ecological implications of LAN.

It is also crucial to set out repeatable field and laboratory trials to see how LAN affects populations, communities, and ecosystems.

Consequently, it is critical to focus current research on effective mitigation measures to balance the human demand for illumination in society with the needs of other animals for darkness.

Small but significant global conservation efforts, such as the Fatal Light Awareness Program (FLAP) in Canada and the Lights Out Program by the Audubon Society in the United States, could help manage the negative effects of LAN by advocating the importance of darker nights. Curbing light pollution and limiting the problem can be beneficial for all species worldwide.

The majority of the information on the negative effects of LAN on cognitive functioning comes from nocturnal rodent research, with a few from diurnal species, as previously indicated.

Additional research on diurnal species, such as birds, should be conducted to better duplicate human exposure and its effects, as well as to clarify the mechanism(s) through which LAN exposures result in deleterious outcomes.

Journal Reference

Taufique, S. K. T. (2022) Artificial Light at Night, Higher Brain Functions and Associated Neuronal Changes: An Avian Perspective. Birds, 3(1), pp. 38–50 Available Online: https://www.mdpi.com/2673-6004/3/1/3/htm

References and Further Reading

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Lights Out Program, Audubon Society, USA. Available online: https://www.audubon.org/about .