Cavities shield birds from effects of artificial light at night on sleep

Anthropogenic noise and light pollution decrease the repeatability of activity patterns and dampen expression of chronotypes in a free-living songbird

Anthropogenic environmental change is introducing a suite of novel disturbance factors, which can have wide-ranging effects on mean behavior and behavioral repeatability. For example, exposure to sensory pollutants, such as anthropogenic noise and artificial light at night (ALAN), may affect consistent and repeatable individual-level timing of daily activity, which is referred to as chronotypes. Although chronotypes have been increasingly documented in wild animal populations and may affect fitness, evidence for long-term stability across life-history stages and seasons is notably lacking. Furthermore, how multiple anthropogenic stressors may interact to erode or magnify the expression of chronotypes remains unclear. We tested for existence of chronotypes across life-history stages and seasons in suburban female great tits (Parus major), using emergence time from nest boxes in the morning as a proxy for activity onset. We then examined joint effects of noise pollution and ALAN on expression of chronotypes, and tested for effects of noise, ALAN, and weather conditions on mean emergence time. We found repeatability of daily activity patterns (emergence times) across life-history stages and seasons, providing evidence of chronotypes, as well as interactive effects of anthropogenic disturbance factors and weather conditions on population mean behavior. Furthermore, across-season repeatability of emergence times was approximately double in magnitude in low light and low noise conditions, relative to in conditions with higher light and/or noise pollution. Thus, joint exposure to these sensory pollutants tends to erode expression of chronotypes. This effect was driven by higher among-individual variance in the relatively undisturbed environment and collapse of this variance in the more disturbed environments. Decreased repeatability in environments with high disturbance levels may reduce potential for behavioral traits, such as chronotype, to be the target of selection and limit adaptability.

Short-time exposure to light at night affects incubation patterns and correlates with subsequent body weight in great tits (Parus major)

Artificial light at night (ALAN) widely affects wildlife by blurring light-dark differences, including transitions such as sunrise and sunset, thereby affecting regulation of diel rhythms. As a result, activity onsets in many wild diurnal songbirds advance under ALAN. From chronobiological studies, it is known that the direction and strength of the response to light depends on when during the night exposure takes place. However, these experiments are mostly done under continuous light conditions, when animals have free-running rhythms. It remains unclear whether phase-dependence also holds in entrained, wild songbirds; i.e., does the effect of ALAN on activity patterns differ between exposure in the morning compared to the evening? This information is essential to assess the effects of mitigation measures by limiting ALAN to selected times of the night. We exposed incubating great tits (Parus major) inside the nest-box to 4 h of dim light, of which 1 h overlapped with dawn before sunrise or dusk after sunset. We found a small advancing effect of morning-light on activity onset and of evening-light on offset compared to dark controls but not vice versa. Breeding success and chick condition were unaffected by the light treatments. However, light-treated females had lower weights 9-18 days after the end of the treatment compared to the controls, independent of whether ALAN occurred in the morning or the evening, indicating possible costs of ALAN. Despite the weak behavioral response, ALAN might have affected the females' circadian clock or physiology resulting in lower body condition.

Experimental light at night explains differences in activity onset between urban and forest great tits

Artificial light at night (ALAN) is rapidly increasing and so is scientific interest in its ecological and evolutionary consequences. In wild species, ALAN can modify and disrupt biological rhythms. However, experimental proof of such effects of ALAN in the wild is still scarce. Here, we compared diel rhythms of incubation behaviour, inferred from temperature sensors, of female great tits (Parus major) breeding in urban and forest sites. In parallel, we simulated ALAN by mounting LED lights (1.8 lx) inside forest nest-boxes, to determine the potentially causal role of ALAN affecting diel patterns of incubation. Urban females had an earlier onset of activity compared to forest females. Experimentally ALAN-exposed forest females were similar to urban females in their advanced onset of activity, compared to unexposed forest birds. However, forest females exposed to experimental ALAN, but not urban females, were more restless at night than forest control females. Our findings demonstrate that ALAN can explain the early activity timing in incubating urban great tits, but its effects on sleep disturbance in the forest are not reflected in urban females. Consequently, future research needs to address potential effects of ALAN-induced timing on individual health, fitness and population dynamics, in particular in populations that were not previously affected by light pollution.

Quantifying the influence of urban biotic and abiotic environmental factors on great tit nestling physiology

There is a long history of avian studies investigating the impacts of urbanization. While differences in several life-history traits have been documented, either between urban and rural populations or across generalized urbanization gradients, a detailed understanding of which specific environmental variables cause these phenotypic differences is still lacking. Here, we quantified several local environmental variables coupled to urbanization (air pollution, tree composition, ambient temperature, and artificial light at night [ALAN]) within territories of breeding great tits (Parus major). We linked the environmental variables to physiological measures of the nestlings (circulating fatty acid composition [FA], antioxidant capacity and an oxidative damage marker [malondialdehyde; MDA]), to garner a mechanistic understanding of the impact of urbanization. We found that the antioxidant capacity of nestlings decreased with higher numbers of oak trees and levels of PM_2.5 (airborne particulate matter with a diameter < 2.5 μm). Furthermore, the ratio of ω6:ω3 polyunsaturated FAs, important for immune function, was positively correlated with PM_2.5 concentration, while being negatively associated with ambient temperature and number of non-native trees in the territory. Body mass and wing length both increased with the number of local oak trees. We also show, through a principal component analysis, that while the environmental variables fall into an urbanization gradient, this gradient is insufficient to explain the observed physiological responses. Therefore, accounting for individual environmental variables in parallel, and thus allowing for interactions between these, is crucial to fully understand the urban ecosystem.

Anthropogenic noise and light pollution additively affect sleep behaviour in free-living birds in sex- and season-dependent fashions

Rapid anthropogenic transformation of environments exposes organisms to diverse disturbance factors, including anthropogenic noise pollution and artificial light at night (ALAN). These sensory pollutants interfere with acquisition of, and response to, environmental cues and can be perceived as stressors. Noise pollution and ALAN are often experienced simultaneously, and are thus likely to jointly affect organisms, either additively or interactively. Yet, combined effects of noise pollution and ALAN remain poorly elucidated. We studied combined effects of noise pollution and ALAN on the sleep behaviour of a free-living songbird, the great tit (Parus major). Sleep is widely conserved across animal taxa and fulfils essential functions, and research has demonstrated independent effects of both noise and ALAN on sleep. We measured noise and light levels at nest boxes and used infrared video-recording to assess sleep behaviour. Results did not support interactive effects of noise and ALAN. However, noise pollution and ALAN were both independently related to variation in sleep behaviour, in sex- and season-dependent fashions. Males, but not females, woke up and left the nest box ∼20 min later in the noisiest as compared to quietest environments (range: 44.2-79.4 dB), perhaps because males are more sensitive to acoustical cues that are masked by noise. Furthermore, as the season progressed from November to early March, birds woke up and left the nest box ∼35 min earlier relative to sunrise on territories with the lowest, but not the highest, light levels (range: 0.01-8.5 lux). Thus, the seasonal difference in sleep duration was dampened on light polluted territories. These effects could arise if ALAN interferes with birds' ability to sense and respond to increasing daylength, and could have fitness ramifications. Our study suggests that noise pollution and ALAN exert additive effects on sleep behaviour, and that these effects can be sex- and season-dependent.

Intrinsic individual variation in daily activity onset and plastic responses on temporal but not spatial scales in female great tits

In a variety of species, individuals appear to be consistent in the daily timing of their activity onset. Such consistent among-individual differences can result from both intrinsic factors, as individuals may e.g. differ genetically, and extrinsic factors, as the environment may vary on spatial and temporal scales. However, previous studies typically did not differentiate between their respective contributions on individual variation in the timing of activities. Here, we repeatedly measured the onset of activity in female great tits (Parus major) on consecutive days during the egg laying phase of the breeding season in four consecutive years. Subsequently, we used a variance partitioning analysis in order to determine which part of the total variation could be attributed to intrinsic (female identity) and extrinsic (nest box identity) factors. Overall, 27% of the total variation could be attributed to female identity. In addition, we found temporal variation in the activity onset, indicating that individuals can plastically adjust their timing. Yet despite their general ability to change the timing of activities over time, spatial environmental factors did not contribute significantly to the observed variation. Individuals may choose a habitat that matches the preferred timing of activities, or might not benefit from adjusting their timing to environmental factors that might vary on spatial scales.

A Systematic Review for Establishing Relevant Environmental Parameters for Urban Lighting: Translating Research into Practice

The application of lighting technologies developed in the 20th century has increased the brightness and changed the spectral composition of nocturnal night-time habitats and night skies across urban, peri-urban, rural, and pristine landscapes, and subsequently, researchers have observed the disturbance of biological rhythms of flora and fauna. To reduce these impacts, it is essential to translate relevant knowledge about the potential adverse effects of artificial light at night (ALAN) from research into applicable urban lighting practice. Therefore, the aim of this paper is to identify and report, via a systematic review, the effects of exposure to different physical properties of artificial light sources on various organism groups, including plants, arthropods, insects, spiders, fish, amphibians, reptiles, birds, and non-human mammals (including bats, rodents, and primates). PRISMA 2020 guidelines were used to identify a total of 1417 studies from Web of Science and PubMed. In 216 studies, diverse behavioral and physiological responses were observed across taxa when organisms were exposed to ALAN. The studies showed that the responses were dependent on high illuminance levels, duration of light exposure, and unnatural color spectra at night and also highlighted where research gaps remain in the domains of ALAN research and urban lighting practice. To avoid misinterpretation, and to define a common language, key terminologies and definitions connected to natural and artificial light have been provided. Furthermore, the adverse impacts of ALAN urgently need to be better researched, understood, and managed for the development of future lighting guidelines and standards to optimize sustainable design applications that preserve night-time environment(s) and their inhabiting flora and fauna.

Effects of artificial light at night on the nest-site selection, reproductive success and behavior of a synanthropic bird

Understanding how artificial light at night (ALAN) impacts wildlife is increasingly important because more and more species are colonizing urban areas. As most of the bird studies on ALAN use controlled light set inside or around nest-boxes, the ecological effect of ALAN resulting from in situ streetlight on birds remains contentious. The barn swallow (Hirundo rustica) often builds open nests on buildings, which are directly exposed to varying intensity of ALAN, and thus provides a good system to examine the effect of in situ ALAN on birds. By examining the nest-site selection, reproductive success and behavior of barn swallows under various ALAN intensity in Taipei City, we found a positive effect of ALAN on their fledging success; nonetheless, such effect was only found in the swallows' first brood, but not second one. We also found that parent birds in the nests with higher ALAN intensity had higher feeding rates and more extended feeding time past sunset, which were likely stimulated by the increased begging behavior of their chicks. The night-feeding behavior might contribute to the increased fledging success, especially at the early breeding season. Interestingly, despite of the reproductive benefits obtained from ALAN, we found that the barn swallows did not select nest sites regarding ALAN intensity. The weak nest-site selection perhaps result from the complex life history interactions involving ALAN and/or confounding factors associated with ALAN in cities. This study improves our understanding of how urban birds, especially open-nesting ones, respond to in situ ALAN and provides useful information for developing urban conservation strategies.

Color of Artificial Light at Night Affects Incubation Behavior in the Great Tit, Parus major

Artificial light at night (ALAN) has been recognized as a biodiversity threat due to the drastic effects it can have on many organisms. In wild birds, artificial illumination alters many natural behaviors that are important for fitness, including chick provisioning. Although incubation is a key determinant of the early developmental environment, studies into the effects of ALAN on bird incubation behavior are lacking. We measured nest temperature in nest boxes of great tits during the incubation period in two consecutive years. Nest boxes were located in eight previously dark field sites that have been experimentally illuminated since 2012 with white, green, or red light, or were left dark. We tested if light treatment affected mean nest temperature, number of times birds leave the nest (off-bout frequency), and off-bout duration during the incubation period. Subsequently, we investigated if incubation behavior is related to fitness. We found that birds incubating in the white light during a cold, early spring had lower mean nest temperatures at the end of incubation, both during the day and during the night, compared to birds in the green light. Moreover, birds incubating in white light took fewer off-bouts, but off-bouts were on average longer. The opposite was true for birds breeding in the green light. Low incubation temperatures and few but long off-bouts can have severe consequences for developing embryos. In our study, eggs from birds that took on average few off-bouts needed more incubation days to hatch compared to eggs from birds that took many off-bouts. Nevertheless, we found no clear fitness effects of light treatment or incubation behavior on the number of hatchlings or hatchling weight. Our results add to the growing body of literature that shows that effects of ALAN can be subtle, can differ due to the spectral composition of light, and can be year-dependent. These subtle alterations of natural behaviors might not have severe fitness consequences in the short-term. However, in the long term they could add up, negatively affecting parent condition and survival as well as offspring recruitment, especially in urban environments where more environmental pollutants are present.

Variable and consistent traffic noise negatively affect the sleep behavior of a free-living songbird

Anthropogenic noise is a ubiquitous disturbance factor, which, owing to the extensive nature of transportation networks, and ability of sound waves to penetrate distances, has wide-reaching impacts on biological communities. Research effort on biological effects of anthropogenic noise is extensive, but has focused on waking behavior, and to our knowledge, no published experimental study exists on how noise affects sleep in free-living animals. Sleep plays vital functions in processes such as cellular repair and memory consolidation. Thus, understanding the potential for noise to disrupt sleep is a critical research objective. Whether different noise regimes exert distinct effects on behavior also remains poorly understood, as does intraspecific variation in noise sensitivity. To address these knowledge gaps, we used a repeated-measures field experiment involving broad-casting traffic noise recordings at great tit (Parus major) nest boxes over a series of consecutive nights. We evaluated whether increasing the temporal variability and amplitude of traffic noise increased deleterious effects on sleep behavior in free-living great tits, and whether individuals differed in the magnitude of responses. We found that traffic noise reduced sleep duration, proportion, and bout length, and induced birds to exit nest boxes earlier in the morning. There was some support for a stronger effect of more variable noise, and relative to lower amplitude noise, higher amplitude noise resulted in less and more fragmented sleep. Effects of noise on sleep duration were stronger in older adults, and substantial, repeatable variation existed in individual responses. We demonstrate for the first time that anthropogenic noise can have strong effects on sleep in free-living animals, which may have cascading effects on waking behavior, physiology and fitness. Results suggest that reducing the amplitude of traffic noise may be an effective mitigation strategy, and that differences in individual sensitivity are important to consider when evaluating effects of noise exposure. CAPSULE: Experimental exposure to temporally variable and consistent traffic noise negatively affected sleep behavior in a free-living songbird.

Light, Sleep and Performance in Diurnal Birds

Sleep has a multitude of benefits and is generally considered necessary for optimal performance. Disruption of sleep by extended photoperiods, moonlight and artificial light could therefore impair performance in humans and non-human animals alike. Here, we review the evidence for effects of light on sleep and subsequent performance in birds. There is accumulating evidence that exposure to natural and artificial sources of light regulates and suppresses sleep in diurnal birds. Sleep also benefits avian cognitive performance, including during early development. Nevertheless, multiple studies suggest that light can prolong wakefulness in birds without impairing performance. Although there is still limited research on this topic, these results raise intriguing questions about the adaptive value of sleep. Further research into the links between light, sleep and performance, including the underlying mechanisms and consequences for fitness, could shed new light on sleep evolution and urban ecology.

Working with Inadequate Tools: Legislative Shortcomings in Protection against Ecological Effects of Artificial Light at Night

The fundamental change in nocturnal landscapes due to the increasing use of artificial light at night (ALAN) is recognized as being detrimental to the environment and raises important regulatory questions as to whether and how it should be regulated based on the manifold risks to the environment. Here, we present the results of an analysis of the current legal obligations on ALAN in context with a systematic review of adverse effects. The legal analysis includes the relevant aspects of European and German environmental law, specifically nature conservation and immission control. The review represents the results of 303 studies indicating significant disturbances of organisms and landscapes. We discuss the conditions for prohibitions by environmental laws and whether protection gaps persist and, hence, whether specific legislation for light pollution is necessary. While protection is predominantly provided for species with special protection status that reveal avoidance behavior of artificially lit landscapes and associated habitat loss, adverse effects on species and landscapes without special protection status are often unaddressed by existing regulations. Legislative shortcomings are caused by difficulties in proving adverse effect on the population level, detecting lighting malpractice, and applying the law to ALAN-related situations. Measures to reduce ALAN-induced environmental impacts are highlighted. We discuss whether an obligation to implement such measures is favorable for environmental protection and how regulations can be implemented.

Proximity to roads, but not exposure to metal pollution, is associated with accelerated developmental telomere shortening in nestling great tits

Comprehensively understanding the factors affecting physiology and fitness in urban wildlife requires concurrently considering multiple stressors. To this end, we simultaneously assessed how metal pollution and proximity to roads affect body condition and telomere shortening between days 8 and 15 of age in nestling great tits (Parus major), a common urban bird. We employed a repeated-measures sampling design to compare telomere shortening and body condition between nestlings from four urban study sites south of Antwerp, Belgium, which are located at different distances from a metal pollution point source. In addition, we explored associations between metal exposure and telomere dynamics on the individual level by measuring blood concentrations of five metals/metalloids, of which lead, copper and zinc were present at concentrations above the limit of detection. To assess whether roadway-associated stressors (e.g. noise and air pollution) might affect nestling condition and telomere shortening, we measured the proximity of nest boxes to roads. Metal exposure was not associated with nestling telomere length or body condition, despite elevated blood lead concentrations close to the metal pollution source (mean ± SE = 0.270 ± 0.095 μg/g wet weight at the most polluted study site), suggesting that nestlings may have some capacity to detoxify metals. However, nestlings from nest boxes near roads exhibited more telomere shortening between days 8 and 15 of age, and shorter telomeres at day 15. Nestlings in poorer condition also had shorter telomeres, but proximity to the road was unrelated to body condition. Thus, nutritional stress is unlikely to mediate the relationship between proximity to roads and telomere length. Rather, proximity to roads could have affected telomere shortening by exposing nestlings to air or noise pollution. Our study highlights that traffic-related pollution, which is implicated in human health problems, might also affect urban wildlife.

Artificial light at night does not affect telomere shortening in a developing free-living songbird: A field experiment: Artificial light at night and telomere dynamics

Artificial light at night (ALAN) is an increasingly pervasive anthropogenic disturbance factor. ALAN can seriously disrupt physiological systems that follow circadian rhythms, and may be particularly influential early in life, when developmental trajectories are sensitive to stressful conditions. Using great tits (Parus major) as a model species, we experimentally examined how ALAN affects physiological stress in developing nestlings. We used a repeated-measure design to assess effects of ALAN on telomere shortening, body mass, tarsus length and body condition. Telomeres are repetitive nucleotide sequences that protect chromosomes from damage and malfunction. Early-life telomere shortening can be accelerated by environmental stressors, and has been linked to later-life declines in survival and reproduction. We also assayed nitric oxide, as an additional metric of physiological stress, and determined fledging success. Change in body condition between day 8 and 15 differed according to treatment. Nestlings exposed to ALAN displayed a trend towards a decline in condition, whereas control nestlings displayed a trend towards increased condition. This pattern was driven by a greater increase in tarsus length relative to mass in nestlings exposed to ALAN. Nestlings in poorer condition and nestlings that were smaller than their nest mates had shorter telomeres. However, exposure to ALAN was unrelated to telomere shortening, and also had no effect on nitric oxide concentrations or fledging success. Thus, exposure to ALAN may not have led to sufficient stress to induce telomere shortening. Indeed, plasticity in other physiological systems could allow nestlings to maintain telomere length despite moderate stress. Alternatively, the cascade of physiological and behavioral responses associated with light exposure may have no net effect on telomere dynamics.

Effects of the Urban Environment on Oxidative Stress in Early Life: Insights from a Cross-fostering Experiment

As urban areas expand rapidly worldwide, wildlife is exposed to a wide range of novel environmental stressors, such as increased air pollution and artificial light at night. Birds in highly polluted and/or urbanized habitats have been found to have increased antioxidant protection, which is likely important to avoid accumulation of oxidative damage, which can have negative fitness consequences. Yet, the current knowledge about the ontogeny of antioxidant protection in urban areas is limited; i.e., is the capacity to up-regulate the antioxidant defences already established during pre-natal development, or does it manifest itself during post-natal development? We cross-fostered great tit (Parus major) nestlings within and between urban and rural habitats, to determine if oxidative stress (measured as non-enzymatic total antioxidant capacity, superoxide dismutase (SOD), and plasma lipid peroxidation) is affected by habitat of origin and/or by habitat of rearing. The results demonstrate that being reared in the urban environment triggers an increase in SOD (an intracellular, enzymatic antioxidant) independent of natal habitat. Oxidative damage increased with hatching date in urban-reared nestlings, but there was little seasonal change in rural-reared nestlings. Total antioxidant capacity was neither affected by habitat of rearing or habitat of origin, but we observed a decline with hatching date in both rearing habitats. Taken together, our results support the growing evidence that the urban environment induces a direct plastic adjustment in antioxidant protection, but that up-regulation is not sufficient to avoid increased oxidative damage in late-hatched broods. Future studies should explore the underlying causes for this effect in late-hatched broods and whether it has any negative long-term implications, both at the individual- and the population level.