Broad spectrum artificial light at night increases the conspicuousness of camouflaged prey

Threatened chronotopes: can chronobiology help endangered species?

Pittendrigh and Daan's 1976 article "Pacemaker structure: A clock for all seasons" marks the foundation of modern seasonal chronobiology. It proposed the internal coincidence model comprised of a Morning (M) and Evening (E) oscillator, which are coupled but synchronized separately by dawn and dusk. It has become an attractive model to explain the seasonal adaptation of circadian rhythms. Using the example of the European hamster, this article connects the classical entrainment concept to species decline and, ultimately, conservation concepts. Seasonality of this species is well studied and circannual rhythms have been described in at least 32 parameters. The European hamster is listed as critically endangered on the International Union for Conservation of Nature (IUCN) red list. Changes in the temporal structure of the environment (the chronotope) caused by climate change and light pollution might be responsible for the global decline. The article shows that classical chronobiological concepts such as the internal coincidence model (Pittendrigh and Daan Pittendrigh and Daan, J Comp Physiol [a] 106:333-355, 1976) are helpful to understand the (chronobiological) causes of the decline and can potentially support species conservation. Knowing the species' physiological limitations as well as its adaptation capacities can potentially prevent its extinction at a time when classical conservation concepts have reached their limits.

Behaviour and landscape contexts determine the effects of artificial light on two crepuscular bird species

Context

Artificial light at night (ALAN) is increasing worldwide, with many ecological effects. Aerial insectivores may benefit from foraging on insects congregating at light sources. However, ALAN could negatively impact them by increasing nest visibility and predation risk, especially for ground-nesting species like nightjars (Caprimulgidae).

Objectives

We tested predictions based on these two alternative hypotheses, potential foraging benefits vs potential predation costs of ALAN, for two nightjar species in British Columbia: Common Nighthawks (Chordeiles minor) and Common Poorwills (Phalaenoptilus nuttallii).

Methods

We modeled the relationship between ALAN and relative abundance using count data from the Canadian Nightjar Survey. We distinguished territorial from extra-territorial Common Nighthawks based on their wingboom behaviour.

Results

We found limited support for the foraging benefit hypothesis: there was an increase in relative abundance of extra-territorial Common Nighthawks in areas with higher ALAN but only in areas with little to no urban land cover. Common Nighthawks' association with ALAN became negative in areas with 18% or more urban land cover. We found support for the nest predation hypothesis: the were strong negative associations with ALAN for both Common Poorwills and territorial Common Nighthawks.

Conclusions

The positive effects of ALAN on foraging nightjars may be limited to species that can forage outside their nesting territory and to non-urban areas, while the negative effects of ALAN on nesting nightjars may persist across species and landscape contexts. Reducing light pollution in breeding habitat may be important for nightjars and other bird species that nest on the ground.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10980-024-01875-3.

Evaluating the interactive effects of artificial light at night and background color on tadpole crypsis, background adaptation efficacy, and growth

Artificial light at night (ALAN) is a global pollutant of rising concern. While alterations to natural day-night cycles caused by ALAN can affect a variety of traits, the broader fitness and ecological implications of these ALAN-induced shifts remain unclear. This study evaluated the interactive effects of ALAN and background color on traits that have important implications for predator-prey interactions and fitness: crypsis, background adaptation efficacy, and growth. Using three amphibian species as our models, we discovered that: (1) Exposure to ALAN reduced the ability for some species to match their backgrounds (background adaptation efficacy), (2) Crypsis and background adaptation efficacy were enhanced when tadpoles were exposed to dark backgrounds only, emphasizing the importance of environmental context when evaluating the effects of ALAN, (3) ALAN and background color have a combined effect on a common metric of fitness (growth), and (4) Effects of ALAN were not generalizable across amphibian species, supporting calls for more studies that utilize a diversity of species. Notably, to our knowledge, we found the first evidence that ALAN can diminish background adaptation efficacy in an amphibian species (American toad tadpoles). Collectively, our study joins others in highlighting the complex effects of ALAN on wildlife and underscores the challenges of generalizing ALAN's effect across species, emphasizing the need for a greater diversity of species and approaches used in ALAN research.

Artificial light at night may decrease predation risk for terrestrial insects

Artificial light at night (ALAN) is thought to be detrimental for terrestrial insect populations. While there exists evidence for lower abundance under ALAN, underlying mechanisms remain unclear. One mechanism by which ALAN may contribute to insect declines may be through facilitating increased predation. We investigated this by experimentally manipulating insect-substitute abundance under differential levels of light. We used insect-containing birdfeed placed at varying distances from streetlights as a proxy for terrestrial insects, inspecting the rate of predation before and after dusk (when streetlights are, respectively, off and on). We found that there was a significantly greater effect of increasing distance on predation after dusk, suggesting that predation was actually reduced by greater levels of artificial light. This may occur because ALAN also increases the vulnerability of insectivores to their own predators. Implications for foraging behaviour and alternative explanations are discussed.

Casting a light on the shoreline: The influence of light pollution on intertidal settings

Light pollution is becoming prevalent among other coastal stressors, particularly along intertidal habitats, arguably the most exposed to anthropogenic light sources. As the number of light pollution studies on sandy beaches, rocky shores and other intertidal habitats raises, commonalities, research gaps and venues can be identified. Hence, the influence of light pollution on the behavior and ecology of a variety of intertidal macro-invertebrates and vertebrates are outlined by examining 54 published studies. To date, a large majority of the reported effects of light pollution are negative, as expected from the analysis of many species with circadian rhythms or nocturnal habits, although the severity of those effects ranges widely. Experimental approaches are well represented throughout but methodological limitations in measurement units and standardization continue to limit the proposal of general conclusions across species and habitats. In addition, studies targeting community variables and the explicit influence of skyglow are heavily underrepresented. Likewise, studies addressing the interaction between light pollution and other natural and anthropogenic stressors are critically needed and represent a key venue of research. The nature of those interactions (synergistic, additive, antagonistic) will likely dictate the impact and management of light pollution in the decades ahead.