Night skies through animals' eyes-Quantifying night-time visual scenes and light pollution as viewed by animals

Skyglow facilitates prey detection in a crepuscular insectivore: Distant light sources create bright skies

Light profoundly shapes ecosystems, influencing the behaviour and niche specialisation of many species. This is especially true for visual predators, particularly crepuscular and nocturnal animals, whose foraging depends on adequate illumination. Despite this, research on how animals perceive light sources and position themselves relative to these sources is scarce. Using a modified dead-reckoning protocol based on GPS, accelerometer, and magnetic compass data, we investigated the body orientation of foraging European Nightjars (Caprimulgus europaeus, hereafter nightjar) to determine their line of sight relative to bright sections of the nocturnal sky, created by natural or artificial light. We found that nightjars are more likely to align themselves with brighter sections of the sky, although not necessarily with the brightest patch. On full moon nights, they positioned the moon within their line of sight when it was low on the horizon, but this likelihood decreased as the moon rose higher. During other moon phases, the likelihood of having the moon within line of sight increased linearly with moon altitude. During moonless parts of the night, nightjars appeared to use skyglow as a background for prey detection, but only when it was sufficiently bright. When both moonlight and skyglow were present, nightjars showed a preference for moonlight. This study shows that European Nightjars use illuminated sections of the sky, including skyglow, as bright backgrounds to detect flying prey. This suggests that, in the absence of the moon, nightjars can actively take advantage of this form of light pollution while foraging. However, the success of their hunting under skyglow-induced lighting remains unclear. We hypothesise that the effectiveness of these backgrounds depends on their brightness and colour composition. Further research is needed to better understand the complex dynamics of contrast detection under varying lighting conditions.

A hyperspectral open-source imager (HOSI)

BACKGROUND

The spatial and spectral properties of the light environment underpin many aspects of animal behaviour, ecology and evolution, and quantifying this information is crucial in fields ranging from optical physics, agriculture/plant sciences, human psychophysics, food science, architecture and materials sciences. The escalating threat of artificial light at night (ALAN) presents unique challenges for measuring the visual impact of light pollution, requiring measurement at low light levels across the human-visible and ultraviolet ranges, across all viewing angles, and often with high within-scene contrast.

RESULTS

Here, I present a hyperspectral open-source imager (HOSI), an innovative and low-cost solution for collecting full-field hyperspectral data. The system uses a Hamamatsu C12880MA micro spectrometer to take single-point measurements, together with a motorised gimbal for spatial control. The hardware uses off-the-shelf components and 3D printed parts, costing around £350 in total. The system can run directly from a computer or smartphone with a graphical user interface, making it highly portable and user-friendly. The HOSI system can take panoramic hyperspectral images that meet the difficult requirements of ALAN research, sensitive to low light around 0.001 cd.m-2, across 320-880 nm range with spectral resolution of ~ 9 nm (FWHM) and spatial resolution of ~ 2 cycles per degree. The independent exposure of each pixel also allows for an extremely wide dynamic range that can encompass typical natural and artificially illuminated scenes, with sample night-time scans achieving full-spectrum peak-to-peak dynamic ranges of > 50,000:1.

CONCLUSIONS

This system's adaptability, cost-effectiveness and open-source nature position it as a valuable tool for researchers investigating the complex relationships between light, environment, behaviour, ecology and biodiversity, with further potential uses in many other fields.

The Hawkmoth Proboscis: An Insect Model for Sensorimotor Control of Reaching and Exploration

Reaching and inspecting objects is an intricate part of human life, which is shared by a diversity of animals across phyla. In addition to appendages like legs and antennae, some insects use their mouthparts to reach and inspect targets. Hawkmoths of the family Sphingidae (Lepidoptera) use their extremely long and straw-like proboscis to drink nectar from flowers. As they approach flowers, hawkmoths uncoil their proboscis and explore the floral surface while hovering to target the proboscis to the nectary hole. Several sensory modalities provide feedback to control and guide these extremely versatile proboscis movements. The control task faced by the hawkmoths' nervous system during such behaviors is not unlike that of an animal guiding limbs or a robotic agent guiding a manipulator to a target. Hawkmoths perform these reaching maneuvers while simultaneously hovering, and hence require rapid and continuous coordination between the proboscis, neck, and flight motor systems, thereby providing a unique invertebrate model for studying appendage guidance and reaching. Here, we review what is known about how hawkmoths use their proboscis for floral inspection and nectar discovery, as well as the role of various sensors in proboscis guidance. We give a brief overview of the morphology and muscular apparatus of the hawkmoth proboscis, and discuss how multimodal sensory feedback might be turned into motor action for appendage guidance.

A mouse in the spotlight: Response capacity to artificial light at night in a rodent pest species, the southern multimammate mouse (Mastomys coucha)

Multimammate mice are prolific breeders, can cause significant agricultural damage, and are reservoir hosts for a number of pathogens. They are nocturnal and given their success in urbanised rural environments, we were interested in how they would respond to increasingly bright anthropogenic spaces. We evaluated the locomotor activity of southern multimammate mice (Mastomys coucha), under four treatments: in an outdoor enclosure with natural light and temperature fluctuations, in a laboratory under a standard light regime, and two artificial light at night (ALAN) regimes (2 Lux) of varying proximity. The study animals remained nocturnal for the duration of the experiments. They were more active under the laboratory conditions with lower day-time light levels compared to the outdoor treatment but reduced their activity under ALAN. When the night light originated remotely, activity levels decreased by more than 50%, whereas under direct ALAN from above the cages, there was a 75% decrease in activity. The onset of activity was later during the two LAN treatments. We concluded that Mastomys coucha is strongly averse to light and show severe behavioural and circadian responses to light at night. We predict that it is unlikely that Mastomys will flourish in cities, but that they could thrive in and around dark urbanised refugia.

Digest: How environmental light conditions shape the evolution of visual systems in birds

How do varying environmental light conditions influence the evolution of avian visual systems? Fröhlich et al. (2024) demonstrate that nocturnal birds evolved broader corneas and slightly longer axial lengths than their diurnal counterparts, increasing light capture efficiency. Nocturnal species also tended to maintain or reduce the size of brain regions responsible for vision, i.e., the optic tectum and the visual wulst. These results highlight adaptive trends in nocturnal species, where evolutionary improvement in low-light performance of eyes may be accompanied by compromised brain function.

Migratory birds are able to choose the appropriate migratory direction under dim yellow narrowband light

Currently, it is generally assumed that migratory birds are oriented in the appropriate migratory direction under UV, blue and green light (short-wavelength) and are unable to use their magnetic compass in total darkness and under yellow and red light (long-wavelength). However, it has also been suggested that the magnetic compass has two sensitivity peaks: in the short and long wavelengths, but with different intensities. In this project, we aimed to study the orientation of long-distance migrants, pied flycatchers (Ficedula hypoleuca), under different narrowband light conditions during autumn and spring migrations. The birds were tested in the natural magnetic field (NMF) and a changed magnetic field (CMF) rotated counterclockwise by 120° under dim green (autumn) and yellow (spring and autumn) light, which are on the 'threshold' between the short-wavelength and long-wavelength light. We showed that pied flycatchers (i) were completely disoriented under green light both in the NMF and CMF but (ii) showed the migratory direction in the NMF and the appropriate response to CMF under yellow light. Our data contradict the results of previous experiments under narrowband green and yellow light and raise doubts about the existence of only short-wavelength magnetoreception. The parameters of natural light change dramatically in spectral composition and intensity after local sunset, and the avian magnetic compass should be adapted to function properly under such constantly changing light conditions.