NPS / Adams By day, visitors to Grand Teton National Park can view striking mountain vistas, winding rivers, or iconic wildlife. But as the sun sinks below the Teton Range, and night falls on the park, the skies reveal another scene—an array of constellations, moons, and stars. Just as modern park visitors often marvel at the undimmed beauty of the park’s night sky, these celestial bodies played an important role in early human history, providing light and tools for navigation. Wildlife also use the light from the night sky as a directional aid and to illuminate their nocturnal activities. Protecting this resource is a priority of park managers and conservationists. With minimal light pollution, Grand Teton provides the perfect setting to experiment with low-impact lighting options. In 2019, researchers from Boise State University's Sensory Ecology Lab (Sensory Lab), led by Dr. Jesse Barber, spurred a collaboration with park staff to observe the effect of different light hues and intensities on local bat and insect populations. Their work was paired with visitor surveys conducted by park social scientists, investigating visitor perceptions of wildlife-friendly lighting. This project is part of a long running initiative of the National Park Service (NPS) to preserve night skies as a natural and cultural resource. Light pollution is one of the most prevalent forms of natural disturbance. Artificial light unnaturally brightens the night by ten percent each year, diminishing the visibility of stars. Grand Teton National Park is home to nocturnal mammals, insects, and birds that depend on the daily and seasonal rhythms of natural lighting. 
Stuart Research on the impacts of light pollution within Grand Teton began at Colter Bay in the summer of 2018. The Sensory Lab partnered with the NPS Dark Skies Initiative and Signify Lighting to install experimental light emitting diode lamps (LEDs) into the 32 streetlamps of the Colter Bay parking area. Installed in 2019, the color and intensity of these lamps could be altered remotely according to an experimental research plan. Sensory Lab researchers study how animals process and react to sensory input. Bats and nocturnal insects can be disrupted by light pollution. The Sensory Lab’s goal in collaborating with park staff is to mitigate the impacts that artificial lighting at night has on nocturnal animals, while preserving visitors’ stargazing experience. The reduced luminance of the red lights would also allow for a better view of the night’s sky. Through the summers of 2019 and 2020, the research team experimentally switched the color (between white and red) and intensity (from ten to one hundred percent wattage) of the newly installed LEDs. They examined the response of bats and insects. The colors were switched every three days in 2019 and every seven days in 2020. Bat activity was recorded using ultrasonic acoustic monitoring devices, which recorded the total number of calls in a given night. Insect activity was monitored with two different types of traps: flight-intercept traps, and UV-bucket traps. The red lights did attract less insects, but bats continued to congregate in the parking lot, regardless of the lighting hue. The research team suggests that the parking lot area had been established for many years as a good hunting ground for bats, with several individuals roosting in the buildings surrounding it. In addition, switching the light hues frequently may not have provided enough time for bats to adjust to the new lighting conditions. 
NPS / Churchwell The requested video is no longer available.
The project expanded in the summer of 2023 to gain insight on this possibility. From July 1st to September 14th, thirteen luminaries were operated across the park. These temporary tripods were installed throughout the park, in previously unlit areas, to prevent lingering effects of altered hunting behavior in bats. On intervals of three consecutive nights, from 7 pm to 6 am, luminaries would cast back the night’s ambient blanket, lighting a small area with one of four colors: 3,000k white, phosphor-converted amber, Clearfield amber, or Clearfield red. A 3-day dark block was included as fifth treatment, to monitor bat activity at each location under natural, dark conditions. Previous studies have shown that warm colors may lower the impact of nighttime lighting. Spectral characteristics, like wavelength, determine a light’s color; insects are less attracted to the longer wavelength of warm lighting—yellows and reds—compared to the shorter wavelengths of white and cool lighting—blue tinted colors. With the new color treatments, this project was the first to compare different warm hues with one another, offering increased possibilities for mitigating obtrusive lighting. 
NPS / Churchwell Grand Teton has six dominant bat species: little brown bats (Myotis lucifugus), big brown bats (Eptesicus fuscus), silver-haired bats (Lasionycteris noctivagans), hoary bats (Lasiurus cinereus), long-legged bats (Myotis volans) and long-eared bats (Myotis evotus). Based on earlier studies, researchers predicted species-specific responses to the differing light hues. While some bat species have an observed attraction to artificial lighting, others do not. The flight speed of specific bat species might factor into their light attraction versus avoidance. Fast flying bats tend to take advantage of the swarming insects around light sources. Meanwhile, slower flying species tend to avoid artificial lighting, possibly because of the elevated exposure to their own predators, such as owls. Researchers predicted fast-flying bats—big brown bats, hoary bats, and long-legged bats—would tolerate white lighting conditions, possibly even increasing their activity. They predicted slow-flying bats—little brown bats, silver-haired bats, and long-eared bats—would be least active under white lights. The researchers could not predict the individual effects of different warm hues. The ideal lighting solution would have activity similar to dark conditions for most of the bat species investigated. Based on preliminary findings, researchers believe that different warm colors will evoke species-specific responses. However, these did not seem to be entirely based on flight patterns. In the summer of 2024, the study continued, gathering more data, increasing the sample size of species-specific bats detected under each lighting condition. The final analyses will also consider crucial environmental dimensions such as tree cover, moonlight, average temperature, distance from streams, and other conditions. These factors may explain some of the observed variability in species-specific bat responses. With additional funding awarded from the Meg and Bert Raynes Wildlife Fund, the research team hope to include new insect collection methods and acoustic devices to monitor bird activity. The UV bucket and flight intercept traps were used again with the addition of sticky traps. Researchers also experimented with ways to measure activity, without capturing or harming any insects. The eVolito sensor system from FaunaPhotonics detects disturbances in the surrounding electrical field made by passing insects. It uses known wingbeat frequencies to identify what species of insect made the disturbance. If the sensor data is corroborated by the other methods, it could be a viable, low-impact option for future studies. 
NPS / Churchwell Concurrent with the biological studies, the park social scientists gathered information on the human perception and preferences of different light hues. Greta Holliday, a researcher working for the Sensory Lab, said “National Parks are created for people to enjoy... if we change streetlights, it has to work for people too.” A series of late-night visitor surveys were conducted in the summer of 2019, when the alternating LEDs were first installed. Park staff, along with researchers from Penn State University, gauged people’s opinions of the red and white treatments. People supported the red lights, even more so when they were surveyed on nights when the red parking lot lights were illuminated. In the summer of 2023, park staff conducted more surveys to compliment the introduced hue and intensity treatments. The results were: 83% of respondents said night sky viewing was an important part of their experience in the park; 68% said wildlife friendly solutions should be prioritized over other factors; 86% of visitors preferred the lowest intensity across all hues, with the most favored lighting condition—preferred by 37% of visitors—being the lowest intensity red setting. The multidisciplinary research results—obtained by the joint efforts of the Sensory Lab team and park researchers—will grant a more comprehensive perspective to address both the necessity and impacts of outdoor artificial lighting. The science explores people’s perception on lighting and the broader effects artificial light can have on ecosystem health; park visitors value night sky viewing, and certain wildlife behaviors can be light-dependent. This research aids park managers in search of solutions that benefit people and wildlife. It explores the social and biological effects of different mitigation measures against light pollution that could provide necessary outdoor lighting while reducing its disruption at night. Park managers at Grand Teton will continue to seek opportunities to protect and improve the quality of the park’s night skies. ReferencesBarber, J. R., Cole, H. J. (2020). Rewilding the night sky: Mitigating the costs of light pollution for bats and insects. UW-National Park Service Research Station Annual Report, 43, 8-17. https://doi.org/10.13001/uwnps.2020.7399Corsini, M., Barber, J. R., (2023). Preserving the dark side of the night: Preliminary insights into species-specific bat responses to four different light hues across Grand Teton National Park. UW-National Park Service Research Station Annual Report, 45, 1-9.
|
Last updated: August 14, 2024