JACKSON, Wyo. — While holiday lights can add a festive tone to the season, research suggests their impact on bird migration and predator/prey dynamics, among other wildlife behavior, warrants replacing cooler blues and whites with warmer colored bulbs.
According to Teton County’s Land Development Regulations (LDRs), mitigating for “negative impacts on the nocturnal environment” includes efforts to eliminate or reduce the hazards of excessive light and glare. Teton County regulations restrict outdoor decorative lighting like holiday string lights between Nov. 15 and Jan. 10; similarly, the Town of Jackson (TOJ) only allows decorative lighting to be displayed Nov. 1 through April 15.
Both the Town and County prohibit flickering or flashing lights, and any lighting in which a single light unit exceeds 20,000 initial lumens, or the visible light output before the loss of any operational efficiency starts. The County LDRs also recommend “warm” tone lights over “cool” tone lights to keep the color temperature of exterior lighting under 3000 Kelvins.
These regulations are backed by a number of studies. In 2018, a study published in Scientific Reports confirms excessive artificial light, which includes holiday light displays, disrupts avian circadian rhythms, disorients birds during flight and seasonal migration and even increases mortality. The research reveals this extensive impact is due to bird species’ positive phototaxis effect, or attraction to lights.
Another study published in Ecography in 2020 identifies that artificial nightlight alters predator-prey dynamics, particularly between mountain lions and mule deer in the Intermountain West. The research confirms nightlight interferes with space use and movement behaviors of both species, and creates a “predator shield,” where there’s too much nightlight for cougar activity, and an “ecological trap,” where the darkest areas become the funnel for the most successful hunting.
This study also validates additional links between elevated light levels and disruptions in other ecological processes. Those disruptions include changes to pollination, migration, habitat connectivity, increased physiological stress, decreased reproduction and changes to predation risk, movement patterns and vigilance time.
A more recent 2022 study published in Human–Wildlife Interactions, which classifies holiday lights as a “seasonal source of light pollution,” suggests that colored lights as an alternative to clear white bulbs could lessen the negative impact on wildlife behavior by reducing the light intensity that’s emitted. This hypothesis is corroborated by Wyoming Stargazing, whose website substantiates that increased brightness from white lights increases the overall light pollution and adversely affects wildlife, in addition to human, health.
“What many people don’t realize is that at the same wattage, white is significantly brighter than a warmer-appearing color,” Wyoming Stargazing’s website says. “In fact, at the same wattage output, a white LED light will put out more than eight times more brightness (and thus, light pollution) than a warmer-looking counterpart.”
The International Dark-Sky Association says blue lights have similar impacts on wildlife to white lights, and a peer-reviewed paper provides evidence that lights with yellow-green and amber tones are in fact lower impact than blue-rich lighting, emphasizing “warmer” tones have less negative impact than “cooler.”
Adhering to best artificial lighting practices, especially during the holiday season, aligns with the idea of Ecosystem Stewardship listed as the first of the “Common Values of Community Character” in both the Teton County and Town of Jackson LDRs.
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