In Southern California, mountain lions avoid areas which are lit artificially. It is believed that they do this to avoid people. Clearly, mountain lion regards humans as dangerous. This brings to mind, by the way, the common leopard which in some areas has become entirely nocturnal to avoid people. A recent study found that African wildlife at a waterhole ran away when they heard human voices played by a speaker. This applied to the iconic big species like rhinoceroses as well and top predators like leopards. Humans create more fear in animals than apex predators.
The point there is that the top predator on the planet is the human and large cats, normally dominant and apex predators are fearful of humans and avoid them. Lights illuminating roadways and settlements are indicative of a human presence.
This affects where they place themselves which can lead to fragmentation of habitat just as roads criss-crossing Southern California can as well. Fragmentation of habitat is highly problematic for wild species because it creates small pockets of individuals who mate amongst themselves possibly resulting in inbreeding which can result in sterility which further diminishes their chances of survival.
And in Southern California and I believe in California generally there are some pretty nice wildlife crossings over freeways to help to join up habitat and to avoid the freeway becoming a barrier. The trouble is these freeways are illuminated by road lights which can deter mountain lions from using a very well-engineered roadway crossing. There is a beautiful one in The Netherlands by the way:
Our research has shown that even when structures exist to allow mountain lion passage under freeways, the light and noise can deter mountain lions from use of these safe crossing structures– mountain lion expert and co-author Winston Vickers, a wildlife veterinarian with the UC Davis School of Veterinary Medicine and its Karen C. Drayer Wildlife Health Center.
The Wallis Annenberg crossing over U.S. Highway 101, which broke ground in April 2022, has, I understand, been designed to deal with this problem.
Vickers also said that, “On the positive side, the deterrent effect of light might be put to positive use to prevent livestock losses to mountain lions, and the subsequent killing of mountain lions in response.”
Roadways are historically a great danger to mountain lions particularly in places like Florida where the Florida Panther is threatened by road traffic and where there is a survival problem with this small pocket of remaining pumas in the East of the USA. Conservationists imported pumas from the West which must have diluted the Florida Panther genes.
The mountain lion’s fear of artificial light can “have cascading effects on the redistribution of the species in the region, as well as the benefits wildlife provide in this ecosystem”, according to the lead author, Rafael Barrientos, an ecologist with the Universidad Complutense in Madrid, Spain.
One last point: the study found that natural light such as moonlight did not influence mountain lions. They were solely affected by artificial light from nearby ground sources.
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Source reference: Rafael Barrientos, Winston Vickers, Travis Longcore, Eric S. Abelson, Justin Dellinger, David P. Waetjen, Guillermo Fandos, Fraser M. Shilling. Nearby night lighting, rather than sky glow, is associated with habitat selection by a top predator in human-dominated landscapes. Philosophical Transactions of the Royal Society B: Biological Sciences, 2023; 378 (1892) DOI: 10.1098/rstb.2022.0370
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